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/systrace.h" 22 #include "base/utils.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 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 GC_CARD_SIZE bytes, as 45 * determined by GC_CARD_SHIFT. 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 GC_CARD_CLEAN or GC_CARD_DIRTY. 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 GC_DIRTY_CARD 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 GC_DIRTY_CARD. See CardTable::Create for details. 59 */ 60 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 std::unique_ptr<MemMap> mem_map( 68 MemMap::MapAnonymous("card table", nullptr, capacity + 256, PROT_READ | PROT_WRITE, 69 false, false, &error_msg)); 70 CHECK(mem_map.get() != nullptr) << "couldn't allocate card table: " << error_msg; 71 // All zeros is the correct initial value; all clean. Anonymous mmaps are initialized to zero, we 72 // don't clear the card table to avoid unnecessary pages being allocated 73 static_assert(kCardClean == 0, "kCardClean must be 0"); 74 75 uint8_t* cardtable_begin = mem_map->Begin(); 76 CHECK(cardtable_begin != nullptr); 77 78 // We allocated up to a bytes worth of extra space to allow biased_begin's byte value to equal 79 // kCardDirty, compute a offset value to make this the case 80 size_t offset = 0; 81 uint8_t* biased_begin = reinterpret_cast<uint8_t*>(reinterpret_cast<uintptr_t>(cardtable_begin) - 82 (reinterpret_cast<uintptr_t>(heap_begin) >> kCardShift)); 83 uintptr_t biased_byte = reinterpret_cast<uintptr_t>(biased_begin) & 0xff; 84 if (biased_byte != kCardDirty) { 85 int delta = kCardDirty - biased_byte; 86 offset = delta + (delta < 0 ? 0x100 : 0); 87 biased_begin += offset; 88 } 89 CHECK_EQ(reinterpret_cast<uintptr_t>(biased_begin) & 0xff, kCardDirty); 90 return new CardTable(mem_map.release(), biased_begin, offset); 91 } 92 93 CardTable::CardTable(MemMap* mem_map, uint8_t* biased_begin, size_t offset) 94 : mem_map_(mem_map), biased_begin_(biased_begin), offset_(offset) { 95 } 96 97 CardTable::~CardTable() { 98 // Destroys MemMap via std::unique_ptr<>. 99 } 100 101 void CardTable::ClearCardTable() { 102 static_assert(kCardClean == 0, "kCardClean must be 0"); 103 mem_map_->MadviseDontNeedAndZero(); 104 } 105 106 void CardTable::ClearCardRange(uint8_t* start, uint8_t* end) { 107 CHECK_ALIGNED(reinterpret_cast<uintptr_t>(start), kCardSize); 108 CHECK_ALIGNED(reinterpret_cast<uintptr_t>(end), kCardSize); 109 static_assert(kCardClean == 0, "kCardClean must be 0"); 110 uint8_t* start_card = CardFromAddr(start); 111 uint8_t* end_card = CardFromAddr(end); 112 ZeroAndReleasePages(start_card, end_card - start_card); 113 } 114 115 bool CardTable::AddrIsInCardTable(const void* addr) const { 116 return IsValidCard(biased_begin_ + ((uintptr_t)addr >> kCardShift)); 117 } 118 119 void CardTable::CheckAddrIsInCardTable(const uint8_t* addr) const { 120 uint8_t* card_addr = biased_begin_ + ((uintptr_t)addr >> kCardShift); 121 uint8_t* begin = mem_map_->Begin() + offset_; 122 uint8_t* end = mem_map_->End(); 123 CHECK(AddrIsInCardTable(addr)) 124 << "Card table " << this 125 << " begin: " << reinterpret_cast<void*>(begin) 126 << " end: " << reinterpret_cast<void*>(end) 127 << " card_addr: " << reinterpret_cast<void*>(card_addr) 128 << " heap begin: " << AddrFromCard(begin) 129 << " heap end: " << AddrFromCard(end) 130 << " addr: " << reinterpret_cast<const void*>(addr); 131 } 132 133 void CardTable::VerifyCardTable() { 134 UNIMPLEMENTED(WARNING) << "Card table verification"; 135 } 136 137 } // namespace accounting 138 } // namespace gc 139 } // namespace art 140
