text: //===- Driver.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
  //
  //===----------------------------------------------------------------------===//
  //
  // The driver drives the entire linking process. It is responsible for
  // parsing command line options and doing whatever it is instructed to do.
  //
  // One notable thing in the LLD's driver when compared to other linkers is
  // that the LLD's driver is agnostic on the host operating system.
  // Other linkers usually have implicit default values (such as a dynamic
  // linker path or library paths) for each host OS.
  //
  // I don't think implicit default values are useful because they are
  // usually explicitly specified by the compiler driver. They can even
  // be harmful when you are doing cross-linking. Therefore, in LLD, we
  // simply trust the compiler driver to pass all required options and
  // don't try to make effort on our side.
  //
  //===----------------------------------------------------------------------===//
  
  #include "Driver.h"
  #include "Config.h"
  #include "ICF.h"
  #include "InputFiles.h"
  #include "InputSection.h"
  #include "LinkerScript.h"
  #include "MarkLive.h"
  #include "OutputSections.h"
  #include "ScriptParser.h"
  #include "SymbolTable.h"
  #include "Symbols.h"
  #include "SyntheticSections.h"
  #include "Target.h"
  #include "Writer.h"
  #include "lld/Common/Args.h"
  #include "lld/Common/Driver.h"
  #include "lld/Common/ErrorHandler.h"
  #include "lld/Common/Filesystem.h"
  #include "lld/Common/Memory.h"
  #include "lld/Common/Strings.h"
  #include "lld/Common/TargetOptionsCommandFlags.h"
  #include "lld/Common/Threads.h"
  #include "lld/Common/Version.h"
  #include "llvm/ADT/SetVector.h"
  #include "llvm/ADT/StringExtras.h"
  #include "llvm/ADT/StringSwitch.h"
  #include "llvm/LTO/LTO.h"
  #include "llvm/Support/CommandLine.h"
  #include "llvm/Support/Compression.h"
  #include "llvm/Support/GlobPattern.h"
  #include "llvm/Support/LEB128.h"
  #include "llvm/Support/Path.h"
  #include "llvm/Support/TarWriter.h"
  #include "llvm/Support/TargetSelect.h"
  #include "llvm/Support/TimeProfiler.h"
  #include "llvm/Support/raw_ostream.h"
  #include <cstdlib>
  #include <utility>
  
  using namespace llvm;
  using namespace llvm::ELF;
  using namespace llvm::object;
  using namespace llvm::sys;
  using namespace llvm::support;
  
  namespace lld {
  namespace elf {
  
  Configuration *config;
  LinkerDriver *driver;
  
  static void setConfigs(opt::InputArgList &args);
  static void readConfigs(opt::InputArgList &args);
  
  bool link(ArrayRef<const char *> args, bool canExitEarly, raw_ostream &stdoutOS,
            raw_ostream &stderrOS) {
    lld::stdoutOS = &stdoutOS;
    lld::stderrOS = &stderrOS;
  
    errorHandler().logName = args::getFilenameWithoutExe(args[0]);
    errorHandler().errorLimitExceededMsg =
        "too many errors emitted, stopping now (use "
        "-error-limit=0 to see all errors)";
    errorHandler().exitEarly = canExitEarly;
    stderrOS.enable_colors(stderrOS.has_colors());
  
    inputSections.clear();
    outputSections.clear();
    binaryFiles.clear();
    bitcodeFiles.clear();
    objectFiles.clear();
    sharedFiles.clear();
    backwardReferences.clear();
  
    config = make<Configuration>();
    driver = make<LinkerDriver>();
    script = make<LinkerScript>();
    symtab = make<SymbolTable>();
  
    tar = nullptr;
    memset(&in, 0, sizeof(in));
  
    partitions = {Partition()};
  
    SharedFile::vernauxNum = 0;
  
    config->progName = args[0];
  
    driver->main(args);
  
    // Exit immediately if we don't need to return to the caller.
    // This saves time because the overhead of calling destructors
    // for all globally-allocated objects is not negligible.
    if (canExitEarly)
      exitLld(errorCount() ? 1 : 0);
  
    freeArena();
    return !errorCount();
  }
  
  // Parses a linker -m option.
  static std::tuple<ELFKind, uint16_t, uint8_t> parseEmulation(StringRef emul) {
    uint8_t osabi = 0;
    StringRef s = emul;
    if (s.endswith("_fbsd")) {
      s = s.drop_back(5);
      osabi = ELFOSABI_FREEBSD;
    }
  
    std::pair<ELFKind, uint16_t> ret =
        StringSwitch<std::pair<ELFKind, uint16_t>>(s)
            .Cases("aarch64elf", "aarch64linux", "aarch64_elf64_le_vec",
                   {ELF64LEKind, EM_AARCH64})
            .Cases("armelf", "armelf_linux_eabi", {ELF32LEKind, EM_ARM})
            .Case("elf32_x86_64", {ELF32LEKind, EM_X86_64})
            .Cases("elf32btsmip", "elf32btsmipn32", {ELF32BEKind, EM_MIPS})
            .Cases("elf32ltsmip", "elf32ltsmipn32", {ELF32LEKind, EM_MIPS})
            .Case("elf32lriscv", {ELF32LEKind, EM_RISCV})
            .Cases("elf32ppc", "elf32ppclinux", {ELF32BEKind, EM_PPC})
            .Case("elf64btsmip", {ELF64BEKind, EM_MIPS})
            .Case("elf64ltsmip", {ELF64LEKind, EM_MIPS})
            .Case("elf64lriscv", {ELF64LEKind, EM_RISCV})
            .Case("elf64ppc", {ELF64BEKind, EM_PPC64})
            .Case("elf64lppc", {ELF64LEKind, EM_PPC64})
            .Cases("elf_amd64", "elf_x86_64", {ELF64LEKind, EM_X86_64})
            .Case("elf_i386", {ELF32LEKind, EM_386})
            .Case("elf_iamcu", {ELF32LEKind, EM_IAMCU})
            .Default({ELFNoneKind, EM_NONE});
  
    if (ret.first == ELFNoneKind)
      error("unknown emulation: " + emul);
    return std::make_tuple(ret.first, ret.second, osabi);
  }
  
  // Returns slices of MB by parsing MB as an archive file.
  // Each slice consists of a member file in the archive.
  std::vector<std::pair<MemoryBufferRef, uint64_t>> static getArchiveMembers(
      MemoryBufferRef mb) {
    std::unique_ptr<Archive> file =
        CHECK(Archive::create(mb),
              mb.getBufferIdentifier() + ": failed to parse archive");
  
    std::vector<std::pair<MemoryBufferRef, uint64_t>> v;
    Error err = Error::success();
    bool addToTar = file->isThin() && tar;
    for (const Archive::Child &c : file->children(err)) {
      MemoryBufferRef mbref =
          CHECK(c.getMemoryBufferRef(),
                mb.getBufferIdentifier() +
                    ": could not get the buffer for a child of the archive");
      if (addToTar)
        tar->append(relativeToRoot(check(c.getFullName())), mbref.getBuffer());
      v.push_back(std::make_pair(mbref, c.getChildOffset()));
    }
    if (err)
      fatal(mb.getBufferIdentifier() + ": Archive::children failed: " +
            toString(std::move(err)));
  
    // Take ownership of memory buffers created for members of thin archives.
    for (std::unique_ptr<MemoryBuffer> &mb : file->takeThinBuffers())
      make<std::unique_ptr<MemoryBuffer>>(std::move(mb));
  
    return v;
  }
  
  // Opens a file and create a file object. Path has to be resolved already.
  void LinkerDriver::addFile(StringRef path, bool withLOption) {
    using namespace sys::fs;
  
    Optional<MemoryBufferRef> buffer = readFile(path);
    if (!buffer.hasValue())
      return;
    MemoryBufferRef mbref = *buffer;
  
    if (config->formatBinary) {
      files.push_back(make<BinaryFile>(mbref));
      return;
    }
  
    switch (identify_magic(mbref.getBuffer())) {
    case file_magic::unknown:
      readLinkerScript(mbref);
      return;
    case file_magic::archive: {
      // Handle -whole-archive.
      if (inWholeArchive) {
        for (const auto &p : getArchiveMembers(mbref))
          files.push_back(createObjectFile(p.first, path, p.second));
        return;
      }
  
      std::unique_ptr<Archive> file =
          CHECK(Archive::create(mbref), path + ": failed to parse archive");
  
      // If an archive file has no symbol table, it is likely that a user
      // is attempting LTO and using a default ar command that doesn't
      // understand the LLVM bitcode file. It is a pretty common error, so
      // we'll handle it as if it had a symbol table.
      if (!file->isEmpty() && !file->hasSymbolTable()) {
        // Check if all members are bitcode files. If not, ignore, which is the
        // default action without the LTO hack described above.
        for (const std::pair<MemoryBufferRef, uint64_t> &p :
             getArchiveMembers(mbref))
          if (identify_magic(p.first.getBuffer()) != file_magic::bitcode) {
            error(path + ": archive has no index; run ranlib to add one");
            return;
          }
  
        for (const std::pair<MemoryBufferRef, uint64_t> &p :
             getArchiveMembers(mbref))
          files.push_back(make<LazyObjFile>(p.first, path, p.second));
        return;
      }
  
      // Handle the regular case.
      files.push_back(make<ArchiveFile>(std::move(file)));
      return;
    }
    case file_magic::elf_shared_object:
      if (config->isStatic || config->relocatable) {
        error("attempted static link of dynamic object " + path);
        return;
      }
  
      // DSOs usually have DT_SONAME tags in their ELF headers, and the
      // sonames are used to identify DSOs. But if they are missing,
      // they are identified by filenames. We don't know whether the new
      // file has a DT_SONAME or not because we haven't parsed it yet.
      // Here, we set the default soname for the file because we might
      // need it later.
      //
      // If a file was specified by -lfoo, the directory part is not
      // significant, as a user did not specify it. This behavior is
      // compatible with GNU.
      files.push_back(
          make<SharedFile>(mbref, withLOption ? path::filename(path) : path));
      return;
    case file_magic::bitcode:
    case file_magic::elf_relocatable:
      if (inLib)
        files.push_back(make<LazyObjFile>(mbref, "", 0));
      else
        files.push_back(createObjectFile(mbref));
      break;
    default:
      error(path + ": unknown file type");
    }
  }
  
  // Add a given library by searching it from input search paths.
  void LinkerDriver::addLibrary(StringRef name) {
    if (Optional<std::string> path = searchLibrary(name))
      addFile(*path, /*withLOption=*/true);
    else
      error("unable to find library -l" + name);
  }
  
  // This function is called on startup. We need this for LTO since
  // LTO calls LLVM functions to compile bitcode files to native code.
  // Technically this can be delayed until we read bitcode files, but
  // we don't bother to do lazily because the initialization is fast.
  static void initLLVM() {
    InitializeAllTargets();
    InitializeAllTargetMCs();
    InitializeAllAsmPrinters();
    InitializeAllAsmParsers();
  }
  
  // Some command line options or some combinations of them are not allowed.
  // This function checks for such errors.
  static void checkOptions() {
    // The MIPS ABI as of 2016 does not support the GNU-style symbol lookup
    // table which is a relatively new feature.
    if (config->emachine == EM_MIPS && config->gnuHash)
      error("the .gnu.hash section is not compatible with the MIPS target");
  
    if (config->fixCortexA53Errata843419 && config->emachine != EM_AARCH64)
      error("--fix-cortex-a53-843419 is only supported on AArch64 targets");
  
    if (config->fixCortexA8 && config->emachine != EM_ARM)
      error("--fix-cortex-a8 is only supported on ARM targets");
  
    if (config->tocOptimize && config->emachine != EM_PPC64)
      error("--toc-optimize is only supported on the PowerPC64 target");
  
    if (config->pie && config->shared)
      error("-shared and -pie may not be used together");
  
    if (!config->shared && !config->filterList.empty())
      error("-F may not be used without -shared");
  
    if (!config->shared && !config->auxiliaryList.empty())
      error("-f may not be used without -shared");
  
    if (!config->relocatable && !config->defineCommon)
      error("-no-define-common not supported in non relocatable output");
  
    if (config->strip == StripPolicy::All && config->emitRelocs)
      error("--strip-all and --emit-relocs may not be used together");
  
    if (config->zText && config->zIfuncNoplt)
      error("-z text and -z ifunc-noplt may not be used together");
  
    if (config->relocatable) {
      if (config->shared)
        error("-r and -shared may not be used together");
      if (config->gcSections)
        error("-r and --gc-sections may not be used together");
      if (config->gdbIndex)
        error("-r and --gdb-index may not be used together");
      if (config->icf != ICFLevel::None)
        error("-r and --icf may not be used together");
      if (config->pie)
        error("-r and -pie may not be used together");
      if (config->exportDynamic)
        error("-r and --export-dynamic may not be used together");
    }
  
    if (config->executeOnly) {
      if (config->emachine != EM_AARCH64)
        error("-execute-only is only supported on AArch64 targets");
  
      if (config->singleRoRx && !script->hasSectionsCommand)
        error("-execute-only and -no-rosegment cannot be used together");
    }
  
    if (config->zRetpolineplt && config->zForceIbt)
      error("-z force-ibt may not be used with -z retpolineplt");
  
    if (config->emachine != EM_AARCH64) {
      if (config->zPacPlt)
        error("-z pac-plt only supported on AArch64");
      if (config->zForceBti)
        error("-z force-bti only supported on AArch64");
    }
  }
  
  static const char *getReproduceOption(opt::InputArgList &args) {
    if (auto *arg = args.getLastArg(OPT_reproduce))
      return arg->getValue();
    return getenv("LLD_REPRODUCE");
  }
  
  static bool hasZOption(opt::InputArgList &args, StringRef key) {
    for (auto *arg : args.filtered(OPT_z))
      if (key == arg->getValue())
        return true;
    return false;
  }
  
  static bool getZFlag(opt::InputArgList &args, StringRef k1, StringRef k2,
                       bool Default) {
    for (auto *arg : args.filtered_reverse(OPT_z)) {
      if (k1 == arg->getValue())
        return true;
      if (k2 == arg->getValue())
        return false;
    }
    return Default;
  }
  
  static SeparateSegmentKind getZSeparate(opt::InputArgList &args) {
    for (auto *arg : args.filtered_reverse(OPT_z)) {
      StringRef v = arg->getValue();
      if (v == "noseparate-code")
        return SeparateSegmentKind::None;
      if (v == "separate-code")
        return SeparateSegmentKind::Code;
      if (v == "separate-loadable-segments")
        return SeparateSegmentKind::Loadable;
    }
    return SeparateSegmentKind::None;
  }
  
  static GnuStackKind getZGnuStack(opt::InputArgList &args) {
    for (auto *arg : args.filtered_reverse(OPT_z)) {
      if (StringRef("execstack") == arg->getValue())
        return GnuStackKind::Exec;
      if (StringRef("noexecstack") == arg->getValue())
        return GnuStackKind::NoExec;
      if (StringRef("nognustack") == arg->getValue())
        return GnuStackKind::None;
    }
  
    return GnuStackKind::NoExec;
  }
  
  static bool isKnownZFlag(StringRef s) {
    return s == "combreloc" || s == "copyreloc" || s == "defs" ||
           s == "execstack" || s == "force-bti" || s == "force-ibt" ||
           s == "global" || s == "hazardplt" || s == "ifunc-noplt" ||
           s == "initfirst" || s == "interpose" ||
           s == "keep-text-section-prefix" || s == "lazy" || s == "muldefs" ||
           s == "separate-code" || s == "separate-loadable-segments" ||
           s == "nocombreloc" || s == "nocopyreloc" || s == "nodefaultlib" ||
           s == "nodelete" || s == "nodlopen" || s == "noexecstack" ||
           s == "nognustack" || s == "nokeep-text-section-prefix" ||
           s == "norelro" || s == "noseparate-code" || s == "notext" ||
           s == "now" || s == "origin" || s == "pac-plt" || s == "relro" ||
           s == "retpolineplt" || s == "rodynamic" || s == "shstk" ||
           s == "text" || s == "undefs" || s == "wxneeded" ||
           s.startswith("common-page-size=") || s.startswith("max-page-size=") ||
           s.startswith("stack-size=");
  }
  
  // Report an error for an unknown -z option.
  static void checkZOptions(opt::InputArgList &args) {
    for (auto *arg : args.filtered(OPT_z))
      if (!isKnownZFlag(arg->getValue()))
        error("unknown -z value: " + StringRef(arg->getValue()));
  }
  
  void LinkerDriver::main(ArrayRef<const char *> argsArr) {
    ELFOptTable parser;
    opt::InputArgList args = parser.parse(argsArr.slice(1));
  
    // Interpret this flag early because error() depends on them.
    errorHandler().errorLimit = args::getInteger(args, OPT_error_limit, 20);
    checkZOptions(args);
  
    // Handle -help
    if (args.hasArg(OPT_help)) {
      printHelp();
      return;
    }
  
    // Handle -v or -version.
    //
    // A note about "compatible with GNU linkers" message: this is a hack for
    // scripts generated by GNU Libtool 2.4.6 (released in February 2014 and
    // still the newest version in March 2017) or earlier to recognize LLD as
    // a GNU compatible linker. As long as an output for the -v option
    // contains "GNU" or "with BFD", they recognize us as GNU-compatible.
    //
    // This is somewhat ugly hack, but in reality, we had no choice other
    // than doing this. Considering the very long release cycle of Libtool,
    // it is not easy to improve it to recognize LLD as a GNU compatible
    // linker in a timely manner. Even if we can make it, there are still a
    // lot of "configure" scripts out there that are generated by old version
    // of Libtool. We cannot convince every software developer to migrate to
    // the latest version and re-generate scripts. So we have this hack.
    if (args.hasArg(OPT_v) || args.hasArg(OPT_version))
      message(getLLDVersion() + " (compatible with GNU linkers)");
  
    if (const char *path = getReproduceOption(args)) {
      // Note that --reproduce is a debug option so you can ignore it
      // if you are trying to understand the whole picture of the code.
      Expected<std::unique_ptr<TarWriter>> errOrWriter =
          TarWriter::create(path, path::stem(path));
      if (errOrWriter) {
        tar = std::move(*errOrWriter);
        tar->append("response.txt", createResponseFile(args));
        tar->append("version.txt", getLLDVersion() + "\n");
      } else {
        error("--reproduce: " + toString(errOrWriter.takeError()));
      }
    }
  
    readConfigs(args);
  
    // The behavior of -v or --version is a bit strange, but this is
    // needed for compatibility with GNU linkers.
    if (args.hasArg(OPT_v) && !args.hasArg(OPT_INPUT))
      return;
    if (args.hasArg(OPT_version))
      return;
  
    // Initialize time trace profiler.
    if (config->timeTraceEnabled)
      timeTraceProfilerInitialize(config->timeTraceGranularity, config->progName);
  
    {
      llvm::TimeTraceScope timeScope("ExecuteLinker");
  
      initLLVM();
      createFiles(args);
      if (errorCount())
        return;
  
      inferMachineType();
      setConfigs(args);
      checkOptions();
      if (errorCount())
        return;
  
      // The Target instance handles target-specific stuff, such as applying
      // relocations or writing a PLT section. It also contains target-dependent
      // values such as a default image base address.
      target = getTarget();
  
      switch (config->ekind) {
      case ELF32LEKind:
        link<ELF32LE>(args);
        break;
      case ELF32BEKind:
        link<ELF32BE>(args);
        break;
      case ELF64LEKind:
        link<ELF64LE>(args);
        break;
      case ELF64BEKind:
        link<ELF64BE>(args);
        break;
      default:
        llvm_unreachable("unknown Config->EKind");
      }
    }
  
    if (config->timeTraceEnabled) {
      if (auto E = timeTraceProfilerWrite(args.getLastArgValue(OPT_time_trace_file_eq).str(),
                                          config->outputFile)) {
        handleAllErrors(std::move(E), [&](const StringError &SE) {
          error(SE.getMessage());
        });
        return;
      }
  
      timeTraceProfilerCleanup();
    }
  }
  
  static std::string getRpath(opt::InputArgList &args) {
    std::vector<StringRef> v = args::getStrings(args, OPT_rpath);
    return llvm::join(v.begin(), v.end(), ":");
  }
  
  // Determines what we should do if there are remaining unresolved
  // symbols after the name resolution.
  static UnresolvedPolicy getUnresolvedSymbolPolicy(opt::InputArgList &args) {
    UnresolvedPolicy errorOrWarn = args.hasFlag(OPT_error_unresolved_symbols,
                                                OPT_warn_unresolved_symbols, true)
                                       ? UnresolvedPolicy::ReportError
                                       : UnresolvedPolicy::Warn;
  
    // Process the last of -unresolved-symbols, -no-undefined or -z defs.
    for (auto *arg : llvm::reverse(args)) {
      switch (arg->getOption().getID()) {
      case OPT_unresolved_symbols: {
        StringRef s = arg->getValue();
        if (s == "ignore-all" || s == "ignore-in-object-files")
          return UnresolvedPolicy::Ignore;
        if (s == "ignore-in-shared-libs" || s == "report-all")
          return errorOrWarn;
        error("unknown --unresolved-symbols value: " + s);
        continue;
      }
      case OPT_no_undefined:
        return errorOrWarn;
      case OPT_z:
        if (StringRef(arg->getValue()) == "defs")
          return errorOrWarn;
        if (StringRef(arg->getValue()) == "undefs")
          return UnresolvedPolicy::Ignore;
        continue;
      }
    }
  
    // -shared implies -unresolved-symbols=ignore-all because missing
    // symbols are likely to be resolved at runtime using other DSOs.
    if (config->shared)
      return UnresolvedPolicy::Ignore;
    return errorOrWarn;
  }
  
  static Target2Policy getTarget2(opt::InputArgList &args) {
    StringRef s = args.getLastArgValue(OPT_target2, "got-rel");
    if (s == "rel")
      return Target2Policy::Rel;
    if (s == "abs")
      return Target2Policy::Abs;
    if (s == "got-rel")
      return Target2Policy::GotRel;
    error("unknown --target2 option: " + s);
    return Target2Policy::GotRel;
  }
  
  static bool isOutputFormatBinary(opt::InputArgList &args) {
    StringRef s = args.getLastArgValue(OPT_oformat, "elf");
    if (s == "binary")
      return true;
    if (!s.startswith("elf"))
      error("unknown --oformat value: " + s);
    return false;
  }
  
  static DiscardPolicy getDiscard(opt::InputArgList &args) {
    if (args.hasArg(OPT_relocatable))
      return DiscardPolicy::None;
  
    auto *arg =
        args.getLastArg(OPT_discard_all, OPT_discard_locals, OPT_discard_none);
    if (!arg)
      return DiscardPolicy::Default;
    if (arg->getOption().getID() == OPT_discard_all)
      return DiscardPolicy::All;
    if (arg->getOption().getID() == OPT_discard_locals)
      return DiscardPolicy::Locals;
    return DiscardPolicy::None;
  }
  
  static StringRef getDynamicLinker(opt::InputArgList &args) {
    auto *arg = args.getLastArg(OPT_dynamic_linker, OPT_no_dynamic_linker);
    if (!arg)
      return "";
    if (arg->getOption().getID() == OPT_no_dynamic_linker) {
      // --no-dynamic-linker suppresses undefined weak symbols in .dynsym
      config->noDynamicLinker = true;
      return "";
    }
    return arg->getValue();
  }
  
  static ICFLevel getICF(opt::InputArgList &args) {
    auto *arg = args.getLastArg(OPT_icf_none, OPT_icf_safe, OPT_icf_all);
    if (!arg || arg->getOption().getID() == OPT_icf_none)
      return ICFLevel::None;
    if (arg->getOption().getID() == OPT_icf_safe)
      return ICFLevel::Safe;
    return ICFLevel::All;
  }
  
  static StripPolicy getStrip(opt::InputArgList &args) {
    if (args.hasArg(OPT_relocatable))
      return StripPolicy::None;
  
    auto *arg = args.getLastArg(OPT_strip_all, OPT_strip_debug);
    if (!arg)
      return StripPolicy::None;
    if (arg->getOption().getID() == OPT_strip_all)
      return StripPolicy::All;
    return StripPolicy::Debug;
  }
  
  static uint64_t parseSectionAddress(StringRef s, opt::InputArgList &args,
                                      const opt::Arg &arg) {
    uint64_t va = 0;
    if (s.startswith("0x"))
      s = s.drop_front(2);
    if (!to_integer(s, va, 16))
      error("invalid argument: " + arg.getAsString(args));
    return va;
  }
  
  static StringMap<uint64_t> getSectionStartMap(opt::InputArgList &args) {
    StringMap<uint64_t> ret;
    for (auto *arg : args.filtered(OPT_section_start)) {
      StringRef name;
      StringRef addr;
      std::tie(name, addr) = StringRef(arg->getValue()).split('=');
      ret[name] = parseSectionAddress(addr, args, *arg);
    }
  
    if (auto *arg = args.getLastArg(OPT_Ttext))
      ret[".text"] = parseSectionAddress(arg->getValue(), args, *arg);
    if (auto *arg = args.getLastArg(OPT_Tdata))
      ret[".data"] = parseSectionAddress(arg->getValue(), args, *arg);
    if (auto *arg = args.getLastArg(OPT_Tbss))
      ret[".bss"] = parseSectionAddress(arg->getValue(), args, *arg);
    return ret;
  }
  
  static SortSectionPolicy getSortSection(opt::InputArgList &args) {
    StringRef s = args.getLastArgValue(OPT_sort_section);
    if (s == "alignment")
      return SortSectionPolicy::Alignment;
    if (s == "name")
      return SortSectionPolicy::Name;
    if (!s.empty())
      error("unknown --sort-section rule: " + s);
    return SortSectionPolicy::Default;
  }
  
  static OrphanHandlingPolicy getOrphanHandling(opt::InputArgList &args) {
    StringRef s = args.getLastArgValue(OPT_orphan_handling, "place");
    if (s == "warn")
      return OrphanHandlingPolicy::Warn;
    if (s == "error")
      return OrphanHandlingPolicy::Error;
    if (s != "place")
      error("unknown --orphan-handling mode: " + s);
    return OrphanHandlingPolicy::Place;
  }
  
  // Parse --build-id or --build-id=<style>. We handle "tree" as a
  // synonym for "sha1" because all our hash functions including
  // -build-id=sha1 are actually tree hashes for performance reasons.
  static std::pair<BuildIdKind, std::vector<uint8_t>>
  getBuildId(opt::InputArgList &args) {
    auto *arg = args.getLastArg(OPT_build_id, OPT_build_id_eq);
    if (!arg)
      return {BuildIdKind::None, {}};
  
    if (arg->getOption().getID() == OPT_build_id)
      return {BuildIdKind::Fast, {}};
  
    StringRef s = arg->getValue();
    if (s == "fast")
      return {BuildIdKind::Fast, {}};
    if (s == "md5")
      return {BuildIdKind::Md5, {}};
    if (s == "sha1" || s == "tree")
      return {BuildIdKind::Sha1, {}};
    if (s == "uuid")
      return {BuildIdKind::Uuid, {}};
    if (s.startswith("0x"))
      return {BuildIdKind::Hexstring, parseHex(s.substr(2))};
  
    if (s != "none")
      error("unknown --build-id style: " + s);
    return {BuildIdKind::None, {}};
  }
  
  static std::pair<bool, bool> getPackDynRelocs(opt::InputArgList &args) {
    StringRef s = args.getLastArgValue(OPT_pack_dyn_relocs, "none");
    if (s == "android")
      return {true, false};
    if (s == "relr")
      return {false, true};
    if (s == "android+relr")
      return {true, true};
  
    if (s != "none")
      error("unknown -pack-dyn-relocs format: " + s);
    return {false, false};
  }
  
  static void readCallGraph(MemoryBufferRef mb) {
    // Build a map from symbol name to section
    DenseMap<StringRef, Symbol *> map;
    for (InputFile *file : objectFiles)
      for (Symbol *sym : file->getSymbols())
        map[sym->getName()] = sym;
  
    auto findSection = [&](StringRef name) -> InputSectionBase * {
      Symbol *sym = map.lookup(name);
      if (!sym) {
        if (config->warnSymbolOrdering)
          warn(mb.getBufferIdentifier() + ": no such symbol: " + name);
        return nullptr;
      }
      maybeWarnUnorderableSymbol(sym);
  
      if (Defined *dr = dyn_cast_or_null<Defined>(sym))
        return dyn_cast_or_null<InputSectionBase>(dr->section);
      return nullptr;
    };
  
    for (StringRef line : args::getLines(mb)) {
      SmallVector<StringRef, 3> fields;
      line.split(fields, ' ');
      uint64_t count;
  
      if (fields.size() != 3 || !to_integer(fields[2], count)) {
        error(mb.getBufferIdentifier() + ": parse error");
        return;
      }
  
      if (InputSectionBase *from = findSection(fields[0]))
        if (InputSectionBase *to = findSection(fields[1]))
          config->callGraphProfile[std::make_pair(from, to)] += count;
    }
  }
  
  template <class ELFT> static void readCallGraphsFromObjectFiles() {
    for (auto file : objectFiles) {
      auto *obj = cast<ObjFile<ELFT>>(file);
  
      for (const Elf_CGProfile_Impl<ELFT> &cgpe : obj->cgProfile) {
        auto *fromSym = dyn_cast<Defined>(&obj->getSymbol(cgpe.cgp_from));
        auto *toSym = dyn_cast<Defined>(&obj->getSymbol(cgpe.cgp_to));
        if (!fromSym || !toSym)
          continue;
  
        auto *from = dyn_cast_or_null<InputSectionBase>(fromSym->section);
        auto *to = dyn_cast_or_null<InputSectionBase>(toSym->section);
        if (from && to)
          config->callGraphProfile[{from, to}] += cgpe.cgp_weight;
      }
    }
  }
  
  static bool getCompressDebugSections(opt::InputArgList &args) {
    StringRef s = args.getLastArgValue(OPT_compress_debug_sections, "none");
    if (s == "none")
      return false;
    if (s != "zlib")
      error("unknown --compress-debug-sections value: " + s);
    if (!zlib::isAvailable())
      error("--compress-debug-sections: zlib is not available");
    return true;
  }
  
  static StringRef getAliasSpelling(opt::Arg *arg) {
    if (const opt::Arg *alias = arg->getAlias())
      return alias->getSpelling();
    return arg->getSpelling();
  }
  
  static std::pair<StringRef, StringRef> getOldNewOptions(opt::InputArgList &args,
                                                          unsigned id) {
    auto *arg = args.getLastArg(id);
    if (!arg)
      return {"", ""};
  
    StringRef s = arg->getValue();
    std::pair<StringRef, StringRef> ret = s.split(';');
    if (ret.second.empty())
      error(getAliasSpelling(arg) + " expects 'old;new' format, but got " + s);
    return ret;
  }
  
  // Parse the symbol ordering file and warn for any duplicate entries.
  static std::vector<StringRef> getSymbolOrderingFile(MemoryBufferRef mb) {
    SetVector<StringRef> names;
    for (StringRef s : args::getLines(mb))
      if (!names.insert(s) && config->warnSymbolOrdering)
        warn(mb.getBufferIdentifier() + ": duplicate ordered symbol: " + s);
  
    return names.takeVector();
  }
  
  static void parseClangOption(StringRef opt, const Twine &msg) {
    std::string err;
    raw_string_ostream os(err);
  
    const char *argv[] = {config->progName.data(), opt.data()};
    if (cl::ParseCommandLineOptions(2, argv, "", &os))
      return;
    os.flush();
    error(msg + ": " + StringRef(err).trim());
  }
  
  // Initializes Config members by the command line options.
  static void readConfigs(opt::InputArgList &args) {
    errorHandler().verbose = args.hasArg(OPT_verbose);
    errorHandler().fatalWarnings =
        args.hasFlag(OPT_fatal_warnings, OPT_no_fatal_warnings, false);
    errorHandler().vsDiagnostics =
        args.hasArg(OPT_visual_studio_diagnostics_format, false);
  
    config->allowMultipleDefinition =
        args.hasFlag(OPT_allow_multiple_definition,
                     OPT_no_allow_multiple_definition, false) ||
        hasZOption(args, "muldefs");
    config->allowShlibUndefined =
        args.hasFlag(OPT_allow_shlib_undefined, OPT_no_allow_shlib_undefined,
                     args.hasArg(OPT_shared));
    config->auxiliaryList = args::getStrings(args, OPT_auxiliary);
    config->bsymbolic = args.hasArg(OPT_Bsymbolic);
    config->bsymbolicFunctions = args.hasArg(OPT_Bsymbolic_functions);
    config->checkSections =
        args.hasFlag(OPT_check_sections, OPT_no_check_sections, true);
    config->chroot = args.getLastArgValue(OPT_chroot);
    config->compressDebugSections = getCompressDebugSections(args);
    config->cref = args.hasFlag(OPT_cref, OPT_no_cref, false);
    config->defineCommon = args.hasFlag(OPT_define_common, OPT_no_define_common,
                                        !args.hasArg(OPT_relocatable));
    config->optimizeBBJumps =
        args.hasFlag(OPT_optimize_bb_jumps, OPT_no_optimize_bb_jumps, false);
    config->demangle = args.hasFlag(OPT_demangle, OPT_no_demangle, true);
    config->dependentLibraries = args.hasFlag(OPT_dependent_libraries, OPT_no_dependent_libraries, true);
    config->disableVerify = args.hasArg(OPT_disable_verify);
    config->discard = getDiscard(args);
    config->dwoDir = args.getLastArgValue(OPT_plugin_opt_dwo_dir_eq);
    config->dynamicLinker = getDynamicLinker(args);
    config->ehFrameHdr =
        args.hasFlag(OPT_eh_frame_hdr, OPT_no_eh_frame_hdr, false);
    config->emitLLVM = args.hasArg(OPT_plugin_opt_emit_llvm, false);
    config->emitRelocs = args.hasArg(OPT_emit_relocs);
    config->callGraphProfileSort = args.hasFlag(
        OPT_call_graph_profile_sort, OPT_no_call_graph_profile_sort, true);
    config->enableNewDtags =
        args.hasFlag(OPT_enable_new_dtags, OPT_disable_new_dtags, true);
    config->entry = args.getLastArgValue(OPT_entry);
    config->executeOnly =
        args.hasFlag(OPT_execute_only, OPT_no_execute_only, false);
    config->exportDynamic =
        args.hasFlag(OPT_export_dynamic, OPT_no_export_dynamic, false);
    config->filterList = args::getStrings(args, OPT_filter);
    config->fini = args.getLastArgValue(OPT_fini, "_fini");
    config->fixCortexA53Errata843419 = args.hasArg(OPT_fix_cortex_a53_843419) &&
                                       !args.hasArg(OPT_relocatable);
    config->fixCortexA8 =
        args.hasArg(OPT_fix_cortex_a8) && !args.hasArg(OPT_relocatable);
    config->gcSections = args.hasFlag(OPT_gc_sections, OPT_no_gc_sections, false);
    config->gnuUnique = args.hasFlag(OPT_gnu_unique, OPT_no_gnu_unique, true);
    config->gdbIndex = args.hasFlag(OPT_gdb_index, OPT_no_gdb_index, false);
    config->icf = getICF(args);
    config->ignoreDataAddressEquality =
        args.hasArg(OPT_ignore_data_address_equality);
    config->ignoreFunctionAddressEquality =
        args.hasArg(OPT_ignore_function_address_equality);
    config->init = args.getLastArgValue(OPT_init, "_init");
    config->ltoAAPipeline = args.getLastArgValue(OPT_lto_aa_pipeline);
    config->ltoCSProfileGenerate = args.hasArg(OPT_lto_cs_profile_generate);
    config->ltoCSProfileFile = args.getLastArgValue(OPT_lto_cs_profile_file);
    config->ltoDebugPassManager = args.hasArg(OPT_lto_debug_pass_manager);
    config->ltoNewPassManager = args.hasArg(OPT_lto_new_pass_manager);
    config->ltoNewPmPasses = args.getLastArgValue(OPT_lto_newpm_passes);
    config->ltoWholeProgramVisibility =
        args.hasArg(OPT_lto_whole_program_visibility);
    config->ltoo = args::getInteger(args, OPT_lto_O, 2);
    config->ltoObjPath = args.getLastArgValue(OPT_lto_obj_path_eq);
    config->ltoPartitions = args::getInteger(args, OPT_lto_partitions, 1);
    config->ltoSampleProfile = args.getLastArgValue(OPT_lto_sample_profile);
    config->ltoBasicBlockSections =
        args.getLastArgValue(OPT_lto_basicblock_sections);
    config->ltoUniqueBBSectionNames =
        args.hasFlag(OPT_lto_unique_bb_section_names,
                     OPT_no_lto_unique_bb_section_names, false);
    config->mapFile = args.getLastArgValue(OPT_Map);
    config->mipsGotSize = args::getInteger(args, OPT_mips_got_size, 0xfff0);
    config->mergeArmExidx =
        args.hasFlag(OPT_merge_exidx_entries, OPT_no_merge_exidx_entries, true);
    config->mmapOutputFile =
        args.hasFlag(OPT_mmap_output_file, OPT_no_mmap_output_file, true);
    config->nmagic = args.hasFlag(OPT_nmagic, OPT_no_nmagic, false);
    config->noinhibitExec = args.hasArg(OPT_noinhibit_exec);
    config->nostdlib = args.hasArg(OPT_nostdlib);
    config->oFormatBinary = isOutputFormatBinary(args);
    config->omagic = args.hasFlag(OPT_omagic, OPT_no_omagic, false);
    config->optRemarksFilename = args.getLastArgValue(OPT_opt_remarks_filename);
    config->optRemarksPasses = args.getLastArgValue(OPT_opt_remarks_passes);
    config->optRemarksWithHotness = args.hasArg(OPT_opt_remarks_with_hotness);
    config->optRemarksFormat = args.getLastArgValue(OPT_opt_remarks_format);
    config->optimize = args::getInteger(args, OPT_O, 1);
    config->orphanHandling = getOrphanHandling(args);
    config->outputFile = args.getLastArgValue(OPT_o);
    config->pie = args.hasFlag(OPT_pie, OPT_no_pie, false);
    config->printIcfSections =
        args.hasFlag(OPT_print_icf_sections, OPT_no_print_icf_sections, false);
    config->printGcSections =
        args.hasFlag(OPT_print_gc_sections, OPT_no_print_gc_sections, false);
    config->printSymbolOrder =
        args.getLastArgValue(OPT_print_symbol_order);
    config->rpath = getRpath(args);
    config->relocatable = args.hasArg(OPT_relocatable);
    config->saveTemps = args.hasArg(OPT_save_temps);
    if (args.hasArg(OPT_shuffle_sections))
      config->shuffleSectionSeed = args::getInteger(args, OPT_shuffle_sections, 0);
    config->searchPaths = args::getStrings(args, OPT_library_path);
    config->sectionStartMap = getSectionStartMap(args);
    config->shared = args.hasArg(OPT_shared);
    config->singleRoRx = args.hasArg(OPT_no_rosegment);
    config->soName = args.getLastArgValue(OPT_soname);
    config->sortSection = getSortSection(args);
    config->splitStackAdjustSize = args::getInteger(args, OPT_split_stack_adjust_size, 16384);
    config->strip = getStrip(args);
    config->sysroot = args.getLastArgValue(OPT_sysroot);
    config->target1Rel = args.hasFlag(OPT_target1_rel, OPT_target1_abs, false);
    config->target2 = getTarget2(args);
    config->thinLTOCacheDir = args.getLastArgValue(OPT_thinlto_cache_dir);
    config->thinLTOCachePolicy = CHECK(
        parseCachePruningPolicy(args.getLastArgValue(OPT_thinlto_cache_policy)),
        "--thinlto-cache-policy: invalid cache policy");
    config->thinLTOEmitImportsFiles = args.hasArg(OPT_thinlto_emit_imports_files);
    config->thinLTOIndexOnly = args.hasArg(OPT_thinlto_index_only) ||
                               args.hasArg(OPT_thinlto_index_only_eq);
    config->thinLTOIndexOnlyArg = args.getLastArgValue(OPT_thinlto_index_only_eq);
    config->thinLTOObjectSuffixReplace =
        getOldNewOptions(args, OPT_thinlto_object_suffix_replace_eq);
    config->thinLTOPrefixReplace =
        getOldNewOptions(args, OPT_thinlto_prefix_replace_eq);
    config->timeTraceEnabled = args.hasArg(OPT_time_trace);
    config->timeTraceGranularity =
        args::getInteger(args, OPT_time_trace_granularity, 500);
    config->trace = args.hasArg(OPT_trace);
    config->undefined = args::getStrings(args, OPT_undefined);
    config->undefinedVersion =
        args.hasFlag(OPT_undefined_version, OPT_no_undefined_version, true);
    config->unique = args.hasArg(OPT_unique);
    config->useAndroidRelrTags = args.hasFlag(
        OPT_use_android_relr_tags, OPT_no_use_android_relr_tags, false);
    config->unresolvedSymbols = getUnresolvedSymbolPolicy(args);
    config->warnBackrefs =
        args.hasFlag(OPT_warn_backrefs, OPT_no_warn_backrefs, false);
    config->warnCommon = args.hasFlag(OPT_warn_common, OPT_no_warn_common, false);
    config->warnIfuncTextrel =
        args.hasFlag(OPT_warn_ifunc_textrel, OPT_no_warn_ifunc_textrel, false);
    config->warnSymbolOrdering =
        args.hasFlag(OPT_warn_symbol_ordering, OPT_no_warn_symbol_ordering, true);
    config->zCombreloc = getZFlag(args, "combreloc", "nocombreloc", true);
    config->zCopyreloc = getZFlag(args, "copyreloc", "nocopyreloc", true);
    config->zForceBti = hasZOption(args, "force-bti");
    config->zForceIbt = hasZOption(args, "force-ibt");
    config->zGlobal = hasZOption(args, "global");
    config->zGnustack = getZGnuStack(args);
    config->zHazardplt = hasZOption(args, "hazardplt");
    config->zIfuncNoplt = hasZOption(args, "ifunc-noplt");
    config->zInitfirst = hasZOption(args, "initfirst");
    config->zInterpose = hasZOption(args, "interpose");
    config->zKeepTextSectionPrefix = getZFlag(
        args, "keep-text-section-prefix", "nokeep-text-section-prefix", false);
    config->zNodefaultlib = hasZOption(args, "nodefaultlib");
    config->zNodelete = hasZOption(args, "nodelete");
    config->zNodlopen = hasZOption(args, "nodlopen");
    config->zNow = getZFlag(args, "now", "lazy", false);
    config->zOrigin = hasZOption(args, "origin");
    config->zPacPlt = hasZOption(args, "pac-plt");
    config->zRelro = getZFlag(args, "relro", "norelro", true);
    config->zRetpolineplt = hasZOption(args, "retpolineplt");
    config->zRodynamic = hasZOption(args, "rodynamic");
    config->zSeparate = getZSeparate(args);
    config->zShstk = hasZOption(args, "shstk");
    config->zStackSize = args::getZOptionValue(args, OPT_z, "stack-size", 0);
    config->zText = getZFlag(args, "text", "notext", true);
    config->zWxneeded = hasZOption(args, "wxneeded");
  
    // Parse LTO options.
    if (auto *arg = args.getLastArg(OPT_plugin_opt_mcpu_eq))
      parseClangOption(saver.save("-mcpu=" + StringRef(arg->getValue())),
                       arg->getSpelling());
  
    for (opt::Arg *arg : args.filtered(OPT_plugin_opt_eq_minus))
      parseClangOption(std::string("-") + arg->getValue(), arg->getSpelling());
  
    // GCC collect2 passes -plugin-opt=path/to/lto-wrapper with an absolute or
    // relative path. Just ignore. If not ended with "lto-wrapper", consider it an
    // unsupported LLVMgold.so option and error.
    for (opt::Arg *arg : args.filtered(OPT_plugin_opt_eq))
      if (!StringRef(arg->getValue()).endswith("lto-wrapper"))
        error(arg->getSpelling() + ": unknown plugin option '" + arg->getValue() +
              "'");
  
    // Parse -mllvm options.
    for (auto *arg : args.filtered(OPT_mllvm))
      parseClangOption(arg->getValue(), arg->getSpelling());
  
    // --threads= takes a positive integer and provides the default value for
    // --thinlto-jobs=.
    if (auto *arg = args.getLastArg(OPT_threads)) {
      StringRef v(arg->getValue());
      unsigned threads = 0;
      if (!llvm::to_integer(v, threads, 0) || threads == 0)
        error(arg->getSpelling() + ": expected a positive integer, but got '" +
              arg->getValue() + "'");
      parallel::strategy = hardware_concurrency(threads);
      config->thinLTOJobs = v;
    }
    if (auto *arg = args.getLastArg(OPT_thinlto_jobs))
      config->thinLTOJobs = arg->getValue();
  
    if (config->ltoo > 3)
      error("invalid optimization level for LTO: " + Twine(config->ltoo));
    if (config->ltoPartitions == 0)
      error("--lto-partitions: number of threads must be > 0");
    if (!get_threadpool_strategy(config->thinLTOJobs))
      error("--thinlto-jobs: invalid job count: " + config->thinLTOJobs);
  
    if (config->splitStackAdjustSize < 0)
      error("--split-stack-adjust-size: size must be >= 0");
  
    // The text segment is traditionally the first segment, whose address equals
    // the base address. However, lld places the R PT_LOAD first. -Ttext-segment
    // is an old-fashioned option that does not play well with lld's layout.
    // Suggest --image-base as a likely alternative.
    if (args.hasArg(OPT_Ttext_segment))
      error("-Ttext-segment is not supported. Use --image-base if you "
            "intend to set the base address");
  
    // Parse ELF{32,64}{LE,BE} and CPU type.
    if (auto *arg = args.getLastArg(OPT_m)) {
      StringRef s = arg->getValue();
      std::tie(config->ekind, config->emachine, config->osabi) =
          parseEmulation(s);
      config->mipsN32Abi =
          (s.startswith("elf32btsmipn32") || s.startswith("elf32ltsmipn32"));
      config->emulation = s;
    }
  
    // Parse -hash-style={sysv,gnu,both}.
    if (auto *arg = args.getLastArg(OPT_hash_style)) {
      StringRef s = arg->getValue();
      if (s == "sysv")
        config->sysvHash = true;
      else if (s == "gnu")
        config->gnuHash = true;
      else if (s == "both")
        config->sysvHash = config->gnuHash = true;
      else
        error("unknown -hash-style: " + s);
    }
  
    if (args.hasArg(OPT_print_map))
      config->mapFile = "-";
  
    // Page alignment can be disabled by the -n (--nmagic) and -N (--omagic).
    // As PT_GNU_RELRO relies on Paging, do not create it when we have disabled
    // it.
    if (config->nmagic || config->omagic)
      config->zRelro = false;
  
    std::tie(config->buildId, config->buildIdVector) = getBuildId(args);
  
    std::tie(config->androidPackDynRelocs, config->relrPackDynRelocs) =
        getPackDynRelocs(args);
  
    if (auto *arg = args.getLastArg(OPT_symbol_ordering_file)){
      if (args.hasArg(OPT_call_graph_ordering_file))
        error("--symbol-ordering-file and --call-graph-order-file "
              "may not be used together");
      if (Optional<MemoryBufferRef> buffer = readFile(arg->getValue())){
        config->symbolOrderingFile = getSymbolOrderingFile(*buffer);
        // Also need to disable CallGraphProfileSort to prevent
        // LLD order symbols with CGProfile
        config->callGraphProfileSort = false;
      }
    }
  
    assert(config->versionDefinitions.empty());
    config->versionDefinitions.push_back({"local", (uint16_t)VER_NDX_LOCAL, {}});
    config->versionDefinitions.push_back(
        {"global", (uint16_t)VER_NDX_GLOBAL, {}});
  
    // If --retain-symbol-file is used, we'll keep only the symbols listed in
    // the file and discard all others.
    if (auto *arg = args.getLastArg(OPT_retain_symbols_file)) {
      config->versionDefinitions[VER_NDX_LOCAL].patterns.push_back(
          {"*", /*isExternCpp=*/false, /*hasWildcard=*/true});
      if (Optional<MemoryBufferRef> buffer = readFile(arg->getValue()))
        for (StringRef s : args::getLines(*buffer))
          config->versionDefinitions[VER_NDX_GLOBAL].patterns.push_back(
              {s, /*isExternCpp=*/false, /*hasWildcard=*/false});
    }
  
    // Parses -dynamic-list and -export-dynamic-symbol. They make some
    // symbols private. Note that -export-dynamic takes precedence over them
    // as it says all symbols should be exported.
    if (!config->exportDynamic) {
      for (auto *arg : args.filtered(OPT_dynamic_list))
        if (Optional<MemoryBufferRef> buffer = readFile(arg->getValue()))
          readDynamicList(*buffer);
  
      for (auto *arg : args.filtered(OPT_export_dynamic_symbol))
        config->dynamicList.push_back(
            {arg->getValue(), /*isExternCpp=*/false, /*hasWildcard=*/false});
    }
  
    // If --export-dynamic-symbol=foo is given and symbol foo is defined in
    // an object file in an archive file, that object file should be pulled
    // out and linked. (It doesn't have to behave like that from technical
    // point of view, but this is needed for compatibility with GNU.)
    for (auto *arg : args.filtered(OPT_export_dynamic_symbol))
      config->undefined.push_back(arg->getValue());
  
    for (auto *arg : args.filtered(OPT_version_script))
      if (Optional<std::string> path = searchScript(arg->getValue())) {
        if (Optional<MemoryBufferRef> buffer = readFile(*path))
          readVersionScript(*buffer);
      } else {
        error(Twine("cannot find version script ") + arg->getValue());
      }
  }
  
  // Some Config members do not directly correspond to any particular
  // command line options, but computed based on other Config values.
  // This function initialize such members. See Config.h for the details
  // of these values.
  static void setConfigs(opt::InputArgList &args) {
    ELFKind k = config->ekind;
    uint16_t m = config->emachine;
  
    config->copyRelocs = (config->relocatable || config->emitRelocs);
    config->is64 = (k == ELF64LEKind || k == ELF64BEKind);
    config->isLE = (k == ELF32LEKind || k == ELF64LEKind);
    config->endianness = config->isLE ? endianness::little : endianness::big;
    config->isMips64EL = (k == ELF64LEKind && m == EM_MIPS);
    config->isPic = config->pie || config->shared;
    config->picThunk = args.hasArg(OPT_pic_veneer, config->isPic);
    config->wordsize = config->is64 ? 8 : 4;
  
    // ELF defines two different ways to store relocation addends as shown below:
    //
    //  Rel:  Addends are stored to the location where relocations are applied.
    //  Rela: Addends are stored as part of relocation entry.
    //
    // In other words, Rela makes it easy to read addends at the price of extra
    // 4 or 8 byte for each relocation entry. We don't know why ELF defined two
    // different mechanisms in the first place, but this is how the spec is
    // defined.
    //
    // You cannot choose which one, Rel or Rela, you want to use. Instead each
    // ABI defines which one you need to use. The following expression expresses
    // that.
    config->isRela = m == EM_AARCH64 || m == EM_AMDGPU || m == EM_HEXAGON ||
                     m == EM_PPC || m == EM_PPC64 || m == EM_RISCV ||
                     m == EM_X86_64;
  
    // If the output uses REL relocations we must store the dynamic relocation
    // addends to the output sections. We also store addends for RELA relocations
    // if --apply-dynamic-relocs is used.
    // We default to not writing the addends when using RELA relocations since
    // any standard conforming tool can find it in r_addend.
    config->writeAddends = args.hasFlag(OPT_apply_dynamic_relocs,
                                        OPT_no_apply_dynamic_relocs, false) ||
                           !config->isRela;
  
    config->tocOptimize =
        args.hasFlag(OPT_toc_optimize, OPT_no_toc_optimize, m == EM_PPC64);
  }
  
  // Returns a value of "-format" option.
  static bool isFormatBinary(StringRef s) {
    if (s == "binary")
      return true;
    if (s == "elf" || s == "default")
      return false;
    error("unknown -format value: " + s +
          " (supported formats: elf, default, binary)");
    return false;
  }
  
  void LinkerDriver::createFiles(opt::InputArgList &args) {
    // For --{push,pop}-state.
    std::vector<std::tuple<bool, bool, bool>> stack;
  
    // Iterate over argv to process input files and positional arguments.
    for (auto *arg : args) {
      switch (arg->getOption().getID()) {
      case OPT_library:
        addLibrary(arg->getValue());
        break;
      case OPT_INPUT:
        addFile(arg->getValue(), /*withLOption=*/false);
        break;
      case OPT_defsym: {
        StringRef from;
        StringRef to;
        std::tie(from, to) = StringRef(arg->getValue()).split('=');
        if (from.empty() || to.empty())
          error("-defsym: syntax error: " + StringRef(arg->getValue()));
        else
          readDefsym(from, MemoryBufferRef(to, "-defsym"));
        break;
      }
      case OPT_script:
        if (Optional<std::string> path = searchScript(arg->getValue())) {
          if (Optional<MemoryBufferRef> mb = readFile(*path))
            readLinkerScript(*mb);
          break;
        }
        error(Twine("cannot find linker script ") + arg->getValue());
        break;
      case OPT_as_needed:
        config->asNeeded = true;
        break;
      case OPT_format:
        config->formatBinary = isFormatBinary(arg->getValue());
        break;
      case OPT_no_as_needed:
        config->asNeeded = false;
        break;
      case OPT_Bstatic:
      case OPT_omagic:
      case OPT_nmagic:
        config->isStatic = true;
        break;
      case OPT_Bdynamic:
        config->isStatic = false;
        break;
      case OPT_whole_archive:
        inWholeArchive = true;
        break;
      case OPT_no_whole_archive:
        inWholeArchive = false;
        break;
      case OPT_just_symbols:
        if (Optional<MemoryBufferRef> mb = readFile(arg->getValue())) {
          files.push_back(createObjectFile(*mb));
          files.back()->justSymbols = true;
        }
        break;
      case OPT_start_group:
        if (InputFile::isInGroup)
          error("nested --start-group");
        InputFile::isInGroup = true;
        break;
      case OPT_end_group:
        if (!InputFile::isInGroup)
          error("stray --end-group");
        InputFile::isInGroup = false;
        ++InputFile::nextGroupId;
        break;
      case OPT_start_lib:
        if (inLib)
          error("nested --start-lib");
        if (InputFile::isInGroup)
          error("may not nest --start-lib in --start-group");
        inLib = true;
        InputFile::isInGroup = true;
        break;
      case OPT_end_lib:
        if (!inLib)
          error("stray --end-lib");
        inLib = false;
        InputFile::isInGroup = false;
        ++InputFile::nextGroupId;
        break;
      case OPT_push_state:
        stack.emplace_back(config->asNeeded, config->isStatic, inWholeArchive);
        break;
      case OPT_pop_state:
        if (stack.empty()) {
          error("unbalanced --push-state/--pop-state");
          break;
        }
        std::tie(config->asNeeded, config->isStatic, inWholeArchive) = stack.back();
        stack.pop_back();
        break;
      }
    }
  
    if (files.empty() && errorCount() == 0)
      error("no input files");
  }
  
  // If -m <machine_type> was not given, infer it from object files.
  void LinkerDriver::inferMachineType() {
    if (config->ekind != ELFNoneKind)
      return;
  
    for (InputFile *f : files) {
      if (f->ekind == ELFNoneKind)
        continue;
      config->ekind = f->ekind;
      config->emachine = f->emachine;
      config->osabi = f->osabi;
      config->mipsN32Abi = config->emachine == EM_MIPS && isMipsN32Abi(f);
      return;
    }
    error("target emulation unknown: -m or at least one .o file required");
  }
  
  // Parse -z max-page-size=<value>. The default value is defined by
  // each target.
  static uint64_t getMaxPageSize(opt::InputArgList &args) {
    uint64_t val = args::getZOptionValue(args, OPT_z, "max-page-size",
                                         target->defaultMaxPageSize);
    if (!isPowerOf2_64(val))
      error("max-page-size: value isn't a power of 2");
    if (config->nmagic || config->omagic) {
      if (val != target->defaultMaxPageSize)
        warn("-z max-page-size set, but paging disabled by omagic or nmagic");
      return 1;
    }
    return val;
  }
  
  // Parse -z common-page-size=<value>. The default value is defined by
  // each target.
  static uint64_t getCommonPageSize(opt::InputArgList &args) {
    uint64_t val = args::getZOptionValue(args, OPT_z, "common-page-size",
                                         target->defaultCommonPageSize);
    if (!isPowerOf2_64(val))
      error("common-page-size: value isn't a power of 2");
    if (config->nmagic || config->omagic) {
      if (val != target->defaultCommonPageSize)
        warn("-z common-page-size set, but paging disabled by omagic or nmagic");
      return 1;
    }
    // commonPageSize can't be larger than maxPageSize.
    if (val > config->maxPageSize)
      val = config->maxPageSize;
    return val;
  }
  
  // Parses -image-base option.
  static Optional<uint64_t> getImageBase(opt::InputArgList &args) {
    // Because we are using "Config->maxPageSize" here, this function has to be
    // called after the variable is initialized.
    auto *arg = args.getLastArg(OPT_image_base);
    if (!arg)
      return None;
  
    StringRef s = arg->getValue();
    uint64_t v;
    if (!to_integer(s, v)) {
      error("-image-base: number expected, but got " + s);
      return 0;
    }
    if ((v % config->maxPageSize) != 0)
      warn("-image-base: address isn't multiple of page size: " + s);
    return v;
  }
  
  // Parses `--exclude-libs=lib,lib,...`.
  // The library names may be delimited by commas or colons.
  static DenseSet<StringRef> getExcludeLibs(opt::InputArgList &args) {
    DenseSet<StringRef> ret;
    for (auto *arg : args.filtered(OPT_exclude_libs)) {
      StringRef s = arg->getValue();
      for (;;) {
        size_t pos = s.find_first_of(",:");
        if (pos == StringRef::npos)
          break;
        ret.insert(s.substr(0, pos));
        s = s.substr(pos + 1);
      }
      ret.insert(s);
    }
    return ret;
  }
  
  // Handles the -exclude-libs option. If a static library file is specified
  // by the -exclude-libs option, all public symbols from the archive become
  // private unless otherwise specified by version scripts or something.
  // A special library name "ALL" means all archive files.
  //
  // This is not a popular option, but some programs such as bionic libc use it.
  static void excludeLibs(opt::InputArgList &args) {
    DenseSet<StringRef> libs = getExcludeLibs(args);
    bool all = libs.count("ALL");
  
    auto visit = [&](InputFile *file) {
      if (!file->archiveName.empty())
        if (all || libs.count(path::filename(file->archiveName)))
          for (Symbol *sym : file->getSymbols())
            if (!sym->isUndefined() && !sym->isLocal() && sym->file == file)
              sym->versionId = VER_NDX_LOCAL;
    };
  
    for (InputFile *file : objectFiles)
      visit(file);
  
    for (BitcodeFile *file : bitcodeFiles)
      visit(file);
  }
  
  // Force Sym to be entered in the output. Used for -u or equivalent.
  static void handleUndefined(Symbol *sym) {
    // Since a symbol may not be used inside the program, LTO may
    // eliminate it. Mark the symbol as "used" to prevent it.
    sym->isUsedInRegularObj = true;
  
    // GNU linkers allow -u foo -ldef -lref. We should not treat it as a backward
    // reference.
    backwardReferences.erase(sym);
  
    if (sym->isLazy())
      sym->fetch();
  }
  
  // As an extension to GNU linkers, lld supports a variant of `-u`
  // which accepts wildcard patterns. All symbols that match a given
  // pattern are handled as if they were given by `-u`.
  static void handleUndefinedGlob(StringRef arg) {
    Expected<GlobPattern> pat = GlobPattern::create(arg);
    if (!pat) {
      error("--undefined-glob: " + toString(pat.takeError()));
      return;
    }
  
    std::vector<Symbol *> syms;
    for (Symbol *sym : symtab->symbols()) {
      // Calling Sym->fetch() from here is not safe because it may
      // add new symbols to the symbol table, invalidating the
      // current iterator. So we just keep a note.
      if (pat->match(sym->getName()))
        syms.push_back(sym);
    }
  
    for (Symbol *sym : syms)
      handleUndefined(sym);
  }
  
  static void handleLibcall(StringRef name) {
    Symbol *sym = symtab->find(name);
    if (!sym || !sym->isLazy())
      return;
  
    MemoryBufferRef mb;
    if (auto *lo = dyn_cast<LazyObject>(sym))
      mb = lo->file->mb;
    else
      mb = cast<LazyArchive>(sym)->getMemberBuffer();
  
    if (isBitcode(mb))
      sym->fetch();
  }
  
  // Replaces common symbols with defined symbols reside in .bss sections.
  // This function is called after all symbol names are resolved. As a
  // result, the passes after the symbol resolution won't see any
  // symbols of type CommonSymbol.
  static void replaceCommonSymbols() {
    for (Symbol *sym : symtab->symbols()) {
      auto *s = dyn_cast<CommonSymbol>(sym);
      if (!s)
        continue;
  
      auto *bss = make<BssSection>("COMMON", s->size, s->alignment);
      bss->file = s->file;
      bss->markDead();
      inputSections.push_back(bss);
      s->replace(Defined{s->file, s->getName(), s->binding, s->stOther, s->type,
                         /*value=*/0, s->size, bss});
    }
  }
  
  // If all references to a DSO happen to be weak, the DSO is not added
  // to DT_NEEDED. If that happens, we need to eliminate shared symbols
  // created from the DSO. Otherwise, they become dangling references
  // that point to a non-existent DSO.
  static void demoteSharedSymbols() {
    for (Symbol *sym : symtab->symbols()) {
      auto *s = dyn_cast<SharedSymbol>(sym);
      if (!s || s->getFile().isNeeded)
        continue;
  
      bool used = s->used;
      s->replace(Undefined{nullptr, s->getName(), STB_WEAK, s->stOther, s->type});
      s->used = used;
    }
  }
  
  // The section referred to by `s` is considered address-significant. Set the
  // keepUnique flag on the section if appropriate.
  static void markAddrsig(Symbol *s) {
    if (auto *d = dyn_cast_or_null<Defined>(s))
      if (d->section)
        // We don't need to keep text sections unique under --icf=all even if they
        // are address-significant.
        if (config->icf == ICFLevel::Safe || !(d->section->flags & SHF_EXECINSTR))
          d->section->keepUnique = true;
  }
  
  // Record sections that define symbols mentioned in --keep-unique <symbol>
  // and symbols referred to by address-significance tables. These sections are
  // ineligible for ICF.
  template <class ELFT>
  static void findKeepUniqueSections(opt::InputArgList &args) {
    for (auto *arg : args.filtered(OPT_keep_unique)) {
      StringRef name = arg->getValue();
      auto *d = dyn_cast_or_null<Defined>(symtab->find(name));
      if (!d || !d->section) {
        warn("could not find symbol " + name + " to keep unique");
        continue;
      }
      d->section->keepUnique = true;
    }
  
    // --icf=all --ignore-data-address-equality means that we can ignore
    // the dynsym and address-significance tables entirely.
    if (config->icf == ICFLevel::All && config->ignoreDataAddressEquality)
      return;
  
    // Symbols in the dynsym could be address-significant in other executables
    // or DSOs, so we conservatively mark them as address-significant.
    for (Symbol *sym : symtab->symbols())
      if (sym->includeInDynsym())
        markAddrsig(sym);
  
    // Visit the address-significance table in each object file and mark each
    // referenced symbol as address-significant.
    for (InputFile *f : objectFiles) {
      auto *obj = cast<ObjFile<ELFT>>(f);
      ArrayRef<Symbol *> syms = obj->getSymbols();
      if (obj->addrsigSec) {
        ArrayRef<uint8_t> contents =
            check(obj->getObj().getSectionContents(obj->addrsigSec));
        const uint8_t *cur = contents.begin();
        while (cur != contents.end()) {
          unsigned size;
          const char *err;
          uint64_t symIndex = decodeULEB128(cur, &size, contents.end(), &err);
          if (err)
            fatal(toString(f) + ": could not decode addrsig section: " + err);
          markAddrsig(syms[symIndex]);
          cur += size;
        }
      } else {
        // If an object file does not have an address-significance table,
        // conservatively mark all of its symbols as address-significant.
        for (Symbol *s : syms)
          markAddrsig(s);
      }
    }
  }
  
  // This function reads a symbol partition specification section. These sections
  // are used to control which partition a symbol is allocated to. See
  // https://lld.llvm.org/Partitions.html for more details on partitions.
  template <typename ELFT>
  static void readSymbolPartitionSection(InputSectionBase *s) {
    // Read the relocation that refers to the partition's entry point symbol.
    Symbol *sym;
    if (s->areRelocsRela)
      sym = &s->getFile<ELFT>()->getRelocTargetSym(s->template relas<ELFT>()[0]);
    else
      sym = &s->getFile<ELFT>()->getRelocTargetSym(s->template rels<ELFT>()[0]);
    if (!isa<Defined>(sym) || !sym->includeInDynsym())
      return;
  
    StringRef partName = reinterpret_cast<const char *>(s->data().data());
    for (Partition &part : partitions) {
      if (part.name == partName) {
        sym->partition = part.getNumber();
        return;
      }
    }
  
    // Forbid partitions from being used on incompatible targets, and forbid them
    // from being used together with various linker features that assume a single
    // set of output sections.
    if (script->hasSectionsCommand)
      error(toString(s->file) +
            ": partitions cannot be used with the SECTIONS command");
    if (script->hasPhdrsCommands())
      error(toString(s->file) +
            ": partitions cannot be used with the PHDRS command");
    if (!config->sectionStartMap.empty())
      error(toString(s->file) + ": partitions cannot be used with "
                                "--section-start, -Ttext, -Tdata or -Tbss");
    if (config->emachine == EM_MIPS)
      error(toString(s->file) + ": partitions cannot be used on this target");
  
    // Impose a limit of no more than 254 partitions. This limit comes from the
    // sizes of the Partition fields in InputSectionBase and Symbol, as well as
    // the amount of space devoted to the partition number in RankFlags.
    if (partitions.size() == 254)
      fatal("may not have more than 254 partitions");
  
    partitions.emplace_back();
    Partition &newPart = partitions.back();
    newPart.name = partName;
    sym->partition = newPart.getNumber();
  }
  
  static Symbol *addUndefined(StringRef name) {
    return symtab->addSymbol(
        Undefined{nullptr, name, STB_GLOBAL, STV_DEFAULT, 0});
  }
  
  // This function is where all the optimizations of link-time
  // optimization takes place. When LTO is in use, some input files are
  // not in native object file format but in the LLVM bitcode format.
  // This function compiles bitcode files into a few big native files
  // using LLVM functions and replaces bitcode symbols with the results.
  // Because all bitcode files that the program consists of are passed to
  // the compiler at once, it can do a whole-program optimization.
  template <class ELFT> void LinkerDriver::compileBitcodeFiles() {
    llvm::TimeTraceScope timeScope("LTO");
    // Compile bitcode files and replace bitcode symbols.
    lto.reset(new BitcodeCompiler);
    for (BitcodeFile *file : bitcodeFiles)
      lto->add(*file);
  
    for (InputFile *file : lto->compile()) {
      auto *obj = cast<ObjFile<ELFT>>(file);
      obj->parse(/*ignoreComdats=*/true);
      for (Symbol *sym : obj->getGlobalSymbols())
        sym->parseSymbolVersion();
      objectFiles.push_back(file);
    }
  }
  
  // The --wrap option is a feature to rename symbols so that you can write
  // wrappers for existing functions. If you pass `-wrap=foo`, all
  // occurrences of symbol `foo` are resolved to `wrap_foo` (so, you are
  // expected to write `wrap_foo` function as a wrapper). The original
  // symbol becomes accessible as `real_foo`, so you can call that from your
  // wrapper.
  //
  // This data structure is instantiated for each -wrap option.
  struct WrappedSymbol {
    Symbol *sym;
    Symbol *real;
    Symbol *wrap;
  };
  
  // Handles -wrap option.
  //
  // This function instantiates wrapper symbols. At this point, they seem
  // like they are not being used at all, so we explicitly set some flags so
  // that LTO won't eliminate them.
  static std::vector<WrappedSymbol> addWrappedSymbols(opt::InputArgList &args) {
    std::vector<WrappedSymbol> v;
    DenseSet<StringRef> seen;
  
    for (auto *arg : args.filtered(OPT_wrap)) {
      StringRef name = arg->getValue();
      if (!seen.insert(name).second)
        continue;
  
      Symbol *sym = symtab->find(name);
      if (!sym)
        continue;
  
      Symbol *real = addUndefined(saver.save("__real_" + name));
      Symbol *wrap = addUndefined(saver.save("__wrap_" + name));
      v.push_back({sym, real, wrap});
  
      // We want to tell LTO not to inline symbols to be overwritten
      // because LTO doesn't know the final symbol contents after renaming.
      real->canInline = false;
      sym->canInline = false;
  
      // Tell LTO not to eliminate these symbols.
      sym->isUsedInRegularObj = true;
      wrap->isUsedInRegularObj = true;
    }
    return v;
  }
  
  // Do renaming for -wrap by updating pointers to symbols.
  //
  // When this function is executed, only InputFiles and symbol table
  // contain pointers to symbol objects. We visit them to replace pointers,
  // so that wrapped symbols are swapped as instructed by the command line.
  static void wrapSymbols(ArrayRef<WrappedSymbol> wrapped) {
    DenseMap<Symbol *, Symbol *> map;
    for (const WrappedSymbol &w : wrapped) {
      map[w.sym] = w.wrap;
      map[w.real] = w.sym;
    }
  
    // Update pointers in input files.
    parallelForEach(objectFiles, [&](InputFile *file) {
      MutableArrayRef<Symbol *> syms = file->getMutableSymbols();
      for (size_t i = 0, e = syms.size(); i != e; ++i)
        if (Symbol *s = map.lookup(syms[i]))
          syms[i] = s;
    });
  
    // Update pointers in the symbol table.
    for (const WrappedSymbol &w : wrapped)
      symtab->wrap(w.sym, w.real, w.wrap);
  }
  
  // To enable CET (x86's hardware-assited control flow enforcement), each
  // source file must be compiled with -fcf-protection. Object files compiled
  // with the flag contain feature flags indicating that they are compatible
  // with CET. We enable the feature only when all object files are compatible
  // with CET.
  //
  // This is also the case with AARCH64's BTI and PAC which use the similar
  // GNU_PROPERTY_AARCH64_FEATURE_1_AND mechanism.
  template <class ELFT> static uint32_t getAndFeatures() {
    if (config->emachine != EM_386 && config->emachine != EM_X86_64 &&
        config->emachine != EM_AARCH64)
      return 0;
  
    uint32_t ret = -1;
    for (InputFile *f : objectFiles) {
      uint32_t features = cast<ObjFile<ELFT>>(f)->andFeatures;
      if (config->zForceBti && !(features & GNU_PROPERTY_AARCH64_FEATURE_1_BTI)) {
        warn(toString(f) + ": -z force-bti: file does not have "
                           "GNU_PROPERTY_AARCH64_FEATURE_1_BTI property");
        features |= GNU_PROPERTY_AARCH64_FEATURE_1_BTI;
      } else if (config->zForceIbt &&
                 !(features & GNU_PROPERTY_X86_FEATURE_1_IBT)) {
        warn(toString(f) + ": -z force-ibt: file does not have "
                           "GNU_PROPERTY_X86_FEATURE_1_IBT property");
        features |= GNU_PROPERTY_X86_FEATURE_1_IBT;
      }
      if (config->zPacPlt && !(features & GNU_PROPERTY_AARCH64_FEATURE_1_PAC)) {
        warn(toString(f) + ": -z pac-plt: file does not have "
                           "GNU_PROPERTY_AARCH64_FEATURE_1_PAC property");
        features |= GNU_PROPERTY_AARCH64_FEATURE_1_PAC;
      }
      ret &= features;
    }
  
    // Force enable Shadow Stack.
    if (config->zShstk)
      ret |= GNU_PROPERTY_X86_FEATURE_1_SHSTK;
  
    return ret;
  }
  
  // Do actual linking. Note that when this function is called,
  // all linker scripts have already been parsed.
  template <class ELFT> void LinkerDriver::link(opt::InputArgList &args) {
    llvm::TimeTraceScope timeScope("Link", StringRef("LinkerDriver::Link"));
    // If a -hash-style option was not given, set to a default value,
    // which varies depending on the target.
    if (!args.hasArg(OPT_hash_style)) {
      if (config->emachine == EM_MIPS)
        config->sysvHash = true;
      else
        config->sysvHash = config->gnuHash = true;
    }
  
    // Default output filename is "a.out" by the Unix tradition.
    if (config->outputFile.empty())
      config->outputFile = "a.out";
  
    // Fail early if the output file or map file is not writable. If a user has a
    // long link, e.g. due to a large LTO link, they do not wish to run it and
    // find that it failed because there was a mistake in their command-line.
    if (auto e = tryCreateFile(config->outputFile))
      error("cannot open output file " + config->outputFile + ": " + e.message());
    if (auto e = tryCreateFile(config->mapFile))
      error("cannot open map file " + config->mapFile + ": " + e.message());
    if (errorCount())
      return;
  
    // Use default entry point name if no name was given via the command
    // line nor linker scripts. For some reason, MIPS entry point name is
    // different from others.
    config->warnMissingEntry =
        (!config->entry.empty() || (!config->shared && !config->relocatable));
    if (config->entry.empty() && !config->relocatable)
      config->entry = (config->emachine == EM_MIPS) ? "__start" : "_start";
  
    // Handle --trace-symbol.
    for (auto *arg : args.filtered(OPT_trace_symbol))
      symtab->insert(arg->getValue())->traced = true;
  
    // Add all files to the symbol table. This will add almost all
    // symbols that we need to the symbol table. This process might
    // add files to the link, via autolinking, these files are always
    // appended to the Files vector.
    {
      llvm::TimeTraceScope timeScope("Parse input files");
      for (size_t i = 0; i < files.size(); ++i)
        parseFile(files[i]);
    }
  
    // Now that we have every file, we can decide if we will need a
    // dynamic symbol table.
    // We need one if we were asked to export dynamic symbols or if we are
    // producing a shared library.
    // We also need one if any shared libraries are used and for pie executables
    // (probably because the dynamic linker needs it).
    config->hasDynSymTab =
        !sharedFiles.empty() || config->isPic || config->exportDynamic;
  
    // Some symbols (such as __ehdr_start) are defined lazily only when there
    // are undefined symbols for them, so we add these to trigger that logic.
    for (StringRef name : script->referencedSymbols)
      addUndefined(name);
  
    // Handle the `--undefined <sym>` options.
    for (StringRef arg : config->undefined)
      if (Symbol *sym = symtab->find(arg))
        handleUndefined(sym);
  
    // If an entry symbol is in a static archive, pull out that file now.
    if (Symbol *sym = symtab->find(config->entry))
      handleUndefined(sym);
  
    // Handle the `--undefined-glob <pattern>` options.
    for (StringRef pat : args::getStrings(args, OPT_undefined_glob))
      handleUndefinedGlob(pat);
  
    // Mark -init and -fini symbols so that the LTO doesn't eliminate them.
    if (Symbol *sym = symtab->find(config->init))
      sym->isUsedInRegularObj = true;
    if (Symbol *sym = symtab->find(config->fini))
      sym->isUsedInRegularObj = true;
  
    // If any of our inputs are bitcode files, the LTO code generator may create
    // references to certain library functions that might not be explicit in the
    // bitcode file's symbol table. If any of those library functions are defined
    // in a bitcode file in an archive member, we need to arrange to use LTO to
    // compile those archive members by adding them to the link beforehand.
    //
    // However, adding all libcall symbols to the link can have undesired
    // consequences. For example, the libgcc implementation of
    // __sync_val_compare_and_swap_8 on 32-bit ARM pulls in an .init_array entry
    // that aborts the program if the Linux kernel does not support 64-bit
    // atomics, which would prevent the program from running even if it does not
    // use 64-bit atomics.
    //
    // Therefore, we only add libcall symbols to the link before LTO if we have
    // to, i.e. if the symbol's definition is in bitcode. Any other required
    // libcall symbols will be added to the link after LTO when we add the LTO
    // object file to the link.
    if (!bitcodeFiles.empty())
      for (auto *s : lto::LTO::getRuntimeLibcallSymbols())
        handleLibcall(s);
  
    // Return if there were name resolution errors.
    if (errorCount())
      return;
  
    // We want to declare linker script's symbols early,
    // so that we can version them.
    // They also might be exported if referenced by DSOs.
    script->declareSymbols();
  
    // Handle the -exclude-libs option.
    if (args.hasArg(OPT_exclude_libs))
      excludeLibs(args);
  
    // Create elfHeader early. We need a dummy section in
    // addReservedSymbols to mark the created symbols as not absolute.
    Out::elfHeader = make<OutputSection>("", 0, SHF_ALLOC);
    Out::elfHeader->size = sizeof(typename ELFT::Ehdr);
  
    // Create wrapped symbols for -wrap option.
    std::vector<WrappedSymbol> wrapped = addWrappedSymbols(args);
  
    // We need to create some reserved symbols such as _end. Create them.
    if (!config->relocatable)
      addReservedSymbols();
  
    // Apply version scripts.
    //
    // For a relocatable output, version scripts don't make sense, and
    // parsing a symbol version string (e.g. dropping "@ver1" from a symbol
    // name "foo@ver1") rather do harm, so we don't call this if -r is given.
    if (!config->relocatable)
      symtab->scanVersionScript();
  
    // Do link-time optimization if given files are LLVM bitcode files.
    // This compiles bitcode files into real object files.
    //
    // With this the symbol table should be complete. After this, no new names
    // except a few linker-synthesized ones will be added to the symbol table.
    compileBitcodeFiles<ELFT>();
  
    // Symbol resolution finished. Report backward reference problems.
    reportBackrefs();
    if (errorCount())
      return;
  
    // If -thinlto-index-only is given, we should create only "index
    // files" and not object files. Index file creation is already done
    // in addCombinedLTOObject, so we are done if that's the case.
    if (config->thinLTOIndexOnly)
      return;
  
    // Likewise, --plugin-opt=emit-llvm is an option to make LTO create
    // an output file in bitcode and exit, so that you can just get a
    // combined bitcode file.
    if (config->emitLLVM)
      return;
  
    // Apply symbol renames for -wrap.
    if (!wrapped.empty())
      wrapSymbols(wrapped);
  
    // Now that we have a complete list of input files.
    // Beyond this point, no new files are added.
    // Aggregate all input sections into one place.
    for (InputFile *f : objectFiles)
      for (InputSectionBase *s : f->getSections())
        if (s && s != &InputSection::discarded)
          inputSections.push_back(s);
    for (BinaryFile *f : binaryFiles)
      for (InputSectionBase *s : f->getSections())
        inputSections.push_back(cast<InputSection>(s));
  
    llvm::erase_if(inputSections, [](InputSectionBase *s) {
      if (s->type == SHT_LLVM_SYMPART) {
        readSymbolPartitionSection<ELFT>(s);
        return true;
      }
  
      // We do not want to emit debug sections if --strip-all
      // or -strip-debug are given.
      if (config->strip == StripPolicy::None)
        return false;
  
      if (isDebugSection(*s))
        return true;
      if (auto *isec = dyn_cast<InputSection>(s))
        if (InputSectionBase *rel = isec->getRelocatedSection())
          if (isDebugSection(*rel))
            return true;
  
      return false;
    });
  
    // Now that the number of partitions is fixed, save a pointer to the main
    // partition.
    mainPart = &partitions[0];
  
    // Read .note.gnu.property sections from input object files which
    // contain a hint to tweak linker's and loader's behaviors.
    config->andFeatures = getAndFeatures<ELFT>();
  
    // The Target instance handles target-specific stuff, such as applying
    // relocations or writing a PLT section. It also contains target-dependent
    // values such as a default image base address.
    target = getTarget();
  
    config->eflags = target->calcEFlags();
    // maxPageSize (sometimes called abi page size) is the maximum page size that
    // the output can be run on. For example if the OS can use 4k or 64k page
    // sizes then maxPageSize must be 64k for the output to be useable on both.
    // All important alignment decisions must use this value.
    config->maxPageSize = getMaxPageSize(args);
    // commonPageSize is the most common page size that the output will be run on.
    // For example if an OS can use 4k or 64k page sizes and 4k is more common
    // than 64k then commonPageSize is set to 4k. commonPageSize can be used for
    // optimizations such as DATA_SEGMENT_ALIGN in linker scripts. LLD's use of it
    // is limited to writing trap instructions on the last executable segment.
    config->commonPageSize = getCommonPageSize(args);
  
    config->imageBase = getImageBase(args);
  
    if (config->emachine == EM_ARM) {
      // FIXME: These warnings can be removed when lld only uses these features
      // when the input objects have been compiled with an architecture that
      // supports them.
      if (config->armHasBlx == false)
        warn("lld uses blx instruction, no object with architecture supporting "
             "feature detected");
    }
  
    // This adds a .comment section containing a version string.
    if (!config->relocatable)
      inputSections.push_back(createCommentSection());
  
    // Replace common symbols with regular symbols.
    replaceCommonSymbols();
  
    // Split SHF_MERGE and .eh_frame sections into pieces in preparation for garbage collection.
    splitSections<ELFT>();
  
    // Garbage collection and removal of shared symbols from unused shared objects.
    markLive<ELFT>();
    demoteSharedSymbols();
  
    // Make copies of any input sections that need to be copied into each
    // partition.
    copySectionsIntoPartitions();
  
    // Create synthesized sections such as .got and .plt. This is called before
    // processSectionCommands() so that they can be placed by SECTIONS commands.
    createSyntheticSections<ELFT>();
  
    // Some input sections that are used for exception handling need to be moved
    // into synthetic sections. Do that now so that they aren't assigned to
    // output sections in the usual way.
    if (!config->relocatable)
      combineEhSections();
  
    // Create output sections described by SECTIONS commands.
    script->processSectionCommands();
  
    // Linker scripts control how input sections are assigned to output sections.
    // Input sections that were not handled by scripts are called "orphans", and
    // they are assigned to output sections by the default rule. Process that.
    script->addOrphanSections();
  
    // Migrate InputSectionDescription::sectionBases to sections. This includes
    // merging MergeInputSections into a single MergeSyntheticSection. From this
    // point onwards InputSectionDescription::sections should be used instead of
    // sectionBases.
    for (BaseCommand *base : script->sectionCommands)
      if (auto *sec = dyn_cast<OutputSection>(base))
        sec->finalizeInputSections();
    llvm::erase_if(inputSections,
                   [](InputSectionBase *s) { return isa<MergeInputSection>(s); });
  
    // Two input sections with different output sections should not be folded.
    // ICF runs after processSectionCommands() so that we know the output sections.
    if (config->icf != ICFLevel::None) {
      findKeepUniqueSections<ELFT>(args);
      doIcf<ELFT>();
    }
  
    // Read the callgraph now that we know what was gced or icfed
    if (config->callGraphProfileSort) {
      if (auto *arg = args.getLastArg(OPT_call_graph_ordering_file))
        if (Optional<MemoryBufferRef> buffer = readFile(arg->getValue()))
          readCallGraph(*buffer);
      readCallGraphsFromObjectFiles<ELFT>();
    }
  
    // Write the result to the file.
    writeResult<ELFT>();
  }
  
  } // namespace elf
  } // namespace lld
  