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
27 namespace art {
28 namespace gc {
29 namespace accounting {
30
31 constexpr size_t CardTable::kCardShift;
32 constexpr size_t CardTable::kCardSize;
33 constexpr uint8_t CardTable::kCardClean;
34 constexpr 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
Create(const byte * heap_begin,size_t heap_capacity)58 CardTable* CardTable::Create(const byte* 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, &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 COMPILE_ASSERT(kCardClean == 0, card_clean_must_be_0);
70
71 byte* 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 byte* biased_begin = reinterpret_cast<byte*>(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
CardTable(MemMap * mem_map,byte * biased_begin,size_t offset)89 CardTable::CardTable(MemMap* mem_map, byte* biased_begin, size_t offset)
90 : mem_map_(mem_map), biased_begin_(biased_begin), offset_(offset) {
91 }
92
ClearSpaceCards(space::ContinuousSpace * space)93 void CardTable::ClearSpaceCards(space::ContinuousSpace* space) {
94 // TODO: clear just the range of the table that has been modified
95 byte* card_start = CardFromAddr(space->Begin());
96 byte* card_end = CardFromAddr(space->End()); // Make sure to round up.
97 memset(reinterpret_cast<void*>(card_start), kCardClean, card_end - card_start);
98 }
99
ClearCardTable()100 void CardTable::ClearCardTable() {
101 COMPILE_ASSERT(kCardClean == 0, clean_card_must_be_0);
102 mem_map_->MadviseDontNeedAndZero();
103 }
104
AddrIsInCardTable(const void * addr) const105 bool CardTable::AddrIsInCardTable(const void* addr) const {
106 return IsValidCard(biased_begin_ + ((uintptr_t)addr >> kCardShift));
107 }
108
CheckAddrIsInCardTable(const byte * addr) const109 void CardTable::CheckAddrIsInCardTable(const byte* addr) const {
110 byte* card_addr = biased_begin_ + ((uintptr_t)addr >> kCardShift);
111 byte* begin = mem_map_->Begin() + offset_;
112 byte* end = mem_map_->End();
113 CHECK(AddrIsInCardTable(addr))
114 << "Card table " << this
115 << " begin: " << reinterpret_cast<void*>(begin)
116 << " end: " << reinterpret_cast<void*>(end)
117 << " card_addr: " << reinterpret_cast<void*>(card_addr)
118 << " heap begin: " << AddrFromCard(begin)
119 << " heap end: " << AddrFromCard(end)
120 << " addr: " << reinterpret_cast<const void*>(addr);
121 }
122
VerifyCardTable()123 void CardTable::VerifyCardTable() {
124 UNIMPLEMENTED(WARNING) << "Card table verification";
125 }
126
127 } // namespace accounting
128 } // namespace gc
129 } // namespace art
130