--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lld/ELF/Driver.cpp	Thu Feb 13 15:10:13 2020 +0900
@@ -0,0 +1,2048 @@
+//===- 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();
+
+  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->pacPlt)
+      error("-z pac-plt only supported on AArch64");
+    if (config->forceBTI)
+      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) {
+    // Write the result of the time trace profiler.
+    std::string path = args.getLastArgValue(OPT_time_trace_file_eq).str();
+    if (path.empty())
+      path = (config->outputFile + ".time-trace").str();
+    std::error_code ec;
+    raw_fd_ostream os(path, ec, sys::fs::OF_Text);
+    if (ec) {
+      error("cannot open " + path + ": " + ec.message());
+      return;
+    }
+    timeTraceProfilerWrite(os);
+    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);
+  threadsEnabled = args.hasFlag(OPT_threads, OPT_no_threads, true);
+
+  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->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->forceBTI = hasZOption(args, "force-bti");
+  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->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->pacPlt = hasZOption(args, "pac-plt");
+  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);
+  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->thinLTOJobs = args::getInteger(args, OPT_thinlto_jobs, -1u);
+  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->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->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->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 (auto *arg : args.filtered(OPT_plugin_opt))
+    parseClangOption(arg->getValue(), arg->getSpelling());
+
+  // Parse -mllvm options.
+  for (auto *arg : args.filtered(OPT_mllvm))
+    parseClangOption(arg->getValue(), arg->getSpelling());
+
+  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 (config->thinLTOJobs == 0)
+    error("--thinlto-jobs: number of threads must be > 0");
+
+  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;
+
+  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->forceBTI && !(features & GNU_PROPERTY_AARCH64_FEATURE_1_BTI)) {
+      warn(toString(f) + ": -z force-bti: file does not have 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;
+    }
+    ret &= features;
+  }
+
+  // Force enable pointer authentication Plt, we don't warn in this case as
+  // this does not require support in the object for correctness.
+  if (config->pacPlt)
+    ret |= GNU_PROPERTY_AARCH64_FEATURE_1_PAC;
+  // 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>();
+  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.
+    return config->strip != StripPolicy::None &&
+           (s->name.startswith(".debug") || s->name.startswith(".zdebug"));
+  });
+
+  // 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