DWARFFormValue.cpp

//===- DWARFFormValue.cpp -------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#include "llvm/DebugInfo/DWARF/DWARFFormValue.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/None.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/BinaryFormat/Dwarf.h"
#include "llvm/DebugInfo/DWARF/DWARFContext.h"
#include "llvm/DebugInfo/DWARF/DWARFRelocMap.h"
#include "llvm/DebugInfo/DWARF/DWARFUnit.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/Format.h"
#include "llvm/Support/WithColor.h"
#include "llvm/Support/raw_ostream.h"
#include <cinttypes>
#include <cstdint>
#include <limits>

using namespace llvm;
using namespace dwarf;

static const DWARFFormValue::FormClass DWARF5FormClasses[] = {
    DWARFFormValue::FC_Unknown,  // 0x0
    DWARFFormValue::FC_Address,  // 0x01 DW_FORM_addr
    DWARFFormValue::FC_Unknown,  // 0x02 unused
    DWARFFormValue::FC_Block,    // 0x03 DW_FORM_block2
    DWARFFormValue::FC_Block,    // 0x04 DW_FORM_block4
    DWARFFormValue::FC_Constant, // 0x05 DW_FORM_data2
    // --- These can be FC_SectionOffset in DWARF3 and below:
    DWARFFormValue::FC_Constant, // 0x06 DW_FORM_data4
    DWARFFormValue::FC_Constant, // 0x07 DW_FORM_data8
    // ---
    DWARFFormValue::FC_String,        // 0x08 DW_FORM_string
    DWARFFormValue::FC_Block,         // 0x09 DW_FORM_block
    DWARFFormValue::FC_Block,         // 0x0a DW_FORM_block1
    DWARFFormValue::FC_Constant,      // 0x0b DW_FORM_data1
    DWARFFormValue::FC_Flag,          // 0x0c DW_FORM_flag
    DWARFFormValue::FC_Constant,      // 0x0d DW_FORM_sdata
    DWARFFormValue::FC_String,        // 0x0e DW_FORM_strp
    DWARFFormValue::FC_Constant,      // 0x0f DW_FORM_udata
    DWARFFormValue::FC_Reference,     // 0x10 DW_FORM_ref_addr
    DWARFFormValue::FC_Reference,     // 0x11 DW_FORM_ref1
    DWARFFormValue::FC_Reference,     // 0x12 DW_FORM_ref2
    DWARFFormValue::FC_Reference,     // 0x13 DW_FORM_ref4
    DWARFFormValue::FC_Reference,     // 0x14 DW_FORM_ref8
    DWARFFormValue::FC_Reference,     // 0x15 DW_FORM_ref_udata
    DWARFFormValue::FC_Indirect,      // 0x16 DW_FORM_indirect
    DWARFFormValue::FC_SectionOffset, // 0x17 DW_FORM_sec_offset
    DWARFFormValue::FC_Exprloc,       // 0x18 DW_FORM_exprloc
    DWARFFormValue::FC_Flag,          // 0x19 DW_FORM_flag_present
    DWARFFormValue::FC_String,        // 0x1a DW_FORM_strx
    DWARFFormValue::FC_Address,       // 0x1b DW_FORM_addrx
    DWARFFormValue::FC_Reference,     // 0x1c DW_FORM_ref_sup4
    DWARFFormValue::FC_String,        // 0x1d DW_FORM_strp_sup
    DWARFFormValue::FC_Constant,      // 0x1e DW_FORM_data16
    DWARFFormValue::FC_String,        // 0x1f DW_FORM_line_strp
    DWARFFormValue::FC_Reference,     // 0x20 DW_FORM_ref_sig8
    DWARFFormValue::FC_Constant,      // 0x21 DW_FORM_implicit_const
    DWARFFormValue::FC_SectionOffset, // 0x22 DW_FORM_loclistx
    DWARFFormValue::FC_SectionOffset, // 0x23 DW_FORM_rnglistx
    DWARFFormValue::FC_Reference,     // 0x24 DW_FORM_ref_sup8
    DWARFFormValue::FC_String,        // 0x25 DW_FORM_strx1
    DWARFFormValue::FC_String,        // 0x26 DW_FORM_strx2
    DWARFFormValue::FC_String,        // 0x27 DW_FORM_strx3
    DWARFFormValue::FC_String,        // 0x28 DW_FORM_strx4
    DWARFFormValue::FC_Address,       // 0x29 DW_FORM_addrx1
    DWARFFormValue::FC_Address,       // 0x2a DW_FORM_addrx2
    DWARFFormValue::FC_Address,       // 0x2b DW_FORM_addrx3
    DWARFFormValue::FC_Address,       // 0x2c DW_FORM_addrx4
    DWARFFormValue::FC_Address,       // 0x2001 DW_FORM_addrx_offset
};

DWARFFormValue DWARFFormValue::createFromSValue(dwarf::Form F, int64_t V) {
  return DWARFFormValue(F, ValueType(V));
}

DWARFFormValue DWARFFormValue::createFromUValue(dwarf::Form F, uint64_t V) {
  return DWARFFormValue(F, ValueType(V));
}

DWARFFormValue DWARFFormValue::createFromPValue(dwarf::Form F, const char *V) {
  return DWARFFormValue(F, ValueType(V));
}

DWARFFormValue DWARFFormValue::createFromBlockValue(dwarf::Form F,
                                                    ArrayRef<uint8_t> D) {
  ValueType V;
  V.uval = D.size();
  V.data = D.data();
  return DWARFFormValue(F, V);
}

DWARFFormValue DWARFFormValue::createFromUnit(dwarf::Form F, const DWARFUnit *U,
                                              uint64_t *OffsetPtr) {
  DWARFFormValue FormValue(F);
  FormValue.extractValue(U->getDebugInfoExtractor(), OffsetPtr,
                         U->getFormParams(), U);
  return FormValue;
}

bool DWARFFormValue::skipValue(dwarf::Form Form, DataExtractor DebugInfoData,
                               uint64_t *OffsetPtr,
                               const dwarf::FormParams Params) {
  bool Indirect = false;
  do {
    switch (Form) {
    // Blocks of inlined data that have a length field and the data bytes
    // inlined in the .debug_info.
    case DW_FORM_exprloc:
    case DW_FORM_block: {
      uint64_t size = DebugInfoData.getULEB128(OffsetPtr);
      *OffsetPtr += size;
      return true;
    }
    case DW_FORM_block1: {
      uint8_t size = DebugInfoData.getU8(OffsetPtr);
      *OffsetPtr += size;
      return true;
    }
    case DW_FORM_block2: {
      uint16_t size = DebugInfoData.getU16(OffsetPtr);
      *OffsetPtr += size;
      return true;
    }
    case DW_FORM_block4: {
      uint32_t size = DebugInfoData.getU32(OffsetPtr);
      *OffsetPtr += size;
      return true;
    }

    // Inlined NULL terminated C-strings.
    case DW_FORM_string:
      DebugInfoData.getCStr(OffsetPtr);
      return true;

    case DW_FORM_addr:
    case DW_FORM_ref_addr:
    case DW_FORM_flag_present:
    case DW_FORM_data1:
    case DW_FORM_data2:
    case DW_FORM_data4:
    case DW_FORM_data8:
    case DW_FORM_data16:
    case DW_FORM_flag:
    case DW_FORM_ref1:
    case DW_FORM_ref2:
    case DW_FORM_ref4:
    case DW_FORM_ref8:
    case DW_FORM_ref_sig8:
    case DW_FORM_ref_sup4:
    case DW_FORM_ref_sup8:
    case DW_FORM_strx1:
    case DW_FORM_strx2:
    case DW_FORM_strx4:
    case DW_FORM_addrx1:
    case DW_FORM_addrx2:
    case DW_FORM_addrx4:
    case DW_FORM_sec_offset:
    case DW_FORM_strp:
    case DW_FORM_strp_sup:
    case DW_FORM_line_strp:
    case DW_FORM_GNU_ref_alt:
    case DW_FORM_GNU_strp_alt:
    case DW_FORM_implicit_const:
      if (Optional<uint8_t> FixedSize =
              dwarf::getFixedFormByteSize(Form, Params)) {
        *OffsetPtr += *FixedSize;
        return true;
      }
      return false;

    // signed or unsigned LEB 128 values.
    case DW_FORM_sdata:
      DebugInfoData.getSLEB128(OffsetPtr);
      return true;

    case DW_FORM_udata:
    case DW_FORM_ref_udata:
    case DW_FORM_strx:
    case DW_FORM_addrx:
    case DW_FORM_loclistx:
    case DW_FORM_rnglistx:
    case DW_FORM_GNU_addr_index:
    case DW_FORM_GNU_str_index:
      DebugInfoData.getULEB128(OffsetPtr);
      return true;

    case DW_FORM_LLVM_addrx_offset:
      DebugInfoData.getULEB128(OffsetPtr);
      *OffsetPtr += 4;
      return true;

    case DW_FORM_indirect:
      Indirect = true;
      Form = static_cast<dwarf::Form>(DebugInfoData.getULEB128(OffsetPtr));
      break;

    default:
      return false;
    }
  } while (Indirect);
  return true;
}

bool DWARFFormValue::isFormClass(DWARFFormValue::FormClass FC) const {
  // First, check DWARF5 form classes.
  if (Form < makeArrayRef(DWARF5FormClasses).size() &&
      DWARF5FormClasses[Form] == FC)
    return true;
  // Check more forms from extensions and proposals.
  switch (Form) {
  case DW_FORM_GNU_ref_alt:
    return (FC == FC_Reference);
  case DW_FORM_GNU_addr_index:
    return (FC == FC_Address);
  case DW_FORM_GNU_str_index:
  case DW_FORM_GNU_strp_alt:
    return (FC == FC_String);
  case DW_FORM_LLVM_addrx_offset:
    return (FC == FC_Address);
  default:
    break;
  }

  if (FC == FC_SectionOffset) {
    if (Form == DW_FORM_strp || Form == DW_FORM_line_strp)
      return true;
    // In DWARF3 DW_FORM_data4 and DW_FORM_data8 served also as a section
    // offset. If we don't have a DWARFUnit, default to the old behavior.
    if (Form == DW_FORM_data4 || Form == DW_FORM_data8)
      return !U || U->getVersion() <= 3;
  }

  return false;
}

bool DWARFFormValue::extractValue(const DWARFDataExtractor &Data,
                                  uint64_t *OffsetPtr, dwarf::FormParams FP,
                                  const DWARFContext *Ctx,
                                  const DWARFUnit *CU) {
  if (!Ctx && CU)
    Ctx = &CU->getContext();
  C = Ctx;
  U = CU;
  Format = FP.Format;
  bool Indirect = false;
  bool IsBlock = false;
  Value.data = nullptr;
  // Read the value for the form into value and follow and DW_FORM_indirect
  // instances we run into
  Error Err = Error::success();
  do {
    Indirect = false;
    switch (Form) {
    case DW_FORM_addr:
    case DW_FORM_ref_addr: {
      uint16_t Size =
          (Form == DW_FORM_addr) ? FP.AddrSize : FP.getRefAddrByteSize();
      Value.uval =
          Data.getRelocatedValue(Size, OffsetPtr, &Value.SectionIndex, &Err);
      break;
    }
    case DW_FORM_exprloc:
    case DW_FORM_block:
      Value.uval = Data.getULEB128(OffsetPtr, &Err);
      IsBlock = true;
      break;
    case DW_FORM_block1:
      Value.uval = Data.getU8(OffsetPtr, &Err);
      IsBlock = true;
      break;
    case DW_FORM_block2:
      Value.uval = Data.getU16(OffsetPtr, &Err);
      IsBlock = true;
      break;
    case DW_FORM_block4:
      Value.uval = Data.getU32(OffsetPtr, &Err);
      IsBlock = true;
      break;
    case DW_FORM_data1:
    case DW_FORM_ref1:
    case DW_FORM_flag:
    case DW_FORM_strx1:
    case DW_FORM_addrx1:
      Value.uval = Data.getU8(OffsetPtr, &Err);
      break;
    case DW_FORM_data2:
    case DW_FORM_ref2:
    case DW_FORM_strx2:
    case DW_FORM_addrx2:
      Value.uval = Data.getU16(OffsetPtr, &Err);
      break;
    case DW_FORM_strx3:
      Value.uval = Data.getU24(OffsetPtr, &Err);
      break;
    case DW_FORM_data4:
    case DW_FORM_ref4:
    case DW_FORM_ref_sup4:
    case DW_FORM_strx4:
    case DW_FORM_addrx4:
      Value.uval = Data.getRelocatedValue(4, OffsetPtr, nullptr, &Err);
      break;
    case DW_FORM_data8:
    case DW_FORM_ref8:
    case DW_FORM_ref_sup8:
      Value.uval = Data.getRelocatedValue(8, OffsetPtr, nullptr, &Err);
      break;
    case DW_FORM_data16:
      // Treat this like a 16-byte block.
      Value.uval = 16;
      IsBlock = true;
      break;
    case DW_FORM_sdata:
      Value.sval = Data.getSLEB128(OffsetPtr, &Err);
      break;
    case DW_FORM_udata:
    case DW_FORM_ref_udata:
    case DW_FORM_rnglistx:
    case DW_FORM_loclistx:
    case DW_FORM_GNU_addr_index:
    case DW_FORM_GNU_str_index:
    case DW_FORM_addrx:
    case DW_FORM_strx:
      Value.uval = Data.getULEB128(OffsetPtr, &Err);
      break;
    case DW_FORM_LLVM_addrx_offset:
      Value.uval = Data.getULEB128(OffsetPtr, &Err) << 32;
      Value.uval |= Data.getU32(OffsetPtr, &Err);
      break;
    case DW_FORM_string:
      Value.cstr = Data.getCStr(OffsetPtr, &Err);
      break;
    case DW_FORM_indirect:
      Form = static_cast<dwarf::Form>(Data.getULEB128(OffsetPtr, &Err));
      Indirect = true;
      break;
    case DW_FORM_strp:
    case DW_FORM_sec_offset:
    case DW_FORM_GNU_ref_alt:
    case DW_FORM_GNU_strp_alt:
    case DW_FORM_line_strp:
    case DW_FORM_strp_sup: {
      Value.uval = Data.getRelocatedValue(FP.getDwarfOffsetByteSize(),
                                          OffsetPtr, nullptr, &Err);
      break;
    }
    case DW_FORM_flag_present:
      Value.uval = 1;
      break;
    case DW_FORM_ref_sig8:
      Value.uval = Data.getU64(OffsetPtr, &Err);
      break;
    case DW_FORM_implicit_const:
      // Value has been already set by DWARFFormValue::createFromSValue.
      break;
    default:
      // DWARFFormValue::skipValue() will have caught this and caused all
      // DWARF DIEs to fail to be parsed, so this code is not be reachable.
      llvm_unreachable("unsupported form");
    }
  } while (Indirect && !Err);

  if (IsBlock)
    Value.data = Data.getBytes(OffsetPtr, Value.uval, &Err).bytes_begin();

  return !errorToBool(std::move(Err));
}

void DWARFFormValue::dumpAddress(raw_ostream &OS, uint8_t AddressSize,
                                 uint64_t Address) {
  uint8_t HexDigits = AddressSize * 2;
  OS << format("0x%*.*" PRIx64, HexDigits, HexDigits, Address);
}

void DWARFFormValue::dumpSectionedAddress(raw_ostream &OS,
                                          DIDumpOptions DumpOpts,
                                          object::SectionedAddress SA) const {
  dumpAddress(OS, U->getAddressByteSize(), SA.Address);
  dumpAddressSection(U->getContext().getDWARFObj(), OS, DumpOpts,
                     SA.SectionIndex);
}

void DWARFFormValue::dumpAddressSection(const DWARFObject &Obj, raw_ostream &OS,
                                        DIDumpOptions DumpOpts,
                                        uint64_t SectionIndex) {
  if (!DumpOpts.Verbose || SectionIndex == -1ULL)
    return;
  ArrayRef<SectionName> SectionNames = Obj.getSectionNames();
  const auto &SecRef = SectionNames[SectionIndex];

  OS << " \"" << SecRef.Name << '\"';

  // Print section index if name is not unique.
  if (!SecRef.IsNameUnique)
    OS << format(" [%" PRIu64 "]", SectionIndex);
}

void DWARFFormValue::dump(raw_ostream &OS, DIDumpOptions DumpOpts) const {
  uint64_t UValue = Value.uval;
  bool CURelativeOffset = false;
  raw_ostream &AddrOS = DumpOpts.ShowAddresses
                            ? WithColor(OS, HighlightColor::Address).get()
                            : nulls();
  int OffsetDumpWidth = 2 * dwarf::getDwarfOffsetByteSize(Format);
  switch (Form) {
  case DW_FORM_addr:
    dumpSectionedAddress(AddrOS, DumpOpts, {Value.uval, Value.SectionIndex});
    break;
  case DW_FORM_addrx:
  case DW_FORM_addrx1:
  case DW_FORM_addrx2:
  case DW_FORM_addrx3:
  case DW_FORM_addrx4:
  case DW_FORM_GNU_addr_index: {
    if (U == nullptr) {
      OS << "<invalid dwarf unit>";
      break;
    }
    Optional<object::SectionedAddress> A = U->getAddrOffsetSectionItem(UValue);
    if (!A || DumpOpts.Verbose)
      AddrOS << format("indexed (%8.8x) address = ", (uint32_t)UValue);
    if (A)
      dumpSectionedAddress(AddrOS, DumpOpts, *A);
    else
      OS << "<unresolved>";
    break;
  }
  case DW_FORM_LLVM_addrx_offset: {
    if (U == nullptr) {
      OS << "<invalid dwarf unit>";
      break;
    }
    uint32_t Index = UValue >> 32;
    uint32_t Offset = UValue & 0xffffffff;
    Optional<object::SectionedAddress> A = U->getAddrOffsetSectionItem(Index);
    if (!A || DumpOpts.Verbose)
      AddrOS << format("indexed (%8.8x) + 0x%x address = ", Index, Offset);
    if (A) {
      A->Address += Offset;
      dumpSectionedAddress(AddrOS, DumpOpts, *A);
    } else
      OS << "<unresolved>";
    break;
  }
  case DW_FORM_flag_present:
    OS << "true";
    break;
  case DW_FORM_flag:
  case DW_FORM_data1:
    OS << format("0x%02x", (uint8_t)UValue);
    break;
  case DW_FORM_data2:
    OS << format("0x%04x", (uint16_t)UValue);
    break;
  case DW_FORM_data4:
    OS << format("0x%08x", (uint32_t)UValue);
    break;
  case DW_FORM_ref_sig8:
    AddrOS << format("0x%016" PRIx64, UValue);
    break;
  case DW_FORM_data8:
    OS << format("0x%016" PRIx64, UValue);
    break;
  case DW_FORM_data16:
    OS << format_bytes(ArrayRef<uint8_t>(Value.data, 16), None, 16, 16);
    break;
  case DW_FORM_string:
    OS << '"';
    OS.write_escaped(Value.cstr);
    OS << '"';
    break;
  case DW_FORM_exprloc:
  case DW_FORM_block:
  case DW_FORM_block1:
  case DW_FORM_block2:
  case DW_FORM_block4:
    if (UValue > 0) {
      switch (Form) {
      case DW_FORM_exprloc:
      case DW_FORM_block:
        AddrOS << format("<0x%" PRIx64 "> ", UValue);
        break;
      case DW_FORM_block1:
        AddrOS << format("<0x%2.2x> ", (uint8_t)UValue);
        break;
      case DW_FORM_block2:
        AddrOS << format("<0x%4.4x> ", (uint16_t)UValue);
        break;
      case DW_FORM_block4:
        AddrOS << format("<0x%8.8x> ", (uint32_t)UValue);
        break;
      default:
        break;
      }

      const uint8_t *DataPtr = Value.data;
      if (DataPtr) {
        // UValue contains size of block
        const uint8_t *EndDataPtr = DataPtr + UValue;
        while (DataPtr < EndDataPtr) {
          AddrOS << format("%2.2x ", *DataPtr);
          ++DataPtr;
        }
      } else
        OS << "NULL";
    }
    break;

  case DW_FORM_sdata:
  case DW_FORM_implicit_const:
    OS << Value.sval;
    break;
  case DW_FORM_udata:
    OS << Value.uval;
    break;
  case DW_FORM_strp:
    if (DumpOpts.Verbose)
      OS << format(" .debug_str[0x%0*" PRIx64 "] = ", OffsetDumpWidth, UValue);
    dumpString(OS);
    break;
  case DW_FORM_line_strp:
    if (DumpOpts.Verbose)
      OS << format(" .debug_line_str[0x%0*" PRIx64 "] = ", OffsetDumpWidth,
                   UValue);
    dumpString(OS);
    break;
  case DW_FORM_strx:
  case DW_FORM_strx1:
  case DW_FORM_strx2:
  case DW_FORM_strx3:
  case DW_FORM_strx4:
  case DW_FORM_GNU_str_index:
    if (DumpOpts.Verbose)
      OS << format("indexed (%8.8x) string = ", (uint32_t)UValue);
    dumpString(OS);
    break;
  case DW_FORM_GNU_strp_alt:
    if (DumpOpts.Verbose)
      OS << format("alt indirect string, offset: 0x%" PRIx64 "", UValue);
    dumpString(OS);
    break;
  case DW_FORM_ref_addr:
    AddrOS << format("0x%016" PRIx64, UValue);
    break;
  case DW_FORM_ref1:
    CURelativeOffset = true;
    if (DumpOpts.Verbose)
      AddrOS << format("cu + 0x%2.2x", (uint8_t)UValue);
    break;
  case DW_FORM_ref2:
    CURelativeOffset = true;
    if (DumpOpts.Verbose)
      AddrOS << format("cu + 0x%4.4x", (uint16_t)UValue);
    break;
  case DW_FORM_ref4:
    CURelativeOffset = true;
    if (DumpOpts.Verbose)
      AddrOS << format("cu + 0x%4.4x", (uint32_t)UValue);
    break;
  case DW_FORM_ref8:
    CURelativeOffset = true;
    if (DumpOpts.Verbose)
      AddrOS << format("cu + 0x%8.8" PRIx64, UValue);
    break;
  case DW_FORM_ref_udata:
    CURelativeOffset = true;
    if (DumpOpts.Verbose)
      AddrOS << format("cu + 0x%" PRIx64, UValue);
    break;
  case DW_FORM_GNU_ref_alt:
    AddrOS << format("<alt 0x%" PRIx64 ">", UValue);
    break;

  // All DW_FORM_indirect attributes should be resolved prior to calling
  // this function
  case DW_FORM_indirect:
    OS << "DW_FORM_indirect";
    break;

  case DW_FORM_rnglistx:
    OS << format("indexed (0x%x) rangelist = ", (uint32_t)UValue);
    break;

  case DW_FORM_loclistx:
    OS << format("indexed (0x%x) loclist = ", (uint32_t)UValue);
    break;

  case DW_FORM_sec_offset:
    AddrOS << format("0x%0*" PRIx64, OffsetDumpWidth, UValue);
    break;

  default:
    OS << format("DW_FORM(0x%4.4x)", Form);
    break;
  }

  if (CURelativeOffset) {
    if (DumpOpts.Verbose)
      OS << " => {";
    if (DumpOpts.ShowAddresses)
      WithColor(OS, HighlightColor::Address).get()
          << format("0x%8.8" PRIx64, UValue + (U ? U->getOffset() : 0));
    if (DumpOpts.Verbose)
      OS << "}";
  }
}

void DWARFFormValue::dumpString(raw_ostream &OS) const {
  if (auto DbgStr = dwarf::toString(*this)) {
    auto COS = WithColor(OS, HighlightColor::String);
    COS.get() << '"';
    COS.get().write_escaped(*DbgStr);
    COS.get() << '"';
  }
}

Expected<const char *> DWARFFormValue::getAsCString() const {
  if (!isFormClass(FC_String))
    return make_error<StringError>("Invalid form for string attribute",
                                   inconvertibleErrorCode());
  if (Form == DW_FORM_string)
    return Value.cstr;
  // FIXME: Add support for DW_FORM_GNU_strp_alt
  if (Form == DW_FORM_GNU_strp_alt || C == nullptr)
    return make_error<StringError>("Unsupported form for string attribute",
                                   inconvertibleErrorCode());
  uint64_t Offset = Value.uval;
  Optional<uint32_t> Index;
  if (Form == DW_FORM_GNU_str_index || Form == DW_FORM_strx ||
      Form == DW_FORM_strx1 || Form == DW_FORM_strx2 || Form == DW_FORM_strx3 ||
      Form == DW_FORM_strx4) {
    if (!U)
      return make_error<StringError>("API limitation - string extraction not "
                                     "available without a DWARFUnit",
                                     inconvertibleErrorCode());
    Expected<uint64_t> StrOffset = U->getStringOffsetSectionItem(Offset);
    Index = Offset;
    if (!StrOffset)
      return StrOffset.takeError();
    Offset = *StrOffset;
  }
  // Prefer the Unit's string extractor, because for .dwo it will point to
  // .debug_str.dwo, while the Context's extractor always uses .debug_str.
  DataExtractor StrData = Form == DW_FORM_line_strp
                              ? C->getLineStringExtractor()
                          : U ? U->getStringExtractor()
                              : C->getStringExtractor();
  if (const char *Str = StrData.getCStr(&Offset))
    return Str;
  std::string Msg = FormEncodingString(Form).str();
  if (Index)
    Msg += (" uses index " + Twine(*Index) + ", but the referenced string").str();
  Msg += (" offset " + Twine(Offset) + " is beyond .debug_str bounds").str();
  return make_error<StringError>(Msg,
      inconvertibleErrorCode());
}

Optional<uint64_t> DWARFFormValue::getAsAddress() const {
  if (auto SA = getAsSectionedAddress())
    return SA->Address;
  return None;
}

Optional<object::SectionedAddress>
DWARFFormValue::getAsSectionedAddress() const {
  if (!isFormClass(FC_Address))
    return None;
  bool AddrOffset = Form == dwarf::DW_FORM_LLVM_addrx_offset;
  if (Form == DW_FORM_GNU_addr_index || Form == DW_FORM_addrx || AddrOffset) {

    uint32_t Index = AddrOffset ? (Value.uval >> 32) : Value.uval;
    if (!U)
      return None;
    Optional<object::SectionedAddress> SA = U->getAddrOffsetSectionItem(Index);
    if (!SA)
      return None;
    if (AddrOffset)
      SA->Address += (Value.uval & 0xffffffff);
    return SA;
  }
  return {{Value.uval, Value.SectionIndex}};
}

Optional<uint64_t> DWARFFormValue::getAsReference() const {
  if (auto R = getAsRelativeReference())
    return R->Unit ? R->Unit->getOffset() + R->Offset : R->Offset;
  return None;
}

Optional<DWARFFormValue::UnitOffset> DWARFFormValue::getAsRelativeReference() const {
  if (!isFormClass(FC_Reference))
    return None;
  switch (Form) {
  case DW_FORM_ref1:
  case DW_FORM_ref2:
  case DW_FORM_ref4:
  case DW_FORM_ref8:
  case DW_FORM_ref_udata:
    if (!U)
      return None;
    return UnitOffset{const_cast<DWARFUnit*>(U), Value.uval};
  case DW_FORM_ref_addr:
  case DW_FORM_ref_sig8:
  case DW_FORM_GNU_ref_alt:
    return UnitOffset{nullptr, Value.uval};
  default:
    return None;
  }
}

Optional<uint64_t> DWARFFormValue::getAsSectionOffset() const {
  if (!isFormClass(FC_SectionOffset))
    return None;
  return Value.uval;
}

Optional<uint64_t> DWARFFormValue::getAsUnsignedConstant() const {
  if ((!isFormClass(FC_Constant) && !isFormClass(FC_Flag)) ||
      Form == DW_FORM_sdata)
    return None;
  return Value.uval;
}

Optional<int64_t> DWARFFormValue::getAsSignedConstant() const {
  if ((!isFormClass(FC_Constant) && !isFormClass(FC_Flag)) ||
      (Form == DW_FORM_udata &&
       uint64_t(std::numeric_limits<int64_t>::max()) < Value.uval))
    return None;
  switch (Form) {
  case DW_FORM_data4:
    return int32_t(Value.uval);
  case DW_FORM_data2:
    return int16_t(Value.uval);
  case DW_FORM_data1:
    return int8_t(Value.uval);
  case DW_FORM_sdata:
  case DW_FORM_data8:
  default:
    return Value.sval;
  }
}

Optional<ArrayRef<uint8_t>> DWARFFormValue::getAsBlock() const {
  if (!isFormClass(FC_Block) && !isFormClass(FC_Exprloc) &&
      Form != DW_FORM_data16)
    return None;
  return makeArrayRef(Value.data, Value.uval);
}

Optional<uint64_t> DWARFFormValue::getAsCStringOffset() const {
  if (!isFormClass(FC_String) && Form == DW_FORM_string)
    return None;
  return Value.uval;
}

Optional<uint64_t> DWARFFormValue::getAsReferenceUVal() const {
  if (!isFormClass(FC_Reference))
    return None;
  return Value.uval;
}

Optional<std::string>
DWARFFormValue::getAsFile(DILineInfoSpecifier::FileLineInfoKind Kind) const {
  if (U == nullptr || !isFormClass(FC_Constant))
    return None;
  DWARFUnit *DLU = const_cast<DWARFUnit *>(U)->getLinkedUnit();
  if (auto *LT = DLU->getContext().getLineTableForUnit(DLU)) {
    std::string FileName;
    if (LT->getFileNameByIndex(Value.uval, DLU->getCompilationDir(), Kind,
                               FileName))
      return FileName;
  }
  return None;
}