compiler/debug/elf_debug_line_writer.h - platform/art - Git at Google

 /*
  * Copyright (C) 2016 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.
  */

 #ifndef ART_COMPILER_DEBUG_ELF_DEBUG_LINE_WRITER_H_
 #define ART_COMPILER_DEBUG_ELF_DEBUG_LINE_WRITER_H_

 #include <unordered_set>
 #include <vector>

 #include "debug/elf_compilation_unit.h"
 #include "debug/src_map_elem.h"
 #include "dex/dex_file-inl.h"
 #include "dwarf/debug_line_opcode_writer.h"
 #include "dwarf/headers.h"
 #include "elf/elf_builder.h"
 #include "oat_file.h"
 #include "stack_map.h"

 namespace art {
 namespace debug {

 typedef std::vector<DexFile::PositionInfo> PositionInfos;

 template<typename ElfTypes>
 class ElfDebugLineWriter {
   using Elf_Addr = typename ElfTypes::Addr;

  public:
   explicit ElfDebugLineWriter(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 WriteCompilationUnit(ElfCompilationUnit& compilation_unit) {
     const InstructionSet isa = builder_->GetIsa();
     const bool is64bit = Is64BitInstructionSet(isa);
     const Elf_Addr base_address = compilation_unit.is_code_address_text_relative
         ? builder_->GetText()->GetAddress()
         : 0;

     compilation_unit.debug_line_offset = builder_->GetDebugLine()->GetPosition();

     std::vector<dwarf::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 InstructionSet::kArm:  // arm actually means thumb2.
       case InstructionSet::kThumb2:
         code_factor_bits_ = 1;  // 16-bit instuctions
         dwarf_isa = 1;  // DW_ISA_ARM_thumb.
         break;
       case InstructionSet::kArm64:
         code_factor_bits_ = 2;  // 32-bit instructions
         break;
       case InstructionSet::kNone:
       case InstructionSet::kX86:
       case InstructionSet::kX86_64:
         break;
     }
     std::unordered_set<uint64_t> seen_addresses(compilation_unit.methods.size());
     dwarf::DebugLineOpCodeWriter<> opcodes(is64bit, code_factor_bits_);
     for (const MethodDebugInfo* mi : compilation_unit.methods) {
       // Ignore function if we have already generated line table for the same address.
       // It would confuse the debugger and the DWARF specification forbids it.
       // We allow the line table for method to be replicated in different compilation unit.
       // This ensures that each compilation unit contains line table for all its methods.
       if (!seen_addresses.insert(mi->code_address).second) {
         continue;
       }

       uint32_t prologue_end = std::numeric_limits<uint32_t>::max();
       std::vector<SrcMapElem> pc2dex_map;
       if (mi->code_info != nullptr) {
         // Use stack maps to create mapping table from pc to dex.
         const CodeInfo code_info(mi->code_info);
         pc2dex_map.reserve(code_info.GetNumberOfStackMaps());
         for (StackMap stack_map : code_info.GetStackMaps()) {
           const uint32_t pc = stack_map.GetNativePcOffset(isa);
           const int32_t dex = stack_map.GetDexPc();
           pc2dex_map.push_back({pc, dex});
           if (stack_map.HasDexRegisterMap()) {
             // Guess that the first map with local variables is the end of prologue.
             prologue_end = std::min(prologue_end, pc);
           }
         }
         std::sort(pc2dex_map.begin(), pc2dex_map.end());
       }

       if (pc2dex_map.empty()) {
         continue;
       }

       // Compensate for compiler's off-by-one-instruction error.
       //
       // The compiler generates stackmap with PC *after* the branch instruction
       // (because this is the PC which is easier to obtain when unwinding).
       //
       // However, the debugger is more clever and it will ask us for line-number
       // mapping at the location of the branch instruction (since the following
       // instruction could belong to other line, this is the correct thing to do).
       //
       // So we really want to just decrement the PC by one instruction so that the
       // branch instruction is covered as well. However, we do not know the size
       // of the previous instruction, and we can not subtract just a fixed amount
       // (the debugger would trust us that the PC is valid; it might try to set
       // breakpoint there at some point, and setting breakpoint in mid-instruction
       // would make the process crash in spectacular way).
       //
       // Therefore, we say that the PC which the compiler gave us for the stackmap
       // is the end of its associated address range, and we use the PC from the
       // previous stack map as the start of the range. This ensures that the PC is
       // valid and that the branch instruction is covered.
       //
       // This ensures we have correct line number mapping at call sites (which is
       // important for backtraces), but there is nothing we can do for non-call
       // sites (so stepping through optimized code in debugger is not possible).
       //
       // We do not adjust the stackmaps if the code was compiled as debuggable.
       // In that case, the stackmaps should accurately cover all instructions.
       if (!mi->is_native_debuggable) {
         for (size_t i = pc2dex_map.size() - 1; i > 0; --i) {
           pc2dex_map[i].from_ = pc2dex_map[i - 1].from_;
         }
         pc2dex_map[0].from_ = 0;
       }

       Elf_Addr method_address = base_address + mi->code_address;

       PositionInfos dex2line_map;
       const DexFile* dex = mi->dex_file;
       DCHECK(dex != nullptr);
       CodeItemDebugInfoAccessor accessor(*dex, mi->code_item, mi->dex_method_index);
       if (!accessor.DecodeDebugPositionInfo(
           [&](const DexFile::PositionInfo& entry) {
             dex2line_map.push_back(entry);
             return false;
           })) {
         continue;
       }

       if (dex2line_map.empty()) {
         continue;
       }

       opcodes.SetAddress(method_address);
       if (dwarf_isa != -1) {
         opcodes.SetISA(dwarf_isa);
       }

       // 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(dwarf::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.
       if (file_index != 0) {
         // If the method was not compiled as native-debuggable, we still generate all available
         // lines, but we try to prevent the debugger from stepping and setting breakpoints since
         // the information is too inaccurate for that (breakpoints would be set after the calls).
         const bool default_is_stmt = mi->is_native_debuggable;
         bool first = true;
         for (SrcMapElem pc2dex : pc2dex_map) {
           uint32_t pc = pc2dex.from_;
           int dex_pc = pc2dex.to_;
           // Find mapping with address with is greater than our dex pc; then go back one step.
           auto dex2line = std::upper_bound(
               dex2line_map.begin(),
               dex2line_map.end(),
               dex_pc,
               [](uint32_t address, const DexFile::PositionInfo& entry) {
                   return address < entry.address_;
               });
           // Look for first valid mapping after the prologue.
           if (dex2line != dex2line_map.begin() && pc >= prologue_end) {
             int line = (--dex2line)->line_;
             if (first) {
               first = false;
               if (pc > 0) {
                 // Assume that any preceding code is prologue.
                 int first_line = dex2line_map.front().line_;
                 // Prologue is not a sensible place for a breakpoint.
                 opcodes.SetIsStmt(false);
                 opcodes.AddRow(method_address, first_line);
                 opcodes.SetPrologueEnd();
               }
               opcodes.SetIsStmt(default_is_stmt);
               opcodes.AddRow(method_address + pc, line);
             } else if (line != opcodes.CurrentLine()) {
               opcodes.SetIsStmt(default_is_stmt);
               opcodes.AddRow(method_address + pc, line);
             }
           }
         }
       } else {
         // line 0 - instruction cannot be attributed to any source line.
         opcodes.AddRow(method_address, 0);
       }

       opcodes.AdvancePC(method_address + mi->code_size);
       opcodes.EndSequence();
     }
     std::vector<uint8_t> buffer;
     buffer.reserve(opcodes.data()->size() + KB);
     WriteDebugLineTable(directories, files, opcodes, &buffer);
     builder_->GetDebugLine()->WriteFully(buffer.data(), buffer.size());
     return buffer.size();
   }

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

  private:
   ElfBuilder<ElfTypes>* builder_;
 };

 }  // namespace debug
 }  // namespace art

 #endif  // ART_COMPILER_DEBUG_ELF_DEBUG_LINE_WRITER_H_
	/*
	* Copyright (C) 2016 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.
	*/

	#ifndef ART_COMPILER_DEBUG_ELF_DEBUG_LINE_WRITER_H_
	#define ART_COMPILER_DEBUG_ELF_DEBUG_LINE_WRITER_H_

	#include <unordered_set>
	#include <vector>

	#include "debug/elf_compilation_unit.h"
	#include "debug/src_map_elem.h"
	#include "dex/dex_file-inl.h"
	#include "dwarf/debug_line_opcode_writer.h"
	#include "dwarf/headers.h"
	#include "elf/elf_builder.h"
	#include "oat_file.h"
	#include "stack_map.h"

	namespace art {
	namespace debug {

	typedef std::vector<DexFile::PositionInfo> PositionInfos;

	template<typename ElfTypes>
	class ElfDebugLineWriter {
	using Elf_Addr = typename ElfTypes::Addr;

	public:
	explicit ElfDebugLineWriter(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 WriteCompilationUnit(ElfCompilationUnit& compilation_unit) {
	const InstructionSet isa = builder_->GetIsa();
	const bool is64bit = Is64BitInstructionSet(isa);
	const Elf_Addr base_address = compilation_unit.is_code_address_text_relative
	? builder_->GetText()->GetAddress()
	: 0;

	compilation_unit.debug_line_offset = builder_->GetDebugLine()->GetPosition();

	std::vector<dwarf::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 InstructionSet::kArm: // arm actually means thumb2.
	case InstructionSet::kThumb2:
	code_factor_bits_ = 1; // 16-bit instuctions
	dwarf_isa = 1; // DW_ISA_ARM_thumb.
	break;
	case InstructionSet::kArm64:
	code_factor_bits_ = 2; // 32-bit instructions
	break;
	case InstructionSet::kNone:
	case InstructionSet::kX86:
	case InstructionSet::kX86_64:
	break;
	}
	std::unordered_set<uint64_t> seen_addresses(compilation_unit.methods.size());
	dwarf::DebugLineOpCodeWriter<> opcodes(is64bit, code_factor_bits_);
	for (const MethodDebugInfo* mi : compilation_unit.methods) {
	// Ignore function if we have already generated line table for the same address.
	// It would confuse the debugger and the DWARF specification forbids it.
	// We allow the line table for method to be replicated in different compilation unit.
	// This ensures that each compilation unit contains line table for all its methods.
	if (!seen_addresses.insert(mi->code_address).second) {
	continue;
	}

	uint32_t prologue_end = std::numeric_limits<uint32_t>::max();
	std::vector<SrcMapElem> pc2dex_map;
	if (mi->code_info != nullptr) {
	// Use stack maps to create mapping table from pc to dex.
	const CodeInfo code_info(mi->code_info);
	pc2dex_map.reserve(code_info.GetNumberOfStackMaps());
	for (StackMap stack_map : code_info.GetStackMaps()) {
	const uint32_t pc = stack_map.GetNativePcOffset(isa);
	const int32_t dex = stack_map.GetDexPc();
	pc2dex_map.push_back({pc, dex});
	if (stack_map.HasDexRegisterMap()) {
	// Guess that the first map with local variables is the end of prologue.
	prologue_end = std::min(prologue_end, pc);
	}
	}
	std::sort(pc2dex_map.begin(), pc2dex_map.end());
	}

	if (pc2dex_map.empty()) {
	continue;
	}

	// Compensate for compiler's off-by-one-instruction error.
	//
	// The compiler generates stackmap with PC after the branch instruction
	// (because this is the PC which is easier to obtain when unwinding).
	//
	// However, the debugger is more clever and it will ask us for line-number
	// mapping at the location of the branch instruction (since the following
	// instruction could belong to other line, this is the correct thing to do).
	//
	// So we really want to just decrement the PC by one instruction so that the
	// branch instruction is covered as well. However, we do not know the size
	// of the previous instruction, and we can not subtract just a fixed amount
	// (the debugger would trust us that the PC is valid; it might try to set
	// breakpoint there at some point, and setting breakpoint in mid-instruction
	// would make the process crash in spectacular way).
	//
	// Therefore, we say that the PC which the compiler gave us for the stackmap
	// is the end of its associated address range, and we use the PC from the
	// previous stack map as the start of the range. This ensures that the PC is
	// valid and that the branch instruction is covered.
	//
	// This ensures we have correct line number mapping at call sites (which is
	// important for backtraces), but there is nothing we can do for non-call
	// sites (so stepping through optimized code in debugger is not possible).
	//
	// We do not adjust the stackmaps if the code was compiled as debuggable.
	// In that case, the stackmaps should accurately cover all instructions.
	if (!mi->is_native_debuggable) {
	for (size_t i = pc2dex_map.size() - 1; i > 0; --i) {
	pc2dex_map[i].from_ = pc2dex_map[i - 1].from_;
	}
	pc2dex_map[0].from_ = 0;
	}

	Elf_Addr method_address = base_address + mi->code_address;

	PositionInfos dex2line_map;
	const DexFile* dex = mi->dex_file;
	DCHECK(dex != nullptr);
	CodeItemDebugInfoAccessor accessor(*dex, mi->code_item, mi->dex_method_index);
	if (!accessor.DecodeDebugPositionInfo(
	[&](const DexFile::PositionInfo& entry) {
	dex2line_map.push_back(entry);
	return false;
	})) {
	continue;
	}

	if (dex2line_map.empty()) {
	continue;
	}

	opcodes.SetAddress(method_address);
	if (dwarf_isa != -1) {
	opcodes.SetISA(dwarf_isa);
	}

	// 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(dwarf::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.
	if (file_index != 0) {
	// If the method was not compiled as native-debuggable, we still generate all available
	// lines, but we try to prevent the debugger from stepping and setting breakpoints since
	// the information is too inaccurate for that (breakpoints would be set after the calls).
	const bool default_is_stmt = mi->is_native_debuggable;
	bool first = true;
	for (SrcMapElem pc2dex : pc2dex_map) {
	uint32_t pc = pc2dex.from_;
	int dex_pc = pc2dex.to_;
	// Find mapping with address with is greater than our dex pc; then go back one step.
	auto dex2line = std::upper_bound(
	dex2line_map.begin(),
	dex2line_map.end(),
	dex_pc,
	[](uint32_t address, const DexFile::PositionInfo& entry) {
	return address < entry.address_;
	});
	// Look for first valid mapping after the prologue.
	if (dex2line != dex2line_map.begin() && pc >= prologue_end) {
	int line = (--dex2line)->line_;
	if (first) {
	first = false;
	if (pc > 0) {
	// Assume that any preceding code is prologue.
	int first_line = dex2line_map.front().line_;
	// Prologue is not a sensible place for a breakpoint.
	opcodes.SetIsStmt(false);
	opcodes.AddRow(method_address, first_line);
	opcodes.SetPrologueEnd();
	}
	opcodes.SetIsStmt(default_is_stmt);
	opcodes.AddRow(method_address + pc, line);
	} else if (line != opcodes.CurrentLine()) {
	opcodes.SetIsStmt(default_is_stmt);
	opcodes.AddRow(method_address + pc, line);
	}
	}
	}
	} else {
	// line 0 - instruction cannot be attributed to any source line.
	opcodes.AddRow(method_address, 0);
	}

	opcodes.AdvancePC(method_address + mi->code_size);
	opcodes.EndSequence();
	}
	std::vector<uint8_t> buffer;
	buffer.reserve(opcodes.data()->size() + KB);
	WriteDebugLineTable(directories, files, opcodes, &buffer);
	builder_->GetDebugLine()->WriteFully(buffer.data(), buffer.size());
	return buffer.size();
	}

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

	private:
	ElfBuilder<ElfTypes>* builder_;
	};

	} // namespace debug
	} // namespace art

	#endif // ART_COMPILER_DEBUG_ELF_DEBUG_LINE_WRITER_H_