| /* |
| * Copyright (C) 2015 The Android Open Source Project |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| #include "type_lookup_table.h" |
| |
| #include <cstring> |
| #include <memory> |
| |
| #include "base/bit_utils.h" |
| #include "base/leb128.h" |
| #include "dex/dex_file-inl.h" |
| #include "dex/utf-inl.h" |
| |
| namespace art { |
| |
| static inline bool ModifiedUtf8StringEquals(const char* lhs, const char* rhs) { |
| return CompareModifiedUtf8ToModifiedUtf8AsUtf16CodePointValues(lhs, rhs) == 0; |
| } |
| |
| TypeLookupTable TypeLookupTable::Create(const DexFile& dex_file) { |
| uint32_t num_class_defs = dex_file.NumClassDefs(); |
| if (UNLIKELY(!SupportedSize(num_class_defs))) { |
| return TypeLookupTable(); |
| } |
| size_t mask_bits = CalculateMaskBits(num_class_defs); |
| size_t size = 1u << mask_bits; |
| std::unique_ptr<Entry[]> owned_entries(new Entry[size]); |
| Entry* entries = owned_entries.get(); |
| |
| static_assert(alignof(Entry) == 4u, "Expecting Entry to be 4-byte aligned."); |
| const uint32_t mask = Entry::GetMask(mask_bits); |
| std::vector<uint16_t> conflict_class_defs; |
| // The first stage. Put elements on their initial positions. If an initial position is already |
| // occupied then delay the insertion of the element to the second stage to reduce probing |
| // distance. |
| for (size_t class_def_idx = 0; class_def_idx < dex_file.NumClassDefs(); ++class_def_idx) { |
| const dex::ClassDef& class_def = dex_file.GetClassDef(class_def_idx); |
| const dex::TypeId& type_id = dex_file.GetTypeId(class_def.class_idx_); |
| const dex::StringId& str_id = dex_file.GetStringId(type_id.descriptor_idx_); |
| const uint32_t hash = ComputeModifiedUtf8Hash(dex_file.GetStringData(str_id)); |
| const uint32_t pos = hash & mask; |
| if (entries[pos].IsEmpty()) { |
| entries[pos] = Entry(str_id.string_data_off_, hash, class_def_idx, mask_bits); |
| DCHECK(entries[pos].IsLast(mask_bits)); |
| } else { |
| conflict_class_defs.push_back(class_def_idx); |
| } |
| } |
| // The second stage. The initial position of these elements had a collision. Put these elements |
| // into the nearest free cells and link them together by updating next_pos_delta. |
| for (uint16_t class_def_idx : conflict_class_defs) { |
| const dex::ClassDef& class_def = dex_file.GetClassDef(class_def_idx); |
| const dex::TypeId& type_id = dex_file.GetTypeId(class_def.class_idx_); |
| const dex::StringId& str_id = dex_file.GetStringId(type_id.descriptor_idx_); |
| const uint32_t hash = ComputeModifiedUtf8Hash(dex_file.GetStringData(str_id)); |
| // Find the last entry in the chain. |
| uint32_t tail_pos = hash & mask; |
| DCHECK(!entries[tail_pos].IsEmpty()); |
| while (!entries[tail_pos].IsLast(mask_bits)) { |
| tail_pos = (tail_pos + entries[tail_pos].GetNextPosDelta(mask_bits)) & mask; |
| DCHECK(!entries[tail_pos].IsEmpty()); |
| } |
| // Find an empty entry for insertion. |
| uint32_t insert_pos = tail_pos; |
| do { |
| insert_pos = (insert_pos + 1) & mask; |
| } while (!entries[insert_pos].IsEmpty()); |
| // Insert and chain the new entry. |
| entries[insert_pos] = Entry(str_id.string_data_off_, hash, class_def_idx, mask_bits); |
| entries[tail_pos].SetNextPosDelta((insert_pos - tail_pos) & mask, mask_bits); |
| DCHECK(entries[insert_pos].IsLast(mask_bits)); |
| DCHECK(!entries[tail_pos].IsLast(mask_bits)); |
| } |
| |
| return TypeLookupTable(dex_file.DataBegin(), mask_bits, entries, std::move(owned_entries)); |
| } |
| |
| TypeLookupTable TypeLookupTable::Open(const uint8_t* dex_data_pointer, |
| const uint8_t* raw_data, |
| uint32_t num_class_defs) { |
| DCHECK_ALIGNED(raw_data, alignof(Entry)); |
| const Entry* entries = reinterpret_cast<const Entry*>(raw_data); |
| size_t mask_bits = CalculateMaskBits(num_class_defs); |
| return TypeLookupTable(dex_data_pointer, mask_bits, entries, /* owned_entries= */ nullptr); |
| } |
| |
| uint32_t TypeLookupTable::Lookup(const char* str, uint32_t hash) const { |
| uint32_t mask = Entry::GetMask(mask_bits_); |
| uint32_t pos = hash & mask; |
| // Thanks to special insertion algorithm, the element at position pos can be empty |
| // or start of the right bucket, or anywhere in the wrong bucket's chain. |
| const Entry* entry = &entries_[pos]; |
| if (entry->IsEmpty()) { |
| return dex::kDexNoIndex; |
| } |
| // Look for the partial hash match first, even if traversing the wrong bucket's chain. |
| uint32_t compared_hash_bits = (hash << mask_bits_) >> (2 * mask_bits_); |
| while (compared_hash_bits != entry->GetHashBits(mask_bits_)) { |
| if (entry->IsLast(mask_bits_)) { |
| return dex::kDexNoIndex; |
| } |
| pos = (pos + entry->GetNextPosDelta(mask_bits_)) & mask; |
| entry = &entries_[pos]; |
| DCHECK(!entry->IsEmpty()); |
| } |
| // Found partial hash match, compare strings (expecting this to succeed). |
| const char* first_checked_str = GetStringData(*entry); |
| if (ModifiedUtf8StringEquals(str, first_checked_str)) { |
| return entry->GetClassDefIdx(mask_bits_); |
| } |
| // If we're at the end of the chain, return before doing further expensive work. |
| if (entry->IsLast(mask_bits_)) { |
| return dex::kDexNoIndex; |
| } |
| // Check if we're traversing the right bucket. This is important if the compared |
| // partial hash has only a few bits (i.e. it can match frequently). |
| if (((ComputeModifiedUtf8Hash(first_checked_str) ^ hash) & mask) != 0u) { |
| return dex::kDexNoIndex; // Low hash bits mismatch. |
| } |
| // Continue looking for the string in the rest of the chain. |
| do { |
| pos = (pos + entry->GetNextPosDelta(mask_bits_)) & mask; |
| entry = &entries_[pos]; |
| DCHECK(!entry->IsEmpty()); |
| if (compared_hash_bits == entry->GetHashBits(mask_bits_) && |
| ModifiedUtf8StringEquals(str, GetStringData(*entry))) { |
| return entry->GetClassDefIdx(mask_bits_); |
| } |
| } while (!entry->IsLast(mask_bits_)); |
| // Not found. |
| return dex::kDexNoIndex; |
| } |
| |
| uint32_t TypeLookupTable::RawDataLength(uint32_t num_class_defs) { |
| return SupportedSize(num_class_defs) ? RoundUpToPowerOfTwo(num_class_defs) * sizeof(Entry) : 0u; |
| } |
| |
| uint32_t TypeLookupTable::CalculateMaskBits(uint32_t num_class_defs) { |
| return SupportedSize(num_class_defs) ? MinimumBitsToStore(num_class_defs - 1u) : 0u; |
| } |
| |
| bool TypeLookupTable::SupportedSize(uint32_t num_class_defs) { |
| return num_class_defs != 0u && num_class_defs <= std::numeric_limits<uint16_t>::max(); |
| } |
| |
| TypeLookupTable::TypeLookupTable(const uint8_t* dex_data_pointer, |
| uint32_t mask_bits, |
| const Entry* entries, |
| std::unique_ptr<Entry[]> owned_entries) |
| : dex_data_begin_(dex_data_pointer), |
| mask_bits_(mask_bits), |
| entries_(entries), |
| owned_entries_(std::move(owned_entries)) {} |
| |
| const char* TypeLookupTable::GetStringData(const Entry& entry) const { |
| DCHECK(dex_data_begin_ != nullptr); |
| const uint8_t* ptr = dex_data_begin_ + entry.GetStringOffset(); |
| // Skip string length. |
| DecodeUnsignedLeb128(&ptr); |
| return reinterpret_cast<const char*>(ptr); |
| } |
| |
| } // namespace art |