1 /* 2 * Copyright (C) 2014 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 "verified_method.h" 18 19 #include <algorithm> 20 #include <memory> 21 #include <vector> 22 23 #include "base/logging.h" 24 #include "base/stl_util.h" 25 #include "dex_file.h" 26 #include "dex_instruction.h" 27 #include "dex_instruction-inl.h" 28 #include "base/mutex.h" 29 #include "base/mutex-inl.h" 30 #include "mirror/art_method.h" 31 #include "mirror/art_method-inl.h" 32 #include "mirror/class.h" 33 #include "mirror/class-inl.h" 34 #include "mirror/dex_cache.h" 35 #include "mirror/dex_cache-inl.h" 36 #include "mirror/object.h" 37 #include "mirror/object-inl.h" 38 #include "verifier/dex_gc_map.h" 39 #include "verifier/method_verifier.h" 40 #include "verifier/method_verifier-inl.h" 41 #include "verifier/register_line.h" 42 #include "verifier/register_line-inl.h" 43 44 namespace art { 45 46 const VerifiedMethod* VerifiedMethod::Create(verifier::MethodVerifier* method_verifier, 47 bool compile) { 48 std::unique_ptr<VerifiedMethod> verified_method(new VerifiedMethod); 49 if (compile) { 50 /* Generate a register map. */ 51 if (!verified_method->GenerateGcMap(method_verifier)) { 52 return nullptr; // Not a real failure, but a failure to encode. 53 } 54 if (kIsDebugBuild) { 55 VerifyGcMap(method_verifier, verified_method->dex_gc_map_); 56 } 57 58 // TODO: move this out when DEX-to-DEX supports devirtualization. 59 if (method_verifier->HasVirtualOrInterfaceInvokes()) { 60 verified_method->GenerateDevirtMap(method_verifier); 61 } 62 } 63 64 if (method_verifier->HasCheckCasts()) { 65 verified_method->GenerateSafeCastSet(method_verifier); 66 } 67 return verified_method.release(); 68 } 69 70 const MethodReference* VerifiedMethod::GetDevirtTarget(uint32_t dex_pc) const { 71 auto it = devirt_map_.find(dex_pc); 72 return (it != devirt_map_.end()) ? &it->second : nullptr; 73 } 74 75 bool VerifiedMethod::IsSafeCast(uint32_t pc) const { 76 return std::binary_search(safe_cast_set_.begin(), safe_cast_set_.end(), pc); 77 } 78 79 bool VerifiedMethod::GenerateGcMap(verifier::MethodVerifier* method_verifier) { 80 DCHECK(dex_gc_map_.empty()); 81 size_t num_entries, ref_bitmap_bits, pc_bits; 82 ComputeGcMapSizes(method_verifier, &num_entries, &ref_bitmap_bits, &pc_bits); 83 // There's a single byte to encode the size of each bitmap. 84 if (ref_bitmap_bits >= (8 /* bits per byte */ * 8192 /* 13-bit size */ )) { 85 LOG(WARNING) << "Cannot encode GC map for method with " << ref_bitmap_bits << " registers: " 86 << PrettyMethod(method_verifier->GetMethodReference().dex_method_index, 87 *method_verifier->GetMethodReference().dex_file); 88 return false; 89 } 90 size_t ref_bitmap_bytes = (ref_bitmap_bits + 7) / 8; 91 // There are 2 bytes to encode the number of entries. 92 if (num_entries >= 65536) { 93 LOG(WARNING) << "Cannot encode GC map for method with " << num_entries << " entries: " 94 << PrettyMethod(method_verifier->GetMethodReference().dex_method_index, 95 *method_verifier->GetMethodReference().dex_file); 96 return false; 97 } 98 size_t pc_bytes; 99 verifier::RegisterMapFormat format; 100 if (pc_bits <= 8) { 101 format = verifier::kRegMapFormatCompact8; 102 pc_bytes = 1; 103 } else if (pc_bits <= 16) { 104 format = verifier::kRegMapFormatCompact16; 105 pc_bytes = 2; 106 } else { 107 LOG(WARNING) << "Cannot encode GC map for method with " 108 << (1 << pc_bits) << " instructions (number is rounded up to nearest power of 2): " 109 << PrettyMethod(method_verifier->GetMethodReference().dex_method_index, 110 *method_verifier->GetMethodReference().dex_file); 111 return false; 112 } 113 size_t table_size = ((pc_bytes + ref_bitmap_bytes) * num_entries) + 4; 114 dex_gc_map_.reserve(table_size); 115 // Write table header. 116 dex_gc_map_.push_back(format | ((ref_bitmap_bytes & ~0xFF) >> 5)); 117 dex_gc_map_.push_back(ref_bitmap_bytes & 0xFF); 118 dex_gc_map_.push_back(num_entries & 0xFF); 119 dex_gc_map_.push_back((num_entries >> 8) & 0xFF); 120 // Write table data. 121 const DexFile::CodeItem* code_item = method_verifier->CodeItem(); 122 for (size_t i = 0; i < code_item->insns_size_in_code_units_; i++) { 123 if (method_verifier->GetInstructionFlags(i).IsCompileTimeInfoPoint()) { 124 dex_gc_map_.push_back(i & 0xFF); 125 if (pc_bytes == 2) { 126 dex_gc_map_.push_back((i >> 8) & 0xFF); 127 } 128 verifier::RegisterLine* line = method_verifier->GetRegLine(i); 129 line->WriteReferenceBitMap(dex_gc_map_, ref_bitmap_bytes); 130 } 131 } 132 DCHECK_EQ(dex_gc_map_.size(), table_size); 133 return true; 134 } 135 136 void VerifiedMethod::VerifyGcMap(verifier::MethodVerifier* method_verifier, 137 const std::vector<uint8_t>& data) { 138 // Check that for every GC point there is a map entry, there aren't entries for non-GC points, 139 // that the table data is well formed and all references are marked (or not) in the bitmap. 140 verifier::DexPcToReferenceMap map(&data[0]); 141 DCHECK_EQ(data.size(), map.RawSize()); 142 size_t map_index = 0; 143 const DexFile::CodeItem* code_item = method_verifier->CodeItem(); 144 for (size_t i = 0; i < code_item->insns_size_in_code_units_; i++) { 145 const uint8_t* reg_bitmap = map.FindBitMap(i, false); 146 if (method_verifier->GetInstructionFlags(i).IsCompileTimeInfoPoint()) { 147 DCHECK_LT(map_index, map.NumEntries()); 148 DCHECK_EQ(map.GetDexPc(map_index), i); 149 DCHECK_EQ(map.GetBitMap(map_index), reg_bitmap); 150 map_index++; 151 verifier::RegisterLine* line = method_verifier->GetRegLine(i); 152 for (size_t j = 0; j < code_item->registers_size_; j++) { 153 if (line->GetRegisterType(j).IsNonZeroReferenceTypes()) { 154 DCHECK_LT(j / 8, map.RegWidth()); 155 DCHECK_EQ((reg_bitmap[j / 8] >> (j % 8)) & 1, 1); 156 } else if ((j / 8) < map.RegWidth()) { 157 DCHECK_EQ((reg_bitmap[j / 8] >> (j % 8)) & 1, 0); 158 } else { 159 // If a register doesn't contain a reference then the bitmap may be shorter than the line. 160 } 161 } 162 } else { 163 DCHECK(i >= 65536 || reg_bitmap == NULL); 164 } 165 } 166 } 167 168 void VerifiedMethod::ComputeGcMapSizes(verifier::MethodVerifier* method_verifier, 169 size_t* gc_points, size_t* ref_bitmap_bits, 170 size_t* log2_max_gc_pc) { 171 size_t local_gc_points = 0; 172 size_t max_insn = 0; 173 size_t max_ref_reg = -1; 174 const DexFile::CodeItem* code_item = method_verifier->CodeItem(); 175 for (size_t i = 0; i < code_item->insns_size_in_code_units_; i++) { 176 if (method_verifier->GetInstructionFlags(i).IsCompileTimeInfoPoint()) { 177 local_gc_points++; 178 max_insn = i; 179 verifier::RegisterLine* line = method_verifier->GetRegLine(i); 180 max_ref_reg = line->GetMaxNonZeroReferenceReg(max_ref_reg); 181 } 182 } 183 *gc_points = local_gc_points; 184 *ref_bitmap_bits = max_ref_reg + 1; // If max register is 0 we need 1 bit to encode (ie +1). 185 size_t i = 0; 186 while ((1U << i) <= max_insn) { 187 i++; 188 } 189 *log2_max_gc_pc = i; 190 } 191 192 void VerifiedMethod::GenerateDevirtMap(verifier::MethodVerifier* method_verifier) { 193 // It is risky to rely on reg_types for sharpening in cases of soft 194 // verification, we might end up sharpening to a wrong implementation. Just abort. 195 if (method_verifier->HasFailures()) { 196 return; 197 } 198 199 const DexFile::CodeItem* code_item = method_verifier->CodeItem(); 200 const uint16_t* insns = code_item->insns_; 201 const Instruction* inst = Instruction::At(insns); 202 const Instruction* end = Instruction::At(insns + code_item->insns_size_in_code_units_); 203 204 for (; inst < end; inst = inst->Next()) { 205 bool is_virtual = (inst->Opcode() == Instruction::INVOKE_VIRTUAL) || 206 (inst->Opcode() == Instruction::INVOKE_VIRTUAL_RANGE); 207 bool is_interface = (inst->Opcode() == Instruction::INVOKE_INTERFACE) || 208 (inst->Opcode() == Instruction::INVOKE_INTERFACE_RANGE); 209 210 if (!is_interface && !is_virtual) { 211 continue; 212 } 213 // Get reg type for register holding the reference to the object that will be dispatched upon. 214 uint32_t dex_pc = inst->GetDexPc(insns); 215 verifier::RegisterLine* line = method_verifier->GetRegLine(dex_pc); 216 bool is_range = (inst->Opcode() == Instruction::INVOKE_VIRTUAL_RANGE) || 217 (inst->Opcode() == Instruction::INVOKE_INTERFACE_RANGE); 218 verifier::RegType& 219 reg_type(line->GetRegisterType(is_range ? inst->VRegC_3rc() : inst->VRegC_35c())); 220 221 if (!reg_type.HasClass()) { 222 // We will compute devirtualization information only when we know the Class of the reg type. 223 continue; 224 } 225 mirror::Class* reg_class = reg_type.GetClass(); 226 if (reg_class->IsInterface()) { 227 // We can't devirtualize when the known type of the register is an interface. 228 continue; 229 } 230 if (reg_class->IsAbstract() && !reg_class->IsArrayClass()) { 231 // We can't devirtualize abstract classes except on arrays of abstract classes. 232 continue; 233 } 234 mirror::ArtMethod* abstract_method = method_verifier->GetDexCache()->GetResolvedMethod( 235 is_range ? inst->VRegB_3rc() : inst->VRegB_35c()); 236 if (abstract_method == NULL) { 237 // If the method is not found in the cache this means that it was never found 238 // by ResolveMethodAndCheckAccess() called when verifying invoke_*. 239 continue; 240 } 241 // Find the concrete method. 242 mirror::ArtMethod* concrete_method = NULL; 243 if (is_interface) { 244 concrete_method = reg_type.GetClass()->FindVirtualMethodForInterface(abstract_method); 245 } 246 if (is_virtual) { 247 concrete_method = reg_type.GetClass()->FindVirtualMethodForVirtual(abstract_method); 248 } 249 if (concrete_method == NULL || concrete_method->IsAbstract()) { 250 // In cases where concrete_method is not found, or is abstract, continue to the next invoke. 251 continue; 252 } 253 if (reg_type.IsPreciseReference() || concrete_method->IsFinal() || 254 concrete_method->GetDeclaringClass()->IsFinal()) { 255 // If we knew exactly the class being dispatched upon, or if the target method cannot be 256 // overridden record the target to be used in the compiler driver. 257 MethodReference concrete_ref( 258 concrete_method->GetDeclaringClass()->GetDexCache()->GetDexFile(), 259 concrete_method->GetDexMethodIndex()); 260 devirt_map_.Put(dex_pc, concrete_ref); 261 } 262 } 263 } 264 265 void VerifiedMethod::GenerateSafeCastSet(verifier::MethodVerifier* method_verifier) { 266 /* 267 * Walks over the method code and adds any cast instructions in which 268 * the type cast is implicit to a set, which is used in the code generation 269 * to elide these casts. 270 */ 271 if (method_verifier->HasFailures()) { 272 return; 273 } 274 const DexFile::CodeItem* code_item = method_verifier->CodeItem(); 275 const Instruction* inst = Instruction::At(code_item->insns_); 276 const Instruction* end = Instruction::At(code_item->insns_ + 277 code_item->insns_size_in_code_units_); 278 279 for (; inst < end; inst = inst->Next()) { 280 Instruction::Code code = inst->Opcode(); 281 if ((code == Instruction::CHECK_CAST) || (code == Instruction::APUT_OBJECT)) { 282 uint32_t dex_pc = inst->GetDexPc(code_item->insns_); 283 const verifier::RegisterLine* line = method_verifier->GetRegLine(dex_pc); 284 bool is_safe_cast = false; 285 if (code == Instruction::CHECK_CAST) { 286 verifier::RegType& reg_type(line->GetRegisterType(inst->VRegA_21c())); 287 verifier::RegType& cast_type = 288 method_verifier->ResolveCheckedClass(inst->VRegB_21c()); 289 is_safe_cast = cast_type.IsStrictlyAssignableFrom(reg_type); 290 } else { 291 verifier::RegType& array_type(line->GetRegisterType(inst->VRegB_23x())); 292 // We only know its safe to assign to an array if the array type is precise. For example, 293 // an Object[] can have any type of object stored in it, but it may also be assigned a 294 // String[] in which case the stores need to be of Strings. 295 if (array_type.IsPreciseReference()) { 296 verifier::RegType& value_type(line->GetRegisterType(inst->VRegA_23x())); 297 verifier::RegType& component_type = method_verifier->GetRegTypeCache() 298 ->GetComponentType(array_type, method_verifier->GetClassLoader()); 299 is_safe_cast = component_type.IsStrictlyAssignableFrom(value_type); 300 } 301 } 302 if (is_safe_cast) { 303 // Verify ordering for push_back() to the sorted vector. 304 DCHECK(safe_cast_set_.empty() || safe_cast_set_.back() < dex_pc); 305 safe_cast_set_.push_back(dex_pc); 306 } 307 } 308 } 309 } 310 311 } // namespace art 312
