compiler/elf_writer_debug.cc - platform/art - Gitiles

 /*
  * 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 "elf_writer_debug.h"

 #include <unordered_set>

 #include "base/casts.h"
 #include "compiled_method.h"
 #include "driver/compiler_driver.h"
 #include "dex_file-inl.h"
 #include "dwarf/headers.h"
 #include "dwarf/register.h"
 #include "elf_builder.h"
 #include "oat_writer.h"
 #include "utils.h"

 namespace art {
 namespace dwarf {

 static void WriteCIE(InstructionSet isa,
                      CFIFormat format,
                      std::vector<uint8_t>* buffer) {
   // Scratch registers should be marked as undefined.  This tells the
   // debugger that its value in the previous frame is not recoverable.
   bool is64bit = Is64BitInstructionSet(isa);
   switch (isa) {
     case kArm:
     case kThumb2: {
       DebugFrameOpCodeWriter<> opcodes;
       opcodes.DefCFA(Reg::ArmCore(13), 0);  // R13(SP).
       // core registers.
       for (int reg = 0; reg < 13; reg++) {
         if (reg < 4 || reg == 12) {
           opcodes.Undefined(Reg::ArmCore(reg));
         } else {
           opcodes.SameValue(Reg::ArmCore(reg));
         }
       }
       // fp registers.
       for (int reg = 0; reg < 32; reg++) {
         if (reg < 16) {
           opcodes.Undefined(Reg::ArmFp(reg));
         } else {
           opcodes.SameValue(Reg::ArmFp(reg));
         }
       }
       auto return_reg = Reg::ArmCore(14);  // R14(LR).
       WriteCIE(is64bit, return_reg, opcodes, format, buffer);
       return;
     }
     case kArm64: {
       DebugFrameOpCodeWriter<> opcodes;
       opcodes.DefCFA(Reg::Arm64Core(31), 0);  // R31(SP).
       // core registers.
       for (int reg = 0; reg < 30; reg++) {
         if (reg < 8 || reg == 16 || reg == 17) {
           opcodes.Undefined(Reg::Arm64Core(reg));
         } else {
           opcodes.SameValue(Reg::Arm64Core(reg));
         }
       }
       // fp registers.
       for (int reg = 0; reg < 32; reg++) {
         if (reg < 8 || reg >= 16) {
           opcodes.Undefined(Reg::Arm64Fp(reg));
         } else {
           opcodes.SameValue(Reg::Arm64Fp(reg));
         }
       }
       auto return_reg = Reg::Arm64Core(30);  // R30(LR).
       WriteCIE(is64bit, return_reg, opcodes, format, buffer);
       return;
     }
     case kMips:
     case kMips64: {
       DebugFrameOpCodeWriter<> opcodes;
       opcodes.DefCFA(Reg::MipsCore(29), 0);  // R29(SP).
       // core registers.
       for (int reg = 1; reg < 26; reg++) {
         if (reg < 16 || reg == 24 || reg == 25) {  // AT, V*, A*, T*.
           opcodes.Undefined(Reg::MipsCore(reg));
         } else {
           opcodes.SameValue(Reg::MipsCore(reg));
         }
       }
       auto return_reg = Reg::MipsCore(31);  // R31(RA).
       WriteCIE(is64bit, return_reg, opcodes, format, buffer);
       return;
     }
     case kX86: {
       // FIXME: Add fp registers once libunwind adds support for them. Bug: 20491296
       constexpr bool generate_opcodes_for_x86_fp = false;
       DebugFrameOpCodeWriter<> opcodes;
       opcodes.DefCFA(Reg::X86Core(4), 4);   // R4(ESP).
       opcodes.Offset(Reg::X86Core(8), -4);  // R8(EIP).
       // core registers.
       for (int reg = 0; reg < 8; reg++) {
         if (reg <= 3) {
           opcodes.Undefined(Reg::X86Core(reg));
         } else if (reg == 4) {
           // Stack pointer.
         } else {
           opcodes.SameValue(Reg::X86Core(reg));
         }
       }
       // fp registers.
       if (generate_opcodes_for_x86_fp) {
         for (int reg = 0; reg < 8; reg++) {
           opcodes.Undefined(Reg::X86Fp(reg));
         }
       }
       auto return_reg = Reg::X86Core(8);  // R8(EIP).
       WriteCIE(is64bit, return_reg, opcodes, format, buffer);
       return;
     }
     case kX86_64: {
       DebugFrameOpCodeWriter<> opcodes;
       opcodes.DefCFA(Reg::X86_64Core(4), 8);  // R4(RSP).
       opcodes.Offset(Reg::X86_64Core(16), -8);  // R16(RIP).
       // core registers.
       for (int reg = 0; reg < 16; reg++) {
         if (reg == 4) {
           // Stack pointer.
         } else if (reg < 12 && reg != 3 && reg != 5) {  // except EBX and EBP.
           opcodes.Undefined(Reg::X86_64Core(reg));
         } else {
           opcodes.SameValue(Reg::X86_64Core(reg));
         }
       }
       // fp registers.
       for (int reg = 0; reg < 16; reg++) {
         if (reg < 12) {
           opcodes.Undefined(Reg::X86_64Fp(reg));
         } else {
           opcodes.SameValue(Reg::X86_64Fp(reg));
         }
       }
       auto return_reg = Reg::X86_64Core(16);  // R16(RIP).
       WriteCIE(is64bit, return_reg, opcodes, format, buffer);
       return;
     }
     case kNone:
       break;
   }
   LOG(FATAL) << "Can not write CIE frame for ISA " << isa;
   UNREACHABLE();
 }

 template<typename ElfTypes>
 void WriteCFISection(ElfBuilder<ElfTypes>* builder,
                      const std::vector<OatWriter::DebugInfo>& method_infos,
                      CFIFormat format) {
   CHECK(format == dwarf::DW_DEBUG_FRAME_FORMAT ||
         format == dwarf::DW_EH_FRAME_FORMAT);
   typedef typename ElfTypes::Addr Elf_Addr;

   std::vector<uint32_t> binary_search_table;
   std::vector<uintptr_t> patch_locations;
   if (format == DW_EH_FRAME_FORMAT) {
     binary_search_table.reserve(2 * method_infos.size());
   } else {
     patch_locations.reserve(method_infos.size());
   }

   // Write .eh_frame/.debug_frame section.
   auto* cfi_section = (format == dwarf::DW_DEBUG_FRAME_FORMAT
                        ? builder->GetDebugFrame()
                        : builder->GetEhFrame());
   {
     cfi_section->Start();
     const bool is64bit = Is64BitInstructionSet(builder->GetIsa());
     const Elf_Addr text_address = builder->GetText()->GetAddress();
     const Elf_Addr cfi_address = cfi_section->GetAddress();
     const Elf_Addr cie_address = cfi_address;
     Elf_Addr buffer_address = cfi_address;
     std::vector<uint8_t> buffer;  // Small temporary buffer.
     WriteCIE(builder->GetIsa(), format, &buffer);
     cfi_section->WriteFully(buffer.data(), buffer.size());
     buffer_address += buffer.size();
     buffer.clear();
     for (const OatWriter::DebugInfo& mi : method_infos) {
       if (!mi.deduped_) {  // Only one FDE per unique address.
         ArrayRef<const uint8_t> opcodes = mi.compiled_method_->GetCFIInfo();
         if (!opcodes.empty()) {
           const Elf_Addr code_address = text_address + mi.low_pc_;
           if (format == DW_EH_FRAME_FORMAT) {
             binary_search_table.push_back(
                 dchecked_integral_cast<uint32_t>(code_address));
             binary_search_table.push_back(
                 dchecked_integral_cast<uint32_t>(buffer_address));
           }
           WriteFDE(is64bit, cfi_address, cie_address,
                    code_address, mi.high_pc_ - mi.low_pc_,
                    opcodes, format, buffer_address, &buffer,
                    &patch_locations);
           cfi_section->WriteFully(buffer.data(), buffer.size());
           buffer_address += buffer.size();
           buffer.clear();
         }
       }
     }
     cfi_section->End();
   }

   if (format == DW_EH_FRAME_FORMAT) {
     auto* header_section = builder->GetEhFrameHdr();
     header_section->Start();
     uint32_t header_address = dchecked_integral_cast<int32_t>(header_section->GetAddress());
     // Write .eh_frame_hdr section.
     std::vector<uint8_t> buffer;
     Writer<> header(&buffer);
     header.PushUint8(1);  // Version.
     // Encoding of .eh_frame pointer - libunwind does not honor datarel here,
     // so we have to use pcrel which means relative to the pointer's location.
     header.PushUint8(DW_EH_PE_pcrel | DW_EH_PE_sdata4);
     // Encoding of binary search table size.
     header.PushUint8(DW_EH_PE_udata4);
     // Encoding of binary search table addresses - libunwind supports only this
     // specific combination, which means relative to the start of .eh_frame_hdr.
     header.PushUint8(DW_EH_PE_datarel | DW_EH_PE_sdata4);
     // .eh_frame pointer
     header.PushInt32(cfi_section->GetAddress() - (header_address + 4u));
     // Binary search table size (number of entries).
     header.PushUint32(dchecked_integral_cast<uint32_t>(binary_search_table.size()/2));
     header_section->WriteFully(buffer.data(), buffer.size());
     // Binary search table.
     for (size_t i = 0; i < binary_search_table.size(); i++) {
       // Make addresses section-relative since we know the header address now.
       binary_search_table[i] -= header_address;
     }
     header_section->WriteFully(binary_search_table.data(), binary_search_table.size());
     header_section->End();
   } else {
     builder->WritePatches(".debug_frame.oat_patches", &patch_locations);
   }
 }

 template<typename ElfTypes>
 class DebugInfoWriter {
   typedef typename ElfTypes::Addr Elf_Addr;

  public:
   explicit DebugInfoWriter(ElfBuilder<ElfTypes>* builder) : builder_(builder) {
   }

   void Start() {
     builder_->GetDebugInfo()->Start();
   }

   void Write(const std::vector<const OatWriter::DebugInfo*>& method_infos,
              size_t debug_line_offset) {
     const bool is64bit = Is64BitInstructionSet(builder_->GetIsa());
     const Elf_Addr text_address = builder_->GetText()->GetAddress();
     uint32_t cunit_low_pc = 0xFFFFFFFFU;
     uint32_t cunit_high_pc = 0;
     for (auto method_info : method_infos) {
       cunit_low_pc = std::min(cunit_low_pc, method_info->low_pc_);
       cunit_high_pc = std::max(cunit_high_pc, method_info->high_pc_);
     }

     size_t debug_abbrev_offset = debug_abbrev_.size();
     DebugInfoEntryWriter<> info(is64bit, &debug_abbrev_);
     info.StartTag(DW_TAG_compile_unit, DW_CHILDREN_yes);
     info.WriteStrp(DW_AT_producer, "Android dex2oat", &debug_str_);
     info.WriteData1(DW_AT_language, DW_LANG_Java);
     info.WriteAddr(DW_AT_low_pc, text_address + cunit_low_pc);
     info.WriteAddr(DW_AT_high_pc, text_address + cunit_high_pc);
     info.WriteData4(DW_AT_stmt_list, debug_line_offset);
     for (auto method_info : method_infos) {
       std::string method_name = PrettyMethod(method_info->dex_method_index_,
                                              *method_info->dex_file_, true);
       info.StartTag(DW_TAG_subprogram, DW_CHILDREN_no);
       info.WriteStrp(DW_AT_name, method_name.data(), &debug_str_);
       info.WriteAddr(DW_AT_low_pc, text_address + method_info->low_pc_);
       info.WriteAddr(DW_AT_high_pc, text_address + method_info->high_pc_);
       info.EndTag();  // DW_TAG_subprogram
     }
     info.EndTag();  // DW_TAG_compile_unit
     std::vector<uint8_t> buffer;
     buffer.reserve(info.data()->size() + KB);
     size_t offset = builder_->GetDebugInfo()->GetSize();
     WriteDebugInfoCU(debug_abbrev_offset, info, offset, &buffer, &debug_info_patches_);
     builder_->GetDebugInfo()->WriteFully(buffer.data(), buffer.size());
   }

   void End() {
     builder_->GetDebugInfo()->End();
     builder_->WritePatches(".debug_info.oat_patches", &debug_info_patches_);
     builder_->WriteSection(".debug_abbrev", &debug_abbrev_);
     builder_->WriteSection(".debug_str", &debug_str_);
   }

  private:
   ElfBuilder<ElfTypes>* builder_;
   std::vector<uintptr_t> debug_info_patches_;
   std::vector<uint8_t> debug_abbrev_;
   std::vector<uint8_t> debug_str_;
 };

 template<typename ElfTypes>
 class DebugLineWriter {
   typedef typename ElfTypes::Addr Elf_Addr;

  public:
   explicit DebugLineWriter(ElfBuilder<ElfTypes>* builder) : builder_(builder) {
   }

   void Start() {
     builder_->GetDebugLine()->Start();
   }

   // Write line table for given set of methods.
   // Returns the number of bytes written.
   size_t Write(const std::vector<const OatWriter::DebugInfo*>& method_infos) {
     const bool is64bit = Is64BitInstructionSet(builder_->GetIsa());
     const Elf_Addr text_address = builder_->GetText()->GetAddress();
     uint32_t cunit_low_pc = 0xFFFFFFFFU;
     uint32_t cunit_high_pc = 0;
     for (auto method_info : method_infos) {
       cunit_low_pc = std::min(cunit_low_pc, method_info->low_pc_);
       cunit_high_pc = std::max(cunit_high_pc, method_info->high_pc_);
     }

     std::vector<FileEntry> files;
     std::unordered_map<std::string, size_t> files_map;
     std::vector<std::string> directories;
     std::unordered_map<std::string, size_t> directories_map;
     int code_factor_bits_ = 0;
     int dwarf_isa = -1;
     switch (builder_->GetIsa()) {
       case kArm:  // arm actually means thumb2.
       case kThumb2:
         code_factor_bits_ = 1;  // 16-bit instuctions
         dwarf_isa = 1;  // DW_ISA_ARM_thumb.
         break;
       case kArm64:
       case kMips:
       case kMips64:
         code_factor_bits_ = 2;  // 32-bit instructions
         break;
       case kNone:
       case kX86:
       case kX86_64:
         break;
     }
     DebugLineOpCodeWriter<> opcodes(is64bit, code_factor_bits_);
     opcodes.SetAddress(text_address + cunit_low_pc);
     if (dwarf_isa != -1) {
       opcodes.SetISA(dwarf_isa);
     }
     for (const OatWriter::DebugInfo* mi : method_infos) {
       struct DebugInfoCallbacks {
         static bool NewPosition(void* ctx, uint32_t address, uint32_t line) {
           auto* context = reinterpret_cast<DebugInfoCallbacks*>(ctx);
           context->dex2line_.push_back({address, static_cast<int32_t>(line)});
           return false;
         }
         DefaultSrcMap dex2line_;
       } debug_info_callbacks;

       Elf_Addr method_address = text_address + mi->low_pc_;

       const DexFile* dex = mi->dex_file_;
       if (mi->code_item_ != nullptr) {
         dex->DecodeDebugInfo(mi->code_item_,
                              (mi->access_flags_ & kAccStatic) != 0,
                              mi->dex_method_index_,
                              DebugInfoCallbacks::NewPosition,
                              nullptr,
                              &debug_info_callbacks);
       }

       // Get and deduplicate directory and filename.
       int file_index = 0;  // 0 - primary source file of the compilation.
       auto& dex_class_def = dex->GetClassDef(mi->class_def_index_);
       const char* source_file = dex->GetSourceFile(dex_class_def);
       if (source_file != nullptr) {
         std::string file_name(source_file);
         size_t file_name_slash = file_name.find_last_of('/');
         std::string class_name(dex->GetClassDescriptor(dex_class_def));
         size_t class_name_slash = class_name.find_last_of('/');
         std::string full_path(file_name);

         // Guess directory from package name.
         int directory_index = 0;  // 0 - current directory of the compilation.
         if (file_name_slash == std::string::npos &&  // Just filename.
             class_name.front() == 'L' &&  // Type descriptor for a class.
             class_name_slash != std::string::npos) {  // Has package name.
           std::string package_name = class_name.substr(1, class_name_slash - 1);
           auto it = directories_map.find(package_name);
           if (it == directories_map.end()) {
             directory_index = 1 + directories.size();
             directories_map.emplace(package_name, directory_index);
             directories.push_back(package_name);
           } else {
             directory_index = it->second;
           }
           full_path = package_name + "/" + file_name;
         }

         // Add file entry.
         auto it2 = files_map.find(full_path);
         if (it2 == files_map.end()) {
           file_index = 1 + files.size();
           files_map.emplace(full_path, file_index);
           files.push_back(FileEntry {
             file_name,
             directory_index,
             0,  // Modification time - NA.
             0,  // File size - NA.
           });
         } else {
           file_index = it2->second;
         }
       }
       opcodes.SetFile(file_index);

       // Generate mapping opcodes from PC to Java lines.
       const DefaultSrcMap& dex2line_map = debug_info_callbacks.dex2line_;
       if (file_index != 0 && !dex2line_map.empty()) {
         bool first = true;
         for (SrcMapElem pc2dex : mi->compiled_method_->GetSrcMappingTable()) {
           uint32_t pc = pc2dex.from_;
           int dex_pc = pc2dex.to_;
           auto dex2line = dex2line_map.Find(static_cast<uint32_t>(dex_pc));
           if (dex2line.first) {
             int line = dex2line.second;
             if (first) {
               first = false;
               if (pc > 0) {
                 // Assume that any preceding code is prologue.
                 int first_line = dex2line_map.front().to_;
                 // Prologue is not a sensible place for a breakpoint.
                 opcodes.NegateStmt();
                 opcodes.AddRow(method_address, first_line);
                 opcodes.NegateStmt();
                 opcodes.SetPrologueEnd();
               }
               opcodes.AddRow(method_address + pc, line);
             } else if (line != opcodes.CurrentLine()) {
               opcodes.AddRow(method_address + pc, line);
             }
           }
         }
       } else {
         // line 0 - instruction cannot be attributed to any source line.
         opcodes.AddRow(method_address, 0);
       }
     }
     opcodes.AdvancePC(text_address + cunit_high_pc);
     opcodes.EndSequence();
     std::vector<uint8_t> buffer;
     buffer.reserve(opcodes.data()->size() + KB);
     size_t offset = builder_->GetDebugLine()->GetSize();
     WriteDebugLineTable(directories, files, opcodes, offset, &buffer, &debug_line_patches);
     builder_->GetDebugLine()->WriteFully(buffer.data(), buffer.size());
     return buffer.size();
   }

   void End() {
     builder_->GetDebugLine()->End();
     builder_->WritePatches(".debug_line.oat_patches", &debug_line_patches);
   }

  private:
   ElfBuilder<ElfTypes>* builder_;
   std::vector<uintptr_t> debug_line_patches;
 };

 template<typename ElfTypes>
 void WriteDebugSections(ElfBuilder<ElfTypes>* builder,
                         const std::vector<OatWriter::DebugInfo>& method_infos) {
   struct CompilationUnit {
     std::vector<const OatWriter::DebugInfo*> methods_;
     size_t debug_line_offset_ = 0;
   };

   // Group the methods into compilation units based on source file.
   std::vector<CompilationUnit> compilation_units;
   const char* last_source_file = nullptr;
   for (const OatWriter::DebugInfo& mi : method_infos) {
     // Attribute given instruction range only to single method.
     // Otherwise the debugger might get really confused.
     if (!mi.deduped_) {
       auto& dex_class_def = mi.dex_file_->GetClassDef(mi.class_def_index_);
       const char* source_file = mi.dex_file_->GetSourceFile(dex_class_def);
       if (compilation_units.empty() || source_file != last_source_file) {
         compilation_units.push_back(CompilationUnit());
       }
       compilation_units.back().methods_.push_back(&mi);
       last_source_file = source_file;
     }
   }

   // Write .debug_line section.
   {
     DebugLineWriter<ElfTypes> line_writer(builder);
     line_writer.Start();
     size_t offset = 0;
     for (auto& compilation_unit : compilation_units) {
       compilation_unit.debug_line_offset_ = offset;
       offset += line_writer.Write(compilation_unit.methods_);
     }
     line_writer.End();
   }

   // Write .debug_info section.
   {
     DebugInfoWriter<ElfTypes> info_writer(builder);
     info_writer.Start();
     for (const auto& compilation_unit : compilation_units) {
       info_writer.Write(compilation_unit.methods_, compilation_unit.debug_line_offset_);
     }
     info_writer.End();
   }
 }

 // Explicit instantiations
 template void WriteCFISection<ElfTypes32>(
     ElfBuilder<ElfTypes32>* builder,
     const std::vector<OatWriter::DebugInfo>& method_infos,
     CFIFormat format);
 template void WriteCFISection<ElfTypes64>(
     ElfBuilder<ElfTypes64>* builder,
     const std::vector<OatWriter::DebugInfo>& method_infos,
     CFIFormat format);
 template void WriteDebugSections<ElfTypes32>(
     ElfBuilder<ElfTypes32>* builder,
     const std::vector<OatWriter::DebugInfo>& method_infos);
 template void WriteDebugSections<ElfTypes64>(
     ElfBuilder<ElfTypes64>* builder,
     const std::vector<OatWriter::DebugInfo>& method_infos);

 }  // namespace dwarf
 }  // namespace art
	/*
	* 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 "elf_writer_debug.h"

	#include <unordered_set>

	#include "base/casts.h"
	#include "compiled_method.h"
	#include "driver/compiler_driver.h"
	#include "dex_file-inl.h"
	#include "dwarf/headers.h"
	#include "dwarf/register.h"
	#include "elf_builder.h"
	#include "oat_writer.h"
	#include "utils.h"

	namespace art {
	namespace dwarf {

	static void WriteCIE(InstructionSet isa,
	CFIFormat format,
	std::vector<uint8_t>* buffer) {
	// Scratch registers should be marked as undefined. This tells the
	// debugger that its value in the previous frame is not recoverable.
	bool is64bit = Is64BitInstructionSet(isa);
	switch (isa) {
	case kArm:
	case kThumb2: {
	DebugFrameOpCodeWriter<> opcodes;
	opcodes.DefCFA(Reg::ArmCore(13), 0); // R13(SP).
	// core registers.
	for (int reg = 0; reg < 13; reg++) {
	if (reg < 4 \|\| reg == 12) {
	opcodes.Undefined(Reg::ArmCore(reg));
	} else {
	opcodes.SameValue(Reg::ArmCore(reg));
	}
	}
	// fp registers.
	for (int reg = 0; reg < 32; reg++) {
	if (reg < 16) {
	opcodes.Undefined(Reg::ArmFp(reg));
	} else {
	opcodes.SameValue(Reg::ArmFp(reg));
	}
	}
	auto return_reg = Reg::ArmCore(14); // R14(LR).
	WriteCIE(is64bit, return_reg, opcodes, format, buffer);
	return;
	}
	case kArm64: {
	DebugFrameOpCodeWriter<> opcodes;
	opcodes.DefCFA(Reg::Arm64Core(31), 0); // R31(SP).
	// core registers.
	for (int reg = 0; reg < 30; reg++) {
	if (reg < 8 \|\| reg == 16 \|\| reg == 17) {
	opcodes.Undefined(Reg::Arm64Core(reg));
	} else {
	opcodes.SameValue(Reg::Arm64Core(reg));
	}
	}
	// fp registers.
	for (int reg = 0; reg < 32; reg++) {
	if (reg < 8 \|\| reg >= 16) {
	opcodes.Undefined(Reg::Arm64Fp(reg));
	} else {
	opcodes.SameValue(Reg::Arm64Fp(reg));
	}
	}
	auto return_reg = Reg::Arm64Core(30); // R30(LR).
	WriteCIE(is64bit, return_reg, opcodes, format, buffer);
	return;
	}
	case kMips:
	case kMips64: {
	DebugFrameOpCodeWriter<> opcodes;
	opcodes.DefCFA(Reg::MipsCore(29), 0); // R29(SP).
	// core registers.
	for (int reg = 1; reg < 26; reg++) {
	if (reg < 16 \|\| reg == 24 \|\| reg == 25) { // AT, V, A, T*.
	opcodes.Undefined(Reg::MipsCore(reg));
	} else {
	opcodes.SameValue(Reg::MipsCore(reg));
	}
	}
	auto return_reg = Reg::MipsCore(31); // R31(RA).
	WriteCIE(is64bit, return_reg, opcodes, format, buffer);
	return;
	}
	case kX86: {
	// FIXME: Add fp registers once libunwind adds support for them. Bug: 20491296
	constexpr bool generate_opcodes_for_x86_fp = false;
	DebugFrameOpCodeWriter<> opcodes;
	opcodes.DefCFA(Reg::X86Core(4), 4); // R4(ESP).
	opcodes.Offset(Reg::X86Core(8), -4); // R8(EIP).
	// core registers.
	for (int reg = 0; reg < 8; reg++) {
	if (reg <= 3) {
	opcodes.Undefined(Reg::X86Core(reg));
	} else if (reg == 4) {
	// Stack pointer.
	} else {
	opcodes.SameValue(Reg::X86Core(reg));
	}
	}
	// fp registers.
	if (generate_opcodes_for_x86_fp) {
	for (int reg = 0; reg < 8; reg++) {
	opcodes.Undefined(Reg::X86Fp(reg));
	}
	}
	auto return_reg = Reg::X86Core(8); // R8(EIP).
	WriteCIE(is64bit, return_reg, opcodes, format, buffer);
	return;
	}
	case kX86_64: {
	DebugFrameOpCodeWriter<> opcodes;
	opcodes.DefCFA(Reg::X86_64Core(4), 8); // R4(RSP).
	opcodes.Offset(Reg::X86_64Core(16), -8); // R16(RIP).
	// core registers.
	for (int reg = 0; reg < 16; reg++) {
	if (reg == 4) {
	// Stack pointer.
	} else if (reg < 12 && reg != 3 && reg != 5) { // except EBX and EBP.
	opcodes.Undefined(Reg::X86_64Core(reg));
	} else {
	opcodes.SameValue(Reg::X86_64Core(reg));
	}
	}
	// fp registers.
	for (int reg = 0; reg < 16; reg++) {
	if (reg < 12) {
	opcodes.Undefined(Reg::X86_64Fp(reg));
	} else {
	opcodes.SameValue(Reg::X86_64Fp(reg));
	}
	}
	auto return_reg = Reg::X86_64Core(16); // R16(RIP).
	WriteCIE(is64bit, return_reg, opcodes, format, buffer);
	return;
	}
	case kNone:
	break;
	}
	LOG(FATAL) << "Can not write CIE frame for ISA " << isa;
	UNREACHABLE();
	}

	template<typename ElfTypes>
	void WriteCFISection(ElfBuilder<ElfTypes>* builder,
	const std::vector<OatWriter::DebugInfo>& method_infos,
	CFIFormat format) {
	CHECK(format == dwarf::DW_DEBUG_FRAME_FORMAT \|\|
	format == dwarf::DW_EH_FRAME_FORMAT);
	typedef typename ElfTypes::Addr Elf_Addr;

	std::vector<uint32_t> binary_search_table;
	std::vector<uintptr_t> patch_locations;
	if (format == DW_EH_FRAME_FORMAT) {
	binary_search_table.reserve(2 * method_infos.size());
	} else {
	patch_locations.reserve(method_infos.size());
	}

	// Write .eh_frame/.debug_frame section.
	auto* cfi_section = (format == dwarf::DW_DEBUG_FRAME_FORMAT
	? builder->GetDebugFrame()
	: builder->GetEhFrame());
	{
	cfi_section->Start();
	const bool is64bit = Is64BitInstructionSet(builder->GetIsa());
	const Elf_Addr text_address = builder->GetText()->GetAddress();
	const Elf_Addr cfi_address = cfi_section->GetAddress();
	const Elf_Addr cie_address = cfi_address;
	Elf_Addr buffer_address = cfi_address;
	std::vector<uint8_t> buffer; // Small temporary buffer.
	WriteCIE(builder->GetIsa(), format, &buffer);
	cfi_section->WriteFully(buffer.data(), buffer.size());
	buffer_address += buffer.size();
	buffer.clear();
	for (const OatWriter::DebugInfo& mi : method_infos) {
	if (!mi.deduped_) { // Only one FDE per unique address.
	ArrayRef<const uint8_t> opcodes = mi.compiled_method_->GetCFIInfo();
	if (!opcodes.empty()) {
	const Elf_Addr code_address = text_address + mi.low_pc_;
	if (format == DW_EH_FRAME_FORMAT) {
	binary_search_table.push_back(
	dchecked_integral_cast<uint32_t>(code_address));
	binary_search_table.push_back(
	dchecked_integral_cast<uint32_t>(buffer_address));
	}
	WriteFDE(is64bit, cfi_address, cie_address,
	code_address, mi.high_pc_ - mi.low_pc_,
	opcodes, format, buffer_address, &buffer,
	&patch_locations);
	cfi_section->WriteFully(buffer.data(), buffer.size());
	buffer_address += buffer.size();
	buffer.clear();
	}
	}
	}
	cfi_section->End();
	}

	if (format == DW_EH_FRAME_FORMAT) {
	auto* header_section = builder->GetEhFrameHdr();
	header_section->Start();
	uint32_t header_address = dchecked_integral_cast<int32_t>(header_section->GetAddress());
	// Write .eh_frame_hdr section.
	std::vector<uint8_t> buffer;
	Writer<> header(&buffer);
	header.PushUint8(1); // Version.
	// Encoding of .eh_frame pointer - libunwind does not honor datarel here,
	// so we have to use pcrel which means relative to the pointer's location.
	header.PushUint8(DW_EH_PE_pcrel \| DW_EH_PE_sdata4);
	// Encoding of binary search table size.
	header.PushUint8(DW_EH_PE_udata4);
	// Encoding of binary search table addresses - libunwind supports only this
	// specific combination, which means relative to the start of .eh_frame_hdr.
	header.PushUint8(DW_EH_PE_datarel \| DW_EH_PE_sdata4);
	// .eh_frame pointer
	header.PushInt32(cfi_section->GetAddress() - (header_address + 4u));
	// Binary search table size (number of entries).
	header.PushUint32(dchecked_integral_cast<uint32_t>(binary_search_table.size()/2));
	header_section->WriteFully(buffer.data(), buffer.size());
	// Binary search table.
	for (size_t i = 0; i < binary_search_table.size(); i++) {
	// Make addresses section-relative since we know the header address now.
	binary_search_table[i] -= header_address;
	}
	header_section->WriteFully(binary_search_table.data(), binary_search_table.size());
	header_section->End();
	} else {
	builder->WritePatches(".debug_frame.oat_patches", &patch_locations);
	}
	}

	template<typename ElfTypes>
	class DebugInfoWriter {
	typedef typename ElfTypes::Addr Elf_Addr;

	public:
	explicit DebugInfoWriter(ElfBuilder<ElfTypes>* builder) : builder_(builder) {
	}

	void Start() {
	builder_->GetDebugInfo()->Start();
	}

	void Write(const std::vector<const OatWriter::DebugInfo*>& method_infos,
	size_t debug_line_offset) {
	const bool is64bit = Is64BitInstructionSet(builder_->GetIsa());
	const Elf_Addr text_address = builder_->GetText()->GetAddress();
	uint32_t cunit_low_pc = 0xFFFFFFFFU;
	uint32_t cunit_high_pc = 0;
	for (auto method_info : method_infos) {
	cunit_low_pc = std::min(cunit_low_pc, method_info->low_pc_);
	cunit_high_pc = std::max(cunit_high_pc, method_info->high_pc_);
	}

	size_t debug_abbrev_offset = debug_abbrev_.size();
	DebugInfoEntryWriter<> info(is64bit, &debug_abbrev_);
	info.StartTag(DW_TAG_compile_unit, DW_CHILDREN_yes);
	info.WriteStrp(DW_AT_producer, "Android dex2oat", &debug_str_);
	info.WriteData1(DW_AT_language, DW_LANG_Java);
	info.WriteAddr(DW_AT_low_pc, text_address + cunit_low_pc);
	info.WriteAddr(DW_AT_high_pc, text_address + cunit_high_pc);
	info.WriteData4(DW_AT_stmt_list, debug_line_offset);
	for (auto method_info : method_infos) {
	std::string method_name = PrettyMethod(method_info->dex_method_index_,
	*method_info->dex_file_, true);
	info.StartTag(DW_TAG_subprogram, DW_CHILDREN_no);
	info.WriteStrp(DW_AT_name, method_name.data(), &debug_str_);
	info.WriteAddr(DW_AT_low_pc, text_address + method_info->low_pc_);
	info.WriteAddr(DW_AT_high_pc, text_address + method_info->high_pc_);
	info.EndTag(); // DW_TAG_subprogram
	}
	info.EndTag(); // DW_TAG_compile_unit
	std::vector<uint8_t> buffer;
	buffer.reserve(info.data()->size() + KB);
	size_t offset = builder_->GetDebugInfo()->GetSize();
	WriteDebugInfoCU(debug_abbrev_offset, info, offset, &buffer, &debug_info_patches_);
	builder_->GetDebugInfo()->WriteFully(buffer.data(), buffer.size());
	}

	void End() {
	builder_->GetDebugInfo()->End();
	builder_->WritePatches(".debug_info.oat_patches", &debug_info_patches_);
	builder_->WriteSection(".debug_abbrev", &debug_abbrev_);
	builder_->WriteSection(".debug_str", &debug_str_);
	}

	private:
	ElfBuilder<ElfTypes>* builder_;
	std::vector<uintptr_t> debug_info_patches_;
	std::vector<uint8_t> debug_abbrev_;
	std::vector<uint8_t> debug_str_;
	};

	template<typename ElfTypes>
	class DebugLineWriter {
	typedef typename ElfTypes::Addr Elf_Addr;

	public:
	explicit DebugLineWriter(ElfBuilder<ElfTypes>* builder) : builder_(builder) {
	}

	void Start() {
	builder_->GetDebugLine()->Start();
	}

	// Write line table for given set of methods.
	// Returns the number of bytes written.
	size_t Write(const std::vector<const OatWriter::DebugInfo*>& method_infos) {
	const bool is64bit = Is64BitInstructionSet(builder_->GetIsa());
	const Elf_Addr text_address = builder_->GetText()->GetAddress();
	uint32_t cunit_low_pc = 0xFFFFFFFFU;
	uint32_t cunit_high_pc = 0;
	for (auto method_info : method_infos) {
	cunit_low_pc = std::min(cunit_low_pc, method_info->low_pc_);
	cunit_high_pc = std::max(cunit_high_pc, method_info->high_pc_);
	}

	std::vector<FileEntry> files;
	std::unordered_map<std::string, size_t> files_map;
	std::vector<std::string> directories;
	std::unordered_map<std::string, size_t> directories_map;
	int code_factor_bits_ = 0;
	int dwarf_isa = -1;
	switch (builder_->GetIsa()) {
	case kArm: // arm actually means thumb2.
	case kThumb2:
	code_factor_bits_ = 1; // 16-bit instuctions
	dwarf_isa = 1; // DW_ISA_ARM_thumb.
	break;
	case kArm64:
	case kMips:
	case kMips64:
	code_factor_bits_ = 2; // 32-bit instructions
	break;
	case kNone:
	case kX86:
	case kX86_64:
	break;
	}
	DebugLineOpCodeWriter<> opcodes(is64bit, code_factor_bits_);
	opcodes.SetAddress(text_address + cunit_low_pc);
	if (dwarf_isa != -1) {
	opcodes.SetISA(dwarf_isa);
	}
	for (const OatWriter::DebugInfo* mi : method_infos) {
	struct DebugInfoCallbacks {
	static bool NewPosition(void* ctx, uint32_t address, uint32_t line) {
	auto* context = reinterpret_cast<DebugInfoCallbacks*>(ctx);
	context->dex2line_.push_back({address, static_cast<int32_t>(line)});
	return false;
	}
	DefaultSrcMap dex2line_;
	} debug_info_callbacks;

	Elf_Addr method_address = text_address + mi->low_pc_;

	const DexFile* dex = mi->dex_file_;
	if (mi->code_item_ != nullptr) {
	dex->DecodeDebugInfo(mi->code_item_,
	(mi->access_flags_ & kAccStatic) != 0,
	mi->dex_method_index_,
	DebugInfoCallbacks::NewPosition,
	nullptr,
	&debug_info_callbacks);
	}

	// Get and deduplicate directory and filename.
	int file_index = 0; // 0 - primary source file of the compilation.
	auto& dex_class_def = dex->GetClassDef(mi->class_def_index_);
	const char* source_file = dex->GetSourceFile(dex_class_def);
	if (source_file != nullptr) {
	std::string file_name(source_file);
	size_t file_name_slash = file_name.find_last_of('/');
	std::string class_name(dex->GetClassDescriptor(dex_class_def));
	size_t class_name_slash = class_name.find_last_of('/');
	std::string full_path(file_name);

	// Guess directory from package name.
	int directory_index = 0; // 0 - current directory of the compilation.
	if (file_name_slash == std::string::npos && // Just filename.
	class_name.front() == 'L' && // Type descriptor for a class.
	class_name_slash != std::string::npos) { // Has package name.
	std::string package_name = class_name.substr(1, class_name_slash - 1);
	auto it = directories_map.find(package_name);
	if (it == directories_map.end()) {
	directory_index = 1 + directories.size();
	directories_map.emplace(package_name, directory_index);
	directories.push_back(package_name);
	} else {
	directory_index = it->second;
	}
	full_path = package_name + "/" + file_name;
	}

	// Add file entry.
	auto it2 = files_map.find(full_path);
	if (it2 == files_map.end()) {
	file_index = 1 + files.size();
	files_map.emplace(full_path, file_index);
	files.push_back(FileEntry {
	file_name,
	directory_index,
	0, // Modification time - NA.
	0, // File size - NA.
	});
	} else {
	file_index = it2->second;
	}
	}
	opcodes.SetFile(file_index);

	// Generate mapping opcodes from PC to Java lines.
	const DefaultSrcMap& dex2line_map = debug_info_callbacks.dex2line_;
	if (file_index != 0 && !dex2line_map.empty()) {
	bool first = true;
	for (SrcMapElem pc2dex : mi->compiled_method_->GetSrcMappingTable()) {
	uint32_t pc = pc2dex.from_;
	int dex_pc = pc2dex.to_;
	auto dex2line = dex2line_map.Find(static_cast<uint32_t>(dex_pc));
	if (dex2line.first) {
	int line = dex2line.second;
	if (first) {
	first = false;
	if (pc > 0) {
	// Assume that any preceding code is prologue.
	int first_line = dex2line_map.front().to_;
	// Prologue is not a sensible place for a breakpoint.
	opcodes.NegateStmt();
	opcodes.AddRow(method_address, first_line);
	opcodes.NegateStmt();
	opcodes.SetPrologueEnd();
	}
	opcodes.AddRow(method_address + pc, line);
	} else if (line != opcodes.CurrentLine()) {
	opcodes.AddRow(method_address + pc, line);
	}
	}
	}
	} else {
	// line 0 - instruction cannot be attributed to any source line.
	opcodes.AddRow(method_address, 0);
	}
	}
	opcodes.AdvancePC(text_address + cunit_high_pc);
	opcodes.EndSequence();
	std::vector<uint8_t> buffer;
	buffer.reserve(opcodes.data()->size() + KB);
	size_t offset = builder_->GetDebugLine()->GetSize();
	WriteDebugLineTable(directories, files, opcodes, offset, &buffer, &debug_line_patches);
	builder_->GetDebugLine()->WriteFully(buffer.data(), buffer.size());
	return buffer.size();
	}

	void End() {
	builder_->GetDebugLine()->End();
	builder_->WritePatches(".debug_line.oat_patches", &debug_line_patches);
	}

	private:
	ElfBuilder<ElfTypes>* builder_;
	std::vector<uintptr_t> debug_line_patches;
	};

	template<typename ElfTypes>
	void WriteDebugSections(ElfBuilder<ElfTypes>* builder,
	const std::vector<OatWriter::DebugInfo>& method_infos) {
	struct CompilationUnit {
	std::vector<const OatWriter::DebugInfo*> methods_;
	size_t debug_line_offset_ = 0;
	};

	// Group the methods into compilation units based on source file.
	std::vector<CompilationUnit> compilation_units;
	const char* last_source_file = nullptr;
	for (const OatWriter::DebugInfo& mi : method_infos) {
	// Attribute given instruction range only to single method.
	// Otherwise the debugger might get really confused.
	if (!mi.deduped_) {
	auto& dex_class_def = mi.dex_file_->GetClassDef(mi.class_def_index_);
	const char* source_file = mi.dex_file_->GetSourceFile(dex_class_def);
	if (compilation_units.empty() \|\| source_file != last_source_file) {
	compilation_units.push_back(CompilationUnit());
	}
	compilation_units.back().methods_.push_back(&mi);
	last_source_file = source_file;
	}
	}

	// Write .debug_line section.
	{
	DebugLineWriter<ElfTypes> line_writer(builder);
	line_writer.Start();
	size_t offset = 0;
	for (auto& compilation_unit : compilation_units) {
	compilation_unit.debug_line_offset_ = offset;
	offset += line_writer.Write(compilation_unit.methods_);
	}
	line_writer.End();
	}

	// Write .debug_info section.
	{
	DebugInfoWriter<ElfTypes> info_writer(builder);
	info_writer.Start();
	for (const auto& compilation_unit : compilation_units) {
	info_writer.Write(compilation_unit.methods_, compilation_unit.debug_line_offset_);
	}
	info_writer.End();
	}
	}

	// Explicit instantiations
	template void WriteCFISection<ElfTypes32>(
	ElfBuilder<ElfTypes32>* builder,
	const std::vector<OatWriter::DebugInfo>& method_infos,
	CFIFormat format);
	template void WriteCFISection<ElfTypes64>(
	ElfBuilder<ElfTypes64>* builder,
	const std::vector<OatWriter::DebugInfo>& method_infos,
	CFIFormat format);
	template void WriteDebugSections<ElfTypes32>(
	ElfBuilder<ElfTypes32>* builder,
	const std::vector<OatWriter::DebugInfo>& method_infos);
	template void WriteDebugSections<ElfTypes64>(
	ElfBuilder<ElfTypes64>* builder,
	const std::vector<OatWriter::DebugInfo>& method_infos);

	} // namespace dwarf
	} // namespace art