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1 /*
2  * Copyright (C) 2017 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 #ifndef ART_LIBDEXFILE_DEX_COMPACT_DEX_FILE_H_
18 #define ART_LIBDEXFILE_DEX_COMPACT_DEX_FILE_H_
19 
20 #include "base/casts.h"
21 #include "dex_file.h"
22 #include "dex/compact_offset_table.h"
23 
24 namespace art {
25 
26 // CompactDex is a currently ART internal dex file format that aims to reduce storage/RAM usage.
27 class CompactDexFile : public DexFile {
28  public:
29   static constexpr uint8_t kDexMagic[kDexMagicSize] = { 'c', 'd', 'e', 'x' };
30   // Last change: remove code item deduping.
31   static constexpr uint8_t kDexMagicVersion[] = {'0', '0', '1', '\0'};
32 
33   enum class FeatureFlags : uint32_t {
34     kDefaultMethods = 0x1,
35   };
36 
37   class Header : public DexFile::Header {
38    public:
At(const void * at)39     static const Header* At(const void* at) {
40       return reinterpret_cast<const Header*>(at);
41     }
42 
GetFeatureFlags()43     uint32_t GetFeatureFlags() const {
44       return feature_flags_;
45     }
46 
GetDataOffset()47     uint32_t GetDataOffset() const {
48       return data_off_;
49     }
50 
GetDataSize()51     uint32_t GetDataSize() const {
52       return data_size_;
53     }
54 
55     // Range of the shared data section owned by the dex file. Owned in this context refers to data
56     // for this DEX that was not deduplicated to another DEX.
OwnedDataBegin()57     uint32_t OwnedDataBegin() const {
58       return owned_data_begin_;
59     }
60 
OwnedDataEnd()61     uint32_t OwnedDataEnd() const {
62       return owned_data_end_;
63     }
64 
65    private:
66     uint32_t feature_flags_ = 0u;
67 
68     // Position in the compact dex file for the debug info table data starts.
69     uint32_t debug_info_offsets_pos_ = 0u;
70 
71     // Offset into the debug info table data where the lookup table is.
72     uint32_t debug_info_offsets_table_offset_ = 0u;
73 
74     // Base offset of where debug info starts in the dex file.
75     uint32_t debug_info_base_ = 0u;
76 
77     // Range of the shared data section owned by the dex file.
78     uint32_t owned_data_begin_ = 0u;
79     uint32_t owned_data_end_ = 0u;
80 
81     friend class CompactDexFile;
82     friend class CompactDexWriter;
83   };
84 
85   // Like the standard code item except without a debug info offset. Each code item may have a
86   // preheader to encode large methods. In 99% of cases, the preheader is not used. This enables
87   // smaller size with a good fast path case in the accessors.
88   struct CodeItem : public dex::CodeItem {
89     static constexpr size_t kAlignment = sizeof(uint16_t);
90     // Max preheader size in uint16_ts.
91     static constexpr size_t kMaxPreHeaderSize = 6;
92 
FieldsOffsetCodeItem93     static constexpr size_t FieldsOffset() {
94       return OFFSETOF_MEMBER(CodeItem, fields_);
95     }
96 
InsnsCountAndFlagsOffsetCodeItem97     static constexpr size_t InsnsCountAndFlagsOffset() {
98       return OFFSETOF_MEMBER(CodeItem, insns_count_and_flags_);
99     }
100 
InsnsOffsetCodeItem101     static constexpr size_t InsnsOffset() {
102       return OFFSETOF_MEMBER(CodeItem, insns_);
103     }
104 
105     static constexpr size_t kRegistersSizeShift = 12;
106     static constexpr size_t kInsSizeShift = 8;
107     static constexpr size_t kOutsSizeShift = 4;
108     static constexpr size_t kTriesSizeSizeShift = 0;
109     static constexpr uint16_t kBitPreHeaderRegistersSize = 0;
110     static constexpr uint16_t kBitPreHeaderInsSize = 1;
111     static constexpr uint16_t kBitPreHeaderOutsSize = 2;
112     static constexpr uint16_t kBitPreHeaderTriesSize = 3;
113     static constexpr uint16_t kBitPreHeaderInsnsSize = 4;
114     static constexpr uint16_t kFlagPreHeaderRegistersSize = 0x1 << kBitPreHeaderRegistersSize;
115     static constexpr uint16_t kFlagPreHeaderInsSize = 0x1 << kBitPreHeaderInsSize;
116     static constexpr uint16_t kFlagPreHeaderOutsSize = 0x1 << kBitPreHeaderOutsSize;
117     static constexpr uint16_t kFlagPreHeaderTriesSize = 0x1 << kBitPreHeaderTriesSize;
118     static constexpr uint16_t kFlagPreHeaderInsnsSize = 0x1 << kBitPreHeaderInsnsSize;
119     static constexpr size_t kInsnsSizeShift = 5;
120     static constexpr size_t kInsnsSizeBits = sizeof(uint16_t) * kBitsPerByte -  kInsnsSizeShift;
121 
122    private:
123     CodeItem() = default;
124 
125     // Combined preheader flags for fast testing if we need to go slow path.
126     static constexpr uint16_t kFlagPreHeaderCombined =
127         kFlagPreHeaderRegistersSize |
128         kFlagPreHeaderInsSize |
129         kFlagPreHeaderOutsSize |
130         kFlagPreHeaderTriesSize |
131         kFlagPreHeaderInsnsSize;
132 
133     // Create a code item and associated preheader if required based on field values.
134     // Returns the start of the preheader. The preheader buffer must be at least as large as
135     // kMaxPreHeaderSize;
CreateCodeItem136     uint16_t* Create(uint16_t registers_size,
137                      uint16_t ins_size,
138                      uint16_t outs_size,
139                      uint16_t tries_size,
140                      uint32_t insns_size_in_code_units,
141                      uint16_t* out_preheader) {
142       // Dex verification ensures that registers size > ins_size, so we can subtract the registers
143       // size accordingly to reduce how often we need to use the preheader.
144       DCHECK_GE(registers_size, ins_size);
145       registers_size -= ins_size;
146       fields_ = (registers_size & 0xF) << kRegistersSizeShift;
147       fields_ |= (ins_size & 0xF) << kInsSizeShift;
148       fields_ |= (outs_size & 0xF) << kOutsSizeShift;
149       fields_ |= (tries_size & 0xF) << kTriesSizeSizeShift;
150       registers_size &= ~0xF;
151       ins_size &= ~0xF;
152       outs_size &= ~0xF;
153       tries_size &= ~0xF;
154       insns_count_and_flags_ = 0;
155       const size_t masked_count = insns_size_in_code_units & ((1 << kInsnsSizeBits) - 1);
156       insns_count_and_flags_ |= masked_count << kInsnsSizeShift;
157       insns_size_in_code_units -= masked_count;
158 
159       // Since the preheader case is rare (1% of code items), use a suboptimally large but fast
160       // decoding format.
161       if (insns_size_in_code_units != 0) {
162         insns_count_and_flags_ |= kFlagPreHeaderInsnsSize;
163         --out_preheader;
164         *out_preheader = static_cast<uint16_t>(insns_size_in_code_units);
165         --out_preheader;
166         *out_preheader = static_cast<uint16_t>(insns_size_in_code_units >> 16);
167       }
168       auto preheader_encode = [&](uint16_t size, uint16_t flag) {
169         if (size != 0) {
170           insns_count_and_flags_ |= flag;
171           --out_preheader;
172           *out_preheader = size;
173         }
174       };
175       preheader_encode(registers_size, kFlagPreHeaderRegistersSize);
176       preheader_encode(ins_size, kFlagPreHeaderInsSize);
177       preheader_encode(outs_size, kFlagPreHeaderOutsSize);
178       preheader_encode(tries_size, kFlagPreHeaderTriesSize);
179       return out_preheader;
180     }
181 
HasPreHeaderCodeItem182     ALWAYS_INLINE bool HasPreHeader(uint16_t flag) const {
183       return (insns_count_and_flags_ & flag) != 0;
184     }
185 
186     // Return true if the code item has any preheaders.
HasAnyPreHeaderCodeItem187     ALWAYS_INLINE static bool HasAnyPreHeader(uint16_t insns_count_and_flags) {
188       return (insns_count_and_flags & kFlagPreHeaderCombined) != 0;
189     }
190 
GetPreHeaderCodeItem191     ALWAYS_INLINE uint16_t* GetPreHeader() {
192       return reinterpret_cast<uint16_t*>(this);
193     }
194 
GetPreHeaderCodeItem195     ALWAYS_INLINE const uint16_t* GetPreHeader() const {
196       return reinterpret_cast<const uint16_t*>(this);
197     }
198 
199     // Decode fields and read the preheader if necessary. If kDecodeOnlyInstructionCount is
200     // specified then only the instruction count is decoded.
201     template <bool kDecodeOnlyInstructionCount>
DecodeFieldsCodeItem202     ALWAYS_INLINE void DecodeFields(uint32_t* insns_count,
203                                     uint16_t* registers_size,
204                                     uint16_t* ins_size,
205                                     uint16_t* outs_size,
206                                     uint16_t* tries_size) const {
207       *insns_count = insns_count_and_flags_ >> kInsnsSizeShift;
208       if (!kDecodeOnlyInstructionCount) {
209         const uint16_t fields = fields_;
210         *registers_size = (fields >> kRegistersSizeShift) & 0xF;
211         *ins_size = (fields >> kInsSizeShift) & 0xF;
212         *outs_size = (fields >> kOutsSizeShift) & 0xF;
213         *tries_size = (fields >> kTriesSizeSizeShift) & 0xF;
214       }
215       if (UNLIKELY(HasAnyPreHeader(insns_count_and_flags_))) {
216         const uint16_t* preheader = GetPreHeader();
217         if (HasPreHeader(kFlagPreHeaderInsnsSize)) {
218           --preheader;
219           *insns_count += static_cast<uint32_t>(*preheader);
220           --preheader;
221           *insns_count += static_cast<uint32_t>(*preheader) << 16;
222         }
223         if (!kDecodeOnlyInstructionCount) {
224           if (HasPreHeader(kFlagPreHeaderRegistersSize)) {
225             --preheader;
226             *registers_size += preheader[0];
227           }
228           if (HasPreHeader(kFlagPreHeaderInsSize)) {
229             --preheader;
230             *ins_size += preheader[0];
231           }
232           if (HasPreHeader(kFlagPreHeaderOutsSize)) {
233             --preheader;
234             *outs_size += preheader[0];
235           }
236           if (HasPreHeader(kFlagPreHeaderTriesSize)) {
237             --preheader;
238             *tries_size += preheader[0];
239           }
240         }
241       }
242       if (!kDecodeOnlyInstructionCount) {
243         *registers_size += *ins_size;
244       }
245     }
246 
247     // Packed code item data, 4 bits each: [registers_size, ins_size, outs_size, tries_size]
248     uint16_t fields_;
249 
250     // 5 bits for if either of the fields required preheader extension, 11 bits for the number of
251     // instruction code units.
252     uint16_t insns_count_and_flags_;
253 
254     uint16_t insns_[1];                  // actual array of bytecode.
255 
256     ART_FRIEND_TEST(CodeItemAccessorsTest, TestDexInstructionsAccessor);
257     ART_FRIEND_TEST(CompactDexFileTest, CodeItemFields);
258     friend class CodeItemDataAccessor;
259     friend class CodeItemDebugInfoAccessor;
260     friend class CodeItemInstructionAccessor;
261     friend class CompactDexFile;
262     friend class CompactDexWriter;
263     DISALLOW_COPY_AND_ASSIGN(CodeItem);
264   };
265 
266   // Write the compact dex specific magic.
267   static void WriteMagic(uint8_t* magic);
268 
269   // Write the current version, note that the input is the address of the magic.
270   static void WriteCurrentVersion(uint8_t* magic);
271 
272   // Returns true if the byte string points to the magic value.
273   static bool IsMagicValid(const uint8_t* magic);
274   bool IsMagicValid() const override;
275 
276   // Returns true if the byte string after the magic is the correct value.
277   static bool IsVersionValid(const uint8_t* magic);
278   bool IsVersionValid() const override;
279 
280   // TODO This is completely a guess. We really need to do better. b/72402467
281   // We ask for 64 megabytes which should be big enough for any realistic dex file.
GetDequickenedSize()282   size_t GetDequickenedSize() const override {
283     return 64 * MB;
284   }
285 
GetHeader()286   const Header& GetHeader() const {
287     return down_cast<const Header&>(DexFile::GetHeader());
288   }
289 
290   bool SupportsDefaultMethods() const override;
291 
292   uint32_t GetCodeItemSize(const dex::CodeItem& item) const override;
293 
GetDebugInfoOffset(uint32_t dex_method_index)294   uint32_t GetDebugInfoOffset(uint32_t dex_method_index) const {
295     return debug_info_offsets_.GetOffset(dex_method_index);
296   }
297 
298   static uint32_t CalculateChecksum(const uint8_t* base_begin,
299                                     size_t base_size,
300                                     const uint8_t* data_begin,
301                                     size_t data_size);
302   uint32_t CalculateChecksum() const override;
303 
304  private:
305   CompactDexFile(const uint8_t* base,
306                  size_t size,
307                  const uint8_t* data_begin,
308                  size_t data_size,
309                  const std::string& location,
310                  uint32_t location_checksum,
311                  const OatDexFile* oat_dex_file,
312                  std::unique_ptr<DexFileContainer> container);
313 
314   CompactOffsetTable::Accessor debug_info_offsets_;
315 
316   friend class DexFile;
317   friend class DexFileLoader;
318   DISALLOW_COPY_AND_ASSIGN(CompactDexFile);
319 };
320 
321 }  // namespace art
322 
323 #endif  // ART_LIBDEXFILE_DEX_COMPACT_DEX_FILE_H_
324