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 <sys/mman.h>
20
21 #include "base/logging.h"
22 #include "base/systrace.h"
23 #include "card_table-inl.h"
24 #include "gc/heap.h"
25 #include "gc/space/space.h"
26 #include "heap_bitmap.h"
27 #include "mem_map.h"
28 #include "runtime.h"
29 #include "utils.h"
30
31 namespace art {
32 namespace gc {
33 namespace accounting {
34
35 constexpr size_t CardTable::kCardShift;
36 constexpr size_t CardTable::kCardSize;
37 constexpr uint8_t CardTable::kCardClean;
38 constexpr uint8_t CardTable::kCardDirty;
39
40 /*
41 * Maintain a card table from the write barrier. All writes of
42 * non-null values to heap addresses should go through an entry in
43 * WriteBarrier, and from there to here.
44 *
45 * The heap is divided into "cards" of GC_CARD_SIZE bytes, as
46 * determined by GC_CARD_SHIFT. The card table contains one byte of
47 * data per card, to be used by the GC. The value of the byte will be
48 * one of GC_CARD_CLEAN or GC_CARD_DIRTY.
49 *
50 * After any store of a non-null object pointer into a heap object,
51 * code is obliged to mark the card dirty. The setters in
52 * object.h [such as SetFieldObject] do this for you. The
53 * compiler also contains code to mark cards as dirty.
54 *
55 * The card table's base [the "biased card table"] gets set to a
56 * rather strange value. In order to keep the JIT from having to
57 * fabricate or load GC_DIRTY_CARD to store into the card table,
58 * biased base is within the mmap allocation at a point where its low
59 * byte is equal to GC_DIRTY_CARD. See CardTable::Create for details.
60 */
61
Create(const uint8_t * heap_begin,size_t heap_capacity)62 CardTable* CardTable::Create(const uint8_t* heap_begin, size_t heap_capacity) {
63 ScopedTrace trace(__PRETTY_FUNCTION__);
64 /* Set up the card table */
65 size_t capacity = heap_capacity / kCardSize;
66 /* Allocate an extra 256 bytes to allow fixed low-byte of base */
67 std::string error_msg;
68 std::unique_ptr<MemMap> mem_map(
69 MemMap::MapAnonymous("card table", nullptr, capacity + 256, PROT_READ | PROT_WRITE,
70 false, false, &error_msg));
71 CHECK(mem_map.get() != nullptr) << "couldn't allocate card table: " << error_msg;
72 // All zeros is the correct initial value; all clean. Anonymous mmaps are initialized to zero, we
73 // don't clear the card table to avoid unnecessary pages being allocated
74 static_assert(kCardClean == 0, "kCardClean must be 0");
75
76 uint8_t* cardtable_begin = mem_map->Begin();
77 CHECK(cardtable_begin != nullptr);
78
79 // We allocated up to a bytes worth of extra space to allow biased_begin's byte value to equal
80 // kCardDirty, compute a offset value to make this the case
81 size_t offset = 0;
82 uint8_t* biased_begin = reinterpret_cast<uint8_t*>(reinterpret_cast<uintptr_t>(cardtable_begin) -
83 (reinterpret_cast<uintptr_t>(heap_begin) >> kCardShift));
84 uintptr_t biased_byte = reinterpret_cast<uintptr_t>(biased_begin) & 0xff;
85 if (biased_byte != kCardDirty) {
86 int delta = kCardDirty - biased_byte;
87 offset = delta + (delta < 0 ? 0x100 : 0);
88 biased_begin += offset;
89 }
90 CHECK_EQ(reinterpret_cast<uintptr_t>(biased_begin) & 0xff, kCardDirty);
91 return new CardTable(mem_map.release(), biased_begin, offset);
92 }
93
CardTable(MemMap * mem_map,uint8_t * biased_begin,size_t offset)94 CardTable::CardTable(MemMap* mem_map, uint8_t* biased_begin, size_t offset)
95 : mem_map_(mem_map), biased_begin_(biased_begin), offset_(offset) {
96 }
97
~CardTable()98 CardTable::~CardTable() {
99 // Destroys MemMap via std::unique_ptr<>.
100 }
101
ClearCardTable()102 void CardTable::ClearCardTable() {
103 static_assert(kCardClean == 0, "kCardClean must be 0");
104 mem_map_->MadviseDontNeedAndZero();
105 }
106
ClearCardRange(uint8_t * start,uint8_t * end)107 void CardTable::ClearCardRange(uint8_t* start, uint8_t* end) {
108 CHECK_ALIGNED(reinterpret_cast<uintptr_t>(start), kCardSize);
109 CHECK_ALIGNED(reinterpret_cast<uintptr_t>(end), kCardSize);
110 static_assert(kCardClean == 0, "kCardClean must be 0");
111 uint8_t* start_card = CardFromAddr(start);
112 uint8_t* end_card = CardFromAddr(end);
113 ZeroAndReleasePages(start_card, end_card - start_card);
114 }
115
AddrIsInCardTable(const void * addr) const116 bool CardTable::AddrIsInCardTable(const void* addr) const {
117 return IsValidCard(biased_begin_ + ((uintptr_t)addr >> kCardShift));
118 }
119
CheckAddrIsInCardTable(const uint8_t * addr) const120 void CardTable::CheckAddrIsInCardTable(const uint8_t* addr) const {
121 uint8_t* card_addr = biased_begin_ + ((uintptr_t)addr >> kCardShift);
122 uint8_t* begin = mem_map_->Begin() + offset_;
123 uint8_t* end = mem_map_->End();
124 CHECK(AddrIsInCardTable(addr))
125 << "Card table " << this
126 << " begin: " << reinterpret_cast<void*>(begin)
127 << " end: " << reinterpret_cast<void*>(end)
128 << " card_addr: " << reinterpret_cast<void*>(card_addr)
129 << " heap begin: " << AddrFromCard(begin)
130 << " heap end: " << AddrFromCard(end)
131 << " addr: " << reinterpret_cast<const void*>(addr);
132 }
133
VerifyCardTable()134 void CardTable::VerifyCardTable() {
135 UNIMPLEMENTED(WARNING) << "Card table verification";
136 }
137
138 } // namespace accounting
139 } // namespace gc
140 } // namespace art
141