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 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 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 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 } 99 100 void CardTable::ClearCardTable() { 101 COMPILE_ASSERT(kCardClean == 0, clean_card_must_be_0); 102 mem_map_->MadviseDontNeedAndZero(); 103 } 104 105 bool CardTable::AddrIsInCardTable(const void* addr) const { 106 return IsValidCard(biased_begin_ + ((uintptr_t)addr >> kCardShift)); 107 } 108 109 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 } 122 123 void CardTable::VerifyCardTable() { 124 UNIMPLEMENTED(WARNING) << "Card table verification"; 125 } 126 127 } // namespace accounting 128 } // namespace gc 129 } // namespace art 130
