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 "compiled_method.h"
#include "debug/dwarf/debug_info_entry_writer.h"
#include "debug/dwarf/register.h"
#include "debug/method_debug_info.h"
#include "stack_map.h"

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

static Reg GetDwarfCoreReg(InstructionSet isa, int machine_reg) {
  switch (isa) {
    case kArm:
    case kThumb2:
      return Reg::ArmCore(machine_reg);
    case kArm64:
      return Reg::Arm64Core(machine_reg);
    case kX86:
      return Reg::X86Core(machine_reg);
    case kX86_64:
      return Reg::X86_64Core(machine_reg);
    case kMips:
      return Reg::MipsCore(machine_reg);
    case kMips64:
      return Reg::Mips64Core(machine_reg);
    case kNone:
      LOG(FATAL) << "No instruction set";
  }
  UNREACHABLE();
}

static Reg GetDwarfFpReg(InstructionSet isa, int machine_reg) {
  switch (isa) {
    case kArm:
    case kThumb2:
      return Reg::ArmFp(machine_reg);
    case kArm64:
      return Reg::Arm64Fp(machine_reg);
    case kX86:
      return Reg::X86Fp(machine_reg);
    case kX86_64:
      return Reg::X86_64Fp(machine_reg);
    case kMips:
      return Reg::MipsFp(machine_reg);
    case kMips64:
      return Reg::Mips64Fp(machine_reg);
    case kNone:
      LOG(FATAL) << "No instruction set";
  }
  UNREACHABLE();
}

struct VariableLocation {
  uint32_t low_pc;
  uint32_t high_pc;
  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.
std::vector<VariableLocation> GetVariableLocations(const MethodDebugInfo* method_info,
                                                   uint16_t vreg,
                                                   bool is64bitValue,
                                                   uint32_t dex_pc_low,
                                                   uint32_t dex_pc_high) {
  std::vector<VariableLocation> variable_locations;

  // Get stack maps sorted by pc (they might not be sorted internally).
  const CodeInfo code_info(method_info->compiled_method->GetVmapTable().data());
  const StackMapEncoding encoding = code_info.ExtractEncoding();
  std::map<uint32_t, StackMap> stack_maps;
  for (uint32_t s = 0; s < code_info.GetNumberOfStackMaps(); s++) {
    StackMap stack_map = code_info.GetStackMapAt(s, encoding);
    DCHECK(stack_map.IsValid());
    const uint32_t low_pc = method_info->low_pc + stack_map.GetNativePcOffset(encoding);
    DCHECK_LE(low_pc, method_info->high_pc);
    stack_maps.emplace(low_pc, stack_map);
  }

  // Create entries for the requested register based on stack map data.
  for (auto it = stack_maps.begin(); it != stack_maps.end(); it++) {
    const StackMap& stack_map = it->second;
    const uint32_t low_pc = it->first;
    auto next_it = it;
    next_it++;
    const uint32_t high_pc = next_it != stack_maps.end() ? next_it->first
                                                         : method_info->high_pc;
    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(encoding);
    if (!(dex_pc_low <= dex_pc && dex_pc < dex_pc_high)) {
      continue;
    }

    // Find the location of the dex register.
    DexRegisterLocation reg_lo = DexRegisterLocation::None();
    DexRegisterLocation reg_hi = DexRegisterLocation::None();
    if (stack_map.HasDexRegisterMap(encoding)) {
      DexRegisterMap dex_register_map = code_info.GetDexRegisterMapOf(
          stack_map, encoding, method_info->code_item->registers_size_);
      reg_lo = dex_register_map.GetDexRegisterLocation(
          vreg, method_info->code_item->registers_size_, code_info, encoding);
      if (is64bitValue) {
        reg_hi = dex_register_map.GetDexRegisterLocation(
            vreg + 1, method_info->code_item->registers_size_, code_info, encoding);
      }
    }

    // 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 if (!variable_locations.empty() && reg_lo == DexRegisterLocation::None()) {
      // Unknown location - use the last known location as best-effort guess.
      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,
                               uint16_t vreg,
                               bool is64bitValue,
                               uint32_t compilation_unit_low_pc,
                               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->IsFromOptimizingCompiler()) {
    return;
  }

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

  // 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) {
        const size_t frame_size = method_info->compiled_method->GetFrameSizeInBytes();
        // The stack offset is relative to SP. Make it relative to CFA.
        expr.WriteOpFbreg(value - frame_size);
        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 == kArm || isa == 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(ERROR) << "Unexpected register location kind: "
                   << DexRegisterLocation::PrettyDescriptor(kind);
        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 - compilation_unit_low_pc);
        debug_loc.PushUint64(variable_location.high_pc - compilation_unit_low_pc);
      } else {
        debug_loc.PushUint32(variable_location.low_pc - compilation_unit_low_pc);
        debug_loc.PushUint32(variable_location.high_pc - compilation_unit_low_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 - compilation_unit_low_pc);
      debug_ranges.PushUint64(high_pc - compilation_unit_low_pc);
    } else {
      debug_ranges.PushUint32(low_pc - compilation_unit_low_pc);
      debug_ranges.PushUint32(high_pc - compilation_unit_low_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_