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 /*
35 * Maintain a card table from the write barrier. All writes of
36 * non-null values to heap addresses should go through an entry in
37 * WriteBarrier, and from there to here.
38 *
39 * The heap is divided into "cards" of `kCardSize` bytes, as
40 * determined by `kCardShift`. The card table contains one byte of
41 * data per card, to be used by the GC. The value of the byte will be
42 * one of `kCardClean` or `kCardDirty`.
43 *
44 * After any store of a non-null object pointer into a heap object,
45 * code is obliged to mark the card dirty. The setters in
46 * object.h [such as SetFieldObject] do this for you. The
47 * compiler also contains code to mark cards as dirty.
48 *
49 * The card table's base [the "biased card table"] gets set to a
50 * rather strange value. In order to keep the JIT from having to
51 * fabricate or load `kCardDirty` to store into the card table,
52 * biased base is within the mmap allocation at a point where its low
53 * byte is equal to `kCardDirty`. See CardTable::Create for details.
54 */
55
Create(const uint8_t * heap_begin,size_t heap_capacity)56 CardTable* CardTable::Create(const uint8_t* heap_begin, size_t heap_capacity) {
57 ScopedTrace trace(__PRETTY_FUNCTION__);
58 /* Set up the card table */
59 size_t capacity = heap_capacity / kCardSize;
60 /* Allocate an extra 256 bytes to allow fixed low-byte of base */
61 std::string error_msg;
62 MemMap mem_map = MemMap::MapAnonymous("card table",
63 capacity + 256,
64 PROT_READ | PROT_WRITE,
65 /*low_4gb=*/ false,
66 &error_msg);
67 CHECK(mem_map.IsValid()) << "couldn't allocate card table: " << error_msg;
68 // All zeros is the correct initial value; all clean. Anonymous mmaps are initialized to zero, we
69 // don't clear the card table to avoid unnecessary pages being allocated
70 static_assert(kCardClean == 0, "kCardClean must be 0");
71
72 uint8_t* cardtable_begin = mem_map.Begin();
73 CHECK(cardtable_begin != nullptr);
74
75 // We allocated up to a bytes worth of extra space to allow `biased_begin`'s byte value to equal
76 // `kCardDirty`, compute a offset value to make this the case
77 size_t offset = 0;
78 uint8_t* biased_begin = reinterpret_cast<uint8_t*>(reinterpret_cast<uintptr_t>(cardtable_begin) -
79 (reinterpret_cast<uintptr_t>(heap_begin) >> kCardShift));
80 uintptr_t biased_byte = reinterpret_cast<uintptr_t>(biased_begin) & 0xff;
81 if (biased_byte != kCardDirty) {
82 int delta = kCardDirty - biased_byte;
83 offset = delta + (delta < 0 ? 0x100 : 0);
84 biased_begin += offset;
85 }
86 CHECK_EQ(reinterpret_cast<uintptr_t>(biased_begin) & 0xff, kCardDirty);
87 return new CardTable(std::move(mem_map), biased_begin, offset);
88 }
89
CardTable(MemMap && mem_map,uint8_t * biased_begin,size_t offset)90 CardTable::CardTable(MemMap&& mem_map, uint8_t* biased_begin, size_t offset)
91 : mem_map_(std::move(mem_map)), biased_begin_(biased_begin), offset_(offset) {
92 }
93
~CardTable()94 CardTable::~CardTable() {
95 // Destroys MemMap via std::unique_ptr<>.
96 }
97
ClearCardTable()98 void CardTable::ClearCardTable() {
99 static_assert(kCardClean == 0, "kCardClean must be 0");
100 mem_map_.MadviseDontNeedAndZero();
101 }
102
ClearCardRange(uint8_t * start,uint8_t * end)103 void CardTable::ClearCardRange(uint8_t* start, uint8_t* end) {
104 CHECK_ALIGNED(reinterpret_cast<uintptr_t>(start), kCardSize);
105 CHECK_ALIGNED(reinterpret_cast<uintptr_t>(end), kCardSize);
106 static_assert(kCardClean == 0, "kCardClean must be 0");
107 uint8_t* start_card = CardFromAddr(start);
108 uint8_t* end_card = CardFromAddr(end);
109 ZeroAndReleasePages(start_card, end_card - start_card);
110 }
111
AddrIsInCardTable(const void * addr) const112 bool CardTable::AddrIsInCardTable(const void* addr) const {
113 return IsValidCard(biased_begin_ + ((uintptr_t)addr >> kCardShift));
114 }
115
CheckAddrIsInCardTable(const uint8_t * addr) const116 void CardTable::CheckAddrIsInCardTable(const uint8_t* addr) const {
117 uint8_t* card_addr = biased_begin_ + ((uintptr_t)addr >> kCardShift);
118 uint8_t* begin = mem_map_.Begin() + offset_;
119 uint8_t* end = mem_map_.End();
120 CHECK(AddrIsInCardTable(addr))
121 << "Card table " << this
122 << " begin: " << reinterpret_cast<void*>(begin)
123 << " end: " << reinterpret_cast<void*>(end)
124 << " card_addr: " << reinterpret_cast<void*>(card_addr)
125 << " heap begin: " << AddrFromCard(begin)
126 << " heap end: " << AddrFromCard(end)
127 << " addr: " << reinterpret_cast<const void*>(addr);
128 }
129
VerifyCardTable()130 void CardTable::VerifyCardTable() {
131 UNIMPLEMENTED(WARNING) << "Card table verification";
132 }
133
134 } // namespace accounting
135 } // namespace gc
136 } // namespace art
137