llvm-project/llvm/tools/dsymutil/DwarfLinkerForBinary.cpp

//===- tools/dsymutil/DwarfLinkerForBinary.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 "DwarfLinkerForBinary.h"
#include "BinaryHolder.h"
#include "DebugMap.h"
#include "MachOUtils.h"
#include "dsymutil.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DenseMapInfo.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/FoldingSet.h"
#include "llvm/ADT/Hashing.h"
#include "llvm/ADT/IntervalMap.h"
#include "llvm/ADT/None.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/PointerIntPair.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/Triple.h"
#include "llvm/ADT/Twine.h"
#include "llvm/BinaryFormat/Dwarf.h"
#include "llvm/BinaryFormat/MachO.h"
#include "llvm/CodeGen/AccelTable.h"
#include "llvm/CodeGen/AsmPrinter.h"
#include "llvm/CodeGen/DIE.h"
#include "llvm/CodeGen/NonRelocatableStringpool.h"
#include "llvm/Config/config.h"
#include "llvm/DWARFLinker/DWARFLinkerDeclContext.h"
#include "llvm/DebugInfo/DIContext.h"
#include "llvm/DebugInfo/DWARF/DWARFAbbreviationDeclaration.h"
#include "llvm/DebugInfo/DWARF/DWARFContext.h"
#include "llvm/DebugInfo/DWARF/DWARFDataExtractor.h"
#include "llvm/DebugInfo/DWARF/DWARFDebugLine.h"
#include "llvm/DebugInfo/DWARF/DWARFDebugRangeList.h"
#include "llvm/DebugInfo/DWARF/DWARFDie.h"
#include "llvm/DebugInfo/DWARF/DWARFFormValue.h"
#include "llvm/DebugInfo/DWARF/DWARFSection.h"
#include "llvm/DebugInfo/DWARF/DWARFUnit.h"
#include "llvm/MC/MCAsmBackend.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/MC/MCCodeEmitter.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCDwarf.h"
#include "llvm/MC/MCInstrInfo.h"
#include "llvm/MC/MCObjectFileInfo.h"
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/MC/MCRegisterInfo.h"
#include "llvm/MC/MCSection.h"
#include "llvm/MC/MCStreamer.h"
#include "llvm/MC/MCSubtargetInfo.h"
#include "llvm/MC/MCTargetOptions.h"
#include "llvm/Object/MachO.h"
#include "llvm/Object/ObjectFile.h"
#include "llvm/Object/SymbolicFile.h"
#include "llvm/Support/Allocator.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/DJB.h"
#include "llvm/Support/DataExtractor.h"
#include "llvm/Support/Error.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/ErrorOr.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/Format.h"
#include "llvm/Support/LEB128.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/TargetRegistry.h"
#include "llvm/Support/ThreadPool.h"
#include "llvm/Support/ToolOutputFile.h"
#include "llvm/Support/WithColor.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Target/TargetOptions.h"
#include "llvm/MC/MCTargetOptionsCommandFlags.h"
#include <algorithm>
#include <cassert>
#include <cinttypes>
#include <climits>
#include <cstdint>
#include <cstdlib>
#include <cstring>
#include <limits>
#include <map>
#include <memory>
#include <string>
#include <system_error>
#include <tuple>
#include <utility>
#include <vector>

namespace llvm {

static mc::RegisterMCTargetOptionsFlags MOF;

namespace dsymutil {

static Error copySwiftInterfaces(
    const std::map<std::string, std::string> &ParseableSwiftInterfaces,
    StringRef Architecture, const LinkOptions &Options) {
  std::error_code EC;
  SmallString<128> InputPath;
  SmallString<128> Path;
  sys::path::append(Path, *Options.ResourceDir, "Swift", Architecture);
  if ((EC = sys::fs::create_directories(Path.str(), true,
                                        sys::fs::perms::all_all)))
    return make_error<StringError>(
        "cannot create directory: " + toString(errorCodeToError(EC)), EC);
  unsigned BaseLength = Path.size();

  for (auto &I : ParseableSwiftInterfaces) {
    StringRef ModuleName = I.first;
    StringRef InterfaceFile = I.second;
    if (!Options.PrependPath.empty()) {
      InputPath.clear();
      sys::path::append(InputPath, Options.PrependPath, InterfaceFile);
      InterfaceFile = InputPath;
    }
    sys::path::append(Path, ModuleName);
    Path.append(".swiftinterface");
    if (Options.Verbose)
      outs() << "copy parseable Swift interface " << InterfaceFile << " -> "
             << Path.str() << '\n';

    // copy_file attempts an APFS clone first, so this should be cheap.
    if ((EC = sys::fs::copy_file(InterfaceFile, Path.str())))
      warn(Twine("cannot copy parseable Swift interface ") + InterfaceFile +
           ": " + toString(errorCodeToError(EC)));
    Path.resize(BaseLength);
  }
  return Error::success();
}

/// Report a warning to the user, optionally including information about a
/// specific \p DIE related to the warning.
void DwarfLinkerForBinary::reportWarning(const Twine &Warning,
                                         StringRef Context,
                                         const DWARFDie *DIE) const {

  warn(Warning, Context);

  if (!Options.Verbose || !DIE)
    return;

  DIDumpOptions DumpOpts;
  DumpOpts.ChildRecurseDepth = 0;
  DumpOpts.Verbose = Options.Verbose;

  WithColor::note() << "    in DIE:\n";
  DIE->dump(errs(), 6 /* Indent */, DumpOpts);
}

bool DwarfLinkerForBinary::createStreamer(const Triple &TheTriple,
                                          raw_fd_ostream &OutFile) {
  if (Options.NoOutput)
    return true;

  Streamer = std::make_unique<DwarfStreamer>(
      Options.FileType, OutFile, Options.Translator, Options.Minimize,
      [&](const Twine &Error, StringRef Context, const DWARFDie *) {
        error(Error, Context);
      },
      [&](const Twine &Warning, StringRef Context, const DWARFDie *) {
        warn(Warning, Context);
      });
  return Streamer->init(TheTriple);
}

ErrorOr<const object::ObjectFile &>
DwarfLinkerForBinary::loadObject(const DebugMapObject &Obj,
                                 const Triple &Triple) {
  auto ObjectEntry =
      BinHolder.getObjectEntry(Obj.getObjectFilename(), Obj.getTimestamp());
  if (!ObjectEntry) {
    auto Err = ObjectEntry.takeError();
    reportWarning(Twine(Obj.getObjectFilename()) + ": " +
                      toString(std::move(Err)),
                  Obj.getObjectFilename());
    return errorToErrorCode(std::move(Err));
  }

  auto Object = ObjectEntry->getObject(Triple);
  if (!Object) {
    auto Err = Object.takeError();
    reportWarning(Twine(Obj.getObjectFilename()) + ": " +
                      toString(std::move(Err)),
                  Obj.getObjectFilename());
    return errorToErrorCode(std::move(Err));
  }

  return *Object;
}

static Error remarksErrorHandler(const DebugMapObject &DMO,
                                 DwarfLinkerForBinary &Linker,
                                 std::unique_ptr<FileError> FE) {
  bool IsArchive = DMO.getObjectFilename().endswith(")");
  // Don't report errors for missing remark files from static
  // archives.
  if (!IsArchive)
    return Error(std::move(FE));

  std::string Message = FE->message();
  Error E = FE->takeError();
  Error NewE = handleErrors(std::move(E), [&](std::unique_ptr<ECError> EC) {
    if (EC->convertToErrorCode() != std::errc::no_such_file_or_directory)
      return Error(std::move(EC));

    Linker.reportWarning(Message, DMO.getObjectFilename());
    return Error(Error::success());
  });

  if (!NewE)
    return Error::success();

  return createFileError(FE->getFileName(), std::move(NewE));
}

static Error emitRemarks(const LinkOptions &Options, StringRef BinaryPath,
                         StringRef ArchName, const remarks::RemarkLinker &RL) {
  // Make sure we don't create the directories and the file if there is nothing
  // to serialize.
  if (RL.empty())
    return Error::success();

  SmallString<128> InputPath;
  SmallString<128> Path;
  // Create the "Remarks" directory in the "Resources" directory.
  sys::path::append(Path, *Options.ResourceDir, "Remarks");
  if (std::error_code EC = sys::fs::create_directories(Path.str(), true,
                                                       sys::fs::perms::all_all))
    return errorCodeToError(EC);

  // Append the file name.
  // For fat binaries, also append a dash and the architecture name.
  sys::path::append(Path, sys::path::filename(BinaryPath));
  if (Options.NumDebugMaps > 1) {
    // More than one debug map means we have a fat binary.
    Path += '-';
    Path += ArchName;
  }

  std::error_code EC;
  raw_fd_ostream OS(Options.NoOutput ? "-" : Path.str(), EC, sys::fs::OF_None);
  if (EC)
    return errorCodeToError(EC);

  if (Error E = RL.serialize(OS, Options.RemarksFormat))
    return E;

  return Error::success();
}

ErrorOr<DwarfFile &>
DwarfLinkerForBinary::loadObject(const DebugMapObject &Obj,
                                 const DebugMap &DebugMap,
                                 remarks::RemarkLinker &RL) {
  auto ErrorOrObj = loadObject(Obj, DebugMap.getTriple());

  if (ErrorOrObj) {
    ContextForLinking.push_back(
        std::unique_ptr<DWARFContext>(DWARFContext::create(*ErrorOrObj)));
    AddressMapForLinking.push_back(
        std::make_unique<AddressManager>(*this, *ErrorOrObj, Obj));

    ObjectsForLinking.push_back(std::make_unique<DwarfFile>(
        Obj.getObjectFilename(), ContextForLinking.back().get(),
        AddressMapForLinking.back().get(),
        Obj.empty() ? Obj.getWarnings() : EmptyWarnings));

    Error E = RL.link(*ErrorOrObj);
    if (Error NewE = handleErrors(
            std::move(E), [&](std::unique_ptr<FileError> EC) -> Error {
              return remarksErrorHandler(Obj, *this, std::move(EC));
            }))
      return errorToErrorCode(std::move(NewE));

    return *ObjectsForLinking.back();
  }

  return ErrorOrObj.getError();
}

bool DwarfLinkerForBinary::link(const DebugMap &Map) {
  if (!createStreamer(Map.getTriple(), OutFile))
    return false;

  ObjectsForLinking.clear();
  ContextForLinking.clear();
  AddressMapForLinking.clear();

  DebugMap DebugMap(Map.getTriple(), Map.getBinaryPath());

  DWARFLinker GeneralLinker(Streamer.get(), DwarfLinkerClient::Dsymutil);

  remarks::RemarkLinker RL;
  if (!Options.RemarksPrependPath.empty())
    RL.setExternalFilePrependPath(Options.RemarksPrependPath);
  GeneralLinker.setObjectPrefixMap(&Options.ObjectPrefixMap);

  std::function<StringRef(StringRef)> TranslationLambda = [&](StringRef Input) {
    assert(Options.Translator);
    return Options.Translator(Input);
  };

  GeneralLinker.setVerbosity(Options.Verbose);
  GeneralLinker.setStatistics(Options.Statistics);
  GeneralLinker.setNoOutput(Options.NoOutput);
  GeneralLinker.setNoODR(Options.NoODR);
  GeneralLinker.setUpdate(Options.Update);
  GeneralLinker.setNumThreads(Options.Threads);
  GeneralLinker.setAccelTableKind(Options.TheAccelTableKind);
  GeneralLinker.setPrependPath(Options.PrependPath);
  if (Options.Translator)
    GeneralLinker.setStringsTranslator(TranslationLambda);
  GeneralLinker.setWarningHandler(
      [&](const Twine &Warning, StringRef Context, const DWARFDie *DIE) {
        reportWarning(Warning, Context, DIE);
      });
  GeneralLinker.setErrorHandler(
      [&](const Twine &Error, StringRef Context, const DWARFDie *) {
        error(Error, Context);
      });
  GeneralLinker.setObjFileLoader(
      [&DebugMap, &RL, this](StringRef ContainerName,
                             StringRef Path) -> ErrorOr<DwarfFile &> {
        auto &Obj = DebugMap.addDebugMapObject(
            Path, sys::TimePoint<std::chrono::seconds>(), MachO::N_OSO);

        if (auto ErrorOrObj = loadObject(Obj, DebugMap, RL)) {
          return *ErrorOrObj;
        } else {
          // Try and emit more helpful warnings by applying some heuristics.
          StringRef ObjFile = ContainerName;
          bool IsClangModule = sys::path::extension(Path).equals(".pcm");
          bool IsArchive = ObjFile.endswith(")");

          if (IsClangModule) {
            StringRef ModuleCacheDir = sys::path::parent_path(Path);
            if (sys::fs::exists(ModuleCacheDir)) {
              // If the module's parent directory exists, we assume that the
              // module cache has expired and was pruned by clang.  A more
              // adventurous dsymutil would invoke clang to rebuild the module
              // now.
              if (!ModuleCacheHintDisplayed) {
                WithColor::note()
                    << "The clang module cache may have expired since "
                       "this object file was built. Rebuilding the "
                       "object file will rebuild the module cache.\n";
                ModuleCacheHintDisplayed = true;
              }
            } else if (IsArchive) {
              // If the module cache directory doesn't exist at all and the
              // object file is inside a static library, we assume that the
              // static library was built on a different machine. We don't want
              // to discourage module debugging for convenience libraries within
              // a project though.
              if (!ArchiveHintDisplayed) {
                WithColor::note()
                    << "Linking a static library that was built with "
                       "-gmodules, but the module cache was not found.  "
                       "Redistributable static libraries should never be "
                       "built with module debugging enabled.  The debug "
                       "experience will be degraded due to incomplete "
                       "debug information.\n";
                ArchiveHintDisplayed = true;
              }
            }
          }

          return ErrorOrObj.getError();
        }

        llvm_unreachable("Unhandled DebugMap object");
      });
  GeneralLinker.setSwiftInterfacesMap(&ParseableSwiftInterfaces);

  for (const auto &Obj : Map.objects()) {
    // N_AST objects (swiftmodule files) should get dumped directly into the
    // appropriate DWARF section.
    if (Obj->getType() == MachO::N_AST) {
      if (Options.Verbose)
        outs() << "DEBUG MAP OBJECT: " << Obj->getObjectFilename() << "\n";

      StringRef File = Obj->getObjectFilename();
      auto ErrorOrMem = MemoryBuffer::getFile(File);
      if (!ErrorOrMem) {
        warn("Could not open '" + File + "'\n");
        continue;
      }
      sys::fs::file_status Stat;
      if (auto Err = sys::fs::status(File, Stat)) {
        warn(Err.message());
        continue;
      }
      if (!Options.NoTimestamp) {
        // The modification can have sub-second precision so we need to cast
        // away the extra precision that's not present in the debug map.
        auto ModificationTime =
            std::chrono::time_point_cast<std::chrono::seconds>(
                Stat.getLastModificationTime());
        if (ModificationTime != Obj->getTimestamp()) {
          // Not using the helper here as we can easily stream TimePoint<>.
          WithColor::warning() << "Timestamp mismatch for " << File << ": "
                               << Stat.getLastModificationTime() << " and "
                               << sys::TimePoint<>(Obj->getTimestamp()) << "\n";
          continue;
        }
      }

      // Copy the module into the .swift_ast section.
      if (!Options.NoOutput)
        Streamer->emitSwiftAST((*ErrorOrMem)->getBuffer());

      continue;
    }

    if (auto ErrorOrObj = loadObject(*Obj, Map, RL))
      GeneralLinker.addObjectFile(*ErrorOrObj);
    else {
      ObjectsForLinking.push_back(std::make_unique<DwarfFile>(
          Obj->getObjectFilename(), nullptr, nullptr,
          Obj->empty() ? Obj->getWarnings() : EmptyWarnings));
      GeneralLinker.addObjectFile(*ObjectsForLinking.back());
    }
  }

  // link debug info for loaded object files.
  GeneralLinker.link();

  StringRef ArchName = Map.getTriple().getArchName();
  if (Error E = emitRemarks(Options, Map.getBinaryPath(), ArchName, RL))
    return error(toString(std::move(E)));

  if (Options.NoOutput)
    return true;

  if (Options.ResourceDir && !ParseableSwiftInterfaces.empty()) {
    StringRef ArchName = Triple::getArchTypeName(Map.getTriple().getArch());
    if (auto E =
            copySwiftInterfaces(ParseableSwiftInterfaces, ArchName, Options))
      return error(toString(std::move(E)));
  }

  if (Map.getTriple().isOSDarwin() && !Map.getBinaryPath().empty() &&
      Options.FileType == OutputFileType::Object)
    return MachOUtils::generateDsymCompanion(
        Options.VFS, Map, Options.Translator,
        *Streamer->getAsmPrinter().OutStreamer, OutFile);

  Streamer->finish();
  return true;
}

static bool isMachOPairedReloc(uint64_t RelocType, uint64_t Arch) {
  switch (Arch) {
  case Triple::x86:
    return RelocType == MachO::GENERIC_RELOC_SECTDIFF ||
           RelocType == MachO::GENERIC_RELOC_LOCAL_SECTDIFF;
  case Triple::x86_64:
    return RelocType == MachO::X86_64_RELOC_SUBTRACTOR;
  case Triple::arm:
  case Triple::thumb:
    return RelocType == MachO::ARM_RELOC_SECTDIFF ||
           RelocType == MachO::ARM_RELOC_LOCAL_SECTDIFF ||
           RelocType == MachO::ARM_RELOC_HALF ||
           RelocType == MachO::ARM_RELOC_HALF_SECTDIFF;
  case Triple::aarch64:
    return RelocType == MachO::ARM64_RELOC_SUBTRACTOR;
  default:
    return false;
  }
}

/// Iterate over the relocations of the given \p Section and
/// store the ones that correspond to debug map entries into the
/// ValidRelocs array.
void DwarfLinkerForBinary::AddressManager::findValidRelocsMachO(
    const object::SectionRef &Section, const object::MachOObjectFile &Obj,
    const DebugMapObject &DMO) {
  Expected<StringRef> ContentsOrErr = Section.getContents();
  if (!ContentsOrErr) {
    consumeError(ContentsOrErr.takeError());
    Linker.reportWarning("error reading section", DMO.getObjectFilename());
    return;
  }
  DataExtractor Data(*ContentsOrErr, Obj.isLittleEndian(), 0);
  bool SkipNext = false;

  for (const object::RelocationRef &Reloc : Section.relocations()) {
    if (SkipNext) {
      SkipNext = false;
      continue;
    }

    object::DataRefImpl RelocDataRef = Reloc.getRawDataRefImpl();
    MachO::any_relocation_info MachOReloc = Obj.getRelocation(RelocDataRef);

    if (isMachOPairedReloc(Obj.getAnyRelocationType(MachOReloc),
                           Obj.getArch())) {
      SkipNext = true;
      Linker.reportWarning("unsupported relocation in debug_info section.",
                           DMO.getObjectFilename());
      continue;
    }

    unsigned RelocSize = 1 << Obj.getAnyRelocationLength(MachOReloc);
    uint64_t Offset64 = Reloc.getOffset();
    if ((RelocSize != 4 && RelocSize != 8)) {
      Linker.reportWarning("unsupported relocation in debug_info section.",
                           DMO.getObjectFilename());
      continue;
    }
    uint64_t OffsetCopy = Offset64;
    // Mach-o uses REL relocations, the addend is at the relocation offset.
    uint64_t Addend = Data.getUnsigned(&OffsetCopy, RelocSize);
    uint64_t SymAddress;
    int64_t SymOffset;

    if (Obj.isRelocationScattered(MachOReloc)) {
      // The address of the base symbol for scattered relocations is
      // stored in the reloc itself. The actual addend will store the
      // base address plus the offset.
      SymAddress = Obj.getScatteredRelocationValue(MachOReloc);
      SymOffset = int64_t(Addend) - SymAddress;
    } else {
      SymAddress = Addend;
      SymOffset = 0;
    }

    auto Sym = Reloc.getSymbol();
    if (Sym != Obj.symbol_end()) {
      Expected<StringRef> SymbolName = Sym->getName();
      if (!SymbolName) {
        consumeError(SymbolName.takeError());
        Linker.reportWarning("error getting relocation symbol name.",
                             DMO.getObjectFilename());
        continue;
      }
      if (const auto *Mapping = DMO.lookupSymbol(*SymbolName))
        ValidRelocs.emplace_back(Offset64, RelocSize, Addend, Mapping);
    } else if (const auto *Mapping = DMO.lookupObjectAddress(SymAddress)) {
      // Do not store the addend. The addend was the address of the symbol in
      // the object file, the address in the binary that is stored in the debug
      // map doesn't need to be offset.
      ValidRelocs.emplace_back(Offset64, RelocSize, SymOffset, Mapping);
    }
  }
}

/// Dispatch the valid relocation finding logic to the
/// appropriate handler depending on the object file format.
bool DwarfLinkerForBinary::AddressManager::findValidRelocs(
    const object::SectionRef &Section, const object::ObjectFile &Obj,
    const DebugMapObject &DMO) {
  // Dispatch to the right handler depending on the file type.
  if (auto *MachOObj = dyn_cast<object::MachOObjectFile>(&Obj))
    findValidRelocsMachO(Section, *MachOObj, DMO);
  else
    Linker.reportWarning(Twine("unsupported object file type: ") +
                             Obj.getFileName(),
                         DMO.getObjectFilename());
  if (ValidRelocs.empty())
    return false;

  // Sort the relocations by offset. We will walk the DIEs linearly in
  // the file, this allows us to just keep an index in the relocation
  // array that we advance during our walk, rather than resorting to
  // some associative container. See DwarfLinkerForBinary::NextValidReloc.
  llvm::sort(ValidRelocs);
  return true;
}

/// Look for relocations in the debug_info section that match
/// entries in the debug map. These relocations will drive the Dwarf
/// link by indicating which DIEs refer to symbols present in the
/// linked binary.
/// \returns whether there are any valid relocations in the debug info.
bool DwarfLinkerForBinary::AddressManager::findValidRelocsInDebugInfo(
    const object::ObjectFile &Obj, const DebugMapObject &DMO) {
  // Find the debug_info section.
  for (const object::SectionRef &Section : Obj.sections()) {
    StringRef SectionName;
    if (Expected<StringRef> NameOrErr = Section.getName())
      SectionName = *NameOrErr;
    else
      consumeError(NameOrErr.takeError());

    SectionName = SectionName.substr(SectionName.find_first_not_of("._"));
    if (SectionName != "debug_info")
      continue;
    return findValidRelocs(Section, Obj, DMO);
  }
  return false;
}

/// Checks that there is a relocation against an actual debug
/// map entry between \p StartOffset and \p NextOffset.
///
/// This function must be called with offsets in strictly ascending
/// order because it never looks back at relocations it already 'went past'.
/// \returns true and sets Info.InDebugMap if it is the case.
bool DwarfLinkerForBinary::AddressManager::hasValidRelocationAt(
    uint64_t StartOffset, uint64_t EndOffset, CompileUnit::DIEInfo &Info) {
  assert(NextValidReloc == 0 ||
         StartOffset > ValidRelocs[NextValidReloc - 1].Offset);
  if (NextValidReloc >= ValidRelocs.size())
    return false;

  uint64_t RelocOffset = ValidRelocs[NextValidReloc].Offset;

  // We might need to skip some relocs that we didn't consider. For
  // example the high_pc of a discarded DIE might contain a reloc that
  // is in the list because it actually corresponds to the start of a
  // function that is in the debug map.
  while (RelocOffset < StartOffset && NextValidReloc < ValidRelocs.size() - 1)
    RelocOffset = ValidRelocs[++NextValidReloc].Offset;

  if (RelocOffset < StartOffset || RelocOffset >= EndOffset)
    return false;

  const auto &ValidReloc = ValidRelocs[NextValidReloc++];
  const auto &Mapping = ValidReloc.Mapping->getValue();
  const uint64_t BinaryAddress = Mapping.BinaryAddress;
  const uint64_t ObjectAddress = Mapping.ObjectAddress
                                     ? uint64_t(*Mapping.ObjectAddress)
                                     : std::numeric_limits<uint64_t>::max();
  if (Linker.Options.Verbose)
    outs() << "Found valid debug map entry: " << ValidReloc.Mapping->getKey()
           << "\t"
           << format("0x%016" PRIx64 " => 0x%016" PRIx64 "\n", ObjectAddress,
                     BinaryAddress);

  Info.AddrAdjust = BinaryAddress + ValidReloc.Addend;
  if (Mapping.ObjectAddress)
    Info.AddrAdjust -= ObjectAddress;
  Info.InDebugMap = true;
  return true;
}

/// Apply the valid relocations found by findValidRelocs() to
/// the buffer \p Data, taking into account that Data is at \p BaseOffset
/// in the debug_info section.
///
/// Like for findValidRelocs(), this function must be called with
/// monotonic \p BaseOffset values.
///
/// \returns whether any reloc has been applied.
bool DwarfLinkerForBinary::AddressManager::applyValidRelocs(
    MutableArrayRef<char> Data, uint64_t BaseOffset, bool IsLittleEndian) {
  assert(areRelocationsResolved());
  assert((NextValidReloc == 0 ||
          BaseOffset > ValidRelocs[NextValidReloc - 1].Offset) &&
         "BaseOffset should only be increasing.");
  if (NextValidReloc >= ValidRelocs.size())
    return false;

  // Skip relocs that haven't been applied.
  while (NextValidReloc < ValidRelocs.size() &&
         ValidRelocs[NextValidReloc].Offset < BaseOffset)
    ++NextValidReloc;

  bool Applied = false;
  uint64_t EndOffset = BaseOffset + Data.size();
  while (NextValidReloc < ValidRelocs.size() &&
         ValidRelocs[NextValidReloc].Offset >= BaseOffset &&
         ValidRelocs[NextValidReloc].Offset < EndOffset) {
    const auto &ValidReloc = ValidRelocs[NextValidReloc++];
    assert(ValidReloc.Offset - BaseOffset < Data.size());
    assert(ValidReloc.Offset - BaseOffset + ValidReloc.Size <= Data.size());
    char Buf[8];
    uint64_t Value = ValidReloc.Mapping->getValue().BinaryAddress;
    Value += ValidReloc.Addend;
    for (unsigned I = 0; I != ValidReloc.Size; ++I) {
      unsigned Index = IsLittleEndian ? I : (ValidReloc.Size - I - 1);
      Buf[I] = uint8_t(Value >> (Index * 8));
    }
    assert(ValidReloc.Size <= sizeof(Buf));
    memcpy(&Data[ValidReloc.Offset - BaseOffset], Buf, ValidReloc.Size);
    Applied = true;
  }

  return Applied;
}

bool linkDwarf(raw_fd_ostream &OutFile, BinaryHolder &BinHolder,
               const DebugMap &DM, LinkOptions Options) {
  DwarfLinkerForBinary Linker(OutFile, BinHolder, std::move(Options));
  return Linker.link(DM);
}

} // namespace dsymutil
} // namespace llvm