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 "base/systrace.h"
21 #include "card_table-inl.h"
22 #include "gc/heap.h"
23 #include "gc/space/space.h"
24 #include "heap_bitmap.h"
25 #include "mem_map.h"
26 #include "runtime.h"
27 #include "utils.h"
28
29 namespace art {
30 namespace gc {
31 namespace accounting {
32
33 constexpr size_t CardTable::kCardShift;
34 constexpr size_t CardTable::kCardSize;
35 constexpr uint8_t CardTable::kCardClean;
36 constexpr uint8_t CardTable::kCardDirty;
37
38 /*
39 * Maintain a card table from the write barrier. All writes of
40 * non-null values to heap addresses should go through an entry in
41 * WriteBarrier, and from there to here.
42 *
43 * The heap is divided into "cards" of GC_CARD_SIZE bytes, as
44 * determined by GC_CARD_SHIFT. The card table contains one byte of
45 * data per card, to be used by the GC. The value of the byte will be
46 * one of GC_CARD_CLEAN or GC_CARD_DIRTY.
47 *
48 * After any store of a non-null object pointer into a heap object,
49 * code is obliged to mark the card dirty. The setters in
50 * object.h [such as SetFieldObject] do this for you. The
51 * compiler also contains code to mark cards as dirty.
52 *
53 * The card table's base [the "biased card table"] gets set to a
54 * rather strange value. In order to keep the JIT from having to
55 * fabricate or load GC_DIRTY_CARD to store into the card table,
56 * biased base is within the mmap allocation at a point where its low
57 * byte is equal to GC_DIRTY_CARD. See CardTable::Create for details.
58 */
59
Create(const uint8_t * heap_begin,size_t heap_capacity)60 CardTable* CardTable::Create(const uint8_t* heap_begin, size_t heap_capacity) {
61 ScopedTrace trace(__PRETTY_FUNCTION__);
62 /* Set up the card table */
63 size_t capacity = heap_capacity / kCardSize;
64 /* Allocate an extra 256 bytes to allow fixed low-byte of base */
65 std::string error_msg;
66 std::unique_ptr<MemMap> mem_map(
67 MemMap::MapAnonymous("card table", nullptr, capacity + 256, PROT_READ | PROT_WRITE,
68 false, false, &error_msg));
69 CHECK(mem_map.get() != nullptr) << "couldn't allocate card table: " << error_msg;
70 // All zeros is the correct initial value; all clean. Anonymous mmaps are initialized to zero, we
71 // don't clear the card table to avoid unnecessary pages being allocated
72 static_assert(kCardClean == 0, "kCardClean must be 0");
73
74 uint8_t* cardtable_begin = mem_map->Begin();
75 CHECK(cardtable_begin != nullptr);
76
77 // We allocated up to a bytes worth of extra space to allow biased_begin's byte value to equal
78 // kCardDirty, compute a offset value to make this the case
79 size_t offset = 0;
80 uint8_t* biased_begin = reinterpret_cast<uint8_t*>(reinterpret_cast<uintptr_t>(cardtable_begin) -
81 (reinterpret_cast<uintptr_t>(heap_begin) >> kCardShift));
82 uintptr_t biased_byte = reinterpret_cast<uintptr_t>(biased_begin) & 0xff;
83 if (biased_byte != kCardDirty) {
84 int delta = kCardDirty - biased_byte;
85 offset = delta + (delta < 0 ? 0x100 : 0);
86 biased_begin += offset;
87 }
88 CHECK_EQ(reinterpret_cast<uintptr_t>(biased_begin) & 0xff, kCardDirty);
89 return new CardTable(mem_map.release(), biased_begin, offset);
90 }
91
CardTable(MemMap * mem_map,uint8_t * biased_begin,size_t offset)92 CardTable::CardTable(MemMap* mem_map, uint8_t* biased_begin, size_t offset)
93 : mem_map_(mem_map), biased_begin_(biased_begin), offset_(offset) {
94 }
95
~CardTable()96 CardTable::~CardTable() {
97 // Destroys MemMap via std::unique_ptr<>.
98 }
99
ClearSpaceCards(space::ContinuousSpace * space)100 void CardTable::ClearSpaceCards(space::ContinuousSpace* space) {
101 // TODO: clear just the range of the table that has been modified
102 uint8_t* card_start = CardFromAddr(space->Begin());
103 uint8_t* card_end = CardFromAddr(space->End()); // Make sure to round up.
104 memset(reinterpret_cast<void*>(card_start), kCardClean, card_end - card_start);
105 }
106
ClearCardTable()107 void CardTable::ClearCardTable() {
108 static_assert(kCardClean == 0, "kCardClean must be 0");
109 mem_map_->MadviseDontNeedAndZero();
110 }
111
ClearCardRange(uint8_t * start,uint8_t * end)112 void CardTable::ClearCardRange(uint8_t* start, uint8_t* end) {
113 if (!kMadviseZeroes) {
114 memset(start, 0, end - start);
115 return;
116 }
117 CHECK_ALIGNED(reinterpret_cast<uintptr_t>(start), kCardSize);
118 CHECK_ALIGNED(reinterpret_cast<uintptr_t>(end), kCardSize);
119 static_assert(kCardClean == 0, "kCardClean must be 0");
120 uint8_t* start_card = CardFromAddr(start);
121 uint8_t* end_card = CardFromAddr(end);
122 uint8_t* round_start = AlignUp(start_card, kPageSize);
123 uint8_t* round_end = AlignDown(end_card, kPageSize);
124 if (round_start < round_end) {
125 madvise(round_start, round_end - round_start, MADV_DONTNEED);
126 }
127 // Handle unaligned regions at start / end.
128 memset(start_card, 0, std::min(round_start, end_card) - start_card);
129 memset(std::max(round_end, start_card), 0, end_card - std::max(round_end, start_card));
130 }
131
AddrIsInCardTable(const void * addr) const132 bool CardTable::AddrIsInCardTable(const void* addr) const {
133 return IsValidCard(biased_begin_ + ((uintptr_t)addr >> kCardShift));
134 }
135
CheckAddrIsInCardTable(const uint8_t * addr) const136 void CardTable::CheckAddrIsInCardTable(const uint8_t* addr) const {
137 uint8_t* card_addr = biased_begin_ + ((uintptr_t)addr >> kCardShift);
138 uint8_t* begin = mem_map_->Begin() + offset_;
139 uint8_t* end = mem_map_->End();
140 CHECK(AddrIsInCardTable(addr))
141 << "Card table " << this
142 << " begin: " << reinterpret_cast<void*>(begin)
143 << " end: " << reinterpret_cast<void*>(end)
144 << " card_addr: " << reinterpret_cast<void*>(card_addr)
145 << " heap begin: " << AddrFromCard(begin)
146 << " heap end: " << AddrFromCard(end)
147 << " addr: " << reinterpret_cast<const void*>(addr);
148 }
149
VerifyCardTable()150 void CardTable::VerifyCardTable() {
151 UNIMPLEMENTED(WARNING) << "Card table verification";
152 }
153
154 } // namespace accounting
155 } // namespace gc
156 } // namespace art
157