142 lines
5.3 KiB
C++
142 lines
5.3 KiB
C++
/*
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* Copyright (C) 2010 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include "card_table.h"
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#include <sys/mman.h>
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#include "base/mem_map.h"
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#include "base/systrace.h"
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#include "base/utils.h"
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#include "card_table-inl.h"
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#include "gc/heap.h"
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#include "gc/space/space.h"
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#include "heap_bitmap.h"
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#include "runtime.h"
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namespace art {
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namespace gc {
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namespace accounting {
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constexpr size_t CardTable::kCardShift;
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constexpr size_t CardTable::kCardSize;
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constexpr uint8_t CardTable::kCardClean;
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constexpr uint8_t CardTable::kCardDirty;
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/*
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* Maintain a card table from the write barrier. All writes of
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* non-null values to heap addresses should go through an entry in
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* WriteBarrier, and from there to here.
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*
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* The heap is divided into "cards" of `kCardSize` bytes, as
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* determined by `kCardShift`. The card table contains one byte of
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* data per card, to be used by the GC. The value of the byte will be
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* one of `kCardClean` or `kCardDirty`.
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*
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* After any store of a non-null object pointer into a heap object,
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* code is obliged to mark the card dirty. The setters in
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* object.h [such as SetFieldObject] do this for you. The
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* compiler also contains code to mark cards as dirty.
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*
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* The card table's base [the "biased card table"] gets set to a
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* rather strange value. In order to keep the JIT from having to
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* fabricate or load `kCardDirty` to store into the card table,
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* biased base is within the mmap allocation at a point where its low
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* byte is equal to `kCardDirty`. See CardTable::Create for details.
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*/
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CardTable* CardTable::Create(const uint8_t* heap_begin, size_t heap_capacity) {
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ScopedTrace trace(__PRETTY_FUNCTION__);
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/* Set up the card table */
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size_t capacity = heap_capacity / kCardSize;
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/* Allocate an extra 256 bytes to allow fixed low-byte of base */
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std::string error_msg;
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MemMap mem_map = MemMap::MapAnonymous("card table",
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capacity + 256,
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PROT_READ | PROT_WRITE,
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/*low_4gb=*/ false,
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&error_msg);
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CHECK(mem_map.IsValid()) << "couldn't allocate card table: " << error_msg;
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// All zeros is the correct initial value; all clean. Anonymous mmaps are initialized to zero, we
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// don't clear the card table to avoid unnecessary pages being allocated
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static_assert(kCardClean == 0, "kCardClean must be 0");
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uint8_t* cardtable_begin = mem_map.Begin();
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CHECK(cardtable_begin != nullptr);
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// We allocated up to a bytes worth of extra space to allow `biased_begin`'s byte value to equal
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// `kCardDirty`, compute a offset value to make this the case
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size_t offset = 0;
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uint8_t* biased_begin = reinterpret_cast<uint8_t*>(reinterpret_cast<uintptr_t>(cardtable_begin) -
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(reinterpret_cast<uintptr_t>(heap_begin) >> kCardShift));
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uintptr_t biased_byte = reinterpret_cast<uintptr_t>(biased_begin) & 0xff;
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if (biased_byte != kCardDirty) {
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int delta = kCardDirty - biased_byte;
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offset = delta + (delta < 0 ? 0x100 : 0);
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biased_begin += offset;
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}
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CHECK_EQ(reinterpret_cast<uintptr_t>(biased_begin) & 0xff, kCardDirty);
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return new CardTable(std::move(mem_map), biased_begin, offset);
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}
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CardTable::CardTable(MemMap&& mem_map, uint8_t* biased_begin, size_t offset)
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: mem_map_(std::move(mem_map)), biased_begin_(biased_begin), offset_(offset) {
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}
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CardTable::~CardTable() {
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// Destroys MemMap via std::unique_ptr<>.
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}
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void CardTable::ClearCardTable() {
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static_assert(kCardClean == 0, "kCardClean must be 0");
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mem_map_.MadviseDontNeedAndZero();
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}
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void CardTable::ClearCardRange(uint8_t* start, uint8_t* end) {
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CHECK_ALIGNED(reinterpret_cast<uintptr_t>(start), kCardSize);
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CHECK_ALIGNED(reinterpret_cast<uintptr_t>(end), kCardSize);
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static_assert(kCardClean == 0, "kCardClean must be 0");
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uint8_t* start_card = CardFromAddr(start);
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uint8_t* end_card = CardFromAddr(end);
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ZeroAndReleasePages(start_card, end_card - start_card);
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}
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bool CardTable::AddrIsInCardTable(const void* addr) const {
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return IsValidCard(biased_begin_ + ((uintptr_t)addr >> kCardShift));
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}
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void CardTable::CheckAddrIsInCardTable(const uint8_t* addr) const {
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uint8_t* card_addr = biased_begin_ + ((uintptr_t)addr >> kCardShift);
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uint8_t* begin = mem_map_.Begin() + offset_;
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uint8_t* end = mem_map_.End();
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CHECK(AddrIsInCardTable(addr))
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<< "Card table " << this
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<< " begin: " << reinterpret_cast<void*>(begin)
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<< " end: " << reinterpret_cast<void*>(end)
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<< " card_addr: " << reinterpret_cast<void*>(card_addr)
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<< " heap begin: " << AddrFromCard(begin)
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<< " heap end: " << AddrFromCard(end)
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<< " addr: " << reinterpret_cast<const void*>(addr);
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}
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void CardTable::VerifyCardTable() {
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UNIMPLEMENTED(WARNING) << "Card table verification";
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}
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} // namespace accounting
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} // namespace gc
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} // namespace art
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