1 /* 2 * Copyright (C) 2016 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_COMPILER_DEBUG_ELF_DEBUG_LINE_WRITER_H_ 18 #define ART_COMPILER_DEBUG_ELF_DEBUG_LINE_WRITER_H_ 19 20 #include <unordered_set> 21 #include <vector> 22 23 #include "compiled_method.h" 24 #include "debug/dwarf/debug_line_opcode_writer.h" 25 #include "debug/dwarf/headers.h" 26 #include "debug/elf_compilation_unit.h" 27 #include "dex_file-inl.h" 28 #include "elf_builder.h" 29 #include "stack_map.h" 30 31 namespace art { 32 namespace debug { 33 34 typedef std::vector<DexFile::PositionInfo> PositionInfos; 35 36 static bool PositionInfoCallback(void* ctx, const DexFile::PositionInfo& entry) { 37 static_cast<PositionInfos*>(ctx)->push_back(entry); 38 return false; 39 } 40 41 template<typename ElfTypes> 42 class ElfDebugLineWriter { 43 using Elf_Addr = typename ElfTypes::Addr; 44 45 public: 46 explicit ElfDebugLineWriter(ElfBuilder<ElfTypes>* builder) : builder_(builder) { 47 } 48 49 void Start() { 50 builder_->GetDebugLine()->Start(); 51 } 52 53 // Write line table for given set of methods. 54 // Returns the number of bytes written. 55 size_t WriteCompilationUnit(ElfCompilationUnit& compilation_unit) { 56 const InstructionSet isa = builder_->GetIsa(); 57 const bool is64bit = Is64BitInstructionSet(isa); 58 const Elf_Addr base_address = compilation_unit.is_code_address_text_relative 59 ? builder_->GetText()->GetAddress() 60 : 0; 61 62 compilation_unit.debug_line_offset = builder_->GetDebugLine()->GetSize(); 63 64 std::vector<dwarf::FileEntry> files; 65 std::unordered_map<std::string, size_t> files_map; 66 std::vector<std::string> directories; 67 std::unordered_map<std::string, size_t> directories_map; 68 int code_factor_bits_ = 0; 69 int dwarf_isa = -1; 70 switch (isa) { 71 case kArm: // arm actually means thumb2. 72 case kThumb2: 73 code_factor_bits_ = 1; // 16-bit instuctions 74 dwarf_isa = 1; // DW_ISA_ARM_thumb. 75 break; 76 case kArm64: 77 case kMips: 78 case kMips64: 79 code_factor_bits_ = 2; // 32-bit instructions 80 break; 81 case kNone: 82 case kX86: 83 case kX86_64: 84 break; 85 } 86 std::unordered_set<uint64_t> seen_addresses(compilation_unit.methods.size()); 87 dwarf::DebugLineOpCodeWriter<> opcodes(is64bit, code_factor_bits_); 88 for (const MethodDebugInfo* mi : compilation_unit.methods) { 89 // Ignore function if we have already generated line table for the same address. 90 // It would confuse the debugger and the DWARF specification forbids it. 91 // We allow the line table for method to be replicated in different compilation unit. 92 // This ensures that each compilation unit contains line table for all its methods. 93 if (!seen_addresses.insert(mi->code_address).second) { 94 continue; 95 } 96 97 uint32_t prologue_end = std::numeric_limits<uint32_t>::max(); 98 std::vector<SrcMapElem> pc2dex_map; 99 if (mi->code_info != nullptr) { 100 // Use stack maps to create mapping table from pc to dex. 101 const CodeInfo code_info(mi->code_info); 102 const CodeInfoEncoding encoding = code_info.ExtractEncoding(); 103 pc2dex_map.reserve(code_info.GetNumberOfStackMaps(encoding)); 104 for (uint32_t s = 0; s < code_info.GetNumberOfStackMaps(encoding); s++) { 105 StackMap stack_map = code_info.GetStackMapAt(s, encoding); 106 DCHECK(stack_map.IsValid()); 107 const uint32_t pc = stack_map.GetNativePcOffset(encoding.stack_map.encoding, isa); 108 const int32_t dex = stack_map.GetDexPc(encoding.stack_map.encoding); 109 pc2dex_map.push_back({pc, dex}); 110 if (stack_map.HasDexRegisterMap(encoding.stack_map.encoding)) { 111 // Guess that the first map with local variables is the end of prologue. 112 prologue_end = std::min(prologue_end, pc); 113 } 114 } 115 std::sort(pc2dex_map.begin(), pc2dex_map.end()); 116 } 117 118 if (pc2dex_map.empty()) { 119 continue; 120 } 121 122 // Compensate for compiler's off-by-one-instruction error. 123 // 124 // The compiler generates stackmap with PC *after* the branch instruction 125 // (because this is the PC which is easier to obtain when unwinding). 126 // 127 // However, the debugger is more clever and it will ask us for line-number 128 // mapping at the location of the branch instruction (since the following 129 // instruction could belong to other line, this is the correct thing to do). 130 // 131 // So we really want to just decrement the PC by one instruction so that the 132 // branch instruction is covered as well. However, we do not know the size 133 // of the previous instruction, and we can not subtract just a fixed amount 134 // (the debugger would trust us that the PC is valid; it might try to set 135 // breakpoint there at some point, and setting breakpoint in mid-instruction 136 // would make the process crash in spectacular way). 137 // 138 // Therefore, we say that the PC which the compiler gave us for the stackmap 139 // is the end of its associated address range, and we use the PC from the 140 // previous stack map as the start of the range. This ensures that the PC is 141 // valid and that the branch instruction is covered. 142 // 143 // This ensures we have correct line number mapping at call sites (which is 144 // important for backtraces), but there is nothing we can do for non-call 145 // sites (so stepping through optimized code in debugger is not possible). 146 // 147 // We do not adjust the stackmaps if the code was compiled as debuggable. 148 // In that case, the stackmaps should accurately cover all instructions. 149 if (!mi->is_native_debuggable) { 150 for (size_t i = pc2dex_map.size() - 1; i > 0; --i) { 151 pc2dex_map[i].from_ = pc2dex_map[i - 1].from_; 152 } 153 pc2dex_map[0].from_ = 0; 154 } 155 156 Elf_Addr method_address = base_address + mi->code_address; 157 158 PositionInfos dex2line_map; 159 DCHECK(mi->dex_file != nullptr); 160 const DexFile* dex = mi->dex_file; 161 if (!dex->DecodeDebugPositionInfo(mi->code_item, PositionInfoCallback, &dex2line_map)) { 162 continue; 163 } 164 165 if (dex2line_map.empty()) { 166 continue; 167 } 168 169 opcodes.SetAddress(method_address); 170 if (dwarf_isa != -1) { 171 opcodes.SetISA(dwarf_isa); 172 } 173 174 // Get and deduplicate directory and filename. 175 int file_index = 0; // 0 - primary source file of the compilation. 176 auto& dex_class_def = dex->GetClassDef(mi->class_def_index); 177 const char* source_file = dex->GetSourceFile(dex_class_def); 178 if (source_file != nullptr) { 179 std::string file_name(source_file); 180 size_t file_name_slash = file_name.find_last_of('/'); 181 std::string class_name(dex->GetClassDescriptor(dex_class_def)); 182 size_t class_name_slash = class_name.find_last_of('/'); 183 std::string full_path(file_name); 184 185 // Guess directory from package name. 186 int directory_index = 0; // 0 - current directory of the compilation. 187 if (file_name_slash == std::string::npos && // Just filename. 188 class_name.front() == 'L' && // Type descriptor for a class. 189 class_name_slash != std::string::npos) { // Has package name. 190 std::string package_name = class_name.substr(1, class_name_slash - 1); 191 auto it = directories_map.find(package_name); 192 if (it == directories_map.end()) { 193 directory_index = 1 + directories.size(); 194 directories_map.emplace(package_name, directory_index); 195 directories.push_back(package_name); 196 } else { 197 directory_index = it->second; 198 } 199 full_path = package_name + "/" + file_name; 200 } 201 202 // Add file entry. 203 auto it2 = files_map.find(full_path); 204 if (it2 == files_map.end()) { 205 file_index = 1 + files.size(); 206 files_map.emplace(full_path, file_index); 207 files.push_back(dwarf::FileEntry { 208 file_name, 209 directory_index, 210 0, // Modification time - NA. 211 0, // File size - NA. 212 }); 213 } else { 214 file_index = it2->second; 215 } 216 } 217 opcodes.SetFile(file_index); 218 219 // Generate mapping opcodes from PC to Java lines. 220 if (file_index != 0) { 221 // If the method was not compiled as native-debuggable, we still generate all available 222 // lines, but we try to prevent the debugger from stepping and setting breakpoints since 223 // the information is too inaccurate for that (breakpoints would be set after the calls). 224 const bool default_is_stmt = mi->is_native_debuggable; 225 bool first = true; 226 for (SrcMapElem pc2dex : pc2dex_map) { 227 uint32_t pc = pc2dex.from_; 228 int dex_pc = pc2dex.to_; 229 // Find mapping with address with is greater than our dex pc; then go back one step. 230 auto dex2line = std::upper_bound( 231 dex2line_map.begin(), 232 dex2line_map.end(), 233 dex_pc, 234 [](uint32_t address, const DexFile::PositionInfo& entry) { 235 return address < entry.address_; 236 }); 237 // Look for first valid mapping after the prologue. 238 if (dex2line != dex2line_map.begin() && pc >= prologue_end) { 239 int line = (--dex2line)->line_; 240 if (first) { 241 first = false; 242 if (pc > 0) { 243 // Assume that any preceding code is prologue. 244 int first_line = dex2line_map.front().line_; 245 // Prologue is not a sensible place for a breakpoint. 246 opcodes.SetIsStmt(false); 247 opcodes.AddRow(method_address, first_line); 248 opcodes.SetPrologueEnd(); 249 } 250 opcodes.SetIsStmt(default_is_stmt); 251 opcodes.AddRow(method_address + pc, line); 252 } else if (line != opcodes.CurrentLine()) { 253 opcodes.SetIsStmt(default_is_stmt); 254 opcodes.AddRow(method_address + pc, line); 255 } 256 } 257 } 258 } else { 259 // line 0 - instruction cannot be attributed to any source line. 260 opcodes.AddRow(method_address, 0); 261 } 262 263 opcodes.AdvancePC(method_address + mi->code_size); 264 opcodes.EndSequence(); 265 } 266 std::vector<uint8_t> buffer; 267 buffer.reserve(opcodes.data()->size() + KB); 268 size_t offset = builder_->GetDebugLine()->GetSize(); 269 WriteDebugLineTable(directories, files, opcodes, offset, &buffer, &debug_line_patches_); 270 builder_->GetDebugLine()->WriteFully(buffer.data(), buffer.size()); 271 return buffer.size(); 272 } 273 274 void End(bool write_oat_patches) { 275 builder_->GetDebugLine()->End(); 276 if (write_oat_patches) { 277 builder_->WritePatches(".debug_line.oat_patches", 278 ArrayRef<const uintptr_t>(debug_line_patches_)); 279 } 280 } 281 282 private: 283 ElfBuilder<ElfTypes>* builder_; 284 std::vector<uintptr_t> debug_line_patches_; 285 }; 286 287 } // namespace debug 288 } // namespace art 289 290 #endif // ART_COMPILER_DEBUG_ELF_DEBUG_LINE_WRITER_H_ 291 292
