compiler/debug/elf_debug_loc_writer.h - LeafOS-Project/android_art - Gitiles

 /*
  * 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_LOC_WRITER_H_
 #define ART_COMPILER_DEBUG_ELF_DEBUG_LOC_WRITER_H_

 #include <cstring>
 #include <map>

 #include "arch/instruction_set.h"
 #include "base/macros.h"
 #include "debug/method_debug_info.h"
 #include "dwarf/debug_info_entry_writer.h"
 #include "dwarf/register.h"
 #include "stack_map.h"

 namespace art HIDDEN {
 namespace debug {
 using Reg = dwarf::Reg;

 static Reg GetDwarfCoreReg(InstructionSet isa, int machine_reg) {
   switch (isa) {
     case InstructionSet::kArm:
     case InstructionSet::kThumb2:
       return Reg::ArmCore(machine_reg);
     case InstructionSet::kArm64:
       return Reg::Arm64Core(machine_reg);
     case InstructionSet::kRiscv64:
       return Reg::Riscv64Core(machine_reg);
     case InstructionSet::kX86:
       return Reg::X86Core(machine_reg);
     case InstructionSet::kX86_64:
       return Reg::X86_64Core(machine_reg);
     case InstructionSet::kNone:
       LOG(FATAL) << "No instruction set";
   }
   UNREACHABLE();
 }

 static Reg GetDwarfFpReg(InstructionSet isa, int machine_reg) {
   switch (isa) {
     case InstructionSet::kArm:
     case InstructionSet::kThumb2:
       return Reg::ArmFp(machine_reg);
     case InstructionSet::kArm64:
       return Reg::Arm64Fp(machine_reg);
     case InstructionSet::kRiscv64:
       return Reg::Riscv64Fp(machine_reg);
     case InstructionSet::kX86:
       return Reg::X86Fp(machine_reg);
     case InstructionSet::kX86_64:
       return Reg::X86_64Fp(machine_reg);
     case InstructionSet::kNone:
       LOG(FATAL) << "No instruction set";
   }
   UNREACHABLE();
 }

 struct VariableLocation {
   uint32_t low_pc;  // Relative to compilation unit.
   uint32_t high_pc;  // Relative to compilation unit.
   DexRegisterLocation reg_lo;  // May be None if the location is unknown.
   DexRegisterLocation reg_hi;  // Most significant bits of 64-bit value.
 };

 // Get the location of given dex register (e.g. stack or machine register).
 // Note that the location might be different based on the current pc.
 // The result will cover all ranges where the variable is in scope.
 // PCs corresponding to stackmap with dex register map are accurate,
 // all other PCs are best-effort only.
 static std::vector<VariableLocation> GetVariableLocations(
     const MethodDebugInfo* method_info,
     const std::vector<DexRegisterMap>& dex_register_maps,
     uint16_t vreg,
     bool is64bitValue,
     uint64_t compilation_unit_code_address,
     uint32_t dex_pc_low,
     uint32_t dex_pc_high,
     InstructionSet isa) {
   std::vector<VariableLocation> variable_locations;

   // Get stack maps sorted by pc (they might not be sorted internally).
   // TODO(dsrbecky) Remove this once stackmaps get sorted by pc.
   const CodeInfo code_info(method_info->code_info);
   std::map<uint32_t, uint32_t> stack_maps;  // low_pc -> stack_map_index.
   for (uint32_t s = 0; s < code_info.GetNumberOfStackMaps(); s++) {
     StackMap stack_map = code_info.GetStackMapAt(s);
     DCHECK(stack_map.IsValid());
     if (!stack_map.HasDexRegisterMap()) {
       // The compiler creates stackmaps without register maps at the start of
       // basic blocks in order to keep instruction-accurate line number mapping.
       // However, we never stop at those (breakpoint locations always have map).
       // Therefore, for the purpose of local variables, we ignore them.
       // The main reason for this is to save space by avoiding undefined gaps.
       continue;
     }
     const uint32_t pc_offset = stack_map.GetNativePcOffset(isa);
     DCHECK_LE(pc_offset, method_info->code_size);
     DCHECK_LE(compilation_unit_code_address, method_info->code_address);
     const uint32_t low_pc = dchecked_integral_cast<uint32_t>(
         method_info->code_address + pc_offset - compilation_unit_code_address);
     stack_maps.emplace(low_pc, s);
   }

   // Create entries for the requested register based on stack map data.
   for (auto it = stack_maps.begin(); it != stack_maps.end(); it++) {
     const uint32_t low_pc = it->first;
     const uint32_t stack_map_index = it->second;
     const StackMap stack_map = code_info.GetStackMapAt(stack_map_index);
     auto next_it = it;
     next_it++;
     const uint32_t high_pc = next_it != stack_maps.end()
       ? next_it->first
       : method_info->code_address + method_info->code_size - compilation_unit_code_address;
     DCHECK_LE(low_pc, high_pc);
     if (low_pc == high_pc) {
       continue;  // Ignore if the address range is empty.
     }

     // Check that the stack map is in the requested range.
     uint32_t dex_pc = stack_map.GetDexPc();
     if (!(dex_pc_low <= dex_pc && dex_pc < dex_pc_high)) {
       // The variable is not in scope at this PC. Therefore omit the entry.
       // Note that this is different to None() entry which means in scope, but unknown location.
       continue;
     }

     // Find the location of the dex register.
     DexRegisterLocation reg_lo = DexRegisterLocation::None();
     DexRegisterLocation reg_hi = DexRegisterLocation::None();
     DCHECK_LT(stack_map_index, dex_register_maps.size());
     DexRegisterMap dex_register_map = dex_register_maps[stack_map_index];
     DCHECK(!dex_register_map.empty());
     CodeItemDataAccessor accessor(*method_info->dex_file, method_info->code_item);
     reg_lo = dex_register_map[vreg];
     if (is64bitValue) {
       reg_hi = dex_register_map[vreg + 1];
     }

     // Add location entry for this address range.
     if (!variable_locations.empty() &&
         variable_locations.back().reg_lo == reg_lo &&
         variable_locations.back().reg_hi == reg_hi &&
         variable_locations.back().high_pc == low_pc) {
       // Merge with the previous entry (extend its range).
       variable_locations.back().high_pc = high_pc;
     } else {
       variable_locations.push_back({low_pc, high_pc, reg_lo, reg_hi});
     }
   }

   return variable_locations;
 }

 // Write table into .debug_loc which describes location of dex register.
 // The dex register might be valid only at some points and it might
 // move between machine registers and stack.
 static void WriteDebugLocEntry(const MethodDebugInfo* method_info,
                                const std::vector<DexRegisterMap>& dex_register_maps,
                                uint16_t vreg,
                                bool is64bitValue,
                                uint64_t compilation_unit_code_address,
                                uint32_t dex_pc_low,
                                uint32_t dex_pc_high,
                                InstructionSet isa,
                                dwarf::DebugInfoEntryWriter<>* debug_info,
                                std::vector<uint8_t>* debug_loc_buffer,
                                std::vector<uint8_t>* debug_ranges_buffer) {
   using Kind = DexRegisterLocation::Kind;
   if (method_info->code_info == nullptr || dex_register_maps.empty()) {
     return;
   }

   std::vector<VariableLocation> variable_locations = GetVariableLocations(
       method_info,
       dex_register_maps,
       vreg,
       is64bitValue,
       compilation_unit_code_address,
       dex_pc_low,
       dex_pc_high,
       isa);

   // Write .debug_loc entries.
   dwarf::Writer<> debug_loc(debug_loc_buffer);
   const size_t debug_loc_offset = debug_loc.size();
   const bool is64bit = Is64BitInstructionSet(isa);
   std::vector<uint8_t> expr_buffer;
   for (const VariableLocation& variable_location : variable_locations) {
     // Translate dex register location to DWARF expression.
     // Note that 64-bit value might be split to two distinct locations.
     // (for example, two 32-bit machine registers, or even stack and register)
     dwarf::Expression expr(&expr_buffer);
     DexRegisterLocation reg_lo = variable_location.reg_lo;
     DexRegisterLocation reg_hi = variable_location.reg_hi;
     for (int piece = 0; piece < (is64bitValue ? 2 : 1); piece++) {
       DexRegisterLocation reg_loc = (piece == 0 ? reg_lo : reg_hi);
       const Kind kind = reg_loc.GetKind();
       const int32_t value = reg_loc.GetValue();
       if (kind == Kind::kInStack) {
         // The stack offset is relative to SP. Make it relative to CFA.
         expr.WriteOpFbreg(value - method_info->frame_size_in_bytes);
         if (piece == 0 && reg_hi.GetKind() == Kind::kInStack &&
             reg_hi.GetValue() == value + 4) {
           break;  // the high word is correctly implied by the low word.
         }
       } else if (kind == Kind::kInRegister) {
         expr.WriteOpReg(GetDwarfCoreReg(isa, value).num());
         if (piece == 0 && reg_hi.GetKind() == Kind::kInRegisterHigh &&
             reg_hi.GetValue() == value) {
           break;  // the high word is correctly implied by the low word.
         }
       } else if (kind == Kind::kInFpuRegister) {
         if ((isa == InstructionSet::kArm || isa == InstructionSet::kThumb2) &&
             piece == 0 && reg_hi.GetKind() == Kind::kInFpuRegister &&
             reg_hi.GetValue() == value + 1 && value % 2 == 0) {
           // Translate S register pair to D register (e.g. S4+S5 to D2).
           expr.WriteOpReg(Reg::ArmDp(value / 2).num());
           break;
         }
         expr.WriteOpReg(GetDwarfFpReg(isa, value).num());
         if (piece == 0 && reg_hi.GetKind() == Kind::kInFpuRegisterHigh &&
             reg_hi.GetValue() == reg_lo.GetValue()) {
           break;  // the high word is correctly implied by the low word.
         }
       } else if (kind == Kind::kConstant) {
         expr.WriteOpConsts(value);
         expr.WriteOpStackValue();
       } else if (kind == Kind::kNone) {
         break;
       } else {
         // kInStackLargeOffset and kConstantLargeValue are hidden by GetKind().
         // kInRegisterHigh and kInFpuRegisterHigh should be handled by
         // the special cases above and they should not occur alone.
         LOG(WARNING) << "Unexpected register location: " << kind
                      << " (This can indicate either a bug in the dexer when generating"
                      << " local variable information, or a bug in ART compiler."
                      << " Please file a bug at go/art-bug)";
         break;
       }
       if (is64bitValue) {
         // Write the marker which is needed by split 64-bit values.
         // This code is skipped by the special cases.
         expr.WriteOpPiece(4);
       }
     }

     if (expr.size() > 0) {
       if (is64bit) {
         debug_loc.PushUint64(variable_location.low_pc);
         debug_loc.PushUint64(variable_location.high_pc);
       } else {
         debug_loc.PushUint32(variable_location.low_pc);
         debug_loc.PushUint32(variable_location.high_pc);
       }
       // Write the expression.
       debug_loc.PushUint16(expr.size());
       debug_loc.PushData(expr.data());
     } else {
       // Do not generate .debug_loc if the location is not known.
     }
   }
   // Write end-of-list entry.
   if (is64bit) {
     debug_loc.PushUint64(0);
     debug_loc.PushUint64(0);
   } else {
     debug_loc.PushUint32(0);
     debug_loc.PushUint32(0);
   }

   // Write .debug_ranges entries.
   // This includes ranges where the variable is in scope but the location is not known.
   dwarf::Writer<> debug_ranges(debug_ranges_buffer);
   size_t debug_ranges_offset = debug_ranges.size();
   for (size_t i = 0; i < variable_locations.size(); i++) {
     uint32_t low_pc = variable_locations[i].low_pc;
     uint32_t high_pc = variable_locations[i].high_pc;
     while (i + 1 < variable_locations.size() && variable_locations[i+1].low_pc == high_pc) {
       // Merge address range with the next entry.
       high_pc = variable_locations[++i].high_pc;
     }
     if (is64bit) {
       debug_ranges.PushUint64(low_pc);
       debug_ranges.PushUint64(high_pc);
     } else {
       debug_ranges.PushUint32(low_pc);
       debug_ranges.PushUint32(high_pc);
     }
   }
   // Write end-of-list entry.
   if (is64bit) {
     debug_ranges.PushUint64(0);
     debug_ranges.PushUint64(0);
   } else {
     debug_ranges.PushUint32(0);
     debug_ranges.PushUint32(0);
   }

   // Simple de-duplication - check whether this entry is same as the last one (or tail of it).
   size_t debug_ranges_entry_size = debug_ranges.size() - debug_ranges_offset;
   if (debug_ranges_offset >= debug_ranges_entry_size) {
     size_t previous_offset = debug_ranges_offset - debug_ranges_entry_size;
     if (memcmp(debug_ranges_buffer->data() + previous_offset,
                debug_ranges_buffer->data() + debug_ranges_offset,
                debug_ranges_entry_size) == 0) {
       // Remove what we have just written and use the last entry instead.
       debug_ranges_buffer->resize(debug_ranges_offset);
       debug_ranges_offset = previous_offset;
     }
   }

   // Write attributes to .debug_info.
   debug_info->WriteSecOffset(dwarf::DW_AT_location, debug_loc_offset);
   debug_info->WriteSecOffset(dwarf::DW_AT_start_scope, debug_ranges_offset);
 }

 }  // namespace debug
 }  // namespace art

 #endif  // ART_COMPILER_DEBUG_ELF_DEBUG_LOC_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_LOC_WRITER_H_
	#define ART_COMPILER_DEBUG_ELF_DEBUG_LOC_WRITER_H_

	#include <cstring>
	#include <map>

	#include "arch/instruction_set.h"
	#include "base/macros.h"
	#include "debug/method_debug_info.h"
	#include "dwarf/debug_info_entry_writer.h"
	#include "dwarf/register.h"
	#include "stack_map.h"

	namespace art HIDDEN {
	namespace debug {
	using Reg = dwarf::Reg;

	static Reg GetDwarfCoreReg(InstructionSet isa, int machine_reg) {
	switch (isa) {
	case InstructionSet::kArm:
	case InstructionSet::kThumb2:
	return Reg::ArmCore(machine_reg);
	case InstructionSet::kArm64:
	return Reg::Arm64Core(machine_reg);
	case InstructionSet::kRiscv64:
	return Reg::Riscv64Core(machine_reg);
	case InstructionSet::kX86:
	return Reg::X86Core(machine_reg);
	case InstructionSet::kX86_64:
	return Reg::X86_64Core(machine_reg);
	case InstructionSet::kNone:
	LOG(FATAL) << "No instruction set";
	}
	UNREACHABLE();
	}

	static Reg GetDwarfFpReg(InstructionSet isa, int machine_reg) {
	switch (isa) {
	case InstructionSet::kArm:
	case InstructionSet::kThumb2:
	return Reg::ArmFp(machine_reg);
	case InstructionSet::kArm64:
	return Reg::Arm64Fp(machine_reg);
	case InstructionSet::kRiscv64:
	return Reg::Riscv64Fp(machine_reg);
	case InstructionSet::kX86:
	return Reg::X86Fp(machine_reg);
	case InstructionSet::kX86_64:
	return Reg::X86_64Fp(machine_reg);
	case InstructionSet::kNone:
	LOG(FATAL) << "No instruction set";
	}
	UNREACHABLE();
	}

	struct VariableLocation {
	uint32_t low_pc; // Relative to compilation unit.
	uint32_t high_pc; // Relative to compilation unit.
	DexRegisterLocation reg_lo; // May be None if the location is unknown.
	DexRegisterLocation reg_hi; // Most significant bits of 64-bit value.
	};

	// Get the location of given dex register (e.g. stack or machine register).
	// Note that the location might be different based on the current pc.
	// The result will cover all ranges where the variable is in scope.
	// PCs corresponding to stackmap with dex register map are accurate,
	// all other PCs are best-effort only.
	static std::vector<VariableLocation> GetVariableLocations(
	const MethodDebugInfo* method_info,
	const std::vector<DexRegisterMap>& dex_register_maps,
	uint16_t vreg,
	bool is64bitValue,
	uint64_t compilation_unit_code_address,
	uint32_t dex_pc_low,
	uint32_t dex_pc_high,
	InstructionSet isa) {
	std::vector<VariableLocation> variable_locations;

	// Get stack maps sorted by pc (they might not be sorted internally).
	// TODO(dsrbecky) Remove this once stackmaps get sorted by pc.
	const CodeInfo code_info(method_info->code_info);
	std::map<uint32_t, uint32_t> stack_maps; // low_pc -> stack_map_index.
	for (uint32_t s = 0; s < code_info.GetNumberOfStackMaps(); s++) {
	StackMap stack_map = code_info.GetStackMapAt(s);
	DCHECK(stack_map.IsValid());
	if (!stack_map.HasDexRegisterMap()) {
	// The compiler creates stackmaps without register maps at the start of
	// basic blocks in order to keep instruction-accurate line number mapping.
	// However, we never stop at those (breakpoint locations always have map).
	// Therefore, for the purpose of local variables, we ignore them.
	// The main reason for this is to save space by avoiding undefined gaps.
	continue;
	}
	const uint32_t pc_offset = stack_map.GetNativePcOffset(isa);
	DCHECK_LE(pc_offset, method_info->code_size);
	DCHECK_LE(compilation_unit_code_address, method_info->code_address);
	const uint32_t low_pc = dchecked_integral_cast<uint32_t>(
	method_info->code_address + pc_offset - compilation_unit_code_address);
	stack_maps.emplace(low_pc, s);
	}

	// Create entries for the requested register based on stack map data.
	for (auto it = stack_maps.begin(); it != stack_maps.end(); it++) {
	const uint32_t low_pc = it->first;
	const uint32_t stack_map_index = it->second;
	const StackMap stack_map = code_info.GetStackMapAt(stack_map_index);
	auto next_it = it;
	next_it++;
	const uint32_t high_pc = next_it != stack_maps.end()
	? next_it->first
	: method_info->code_address + method_info->code_size - compilation_unit_code_address;
	DCHECK_LE(low_pc, high_pc);
	if (low_pc == high_pc) {
	continue; // Ignore if the address range is empty.
	}

	// Check that the stack map is in the requested range.
	uint32_t dex_pc = stack_map.GetDexPc();
	if (!(dex_pc_low <= dex_pc && dex_pc < dex_pc_high)) {
	// The variable is not in scope at this PC. Therefore omit the entry.
	// Note that this is different to None() entry which means in scope, but unknown location.
	continue;
	}

	// Find the location of the dex register.
	DexRegisterLocation reg_lo = DexRegisterLocation::None();
	DexRegisterLocation reg_hi = DexRegisterLocation::None();
	DCHECK_LT(stack_map_index, dex_register_maps.size());
	DexRegisterMap dex_register_map = dex_register_maps[stack_map_index];
	DCHECK(!dex_register_map.empty());
	CodeItemDataAccessor accessor(*method_info->dex_file, method_info->code_item);
	reg_lo = dex_register_map[vreg];
	if (is64bitValue) {
	reg_hi = dex_register_map[vreg + 1];
	}

	// Add location entry for this address range.
	if (!variable_locations.empty() &&
	variable_locations.back().reg_lo == reg_lo &&
	variable_locations.back().reg_hi == reg_hi &&
	variable_locations.back().high_pc == low_pc) {
	// Merge with the previous entry (extend its range).
	variable_locations.back().high_pc = high_pc;
	} else {
	variable_locations.push_back({low_pc, high_pc, reg_lo, reg_hi});
	}
	}

	return variable_locations;
	}

	// Write table into .debug_loc which describes location of dex register.
	// The dex register might be valid only at some points and it might
	// move between machine registers and stack.
	static void WriteDebugLocEntry(const MethodDebugInfo* method_info,
	const std::vector<DexRegisterMap>& dex_register_maps,
	uint16_t vreg,
	bool is64bitValue,
	uint64_t compilation_unit_code_address,
	uint32_t dex_pc_low,
	uint32_t dex_pc_high,
	InstructionSet isa,
	dwarf::DebugInfoEntryWriter<>* debug_info,
	std::vector<uint8_t>* debug_loc_buffer,
	std::vector<uint8_t>* debug_ranges_buffer) {
	using Kind = DexRegisterLocation::Kind;
	if (method_info->code_info == nullptr \|\| dex_register_maps.empty()) {
	return;
	}

	std::vector<VariableLocation> variable_locations = GetVariableLocations(
	method_info,
	dex_register_maps,
	vreg,
	is64bitValue,
	compilation_unit_code_address,
	dex_pc_low,
	dex_pc_high,
	isa);

	// Write .debug_loc entries.
	dwarf::Writer<> debug_loc(debug_loc_buffer);
	const size_t debug_loc_offset = debug_loc.size();
	const bool is64bit = Is64BitInstructionSet(isa);
	std::vector<uint8_t> expr_buffer;
	for (const VariableLocation& variable_location : variable_locations) {
	// Translate dex register location to DWARF expression.
	// Note that 64-bit value might be split to two distinct locations.
	// (for example, two 32-bit machine registers, or even stack and register)
	dwarf::Expression expr(&expr_buffer);
	DexRegisterLocation reg_lo = variable_location.reg_lo;
	DexRegisterLocation reg_hi = variable_location.reg_hi;
	for (int piece = 0; piece < (is64bitValue ? 2 : 1); piece++) {
	DexRegisterLocation reg_loc = (piece == 0 ? reg_lo : reg_hi);
	const Kind kind = reg_loc.GetKind();
	const int32_t value = reg_loc.GetValue();
	if (kind == Kind::kInStack) {
	// The stack offset is relative to SP. Make it relative to CFA.
	expr.WriteOpFbreg(value - method_info->frame_size_in_bytes);
	if (piece == 0 && reg_hi.GetKind() == Kind::kInStack &&
	reg_hi.GetValue() == value + 4) {
	break; // the high word is correctly implied by the low word.
	}
	} else if (kind == Kind::kInRegister) {
	expr.WriteOpReg(GetDwarfCoreReg(isa, value).num());
	if (piece == 0 && reg_hi.GetKind() == Kind::kInRegisterHigh &&
	reg_hi.GetValue() == value) {
	break; // the high word is correctly implied by the low word.
	}
	} else if (kind == Kind::kInFpuRegister) {
	if ((isa == InstructionSet::kArm \|\| isa == InstructionSet::kThumb2) &&
	piece == 0 && reg_hi.GetKind() == Kind::kInFpuRegister &&
	reg_hi.GetValue() == value + 1 && value % 2 == 0) {
	// Translate S register pair to D register (e.g. S4+S5 to D2).
	expr.WriteOpReg(Reg::ArmDp(value / 2).num());
	break;
	}
	expr.WriteOpReg(GetDwarfFpReg(isa, value).num());
	if (piece == 0 && reg_hi.GetKind() == Kind::kInFpuRegisterHigh &&
	reg_hi.GetValue() == reg_lo.GetValue()) {
	break; // the high word is correctly implied by the low word.
	}
	} else if (kind == Kind::kConstant) {
	expr.WriteOpConsts(value);
	expr.WriteOpStackValue();
	} else if (kind == Kind::kNone) {
	break;
	} else {
	// kInStackLargeOffset and kConstantLargeValue are hidden by GetKind().
	// kInRegisterHigh and kInFpuRegisterHigh should be handled by
	// the special cases above and they should not occur alone.
	LOG(WARNING) << "Unexpected register location: " << kind
	<< " (This can indicate either a bug in the dexer when generating"
	<< " local variable information, or a bug in ART compiler."
	<< " Please file a bug at go/art-bug)";
	break;
	}
	if (is64bitValue) {
	// Write the marker which is needed by split 64-bit values.
	// This code is skipped by the special cases.
	expr.WriteOpPiece(4);
	}
	}

	if (expr.size() > 0) {
	if (is64bit) {
	debug_loc.PushUint64(variable_location.low_pc);
	debug_loc.PushUint64(variable_location.high_pc);
	} else {
	debug_loc.PushUint32(variable_location.low_pc);
	debug_loc.PushUint32(variable_location.high_pc);
	}
	// Write the expression.
	debug_loc.PushUint16(expr.size());
	debug_loc.PushData(expr.data());
	} else {
	// Do not generate .debug_loc if the location is not known.
	}
	}
	// Write end-of-list entry.
	if (is64bit) {
	debug_loc.PushUint64(0);
	debug_loc.PushUint64(0);
	} else {
	debug_loc.PushUint32(0);
	debug_loc.PushUint32(0);
	}

	// Write .debug_ranges entries.
	// This includes ranges where the variable is in scope but the location is not known.
	dwarf::Writer<> debug_ranges(debug_ranges_buffer);
	size_t debug_ranges_offset = debug_ranges.size();
	for (size_t i = 0; i < variable_locations.size(); i++) {
	uint32_t low_pc = variable_locations[i].low_pc;
	uint32_t high_pc = variable_locations[i].high_pc;
	while (i + 1 < variable_locations.size() && variable_locations[i+1].low_pc == high_pc) {
	// Merge address range with the next entry.
	high_pc = variable_locations[++i].high_pc;
	}
	if (is64bit) {
	debug_ranges.PushUint64(low_pc);
	debug_ranges.PushUint64(high_pc);
	} else {
	debug_ranges.PushUint32(low_pc);
	debug_ranges.PushUint32(high_pc);
	}
	}
	// Write end-of-list entry.
	if (is64bit) {
	debug_ranges.PushUint64(0);
	debug_ranges.PushUint64(0);
	} else {
	debug_ranges.PushUint32(0);
	debug_ranges.PushUint32(0);
	}

	// Simple de-duplication - check whether this entry is same as the last one (or tail of it).
	size_t debug_ranges_entry_size = debug_ranges.size() - debug_ranges_offset;
	if (debug_ranges_offset >= debug_ranges_entry_size) {
	size_t previous_offset = debug_ranges_offset - debug_ranges_entry_size;
	if (memcmp(debug_ranges_buffer->data() + previous_offset,
	debug_ranges_buffer->data() + debug_ranges_offset,
	debug_ranges_entry_size) == 0) {
	// Remove what we have just written and use the last entry instead.
	debug_ranges_buffer->resize(debug_ranges_offset);
	debug_ranges_offset = previous_offset;
	}
	}

	// Write attributes to .debug_info.
	debug_info->WriteSecOffset(dwarf::DW_AT_location, debug_loc_offset);
	debug_info->WriteSecOffset(dwarf::DW_AT_start_scope, debug_ranges_offset);
	}

	} // namespace debug
	} // namespace art

	#endif // ART_COMPILER_DEBUG_ELF_DEBUG_LOC_WRITER_H_