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