compiler/elf_writer_debug.cc - platform/art - Git at Google

 /*
  * 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 "compiled_method.h"
 #include "driver/compiler_driver.h"
 #include "dex_file-inl.h"
 #include "dwarf/headers.h"
 #include "dwarf/register.h"
 #include "oat_writer.h"

 namespace art {
 namespace dwarf {

 static void WriteEhFrameCIE(InstructionSet isa, std::vector<uint8_t>* eh_frame) {
   // 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_address_reg = Reg::ArmCore(14);  // R14(LR).
       WriteEhFrameCIE(is64bit, return_address_reg, opcodes, eh_frame);
       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_address_reg = Reg::Arm64Core(30);  // R30(LR).
       WriteEhFrameCIE(is64bit, return_address_reg, opcodes, eh_frame);
       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_address_reg = Reg::MipsCore(31);  // R31(RA).
       WriteEhFrameCIE(is64bit, return_address_reg, opcodes, eh_frame);
       return;
     }
     case kX86: {
       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.
       for (int reg = 0; reg < 8; reg++) {
         opcodes.Undefined(Reg::X86Fp(reg));
       }
       auto return_address_reg = Reg::X86Core(8);  // R8(EIP).
       WriteEhFrameCIE(is64bit, return_address_reg, opcodes, eh_frame);
       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_address_reg = Reg::X86_64Core(16);  // R16(RIP).
       WriteEhFrameCIE(is64bit, return_address_reg, opcodes, eh_frame);
       return;
     }
     case kNone:
       break;
   }
   LOG(FATAL) << "Can not write CIE frame for ISA " << isa;
   UNREACHABLE();
 }

 /*
  * @brief Generate the DWARF sections.
  * @param oat_writer The Oat file Writer.
  * @param eh_frame Call Frame Information.
  * @param debug_info Compilation unit information.
  * @param debug_abbrev Abbreviations used to generate dbg_info.
  * @param debug_str Debug strings.
  * @param debug_line Line number table.
  */
 void WriteDebugSections(const CompilerDriver* compiler,
                         OatWriter* oat_writer,
                         uint32_t text_section_offset,
                         std::vector<uint8_t>* eh_frame,
                         std::vector<uint8_t>* debug_info,
                         std::vector<uint8_t>* debug_abbrev,
                         std::vector<uint8_t>* debug_str,
                         std::vector<uint8_t>* debug_line) {
   const std::vector<OatWriter::DebugInfo>& method_infos = oat_writer->GetMethodDebugInfo();
   const InstructionSet isa = compiler->GetInstructionSet();
   uint32_t cunit_low_pc = static_cast<uint32_t>(-1);
   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_);
   }

   // Write .eh_frame section.
   auto* eh_frame_patches = oat_writer->GetAbsolutePatchLocationsFor(".eh_frame");
   size_t cie_offset = eh_frame->size();
   WriteEhFrameCIE(isa, eh_frame);
   for (const OatWriter::DebugInfo& mi : method_infos) {
     const SwapVector<uint8_t>* opcodes = mi.compiled_method_->GetCFIInfo();
     if (opcodes != nullptr) {
       WriteEhFrameFDE(Is64BitInstructionSet(isa), cie_offset,
                       text_section_offset + mi.low_pc_, mi.high_pc_ - mi.low_pc_,
                       opcodes, eh_frame, eh_frame_patches);
     }
   }

   // Write .debug_info section.
   size_t debug_abbrev_offset = debug_abbrev->size();
   DebugInfoEntryWriter<> info(false /* 32 bit */, 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, cunit_low_pc + text_section_offset);
   info.WriteAddr(DW_AT_high_pc, cunit_high_pc + text_section_offset);
   info.WriteData4(DW_AT_stmt_list, debug_line->size());
   for (auto method_info : method_infos) {
     std::string method_name = PrettyMethod(method_info.dex_method_index_,
                                            *method_info.dex_file_, true);
     if (method_info.deduped_) {
       // TODO We should place the DEDUPED tag on the first instance of a deduplicated symbol
       // so that it will show up in a debuggerd crash report.
       method_name += " [ DEDUPED ]";
     }
     info.StartTag(DW_TAG_subprogram, DW_CHILDREN_no);
     info.WriteStrp(DW_AT_name, method_name.data(), debug_str);
     info.WriteAddr(DW_AT_low_pc, method_info.low_pc_ + text_section_offset);
     info.WriteAddr(DW_AT_high_pc, method_info.high_pc_ + text_section_offset);
     info.EndTag();  // DW_TAG_subprogram
   }
   info.EndTag();  // DW_TAG_compile_unit
   auto* debug_info_patches = oat_writer->GetAbsolutePatchLocationsFor(".debug_info");
   WriteDebugInfoCU(debug_abbrev_offset, info, debug_info, debug_info_patches);

   // TODO: in gdb info functions <regexp> - reports Java functions, but
   // source file is <unknown> because .debug_line is formed as one
   // compilation unit. To fix this it is possible to generate
   // a separate compilation unit for every distinct Java source.
   // Each of the these compilation units can have several non-adjacent
   // method ranges.

   // Write .debug_line section.
   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 (isa) {
     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(false /* 32bit */, code_factor_bits_);
   opcodes.SetAddress(text_section_offset + cunit_low_pc);
   if (dwarf_isa != -1) {
     opcodes.SetISA(dwarf_isa);
   }
   for (const OatWriter::DebugInfo& mi : method_infos) {
     // Addresses in the line table should be unique and increasing.
     if (mi.deduped_) {
       continue;
     }

     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;

     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_;
     uint32_t low_pc = text_section_offset + mi.low_pc_;
     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(low_pc, first_line);
               opcodes.NegateStmt();
               opcodes.SetPrologueEnd();
             }
             opcodes.AddRow(low_pc + pc, line);
           } else if (line != opcodes.CurrentLine()) {
             opcodes.AddRow(low_pc + pc, line);
           }
         }
       }
     } else {
       // line 0 - instruction cannot be attributed to any source line.
       opcodes.AddRow(low_pc, 0);
     }
   }
   opcodes.AdvancePC(text_section_offset + cunit_high_pc);
   opcodes.EndSequence();
   auto* debug_line_patches = oat_writer->GetAbsolutePatchLocationsFor(".debug_line");
   WriteDebugLineTable(directories, files, opcodes, debug_line, debug_line_patches);
 }

 }  // 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 "compiled_method.h"
	#include "driver/compiler_driver.h"
	#include "dex_file-inl.h"
	#include "dwarf/headers.h"
	#include "dwarf/register.h"
	#include "oat_writer.h"

	namespace art {
	namespace dwarf {

	static void WriteEhFrameCIE(InstructionSet isa, std::vector<uint8_t>* eh_frame) {
	// 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_address_reg = Reg::ArmCore(14); // R14(LR).
	WriteEhFrameCIE(is64bit, return_address_reg, opcodes, eh_frame);
	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_address_reg = Reg::Arm64Core(30); // R30(LR).
	WriteEhFrameCIE(is64bit, return_address_reg, opcodes, eh_frame);
	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_address_reg = Reg::MipsCore(31); // R31(RA).
	WriteEhFrameCIE(is64bit, return_address_reg, opcodes, eh_frame);
	return;
	}
	case kX86: {
	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.
	for (int reg = 0; reg < 8; reg++) {
	opcodes.Undefined(Reg::X86Fp(reg));
	}
	auto return_address_reg = Reg::X86Core(8); // R8(EIP).
	WriteEhFrameCIE(is64bit, return_address_reg, opcodes, eh_frame);
	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_address_reg = Reg::X86_64Core(16); // R16(RIP).
	WriteEhFrameCIE(is64bit, return_address_reg, opcodes, eh_frame);
	return;
	}
	case kNone:
	break;
	}
	LOG(FATAL) << "Can not write CIE frame for ISA " << isa;
	UNREACHABLE();
	}

	/*
	* @brief Generate the DWARF sections.
	* @param oat_writer The Oat file Writer.
	* @param eh_frame Call Frame Information.
	* @param debug_info Compilation unit information.
	* @param debug_abbrev Abbreviations used to generate dbg_info.
	* @param debug_str Debug strings.
	* @param debug_line Line number table.
	*/
	void WriteDebugSections(const CompilerDriver* compiler,
	OatWriter* oat_writer,
	uint32_t text_section_offset,
	std::vector<uint8_t>* eh_frame,
	std::vector<uint8_t>* debug_info,
	std::vector<uint8_t>* debug_abbrev,
	std::vector<uint8_t>* debug_str,
	std::vector<uint8_t>* debug_line) {
	const std::vector<OatWriter::DebugInfo>& method_infos = oat_writer->GetMethodDebugInfo();
	const InstructionSet isa = compiler->GetInstructionSet();
	uint32_t cunit_low_pc = static_cast<uint32_t>(-1);
	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_);
	}

	// Write .eh_frame section.
	auto* eh_frame_patches = oat_writer->GetAbsolutePatchLocationsFor(".eh_frame");
	size_t cie_offset = eh_frame->size();
	WriteEhFrameCIE(isa, eh_frame);
	for (const OatWriter::DebugInfo& mi : method_infos) {
	const SwapVector<uint8_t>* opcodes = mi.compiled_method_->GetCFIInfo();
	if (opcodes != nullptr) {
	WriteEhFrameFDE(Is64BitInstructionSet(isa), cie_offset,
	text_section_offset + mi.low_pc_, mi.high_pc_ - mi.low_pc_,
	opcodes, eh_frame, eh_frame_patches);
	}
	}

	// Write .debug_info section.
	size_t debug_abbrev_offset = debug_abbrev->size();
	DebugInfoEntryWriter<> info(false /* 32 bit */, 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, cunit_low_pc + text_section_offset);
	info.WriteAddr(DW_AT_high_pc, cunit_high_pc + text_section_offset);
	info.WriteData4(DW_AT_stmt_list, debug_line->size());
	for (auto method_info : method_infos) {
	std::string method_name = PrettyMethod(method_info.dex_method_index_,
	*method_info.dex_file_, true);
	if (method_info.deduped_) {
	// TODO We should place the DEDUPED tag on the first instance of a deduplicated symbol
	// so that it will show up in a debuggerd crash report.
	method_name += " [ DEDUPED ]";
	}
	info.StartTag(DW_TAG_subprogram, DW_CHILDREN_no);
	info.WriteStrp(DW_AT_name, method_name.data(), debug_str);
	info.WriteAddr(DW_AT_low_pc, method_info.low_pc_ + text_section_offset);
	info.WriteAddr(DW_AT_high_pc, method_info.high_pc_ + text_section_offset);
	info.EndTag(); // DW_TAG_subprogram
	}
	info.EndTag(); // DW_TAG_compile_unit
	auto* debug_info_patches = oat_writer->GetAbsolutePatchLocationsFor(".debug_info");
	WriteDebugInfoCU(debug_abbrev_offset, info, debug_info, debug_info_patches);

	// TODO: in gdb info functions <regexp> - reports Java functions, but
	// source file is <unknown> because .debug_line is formed as one
	// compilation unit. To fix this it is possible to generate
	// a separate compilation unit for every distinct Java source.
	// Each of the these compilation units can have several non-adjacent
	// method ranges.

	// Write .debug_line section.
	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 (isa) {
	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(false /* 32bit */, code_factor_bits_);
	opcodes.SetAddress(text_section_offset + cunit_low_pc);
	if (dwarf_isa != -1) {
	opcodes.SetISA(dwarf_isa);
	}
	for (const OatWriter::DebugInfo& mi : method_infos) {
	// Addresses in the line table should be unique and increasing.
	if (mi.deduped_) {
	continue;
	}

	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;

	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_;
	uint32_t low_pc = text_section_offset + mi.low_pc_;
	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(low_pc, first_line);
	opcodes.NegateStmt();
	opcodes.SetPrologueEnd();
	}
	opcodes.AddRow(low_pc + pc, line);
	} else if (line != opcodes.CurrentLine()) {
	opcodes.AddRow(low_pc + pc, line);
	}
	}
	}
	} else {
	// line 0 - instruction cannot be attributed to any source line.
	opcodes.AddRow(low_pc, 0);
	}
	}
	opcodes.AdvancePC(text_section_offset + cunit_high_pc);
	opcodes.EndSequence();
	auto* debug_line_patches = oat_writer->GetAbsolutePatchLocationsFor(".debug_line");
	WriteDebugLineTable(directories, files, opcodes, debug_line, debug_line_patches);
	}

	} // namespace dwarf
	} // namespace art