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/mem_map.h"
22 #include "base/systrace.h"
23 #include "base/utils.h"
24 #include "card_table-inl.h"
25 #include "gc/heap.h"
26 #include "gc/space/space.h"
27 #include "heap_bitmap.h"
28 #include "runtime.h"
29
30 namespace art {
31 namespace gc {
32 namespace accounting {
33
34 constexpr size_t CardTable::kCardShift;
35 constexpr size_t CardTable::kCardSize;
36 constexpr uint8_t CardTable::kCardClean;
37 constexpr uint8_t CardTable::kCardDirty;
38
39 /*
40 * Maintain a card table from the write barrier. All writes of
41 * non-null values to heap addresses should go through an entry in
42 * WriteBarrier, and from there to here.
43 *
44 * The heap is divided into "cards" of `kCardSize` bytes, as
45 * determined by `kCardShift`. The card table contains one byte of
46 * data per card, to be used by the GC. The value of the byte will be
47 * one of `kCardClean` or `kCardDirty`.
48 *
49 * After any store of a non-null object pointer into a heap object,
50 * code is obliged to mark the card dirty. The setters in
51 * object.h [such as SetFieldObject] do this for you. The
52 * compiler also contains code to mark cards as dirty.
53 *
54 * The card table's base [the "biased card table"] gets set to a
55 * rather strange value. In order to keep the JIT from having to
56 * fabricate or load `kCardDirty` to store into the card table,
57 * biased base is within the mmap allocation at a point where its low
58 * byte is equal to `kCardDirty`. See CardTable::Create for details.
59 */
60
Create(const uint8_t * heap_begin,size_t heap_capacity)61 CardTable* CardTable::Create(const uint8_t* heap_begin, size_t heap_capacity) {
62 ScopedTrace trace(__PRETTY_FUNCTION__);
63 /* Set up the card table */
64 size_t capacity = heap_capacity / kCardSize;
65 /* Allocate an extra 256 bytes to allow fixed low-byte of base */
66 std::string error_msg;
67 MemMap mem_map = MemMap::MapAnonymous("card table",
68 capacity + 256,
69 PROT_READ | PROT_WRITE,
70 /*low_4gb=*/ false,
71 &error_msg);
72 CHECK(mem_map.IsValid()) << "couldn't allocate card table: " << error_msg;
73 // All zeros is the correct initial value; all clean. Anonymous mmaps are initialized to zero, we
74 // don't clear the card table to avoid unnecessary pages being allocated
75 static_assert(kCardClean == 0, "kCardClean must be 0");
76
77 uint8_t* cardtable_begin = mem_map.Begin();
78 CHECK(cardtable_begin != nullptr);
79
80 // We allocated up to a bytes worth of extra space to allow `biased_begin`'s byte value to equal
81 // `kCardDirty`, compute a offset value to make this the case
82 size_t offset = 0;
83 uint8_t* biased_begin = reinterpret_cast<uint8_t*>(reinterpret_cast<uintptr_t>(cardtable_begin) -
84 (reinterpret_cast<uintptr_t>(heap_begin) >> kCardShift));
85 uintptr_t biased_byte = reinterpret_cast<uintptr_t>(biased_begin) & 0xff;
86 if (biased_byte != kCardDirty) {
87 int delta = kCardDirty - biased_byte;
88 offset = delta + (delta < 0 ? 0x100 : 0);
89 biased_begin += offset;
90 }
91 CHECK_EQ(reinterpret_cast<uintptr_t>(biased_begin) & 0xff, kCardDirty);
92 return new CardTable(std::move(mem_map), biased_begin, offset);
93 }
94
CardTable(MemMap && mem_map,uint8_t * biased_begin,size_t offset)95 CardTable::CardTable(MemMap&& mem_map, uint8_t* biased_begin, size_t offset)
96 : mem_map_(std::move(mem_map)), biased_begin_(biased_begin), offset_(offset) {
97 }
98
~CardTable()99 CardTable::~CardTable() {
100 // Destroys MemMap via std::unique_ptr<>.
101 }
102
ClearCardTable()103 void CardTable::ClearCardTable() {
104 static_assert(kCardClean == 0, "kCardClean must be 0");
105 mem_map_.MadviseDontNeedAndZero();
106 }
107
ClearCardRange(uint8_t * start,uint8_t * end)108 void CardTable::ClearCardRange(uint8_t* start, uint8_t* end) {
109 CHECK_ALIGNED(reinterpret_cast<uintptr_t>(start), kCardSize);
110 CHECK_ALIGNED(reinterpret_cast<uintptr_t>(end), kCardSize);
111 static_assert(kCardClean == 0, "kCardClean must be 0");
112 uint8_t* start_card = CardFromAddr(start);
113 uint8_t* end_card = CardFromAddr(end);
114 ZeroAndReleasePages(start_card, end_card - start_card);
115 }
116
AddrIsInCardTable(const void * addr) const117 bool CardTable::AddrIsInCardTable(const void* addr) const {
118 return IsValidCard(biased_begin_ + ((uintptr_t)addr >> kCardShift));
119 }
120
CheckAddrIsInCardTable(const uint8_t * addr) const121 void CardTable::CheckAddrIsInCardTable(const uint8_t* addr) const {
122 uint8_t* card_addr = biased_begin_ + ((uintptr_t)addr >> kCardShift);
123 uint8_t* begin = mem_map_.Begin() + offset_;
124 uint8_t* end = mem_map_.End();
125 CHECK(AddrIsInCardTable(addr))
126 << "Card table " << this
127 << " begin: " << reinterpret_cast<void*>(begin)
128 << " end: " << reinterpret_cast<void*>(end)
129 << " card_addr: " << reinterpret_cast<void*>(card_addr)
130 << " heap begin: " << AddrFromCard(begin)
131 << " heap end: " << AddrFromCard(end)
132 << " addr: " << reinterpret_cast<const void*>(addr);
133 }
134
VerifyCardTable()135 void CardTable::VerifyCardTable() {
136 UNIMPLEMENTED(WARNING) << "Card table verification";
137 }
138
139 } // namespace accounting
140 } // namespace gc
141 } // namespace art
142