--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lld/ELF/Writer.cpp	Thu Feb 13 15:10:13 2020 +0900
@@ -0,0 +1,2739 @@
+//===- Writer.cpp ---------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "Writer.h"
+#include "AArch64ErrataFix.h"
+#include "ARMErrataFix.h"
+#include "CallGraphSort.h"
+#include "Config.h"
+#include "LinkerScript.h"
+#include "MapFile.h"
+#include "OutputSections.h"
+#include "Relocations.h"
+#include "SymbolTable.h"
+#include "Symbols.h"
+#include "SyntheticSections.h"
+#include "Target.h"
+#include "lld/Common/Filesystem.h"
+#include "lld/Common/Memory.h"
+#include "lld/Common/Strings.h"
+#include "lld/Common/Threads.h"
+#include "llvm/ADT/StringMap.h"
+#include "llvm/ADT/StringSwitch.h"
+#include "llvm/Support/RandomNumberGenerator.h"
+#include "llvm/Support/SHA1.h"
+#include "llvm/Support/TimeProfiler.h"
+#include "llvm/Support/xxhash.h"
+#include <climits>
+
+using namespace llvm;
+using namespace llvm::ELF;
+using namespace llvm::object;
+using namespace llvm::support;
+using namespace llvm::support::endian;
+
+namespace lld {
+namespace elf {
+namespace {
+// The writer writes a SymbolTable result to a file.
+template <class ELFT> class Writer {
+public:
+  Writer() : buffer(errorHandler().outputBuffer) {}
+  using Elf_Shdr = typename ELFT::Shdr;
+  using Elf_Ehdr = typename ELFT::Ehdr;
+  using Elf_Phdr = typename ELFT::Phdr;
+
+  void run();
+
+private:
+  void copyLocalSymbols();
+  void addSectionSymbols();
+  void forEachRelSec(llvm::function_ref<void(InputSectionBase &)> fn);
+  void sortSections();
+  void resolveShfLinkOrder();
+  void finalizeAddressDependentContent();
+  void sortInputSections();
+  void finalizeSections();
+  void checkExecuteOnly();
+  void setReservedSymbolSections();
+
+  std::vector<PhdrEntry *> createPhdrs(Partition &part);
+  void addPhdrForSection(Partition &part, unsigned shType, unsigned pType,
+                         unsigned pFlags);
+  void assignFileOffsets();
+  void assignFileOffsetsBinary();
+  void setPhdrs(Partition &part);
+  void checkSections();
+  void fixSectionAlignments();
+  void openFile();
+  void writeTrapInstr();
+  void writeHeader();
+  void writeSections();
+  void writeSectionsBinary();
+  void writeBuildId();
+
+  std::unique_ptr<FileOutputBuffer> &buffer;
+
+  void addRelIpltSymbols();
+  void addStartEndSymbols();
+  void addStartStopSymbols(OutputSection *sec);
+
+  uint64_t fileSize;
+  uint64_t sectionHeaderOff;
+};
+} // anonymous namespace
+
+static bool isSectionPrefix(StringRef prefix, StringRef name) {
+  return name.startswith(prefix) || name == prefix.drop_back();
+}
+
+StringRef getOutputSectionName(const InputSectionBase *s) {
+  if (config->relocatable)
+    return s->name;
+
+  // This is for --emit-relocs. If .text.foo is emitted as .text.bar, we want
+  // to emit .rela.text.foo as .rela.text.bar for consistency (this is not
+  // technically required, but not doing it is odd). This code guarantees that.
+  if (auto *isec = dyn_cast<InputSection>(s)) {
+    if (InputSectionBase *rel = isec->getRelocatedSection()) {
+      OutputSection *out = rel->getOutputSection();
+      if (s->type == SHT_RELA)
+        return saver.save(".rela" + out->name);
+      return saver.save(".rel" + out->name);
+    }
+  }
+
+  // This check is for -z keep-text-section-prefix.  This option separates text
+  // sections with prefix ".text.hot", ".text.unlikely", ".text.startup" or
+  // ".text.exit".
+  // When enabled, this allows identifying the hot code region (.text.hot) in
+  // the final binary which can be selectively mapped to huge pages or mlocked,
+  // for instance.
+  if (config->zKeepTextSectionPrefix)
+    for (StringRef v :
+         {".text.hot.", ".text.unlikely.", ".text.startup.", ".text.exit."})
+      if (isSectionPrefix(v, s->name))
+        return v.drop_back();
+
+  for (StringRef v :
+       {".text.", ".rodata.", ".data.rel.ro.", ".data.", ".bss.rel.ro.",
+        ".bss.", ".init_array.", ".fini_array.", ".ctors.", ".dtors.", ".tbss.",
+        ".gcc_except_table.", ".tdata.", ".ARM.exidx.", ".ARM.extab."})
+    if (isSectionPrefix(v, s->name))
+      return v.drop_back();
+
+  // CommonSection is identified as "COMMON" in linker scripts.
+  // By default, it should go to .bss section.
+  if (s->name == "COMMON")
+    return ".bss";
+
+  return s->name;
+}
+
+static bool needsInterpSection() {
+  return !config->relocatable && !config->shared &&
+         !config->dynamicLinker.empty() && script->needsInterpSection();
+}
+
+template <class ELFT> void writeResult() {
+  llvm::TimeTraceScope timeScope("Write output file");
+  Writer<ELFT>().run();
+}
+
+static void removeEmptyPTLoad(std::vector<PhdrEntry *> &phdrs) {
+  llvm::erase_if(phdrs, [&](const PhdrEntry *p) {
+    if (p->p_type != PT_LOAD)
+      return false;
+    if (!p->firstSec)
+      return true;
+    uint64_t size = p->lastSec->addr + p->lastSec->size - p->firstSec->addr;
+    return size == 0;
+  });
+}
+
+void copySectionsIntoPartitions() {
+  std::vector<InputSectionBase *> newSections;
+  for (unsigned part = 2; part != partitions.size() + 1; ++part) {
+    for (InputSectionBase *s : inputSections) {
+      if (!(s->flags & SHF_ALLOC) || !s->isLive())
+        continue;
+      InputSectionBase *copy;
+      if (s->type == SHT_NOTE)
+        copy = make<InputSection>(cast<InputSection>(*s));
+      else if (auto *es = dyn_cast<EhInputSection>(s))
+        copy = make<EhInputSection>(*es);
+      else
+        continue;
+      copy->partition = part;
+      newSections.push_back(copy);
+    }
+  }
+
+  inputSections.insert(inputSections.end(), newSections.begin(),
+                       newSections.end());
+}
+
+void combineEhSections() {
+  for (InputSectionBase *&s : inputSections) {
+    // Ignore dead sections and the partition end marker (.part.end),
+    // whose partition number is out of bounds.
+    if (!s->isLive() || s->partition == 255)
+      continue;
+
+    Partition &part = s->getPartition();
+    if (auto *es = dyn_cast<EhInputSection>(s)) {
+      part.ehFrame->addSection(es);
+      s = nullptr;
+    } else if (s->kind() == SectionBase::Regular && part.armExidx &&
+               part.armExidx->addSection(cast<InputSection>(s))) {
+      s = nullptr;
+    }
+  }
+
+  std::vector<InputSectionBase *> &v = inputSections;
+  v.erase(std::remove(v.begin(), v.end(), nullptr), v.end());
+}
+
+static Defined *addOptionalRegular(StringRef name, SectionBase *sec,
+                                   uint64_t val, uint8_t stOther = STV_HIDDEN,
+                                   uint8_t binding = STB_GLOBAL) {
+  Symbol *s = symtab->find(name);
+  if (!s || s->isDefined())
+    return nullptr;
+
+  s->resolve(Defined{/*file=*/nullptr, name, binding, stOther, STT_NOTYPE, val,
+                     /*size=*/0, sec});
+  return cast<Defined>(s);
+}
+
+static Defined *addAbsolute(StringRef name) {
+  Symbol *sym = symtab->addSymbol(Defined{nullptr, name, STB_GLOBAL, STV_HIDDEN,
+                                          STT_NOTYPE, 0, 0, nullptr});
+  return cast<Defined>(sym);
+}
+
+// The linker is expected to define some symbols depending on
+// the linking result. This function defines such symbols.
+void addReservedSymbols() {
+  if (config->emachine == EM_MIPS) {
+    // Define _gp for MIPS. st_value of _gp symbol will be updated by Writer
+    // so that it points to an absolute address which by default is relative
+    // to GOT. Default offset is 0x7ff0.
+    // See "Global Data Symbols" in Chapter 6 in the following document:
+    // ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
+    ElfSym::mipsGp = addAbsolute("_gp");
+
+    // On MIPS O32 ABI, _gp_disp is a magic symbol designates offset between
+    // start of function and 'gp' pointer into GOT.
+    if (symtab->find("_gp_disp"))
+      ElfSym::mipsGpDisp = addAbsolute("_gp_disp");
+
+    // The __gnu_local_gp is a magic symbol equal to the current value of 'gp'
+    // pointer. This symbol is used in the code generated by .cpload pseudo-op
+    // in case of using -mno-shared option.
+    // https://sourceware.org/ml/binutils/2004-12/msg00094.html
+    if (symtab->find("__gnu_local_gp"))
+      ElfSym::mipsLocalGp = addAbsolute("__gnu_local_gp");
+  } else if (config->emachine == EM_PPC) {
+    // glibc *crt1.o has a undefined reference to _SDA_BASE_. Since we don't
+    // support Small Data Area, define it arbitrarily as 0.
+    addOptionalRegular("_SDA_BASE_", nullptr, 0, STV_HIDDEN);
+  }
+
+  // The Power Architecture 64-bit v2 ABI defines a TableOfContents (TOC) which
+  // combines the typical ELF GOT with the small data sections. It commonly
+  // includes .got .toc .sdata .sbss. The .TOC. symbol replaces both
+  // _GLOBAL_OFFSET_TABLE_ and _SDA_BASE_ from the 32-bit ABI. It is used to
+  // represent the TOC base which is offset by 0x8000 bytes from the start of
+  // the .got section.
+  // We do not allow _GLOBAL_OFFSET_TABLE_ to be defined by input objects as the
+  // correctness of some relocations depends on its value.
+  StringRef gotSymName =
+      (config->emachine == EM_PPC64) ? ".TOC." : "_GLOBAL_OFFSET_TABLE_";
+
+  if (Symbol *s = symtab->find(gotSymName)) {
+    if (s->isDefined()) {
+      error(toString(s->file) + " cannot redefine linker defined symbol '" +
+            gotSymName + "'");
+      return;
+    }
+
+    uint64_t gotOff = 0;
+    if (config->emachine == EM_PPC64)
+      gotOff = 0x8000;
+
+    s->resolve(Defined{/*file=*/nullptr, gotSymName, STB_GLOBAL, STV_HIDDEN,
+                       STT_NOTYPE, gotOff, /*size=*/0, Out::elfHeader});
+    ElfSym::globalOffsetTable = cast<Defined>(s);
+  }
+
+  // __ehdr_start is the location of ELF file headers. Note that we define
+  // this symbol unconditionally even when using a linker script, which
+  // differs from the behavior implemented by GNU linker which only define
+  // this symbol if ELF headers are in the memory mapped segment.
+  addOptionalRegular("__ehdr_start", Out::elfHeader, 0, STV_HIDDEN);
+
+  // __executable_start is not documented, but the expectation of at
+  // least the Android libc is that it points to the ELF header.
+  addOptionalRegular("__executable_start", Out::elfHeader, 0, STV_HIDDEN);
+
+  // __dso_handle symbol is passed to cxa_finalize as a marker to identify
+  // each DSO. The address of the symbol doesn't matter as long as they are
+  // different in different DSOs, so we chose the start address of the DSO.
+  addOptionalRegular("__dso_handle", Out::elfHeader, 0, STV_HIDDEN);
+
+  // If linker script do layout we do not need to create any standard symbols.
+  if (script->hasSectionsCommand)
+    return;
+
+  auto add = [](StringRef s, int64_t pos) {
+    return addOptionalRegular(s, Out::elfHeader, pos, STV_DEFAULT);
+  };
+
+  ElfSym::bss = add("__bss_start", 0);
+  ElfSym::end1 = add("end", -1);
+  ElfSym::end2 = add("_end", -1);
+  ElfSym::etext1 = add("etext", -1);
+  ElfSym::etext2 = add("_etext", -1);
+  ElfSym::edata1 = add("edata", -1);
+  ElfSym::edata2 = add("_edata", -1);
+}
+
+static OutputSection *findSection(StringRef name, unsigned partition = 1) {
+  for (BaseCommand *base : script->sectionCommands)
+    if (auto *sec = dyn_cast<OutputSection>(base))
+      if (sec->name == name && sec->partition == partition)
+        return sec;
+  return nullptr;
+}
+
+template <class ELFT> void createSyntheticSections() {
+  // Initialize all pointers with NULL. This is needed because
+  // you can call lld::elf::main more than once as a library.
+  memset(&Out::first, 0, sizeof(Out));
+
+  // Add the .interp section first because it is not a SyntheticSection.
+  // The removeUnusedSyntheticSections() function relies on the
+  // SyntheticSections coming last.
+  if (needsInterpSection()) {
+    for (size_t i = 1; i <= partitions.size(); ++i) {
+      InputSection *sec = createInterpSection();
+      sec->partition = i;
+      inputSections.push_back(sec);
+    }
+  }
+
+  auto add = [](SyntheticSection *sec) { inputSections.push_back(sec); };
+
+  in.shStrTab = make<StringTableSection>(".shstrtab", false);
+
+  Out::programHeaders = make<OutputSection>("", 0, SHF_ALLOC);
+  Out::programHeaders->alignment = config->wordsize;
+
+  if (config->strip != StripPolicy::All) {
+    in.strTab = make<StringTableSection>(".strtab", false);
+    in.symTab = make<SymbolTableSection<ELFT>>(*in.strTab);
+    in.symTabShndx = make<SymtabShndxSection>();
+  }
+
+  in.bss = make<BssSection>(".bss", 0, 1);
+  add(in.bss);
+
+  // If there is a SECTIONS command and a .data.rel.ro section name use name
+  // .data.rel.ro.bss so that we match in the .data.rel.ro output section.
+  // This makes sure our relro is contiguous.
+  bool hasDataRelRo =
+      script->hasSectionsCommand && findSection(".data.rel.ro", 0);
+  in.bssRelRo =
+      make<BssSection>(hasDataRelRo ? ".data.rel.ro.bss" : ".bss.rel.ro", 0, 1);
+  add(in.bssRelRo);
+
+  // Add MIPS-specific sections.
+  if (config->emachine == EM_MIPS) {
+    if (!config->shared && config->hasDynSymTab) {
+      in.mipsRldMap = make<MipsRldMapSection>();
+      add(in.mipsRldMap);
+    }
+    if (auto *sec = MipsAbiFlagsSection<ELFT>::create())
+      add(sec);
+    if (auto *sec = MipsOptionsSection<ELFT>::create())
+      add(sec);
+    if (auto *sec = MipsReginfoSection<ELFT>::create())
+      add(sec);
+  }
+
+  StringRef relaDynName = config->isRela ? ".rela.dyn" : ".rel.dyn";
+
+  for (Partition &part : partitions) {
+    auto add = [&](SyntheticSection *sec) {
+      sec->partition = part.getNumber();
+      inputSections.push_back(sec);
+    };
+
+    if (!part.name.empty()) {
+      part.elfHeader = make<PartitionElfHeaderSection<ELFT>>();
+      part.elfHeader->name = part.name;
+      add(part.elfHeader);
+
+      part.programHeaders = make<PartitionProgramHeadersSection<ELFT>>();
+      add(part.programHeaders);
+    }
+
+    if (config->buildId != BuildIdKind::None) {
+      part.buildId = make<BuildIdSection>();
+      add(part.buildId);
+    }
+
+    part.dynStrTab = make<StringTableSection>(".dynstr", true);
+    part.dynSymTab = make<SymbolTableSection<ELFT>>(*part.dynStrTab);
+    part.dynamic = make<DynamicSection<ELFT>>();
+    if (config->androidPackDynRelocs)
+      part.relaDyn = make<AndroidPackedRelocationSection<ELFT>>(relaDynName);
+    else
+      part.relaDyn =
+          make<RelocationSection<ELFT>>(relaDynName, config->zCombreloc);
+
+    if (config->hasDynSymTab) {
+      part.dynSymTab = make<SymbolTableSection<ELFT>>(*part.dynStrTab);
+      add(part.dynSymTab);
+
+      part.verSym = make<VersionTableSection>();
+      add(part.verSym);
+
+      if (!namedVersionDefs().empty()) {
+        part.verDef = make<VersionDefinitionSection>();
+        add(part.verDef);
+      }
+
+      part.verNeed = make<VersionNeedSection<ELFT>>();
+      add(part.verNeed);
+
+      if (config->gnuHash) {
+        part.gnuHashTab = make<GnuHashTableSection>();
+        add(part.gnuHashTab);
+      }
+
+      if (config->sysvHash) {
+        part.hashTab = make<HashTableSection>();
+        add(part.hashTab);
+      }
+
+      add(part.dynamic);
+      add(part.dynStrTab);
+      add(part.relaDyn);
+    }
+
+    if (config->relrPackDynRelocs) {
+      part.relrDyn = make<RelrSection<ELFT>>();
+      add(part.relrDyn);
+    }
+
+    if (!config->relocatable) {
+      if (config->ehFrameHdr) {
+        part.ehFrameHdr = make<EhFrameHeader>();
+        add(part.ehFrameHdr);
+      }
+      part.ehFrame = make<EhFrameSection>();
+      add(part.ehFrame);
+    }
+
+    if (config->emachine == EM_ARM && !config->relocatable) {
+      // The ARMExidxsyntheticsection replaces all the individual .ARM.exidx
+      // InputSections.
+      part.armExidx = make<ARMExidxSyntheticSection>();
+      add(part.armExidx);
+    }
+  }
+
+  if (partitions.size() != 1) {
+    // Create the partition end marker. This needs to be in partition number 255
+    // so that it is sorted after all other partitions. It also has other
+    // special handling (see createPhdrs() and combineEhSections()).
+    in.partEnd = make<BssSection>(".part.end", config->maxPageSize, 1);
+    in.partEnd->partition = 255;
+    add(in.partEnd);
+
+    in.partIndex = make<PartitionIndexSection>();
+    addOptionalRegular("__part_index_begin", in.partIndex, 0);
+    addOptionalRegular("__part_index_end", in.partIndex,
+                       in.partIndex->getSize());
+    add(in.partIndex);
+  }
+
+  // Add .got. MIPS' .got is so different from the other archs,
+  // it has its own class.
+  if (config->emachine == EM_MIPS) {
+    in.mipsGot = make<MipsGotSection>();
+    add(in.mipsGot);
+  } else {
+    in.got = make<GotSection>();
+    add(in.got);
+  }
+
+  if (config->emachine == EM_PPC) {
+    in.ppc32Got2 = make<PPC32Got2Section>();
+    add(in.ppc32Got2);
+  }
+
+  if (config->emachine == EM_PPC64) {
+    in.ppc64LongBranchTarget = make<PPC64LongBranchTargetSection>();
+    add(in.ppc64LongBranchTarget);
+  }
+
+  in.gotPlt = make<GotPltSection>();
+  add(in.gotPlt);
+  in.igotPlt = make<IgotPltSection>();
+  add(in.igotPlt);
+
+  // _GLOBAL_OFFSET_TABLE_ is defined relative to either .got.plt or .got. Treat
+  // it as a relocation and ensure the referenced section is created.
+  if (ElfSym::globalOffsetTable && config->emachine != EM_MIPS) {
+    if (target->gotBaseSymInGotPlt)
+      in.gotPlt->hasGotPltOffRel = true;
+    else
+      in.got->hasGotOffRel = true;
+  }
+
+  if (config->gdbIndex)
+    add(GdbIndexSection::create<ELFT>());
+
+  // We always need to add rel[a].plt to output if it has entries.
+  // Even for static linking it can contain R_[*]_IRELATIVE relocations.
+  in.relaPlt = make<RelocationSection<ELFT>>(
+      config->isRela ? ".rela.plt" : ".rel.plt", /*sort=*/false);
+  add(in.relaPlt);
+
+  // The relaIplt immediately follows .rel[a].dyn to ensure that the IRelative
+  // relocations are processed last by the dynamic loader. We cannot place the
+  // iplt section in .rel.dyn when Android relocation packing is enabled because
+  // that would cause a section type mismatch. However, because the Android
+  // dynamic loader reads .rel.plt after .rel.dyn, we can get the desired
+  // behaviour by placing the iplt section in .rel.plt.
+  in.relaIplt = make<RelocationSection<ELFT>>(
+      config->androidPackDynRelocs ? in.relaPlt->name : relaDynName,
+      /*sort=*/false);
+  add(in.relaIplt);
+
+  if ((config->emachine == EM_386 || config->emachine == EM_X86_64) &&
+      (config->andFeatures & GNU_PROPERTY_X86_FEATURE_1_IBT)) {
+    in.ibtPlt = make<IBTPltSection>();
+    add(in.ibtPlt);
+  }
+
+  in.plt = make<PltSection>();
+  add(in.plt);
+  in.iplt = make<IpltSection>();
+  add(in.iplt);
+
+  if (config->andFeatures)
+    add(make<GnuPropertySection>());
+
+  // .note.GNU-stack is always added when we are creating a re-linkable
+  // object file. Other linkers are using the presence of this marker
+  // section to control the executable-ness of the stack area, but that
+  // is irrelevant these days. Stack area should always be non-executable
+  // by default. So we emit this section unconditionally.
+  if (config->relocatable)
+    add(make<GnuStackSection>());
+
+  if (in.symTab)
+    add(in.symTab);
+  if (in.symTabShndx)
+    add(in.symTabShndx);
+  add(in.shStrTab);
+  if (in.strTab)
+    add(in.strTab);
+}
+
+// The main function of the writer.
+template <class ELFT> void Writer<ELFT>::run() {
+  if (config->discard != DiscardPolicy::All)
+    copyLocalSymbols();
+
+  if (config->copyRelocs)
+    addSectionSymbols();
+
+  // Now that we have a complete set of output sections. This function
+  // completes section contents. For example, we need to add strings
+  // to the string table, and add entries to .got and .plt.
+  // finalizeSections does that.
+  finalizeSections();
+  checkExecuteOnly();
+  if (errorCount())
+    return;
+
+  // If -compressed-debug-sections is specified, we need to compress
+  // .debug_* sections. Do it right now because it changes the size of
+  // output sections.
+  for (OutputSection *sec : outputSections)
+    sec->maybeCompress<ELFT>();
+
+  if (script->hasSectionsCommand)
+    script->allocateHeaders(mainPart->phdrs);
+
+  // Remove empty PT_LOAD to avoid causing the dynamic linker to try to mmap a
+  // 0 sized region. This has to be done late since only after assignAddresses
+  // we know the size of the sections.
+  for (Partition &part : partitions)
+    removeEmptyPTLoad(part.phdrs);
+
+  if (!config->oFormatBinary)
+    assignFileOffsets();
+  else
+    assignFileOffsetsBinary();
+
+  for (Partition &part : partitions)
+    setPhdrs(part);
+
+  if (config->relocatable)
+    for (OutputSection *sec : outputSections)
+      sec->addr = 0;
+
+  if (config->checkSections)
+    checkSections();
+
+  // It does not make sense try to open the file if we have error already.
+  if (errorCount())
+    return;
+  // Write the result down to a file.
+  openFile();
+  if (errorCount())
+    return;
+
+  if (!config->oFormatBinary) {
+    if (config->zSeparate != SeparateSegmentKind::None)
+      writeTrapInstr();
+    writeHeader();
+    writeSections();
+  } else {
+    writeSectionsBinary();
+  }
+
+  // Backfill .note.gnu.build-id section content. This is done at last
+  // because the content is usually a hash value of the entire output file.
+  writeBuildId();
+  if (errorCount())
+    return;
+
+  // Handle -Map and -cref options.
+  writeMapFile();
+  writeCrossReferenceTable();
+  if (errorCount())
+    return;
+
+  if (auto e = buffer->commit())
+    error("failed to write to the output file: " + toString(std::move(e)));
+}
+
+static bool shouldKeepInSymtab(const Defined &sym) {
+  if (sym.isSection())
+    return false;
+
+  if (config->discard == DiscardPolicy::None)
+    return true;
+
+  // If -emit-reloc is given, all symbols including local ones need to be
+  // copied because they may be referenced by relocations.
+  if (config->emitRelocs)
+    return true;
+
+  // In ELF assembly .L symbols are normally discarded by the assembler.
+  // If the assembler fails to do so, the linker discards them if
+  // * --discard-locals is used.
+  // * The symbol is in a SHF_MERGE section, which is normally the reason for
+  //   the assembler keeping the .L symbol.
+  StringRef name = sym.getName();
+  bool isLocal = name.startswith(".L") || name.empty();
+  if (!isLocal)
+    return true;
+
+  if (config->discard == DiscardPolicy::Locals)
+    return false;
+
+  SectionBase *sec = sym.section;
+  return !sec || !(sec->flags & SHF_MERGE);
+}
+
+static bool includeInSymtab(const Symbol &b) {
+  if (!b.isLocal() && !b.isUsedInRegularObj)
+    return false;
+
+  if (auto *d = dyn_cast<Defined>(&b)) {
+    // Always include absolute symbols.
+    SectionBase *sec = d->section;
+    if (!sec)
+      return true;
+    sec = sec->repl;
+
+    // Exclude symbols pointing to garbage-collected sections.
+    if (isa<InputSectionBase>(sec) && !sec->isLive())
+      return false;
+
+    if (auto *s = dyn_cast<MergeInputSection>(sec))
+      if (!s->getSectionPiece(d->value)->live)
+        return false;
+    return true;
+  }
+  return b.used;
+}
+
+// Local symbols are not in the linker's symbol table. This function scans
+// each object file's symbol table to copy local symbols to the output.
+template <class ELFT> void Writer<ELFT>::copyLocalSymbols() {
+  if (!in.symTab)
+    return;
+  for (InputFile *file : objectFiles) {
+    ObjFile<ELFT> *f = cast<ObjFile<ELFT>>(file);
+    for (Symbol *b : f->getLocalSymbols()) {
+      if (!b->isLocal())
+        fatal(toString(f) +
+              ": broken object: getLocalSymbols returns a non-local symbol");
+      auto *dr = dyn_cast<Defined>(b);
+
+      // No reason to keep local undefined symbol in symtab.
+      if (!dr)
+        continue;
+      if (!includeInSymtab(*b))
+        continue;
+      if (!shouldKeepInSymtab(*dr))
+        continue;
+      in.symTab->addSymbol(b);
+    }
+  }
+}
+
+// Create a section symbol for each output section so that we can represent
+// relocations that point to the section. If we know that no relocation is
+// referring to a section (that happens if the section is a synthetic one), we
+// don't create a section symbol for that section.
+template <class ELFT> void Writer<ELFT>::addSectionSymbols() {
+  for (BaseCommand *base : script->sectionCommands) {
+    auto *sec = dyn_cast<OutputSection>(base);
+    if (!sec)
+      continue;
+    auto i = llvm::find_if(sec->sectionCommands, [](BaseCommand *base) {
+      if (auto *isd = dyn_cast<InputSectionDescription>(base))
+        return !isd->sections.empty();
+      return false;
+    });
+    if (i == sec->sectionCommands.end())
+      continue;
+    InputSectionBase *isec = cast<InputSectionDescription>(*i)->sections[0];
+
+    // Relocations are not using REL[A] section symbols.
+    if (isec->type == SHT_REL || isec->type == SHT_RELA)
+      continue;
+
+    // Unlike other synthetic sections, mergeable output sections contain data
+    // copied from input sections, and there may be a relocation pointing to its
+    // contents if -r or -emit-reloc are given.
+    if (isa<SyntheticSection>(isec) && !(isec->flags & SHF_MERGE))
+      continue;
+
+    auto *sym =
+        make<Defined>(isec->file, "", STB_LOCAL, /*stOther=*/0, STT_SECTION,
+                      /*value=*/0, /*size=*/0, isec);
+    in.symTab->addSymbol(sym);
+  }
+}
+
+// Today's loaders have a feature to make segments read-only after
+// processing dynamic relocations to enhance security. PT_GNU_RELRO
+// is defined for that.
+//
+// This function returns true if a section needs to be put into a
+// PT_GNU_RELRO segment.
+static bool isRelroSection(const OutputSection *sec) {
+  if (!config->zRelro)
+    return false;
+
+  uint64_t flags = sec->flags;
+
+  // Non-allocatable or non-writable sections don't need RELRO because
+  // they are not writable or not even mapped to memory in the first place.
+  // RELRO is for sections that are essentially read-only but need to
+  // be writable only at process startup to allow dynamic linker to
+  // apply relocations.
+  if (!(flags & SHF_ALLOC) || !(flags & SHF_WRITE))
+    return false;
+
+  // Once initialized, TLS data segments are used as data templates
+  // for a thread-local storage. For each new thread, runtime
+  // allocates memory for a TLS and copy templates there. No thread
+  // are supposed to use templates directly. Thus, it can be in RELRO.
+  if (flags & SHF_TLS)
+    return true;
+
+  // .init_array, .preinit_array and .fini_array contain pointers to
+  // functions that are executed on process startup or exit. These
+  // pointers are set by the static linker, and they are not expected
+  // to change at runtime. But if you are an attacker, you could do
+  // interesting things by manipulating pointers in .fini_array, for
+  // example. So they are put into RELRO.
+  uint32_t type = sec->type;
+  if (type == SHT_INIT_ARRAY || type == SHT_FINI_ARRAY ||
+      type == SHT_PREINIT_ARRAY)
+    return true;
+
+  // .got contains pointers to external symbols. They are resolved by
+  // the dynamic linker when a module is loaded into memory, and after
+  // that they are not expected to change. So, it can be in RELRO.
+  if (in.got && sec == in.got->getParent())
+    return true;
+
+  // .toc is a GOT-ish section for PowerPC64. Their contents are accessed
+  // through r2 register, which is reserved for that purpose. Since r2 is used
+  // for accessing .got as well, .got and .toc need to be close enough in the
+  // virtual address space. Usually, .toc comes just after .got. Since we place
+  // .got into RELRO, .toc needs to be placed into RELRO too.
+  if (sec->name.equals(".toc"))
+    return true;
+
+  // .got.plt contains pointers to external function symbols. They are
+  // by default resolved lazily, so we usually cannot put it into RELRO.
+  // However, if "-z now" is given, the lazy symbol resolution is
+  // disabled, which enables us to put it into RELRO.
+  if (sec == in.gotPlt->getParent())
+    return config->zNow;
+
+  // .dynamic section contains data for the dynamic linker, and
+  // there's no need to write to it at runtime, so it's better to put
+  // it into RELRO.
+  if (sec->name == ".dynamic")
+    return true;
+
+  // Sections with some special names are put into RELRO. This is a
+  // bit unfortunate because section names shouldn't be significant in
+  // ELF in spirit. But in reality many linker features depend on
+  // magic section names.
+  StringRef s = sec->name;
+  return s == ".data.rel.ro" || s == ".bss.rel.ro" || s == ".ctors" ||
+         s == ".dtors" || s == ".jcr" || s == ".eh_frame" ||
+         s == ".openbsd.randomdata";
+}
+
+// We compute a rank for each section. The rank indicates where the
+// section should be placed in the file.  Instead of using simple
+// numbers (0,1,2...), we use a series of flags. One for each decision
+// point when placing the section.
+// Using flags has two key properties:
+// * It is easy to check if a give branch was taken.
+// * It is easy two see how similar two ranks are (see getRankProximity).
+enum RankFlags {
+  RF_NOT_ADDR_SET = 1 << 27,
+  RF_NOT_ALLOC = 1 << 26,
+  RF_PARTITION = 1 << 18, // Partition number (8 bits)
+  RF_NOT_PART_EHDR = 1 << 17,
+  RF_NOT_PART_PHDR = 1 << 16,
+  RF_NOT_INTERP = 1 << 15,
+  RF_NOT_NOTE = 1 << 14,
+  RF_WRITE = 1 << 13,
+  RF_EXEC_WRITE = 1 << 12,
+  RF_EXEC = 1 << 11,
+  RF_RODATA = 1 << 10,
+  RF_NOT_RELRO = 1 << 9,
+  RF_NOT_TLS = 1 << 8,
+  RF_BSS = 1 << 7,
+  RF_PPC_NOT_TOCBSS = 1 << 6,
+  RF_PPC_TOCL = 1 << 5,
+  RF_PPC_TOC = 1 << 4,
+  RF_PPC_GOT = 1 << 3,
+  RF_PPC_BRANCH_LT = 1 << 2,
+  RF_MIPS_GPREL = 1 << 1,
+  RF_MIPS_NOT_GOT = 1 << 0
+};
+
+static unsigned getSectionRank(const OutputSection *sec) {
+  unsigned rank = sec->partition * RF_PARTITION;
+
+  // We want to put section specified by -T option first, so we
+  // can start assigning VA starting from them later.
+  if (config->sectionStartMap.count(sec->name))
+    return rank;
+  rank |= RF_NOT_ADDR_SET;
+
+  // Allocatable sections go first to reduce the total PT_LOAD size and
+  // so debug info doesn't change addresses in actual code.
+  if (!(sec->flags & SHF_ALLOC))
+    return rank | RF_NOT_ALLOC;
+
+  if (sec->type == SHT_LLVM_PART_EHDR)
+    return rank;
+  rank |= RF_NOT_PART_EHDR;
+
+  if (sec->type == SHT_LLVM_PART_PHDR)
+    return rank;
+  rank |= RF_NOT_PART_PHDR;
+
+  // Put .interp first because some loaders want to see that section
+  // on the first page of the executable file when loaded into memory.
+  if (sec->name == ".interp")
+    return rank;
+  rank |= RF_NOT_INTERP;
+
+  // Put .note sections (which make up one PT_NOTE) at the beginning so that
+  // they are likely to be included in a core file even if core file size is
+  // limited. In particular, we want a .note.gnu.build-id and a .note.tag to be
+  // included in a core to match core files with executables.
+  if (sec->type == SHT_NOTE)
+    return rank;
+  rank |= RF_NOT_NOTE;
+
+  // Sort sections based on their access permission in the following
+  // order: R, RX, RWX, RW.  This order is based on the following
+  // considerations:
+  // * Read-only sections come first such that they go in the
+  //   PT_LOAD covering the program headers at the start of the file.
+  // * Read-only, executable sections come next.
+  // * Writable, executable sections follow such that .plt on
+  //   architectures where it needs to be writable will be placed
+  //   between .text and .data.
+  // * Writable sections come last, such that .bss lands at the very
+  //   end of the last PT_LOAD.
+  bool isExec = sec->flags & SHF_EXECINSTR;
+  bool isWrite = sec->flags & SHF_WRITE;
+
+  if (isExec) {
+    if (isWrite)
+      rank |= RF_EXEC_WRITE;
+    else
+      rank |= RF_EXEC;
+  } else if (isWrite) {
+    rank |= RF_WRITE;
+  } else if (sec->type == SHT_PROGBITS) {
+    // Make non-executable and non-writable PROGBITS sections (e.g .rodata
+    // .eh_frame) closer to .text. They likely contain PC or GOT relative
+    // relocations and there could be relocation overflow if other huge sections
+    // (.dynstr .dynsym) were placed in between.
+    rank |= RF_RODATA;
+  }
+
+  // Place RelRo sections first. After considering SHT_NOBITS below, the
+  // ordering is PT_LOAD(PT_GNU_RELRO(.data.rel.ro .bss.rel.ro) | .data .bss),
+  // where | marks where page alignment happens. An alternative ordering is
+  // PT_LOAD(.data | PT_GNU_RELRO( .data.rel.ro .bss.rel.ro) | .bss), but it may
+  // waste more bytes due to 2 alignment places.
+  if (!isRelroSection(sec))
+    rank |= RF_NOT_RELRO;
+
+  // If we got here we know that both A and B are in the same PT_LOAD.
+
+  // The TLS initialization block needs to be a single contiguous block in a R/W
+  // PT_LOAD, so stick TLS sections directly before the other RelRo R/W
+  // sections. Since p_filesz can be less than p_memsz, place NOBITS sections
+  // after PROGBITS.
+  if (!(sec->flags & SHF_TLS))
+    rank |= RF_NOT_TLS;
+
+  // Within TLS sections, or within other RelRo sections, or within non-RelRo
+  // sections, place non-NOBITS sections first.
+  if (sec->type == SHT_NOBITS)
+    rank |= RF_BSS;
+
+  // Some architectures have additional ordering restrictions for sections
+  // within the same PT_LOAD.
+  if (config->emachine == EM_PPC64) {
+    // PPC64 has a number of special SHT_PROGBITS+SHF_ALLOC+SHF_WRITE sections
+    // that we would like to make sure appear is a specific order to maximize
+    // their coverage by a single signed 16-bit offset from the TOC base
+    // pointer. Conversely, the special .tocbss section should be first among
+    // all SHT_NOBITS sections. This will put it next to the loaded special
+    // PPC64 sections (and, thus, within reach of the TOC base pointer).
+    StringRef name = sec->name;
+    if (name != ".tocbss")
+      rank |= RF_PPC_NOT_TOCBSS;
+
+    if (name == ".toc1")
+      rank |= RF_PPC_TOCL;
+
+    if (name == ".toc")
+      rank |= RF_PPC_TOC;
+
+    if (name == ".got")
+      rank |= RF_PPC_GOT;
+
+    if (name == ".branch_lt")
+      rank |= RF_PPC_BRANCH_LT;
+  }
+
+  if (config->emachine == EM_MIPS) {
+    // All sections with SHF_MIPS_GPREL flag should be grouped together
+    // because data in these sections is addressable with a gp relative address.
+    if (sec->flags & SHF_MIPS_GPREL)
+      rank |= RF_MIPS_GPREL;
+
+    if (sec->name != ".got")
+      rank |= RF_MIPS_NOT_GOT;
+  }
+
+  return rank;
+}
+
+static bool compareSections(const BaseCommand *aCmd, const BaseCommand *bCmd) {
+  const OutputSection *a = cast<OutputSection>(aCmd);
+  const OutputSection *b = cast<OutputSection>(bCmd);
+
+  if (a->sortRank != b->sortRank)
+    return a->sortRank < b->sortRank;
+
+  if (!(a->sortRank & RF_NOT_ADDR_SET))
+    return config->sectionStartMap.lookup(a->name) <
+           config->sectionStartMap.lookup(b->name);
+  return false;
+}
+
+void PhdrEntry::add(OutputSection *sec) {
+  lastSec = sec;
+  if (!firstSec)
+    firstSec = sec;
+  p_align = std::max(p_align, sec->alignment);
+  if (p_type == PT_LOAD)
+    sec->ptLoad = this;
+}
+
+// The beginning and the ending of .rel[a].plt section are marked
+// with __rel[a]_iplt_{start,end} symbols if it is a statically linked
+// executable. The runtime needs these symbols in order to resolve
+// all IRELATIVE relocs on startup. For dynamic executables, we don't
+// need these symbols, since IRELATIVE relocs are resolved through GOT
+// and PLT. For details, see http://www.airs.com/blog/archives/403.
+template <class ELFT> void Writer<ELFT>::addRelIpltSymbols() {
+  if (config->relocatable || needsInterpSection())
+    return;
+
+  // By default, __rela_iplt_{start,end} belong to a dummy section 0
+  // because .rela.plt might be empty and thus removed from output.
+  // We'll override Out::elfHeader with In.relaIplt later when we are
+  // sure that .rela.plt exists in output.
+  ElfSym::relaIpltStart = addOptionalRegular(
+      config->isRela ? "__rela_iplt_start" : "__rel_iplt_start",
+      Out::elfHeader, 0, STV_HIDDEN, STB_WEAK);
+
+  ElfSym::relaIpltEnd = addOptionalRegular(
+      config->isRela ? "__rela_iplt_end" : "__rel_iplt_end",
+      Out::elfHeader, 0, STV_HIDDEN, STB_WEAK);
+}
+
+template <class ELFT>
+void Writer<ELFT>::forEachRelSec(
+    llvm::function_ref<void(InputSectionBase &)> fn) {
+  // Scan all relocations. Each relocation goes through a series
+  // of tests to determine if it needs special treatment, such as
+  // creating GOT, PLT, copy relocations, etc.
+  // Note that relocations for non-alloc sections are directly
+  // processed by InputSection::relocateNonAlloc.
+  for (InputSectionBase *isec : inputSections)
+    if (isec->isLive() && isa<InputSection>(isec) && (isec->flags & SHF_ALLOC))
+      fn(*isec);
+  for (Partition &part : partitions) {
+    for (EhInputSection *es : part.ehFrame->sections)
+      fn(*es);
+    if (part.armExidx && part.armExidx->isLive())
+      for (InputSection *ex : part.armExidx->exidxSections)
+        fn(*ex);
+  }
+}
+
+// This function generates assignments for predefined symbols (e.g. _end or
+// _etext) and inserts them into the commands sequence to be processed at the
+// appropriate time. This ensures that the value is going to be correct by the
+// time any references to these symbols are processed and is equivalent to
+// defining these symbols explicitly in the linker script.
+template <class ELFT> void Writer<ELFT>::setReservedSymbolSections() {
+  if (ElfSym::globalOffsetTable) {
+    // The _GLOBAL_OFFSET_TABLE_ symbol is defined by target convention usually
+    // to the start of the .got or .got.plt section.
+    InputSection *gotSection = in.gotPlt;
+    if (!target->gotBaseSymInGotPlt)
+      gotSection = in.mipsGot ? cast<InputSection>(in.mipsGot)
+                              : cast<InputSection>(in.got);
+    ElfSym::globalOffsetTable->section = gotSection;
+  }
+
+  // .rela_iplt_{start,end} mark the start and the end of in.relaIplt.
+  if (ElfSym::relaIpltStart && in.relaIplt->isNeeded()) {
+    ElfSym::relaIpltStart->section = in.relaIplt;
+    ElfSym::relaIpltEnd->section = in.relaIplt;
+    ElfSym::relaIpltEnd->value = in.relaIplt->getSize();
+  }
+
+  PhdrEntry *last = nullptr;
+  PhdrEntry *lastRO = nullptr;
+
+  for (Partition &part : partitions) {
+    for (PhdrEntry *p : part.phdrs) {
+      if (p->p_type != PT_LOAD)
+        continue;
+      last = p;
+      if (!(p->p_flags & PF_W))
+        lastRO = p;
+    }
+  }
+
+  if (lastRO) {
+    // _etext is the first location after the last read-only loadable segment.
+    if (ElfSym::etext1)
+      ElfSym::etext1->section = lastRO->lastSec;
+    if (ElfSym::etext2)
+      ElfSym::etext2->section = lastRO->lastSec;
+  }
+
+  if (last) {
+    // _edata points to the end of the last mapped initialized section.
+    OutputSection *edata = nullptr;
+    for (OutputSection *os : outputSections) {
+      if (os->type != SHT_NOBITS)
+        edata = os;
+      if (os == last->lastSec)
+        break;
+    }
+
+    if (ElfSym::edata1)
+      ElfSym::edata1->section = edata;
+    if (ElfSym::edata2)
+      ElfSym::edata2->section = edata;
+
+    // _end is the first location after the uninitialized data region.
+    if (ElfSym::end1)
+      ElfSym::end1->section = last->lastSec;
+    if (ElfSym::end2)
+      ElfSym::end2->section = last->lastSec;
+  }
+
+  if (ElfSym::bss)
+    ElfSym::bss->section = findSection(".bss");
+
+  // Setup MIPS _gp_disp/__gnu_local_gp symbols which should
+  // be equal to the _gp symbol's value.
+  if (ElfSym::mipsGp) {
+    // Find GP-relative section with the lowest address
+    // and use this address to calculate default _gp value.
+    for (OutputSection *os : outputSections) {
+      if (os->flags & SHF_MIPS_GPREL) {
+        ElfSym::mipsGp->section = os;
+        ElfSym::mipsGp->value = 0x7ff0;
+        break;
+      }
+    }
+  }
+}
+
+// We want to find how similar two ranks are.
+// The more branches in getSectionRank that match, the more similar they are.
+// Since each branch corresponds to a bit flag, we can just use
+// countLeadingZeros.
+static int getRankProximityAux(OutputSection *a, OutputSection *b) {
+  return countLeadingZeros(a->sortRank ^ b->sortRank);
+}
+
+static int getRankProximity(OutputSection *a, BaseCommand *b) {
+  auto *sec = dyn_cast<OutputSection>(b);
+  return (sec && sec->hasInputSections) ? getRankProximityAux(a, sec) : -1;
+}
+
+// When placing orphan sections, we want to place them after symbol assignments
+// so that an orphan after
+//   begin_foo = .;
+//   foo : { *(foo) }
+//   end_foo = .;
+// doesn't break the intended meaning of the begin/end symbols.
+// We don't want to go over sections since findOrphanPos is the
+// one in charge of deciding the order of the sections.
+// We don't want to go over changes to '.', since doing so in
+//  rx_sec : { *(rx_sec) }
+//  . = ALIGN(0x1000);
+//  /* The RW PT_LOAD starts here*/
+//  rw_sec : { *(rw_sec) }
+// would mean that the RW PT_LOAD would become unaligned.
+static bool shouldSkip(BaseCommand *cmd) {
+  if (auto *assign = dyn_cast<SymbolAssignment>(cmd))
+    return assign->name != ".";
+  return false;
+}
+
+// We want to place orphan sections so that they share as much
+// characteristics with their neighbors as possible. For example, if
+// both are rw, or both are tls.
+static std::vector<BaseCommand *>::iterator
+findOrphanPos(std::vector<BaseCommand *>::iterator b,
+              std::vector<BaseCommand *>::iterator e) {
+  OutputSection *sec = cast<OutputSection>(*e);
+
+  // Find the first element that has as close a rank as possible.
+  auto i = std::max_element(b, e, [=](BaseCommand *a, BaseCommand *b) {
+    return getRankProximity(sec, a) < getRankProximity(sec, b);
+  });
+  if (i == e)
+    return e;
+
+  // Consider all existing sections with the same proximity.
+  int proximity = getRankProximity(sec, *i);
+  for (; i != e; ++i) {
+    auto *curSec = dyn_cast<OutputSection>(*i);
+    if (!curSec || !curSec->hasInputSections)
+      continue;
+    if (getRankProximity(sec, curSec) != proximity ||
+        sec->sortRank < curSec->sortRank)
+      break;
+  }
+
+  auto isOutputSecWithInputSections = [](BaseCommand *cmd) {
+    auto *os = dyn_cast<OutputSection>(cmd);
+    return os && os->hasInputSections;
+  };
+  auto j = std::find_if(llvm::make_reverse_iterator(i),
+                        llvm::make_reverse_iterator(b),
+                        isOutputSecWithInputSections);
+  i = j.base();
+
+  // As a special case, if the orphan section is the last section, put
+  // it at the very end, past any other commands.
+  // This matches bfd's behavior and is convenient when the linker script fully
+  // specifies the start of the file, but doesn't care about the end (the non
+  // alloc sections for example).
+  auto nextSec = std::find_if(i, e, isOutputSecWithInputSections);
+  if (nextSec == e)
+    return e;
+
+  while (i != e && shouldSkip(*i))
+    ++i;
+  return i;
+}
+
+// Builds section order for handling --symbol-ordering-file.
+static DenseMap<const InputSectionBase *, int> buildSectionOrder() {
+  DenseMap<const InputSectionBase *, int> sectionOrder;
+  // Use the rarely used option -call-graph-ordering-file to sort sections.
+  if (!config->callGraphProfile.empty())
+    return computeCallGraphProfileOrder();
+
+  if (config->symbolOrderingFile.empty())
+    return sectionOrder;
+
+  struct SymbolOrderEntry {
+    int priority;
+    bool present;
+  };
+
+  // Build a map from symbols to their priorities. Symbols that didn't
+  // appear in the symbol ordering file have the lowest priority 0.
+  // All explicitly mentioned symbols have negative (higher) priorities.
+  DenseMap<StringRef, SymbolOrderEntry> symbolOrder;
+  int priority = -config->symbolOrderingFile.size();
+  for (StringRef s : config->symbolOrderingFile)
+    symbolOrder.insert({s, {priority++, false}});
+
+  // Build a map from sections to their priorities.
+  auto addSym = [&](Symbol &sym) {
+    auto it = symbolOrder.find(sym.getName());
+    if (it == symbolOrder.end())
+      return;
+    SymbolOrderEntry &ent = it->second;
+    ent.present = true;
+
+    maybeWarnUnorderableSymbol(&sym);
+
+    if (auto *d = dyn_cast<Defined>(&sym)) {
+      if (auto *sec = dyn_cast_or_null<InputSectionBase>(d->section)) {
+        int &priority = sectionOrder[cast<InputSectionBase>(sec->repl)];
+        priority = std::min(priority, ent.priority);
+      }
+    }
+  };
+
+  // We want both global and local symbols. We get the global ones from the
+  // symbol table and iterate the object files for the local ones.
+  for (Symbol *sym : symtab->symbols())
+    if (!sym->isLazy())
+      addSym(*sym);
+
+  for (InputFile *file : objectFiles)
+    for (Symbol *sym : file->getSymbols())
+      if (sym->isLocal())
+        addSym(*sym);
+
+  if (config->warnSymbolOrdering)
+    for (auto orderEntry : symbolOrder)
+      if (!orderEntry.second.present)
+        warn("symbol ordering file: no such symbol: " + orderEntry.first);
+
+  return sectionOrder;
+}
+
+// Sorts the sections in ISD according to the provided section order.
+static void
+sortISDBySectionOrder(InputSectionDescription *isd,
+                      const DenseMap<const InputSectionBase *, int> &order) {
+  std::vector<InputSection *> unorderedSections;
+  std::vector<std::pair<InputSection *, int>> orderedSections;
+  uint64_t unorderedSize = 0;
+
+  for (InputSection *isec : isd->sections) {
+    auto i = order.find(isec);
+    if (i == order.end()) {
+      unorderedSections.push_back(isec);
+      unorderedSize += isec->getSize();
+      continue;
+    }
+    orderedSections.push_back({isec, i->second});
+  }
+  llvm::sort(orderedSections, llvm::less_second());
+
+  // Find an insertion point for the ordered section list in the unordered
+  // section list. On targets with limited-range branches, this is the mid-point
+  // of the unordered section list. This decreases the likelihood that a range
+  // extension thunk will be needed to enter or exit the ordered region. If the
+  // ordered section list is a list of hot functions, we can generally expect
+  // the ordered functions to be called more often than the unordered functions,
+  // making it more likely that any particular call will be within range, and
+  // therefore reducing the number of thunks required.
+  //
+  // For example, imagine that you have 8MB of hot code and 32MB of cold code.
+  // If the layout is:
+  //
+  // 8MB hot
+  // 32MB cold
+  //
+  // only the first 8-16MB of the cold code (depending on which hot function it
+  // is actually calling) can call the hot code without a range extension thunk.
+  // However, if we use this layout:
+  //
+  // 16MB cold
+  // 8MB hot
+  // 16MB cold
+  //
+  // both the last 8-16MB of the first block of cold code and the first 8-16MB
+  // of the second block of cold code can call the hot code without a thunk. So
+  // we effectively double the amount of code that could potentially call into
+  // the hot code without a thunk.
+  size_t insPt = 0;
+  if (target->getThunkSectionSpacing() && !orderedSections.empty()) {
+    uint64_t unorderedPos = 0;
+    for (; insPt != unorderedSections.size(); ++insPt) {
+      unorderedPos += unorderedSections[insPt]->getSize();
+      if (unorderedPos > unorderedSize / 2)
+        break;
+    }
+  }
+
+  isd->sections.clear();
+  for (InputSection *isec : makeArrayRef(unorderedSections).slice(0, insPt))
+    isd->sections.push_back(isec);
+  for (std::pair<InputSection *, int> p : orderedSections)
+    isd->sections.push_back(p.first);
+  for (InputSection *isec : makeArrayRef(unorderedSections).slice(insPt))
+    isd->sections.push_back(isec);
+}
+
+static void sortSection(OutputSection *sec,
+                        const DenseMap<const InputSectionBase *, int> &order) {
+  StringRef name = sec->name;
+
+  // Sort input sections by section name suffixes for
+  // __attribute__((init_priority(N))).
+  if (name == ".init_array" || name == ".fini_array") {
+    if (!script->hasSectionsCommand)
+      sec->sortInitFini();
+    return;
+  }
+
+  // Sort input sections by the special rule for .ctors and .dtors.
+  if (name == ".ctors" || name == ".dtors") {
+    if (!script->hasSectionsCommand)
+      sec->sortCtorsDtors();
+    return;
+  }
+
+  // Never sort these.
+  if (name == ".init" || name == ".fini")
+    return;
+
+  // .toc is allocated just after .got and is accessed using GOT-relative
+  // relocations. Object files compiled with small code model have an
+  // addressable range of [.got, .got + 0xFFFC] for GOT-relative relocations.
+  // To reduce the risk of relocation overflow, .toc contents are sorted so that
+  // sections having smaller relocation offsets are at beginning of .toc
+  if (config->emachine == EM_PPC64 && name == ".toc") {
+    if (script->hasSectionsCommand)
+      return;
+    assert(sec->sectionCommands.size() == 1);
+    auto *isd = cast<InputSectionDescription>(sec->sectionCommands[0]);
+    llvm::stable_sort(isd->sections,
+                      [](const InputSection *a, const InputSection *b) -> bool {
+                        return a->file->ppc64SmallCodeModelTocRelocs &&
+                               !b->file->ppc64SmallCodeModelTocRelocs;
+                      });
+    return;
+  }
+
+  // Sort input sections by priority using the list provided
+  // by --symbol-ordering-file.
+  if (!order.empty())
+    for (BaseCommand *b : sec->sectionCommands)
+      if (auto *isd = dyn_cast<InputSectionDescription>(b))
+        sortISDBySectionOrder(isd, order);
+}
+
+// If no layout was provided by linker script, we want to apply default
+// sorting for special input sections. This also handles --symbol-ordering-file.
+template <class ELFT> void Writer<ELFT>::sortInputSections() {
+  // Build the order once since it is expensive.
+  DenseMap<const InputSectionBase *, int> order = buildSectionOrder();
+  for (BaseCommand *base : script->sectionCommands)
+    if (auto *sec = dyn_cast<OutputSection>(base))
+      sortSection(sec, order);
+}
+
+template <class ELFT> void Writer<ELFT>::sortSections() {
+  script->adjustSectionsBeforeSorting();
+
+  // Don't sort if using -r. It is not necessary and we want to preserve the
+  // relative order for SHF_LINK_ORDER sections.
+  if (config->relocatable)
+    return;
+
+  sortInputSections();
+
+  for (BaseCommand *base : script->sectionCommands) {
+    auto *os = dyn_cast<OutputSection>(base);
+    if (!os)
+      continue;
+    os->sortRank = getSectionRank(os);
+
+    // We want to assign rude approximation values to outSecOff fields
+    // to know the relative order of the input sections. We use it for
+    // sorting SHF_LINK_ORDER sections. See resolveShfLinkOrder().
+    uint64_t i = 0;
+    for (InputSection *sec : getInputSections(os))
+      sec->outSecOff = i++;
+  }
+
+  if (!script->hasSectionsCommand) {
+    // We know that all the OutputSections are contiguous in this case.
+    auto isSection = [](BaseCommand *base) { return isa<OutputSection>(base); };
+    std::stable_sort(
+        llvm::find_if(script->sectionCommands, isSection),
+        llvm::find_if(llvm::reverse(script->sectionCommands), isSection).base(),
+        compareSections);
+
+    // Process INSERT commands. From this point onwards the order of
+    // script->sectionCommands is fixed.
+    script->processInsertCommands();
+    return;
+  }
+
+  script->processInsertCommands();
+
+  // Orphan sections are sections present in the input files which are
+  // not explicitly placed into the output file by the linker script.
+  //
+  // The sections in the linker script are already in the correct
+  // order. We have to figuere out where to insert the orphan
+  // sections.
+  //
+  // The order of the sections in the script is arbitrary and may not agree with
+  // compareSections. This means that we cannot easily define a strict weak
+  // ordering. To see why, consider a comparison of a section in the script and
+  // one not in the script. We have a two simple options:
+  // * Make them equivalent (a is not less than b, and b is not less than a).
+  //   The problem is then that equivalence has to be transitive and we can
+  //   have sections a, b and c with only b in a script and a less than c
+  //   which breaks this property.
+  // * Use compareSectionsNonScript. Given that the script order doesn't have
+  //   to match, we can end up with sections a, b, c, d where b and c are in the
+  //   script and c is compareSectionsNonScript less than b. In which case d
+  //   can be equivalent to c, a to b and d < a. As a concrete example:
+  //   .a (rx) # not in script
+  //   .b (rx) # in script
+  //   .c (ro) # in script
+  //   .d (ro) # not in script
+  //
+  // The way we define an order then is:
+  // *  Sort only the orphan sections. They are in the end right now.
+  // *  Move each orphan section to its preferred position. We try
+  //    to put each section in the last position where it can share
+  //    a PT_LOAD.
+  //
+  // There is some ambiguity as to where exactly a new entry should be
+  // inserted, because Commands contains not only output section
+  // commands but also other types of commands such as symbol assignment
+  // expressions. There's no correct answer here due to the lack of the
+  // formal specification of the linker script. We use heuristics to
+  // determine whether a new output command should be added before or
+  // after another commands. For the details, look at shouldSkip
+  // function.
+
+  auto i = script->sectionCommands.begin();
+  auto e = script->sectionCommands.end();
+  auto nonScriptI = std::find_if(i, e, [](BaseCommand *base) {
+    if (auto *sec = dyn_cast<OutputSection>(base))
+      return sec->sectionIndex == UINT32_MAX;
+    return false;
+  });
+
+  // Sort the orphan sections.
+  std::stable_sort(nonScriptI, e, compareSections);
+
+  // As a horrible special case, skip the first . assignment if it is before any
+  // section. We do this because it is common to set a load address by starting
+  // the script with ". = 0xabcd" and the expectation is that every section is
+  // after that.
+  auto firstSectionOrDotAssignment =
+      std::find_if(i, e, [](BaseCommand *cmd) { return !shouldSkip(cmd); });
+  if (firstSectionOrDotAssignment != e &&
+      isa<SymbolAssignment>(**firstSectionOrDotAssignment))
+    ++firstSectionOrDotAssignment;
+  i = firstSectionOrDotAssignment;
+
+  while (nonScriptI != e) {
+    auto pos = findOrphanPos(i, nonScriptI);
+    OutputSection *orphan = cast<OutputSection>(*nonScriptI);
+
+    // As an optimization, find all sections with the same sort rank
+    // and insert them with one rotate.
+    unsigned rank = orphan->sortRank;
+    auto end = std::find_if(nonScriptI + 1, e, [=](BaseCommand *cmd) {
+      return cast<OutputSection>(cmd)->sortRank != rank;
+    });
+    std::rotate(pos, nonScriptI, end);
+    nonScriptI = end;
+  }
+
+  script->adjustSectionsAfterSorting();
+}
+
+static bool compareByFilePosition(InputSection *a, InputSection *b) {
+  InputSection *la = a->getLinkOrderDep();
+  InputSection *lb = b->getLinkOrderDep();
+  OutputSection *aOut = la->getParent();
+  OutputSection *bOut = lb->getParent();
+
+  if (aOut != bOut)
+    return aOut->sectionIndex < bOut->sectionIndex;
+  return la->outSecOff < lb->outSecOff;
+}
+
+template <class ELFT> void Writer<ELFT>::resolveShfLinkOrder() {
+  for (OutputSection *sec : outputSections) {
+    if (!(sec->flags & SHF_LINK_ORDER))
+      continue;
+
+    // The ARM.exidx section use SHF_LINK_ORDER, but we have consolidated
+    // this processing inside the ARMExidxsyntheticsection::finalizeContents().
+    if (!config->relocatable && config->emachine == EM_ARM &&
+        sec->type == SHT_ARM_EXIDX)
+      continue;
+
+    // Link order may be distributed across several InputSectionDescriptions
+    // but sort must consider them all at once.
+    std::vector<InputSection **> scriptSections;
+    std::vector<InputSection *> sections;
+    for (BaseCommand *base : sec->sectionCommands) {
+      if (auto *isd = dyn_cast<InputSectionDescription>(base)) {
+        for (InputSection *&isec : isd->sections) {
+          scriptSections.push_back(&isec);
+          sections.push_back(isec);
+
+          InputSection *link = isec->getLinkOrderDep();
+          if (!link->getParent())
+            error(toString(isec) + ": sh_link points to discarded section " +
+                  toString(link));
+        }
+      }
+    }
+
+    if (errorCount())
+      continue;
+
+    llvm::stable_sort(sections, compareByFilePosition);
+
+    for (int i = 0, n = sections.size(); i < n; ++i)
+      *scriptSections[i] = sections[i];
+  }
+}
+
+// We need to generate and finalize the content that depends on the address of
+// InputSections. As the generation of the content may also alter InputSection
+// addresses we must converge to a fixed point. We do that here. See the comment
+// in Writer<ELFT>::finalizeSections().
+template <class ELFT> void Writer<ELFT>::finalizeAddressDependentContent() {
+  ThunkCreator tc;
+  AArch64Err843419Patcher a64p;
+  ARMErr657417Patcher a32p;
+  script->assignAddresses();
+
+  int assignPasses = 0;
+  for (;;) {
+    bool changed = target->needsThunks && tc.createThunks(outputSections);
+
+    // With Thunk Size much smaller than branch range we expect to
+    // converge quickly; if we get to 10 something has gone wrong.
+    if (changed && tc.pass >= 10) {
+      error("thunk creation not converged");
+      break;
+    }
+
+    if (config->fixCortexA53Errata843419) {
+      if (changed)
+        script->assignAddresses();
+      changed |= a64p.createFixes();
+    }
+    if (config->fixCortexA8) {
+      if (changed)
+        script->assignAddresses();
+      changed |= a32p.createFixes();
+    }
+
+    if (in.mipsGot)
+      in.mipsGot->updateAllocSize();
+
+    for (Partition &part : partitions) {
+      changed |= part.relaDyn->updateAllocSize();
+      if (part.relrDyn)
+        changed |= part.relrDyn->updateAllocSize();
+    }
+
+    const Defined *changedSym = script->assignAddresses();
+    if (!changed) {
+      // Some symbols may be dependent on section addresses. When we break the
+      // loop, the symbol values are finalized because a previous
+      // assignAddresses() finalized section addresses.
+      if (!changedSym)
+        break;
+      if (++assignPasses == 5) {
+        errorOrWarn("assignment to symbol " + toString(*changedSym) +
+                    " does not converge");
+        break;
+      }
+    }
+  }
+}
+
+static void finalizeSynthetic(SyntheticSection *sec) {
+  if (sec && sec->isNeeded() && sec->getParent())
+    sec->finalizeContents();
+}
+
+// In order to allow users to manipulate linker-synthesized sections,
+// we had to add synthetic sections to the input section list early,
+// even before we make decisions whether they are needed. This allows
+// users to write scripts like this: ".mygot : { .got }".
+//
+// Doing it has an unintended side effects. If it turns out that we
+// don't need a .got (for example) at all because there's no
+// relocation that needs a .got, we don't want to emit .got.
+//
+// To deal with the above problem, this function is called after
+// scanRelocations is called to remove synthetic sections that turn
+// out to be empty.
+static void removeUnusedSyntheticSections() {
+  // All input synthetic sections that can be empty are placed after
+  // all regular ones. We iterate over them all and exit at first
+  // non-synthetic.
+  for (InputSectionBase *s : llvm::reverse(inputSections)) {
+    SyntheticSection *ss = dyn_cast<SyntheticSection>(s);
+    if (!ss)
+      return;
+    OutputSection *os = ss->getParent();
+    if (!os || ss->isNeeded())
+      continue;
+
+    // If we reach here, then SS is an unused synthetic section and we want to
+    // remove it from corresponding input section description of output section.
+    for (BaseCommand *b : os->sectionCommands)
+      if (auto *isd = dyn_cast<InputSectionDescription>(b))
+        llvm::erase_if(isd->sections,
+                       [=](InputSection *isec) { return isec == ss; });
+  }
+}
+
+// Create output section objects and add them to OutputSections.
+template <class ELFT> void Writer<ELFT>::finalizeSections() {
+  Out::preinitArray = findSection(".preinit_array");
+  Out::initArray = findSection(".init_array");
+  Out::finiArray = findSection(".fini_array");
+
+  // The linker needs to define SECNAME_start, SECNAME_end and SECNAME_stop
+  // symbols for sections, so that the runtime can get the start and end
+  // addresses of each section by section name. Add such symbols.
+  if (!config->relocatable) {
+    addStartEndSymbols();
+    for (BaseCommand *base : script->sectionCommands)
+      if (auto *sec = dyn_cast<OutputSection>(base))
+        addStartStopSymbols(sec);
+  }
+
+  // Add _DYNAMIC symbol. Unlike GNU gold, our _DYNAMIC symbol has no type.
+  // It should be okay as no one seems to care about the type.
+  // Even the author of gold doesn't remember why gold behaves that way.
+  // https://sourceware.org/ml/binutils/2002-03/msg00360.html
+  if (mainPart->dynamic->parent)
+    symtab->addSymbol(Defined{/*file=*/nullptr, "_DYNAMIC", STB_WEAK,
+                              STV_HIDDEN, STT_NOTYPE,
+                              /*value=*/0, /*size=*/0, mainPart->dynamic});
+
+  // Define __rel[a]_iplt_{start,end} symbols if needed.
+  addRelIpltSymbols();
+
+  // RISC-V's gp can address +/- 2 KiB, set it to .sdata + 0x800. This symbol
+  // should only be defined in an executable. If .sdata does not exist, its
+  // value/section does not matter but it has to be relative, so set its
+  // st_shndx arbitrarily to 1 (Out::elfHeader).
+  if (config->emachine == EM_RISCV && !config->shared) {
+    OutputSection *sec = findSection(".sdata");
+    ElfSym::riscvGlobalPointer =
+        addOptionalRegular("__global_pointer$", sec ? sec : Out::elfHeader,
+                           0x800, STV_DEFAULT, STB_GLOBAL);
+  }
+
+  if (config->emachine == EM_X86_64) {
+    // On targets that support TLSDESC, _TLS_MODULE_BASE_ is defined in such a
+    // way that:
+    //
+    // 1) Without relaxation: it produces a dynamic TLSDESC relocation that
+    // computes 0.
+    // 2) With LD->LE relaxation: _TLS_MODULE_BASE_@tpoff = 0 (lowest address in
+    // the TLS block).
+    //
+    // 2) is special cased in @tpoff computation. To satisfy 1), we define it as
+    // an absolute symbol of zero. This is different from GNU linkers which
+    // define _TLS_MODULE_BASE_ relative to the first TLS section.
+    Symbol *s = symtab->find("_TLS_MODULE_BASE_");
+    if (s && s->isUndefined()) {
+      s->resolve(Defined{/*file=*/nullptr, s->getName(), STB_GLOBAL, STV_HIDDEN,
+                         STT_TLS, /*value=*/0, 0,
+                         /*section=*/nullptr});
+      ElfSym::tlsModuleBase = cast<Defined>(s);
+    }
+  }
+
+  // This responsible for splitting up .eh_frame section into
+  // pieces. The relocation scan uses those pieces, so this has to be
+  // earlier.
+  for (Partition &part : partitions)
+    finalizeSynthetic(part.ehFrame);
+
+  for (Symbol *sym : symtab->symbols())
+    sym->isPreemptible = computeIsPreemptible(*sym);
+
+  // Change values of linker-script-defined symbols from placeholders (assigned
+  // by declareSymbols) to actual definitions.
+  script->processSymbolAssignments();
+
+  // Scan relocations. This must be done after every symbol is declared so that
+  // we can correctly decide if a dynamic relocation is needed. This is called
+  // after processSymbolAssignments() because it needs to know whether a
+  // linker-script-defined symbol is absolute.
+  if (!config->relocatable) {
+    forEachRelSec(scanRelocations<ELFT>);
+    reportUndefinedSymbols<ELFT>();
+  }
+
+  if (in.plt && in.plt->isNeeded())
+    in.plt->addSymbols();
+  if (in.iplt && in.iplt->isNeeded())
+    in.iplt->addSymbols();
+
+  if (!config->allowShlibUndefined) {
+    // Error on undefined symbols in a shared object, if all of its DT_NEEDED
+    // entries are seen. These cases would otherwise lead to runtime errors
+    // reported by the dynamic linker.
+    //
+    // ld.bfd traces all DT_NEEDED to emulate the logic of the dynamic linker to
+    // catch more cases. That is too much for us. Our approach resembles the one
+    // used in ld.gold, achieves a good balance to be useful but not too smart.
+    for (SharedFile *file : sharedFiles)
+      file->allNeededIsKnown =
+          llvm::all_of(file->dtNeeded, [&](StringRef needed) {
+            return symtab->soNames.count(needed);
+          });
+
+    for (Symbol *sym : symtab->symbols())
+      if (sym->isUndefined() && !sym->isWeak())
+        if (auto *f = dyn_cast_or_null<SharedFile>(sym->file))
+          if (f->allNeededIsKnown)
+            error(toString(f) + ": undefined reference to " + toString(*sym));
+  }
+
+  // Now that we have defined all possible global symbols including linker-
+  // synthesized ones. Visit all symbols to give the finishing touches.
+  for (Symbol *sym : symtab->symbols()) {
+    if (!includeInSymtab(*sym))
+      continue;
+    if (in.symTab)
+      in.symTab->addSymbol(sym);
+
+    if (sym->includeInDynsym()) {
+      partitions[sym->partition - 1].dynSymTab->addSymbol(sym);
+      if (auto *file = dyn_cast_or_null<SharedFile>(sym->file))
+        if (file->isNeeded && !sym->isUndefined())
+          addVerneed(sym);
+    }
+  }
+
+  // We also need to scan the dynamic relocation tables of the other partitions
+  // and add any referenced symbols to the partition's dynsym.
+  for (Partition &part : MutableArrayRef<Partition>(partitions).slice(1)) {
+    DenseSet<Symbol *> syms;
+    for (const SymbolTableEntry &e : part.dynSymTab->getSymbols())
+      syms.insert(e.sym);
+    for (DynamicReloc &reloc : part.relaDyn->relocs)
+      if (reloc.sym && !reloc.useSymVA && syms.insert(reloc.sym).second)
+        part.dynSymTab->addSymbol(reloc.sym);
+  }
+
+  // Do not proceed if there was an undefined symbol.
+  if (errorCount())
+    return;
+
+  if (in.mipsGot)
+    in.mipsGot->build();
+
+  removeUnusedSyntheticSections();
+
+  sortSections();
+
+  // Now that we have the final list, create a list of all the
+  // OutputSections for convenience.
+  for (BaseCommand *base : script->sectionCommands)
+    if (auto *sec = dyn_cast<OutputSection>(base))
+      outputSections.push_back(sec);
+
+  // Prefer command line supplied address over other constraints.
+  for (OutputSection *sec : outputSections) {
+    auto i = config->sectionStartMap.find(sec->name);
+    if (i != config->sectionStartMap.end())
+      sec->addrExpr = [=] { return i->second; };
+  }
+
+  // This is a bit of a hack. A value of 0 means undef, so we set it
+  // to 1 to make __ehdr_start defined. The section number is not
+  // particularly relevant.
+  Out::elfHeader->sectionIndex = 1;
+
+  for (size_t i = 0, e = outputSections.size(); i != e; ++i) {
+    OutputSection *sec = outputSections[i];
+    sec->sectionIndex = i + 1;
+    sec->shName = in.shStrTab->addString(sec->name);
+  }
+
+  // Binary and relocatable output does not have PHDRS.
+  // The headers have to be created before finalize as that can influence the
+  // image base and the dynamic section on mips includes the image base.
+  if (!config->relocatable && !config->oFormatBinary) {
+    for (Partition &part : partitions) {
+      part.phdrs = script->hasPhdrsCommands() ? script->createPhdrs()
+                                              : createPhdrs(part);
+      if (config->emachine == EM_ARM) {
+        // PT_ARM_EXIDX is the ARM EHABI equivalent of PT_GNU_EH_FRAME
+        addPhdrForSection(part, SHT_ARM_EXIDX, PT_ARM_EXIDX, PF_R);
+      }
+      if (config->emachine == EM_MIPS) {
+        // Add separate segments for MIPS-specific sections.
+        addPhdrForSection(part, SHT_MIPS_REGINFO, PT_MIPS_REGINFO, PF_R);
+        addPhdrForSection(part, SHT_MIPS_OPTIONS, PT_MIPS_OPTIONS, PF_R);
+        addPhdrForSection(part, SHT_MIPS_ABIFLAGS, PT_MIPS_ABIFLAGS, PF_R);
+      }
+    }
+    Out::programHeaders->size = sizeof(Elf_Phdr) * mainPart->phdrs.size();
+
+    // Find the TLS segment. This happens before the section layout loop so that
+    // Android relocation packing can look up TLS symbol addresses. We only need
+    // to care about the main partition here because all TLS symbols were moved
+    // to the main partition (see MarkLive.cpp).
+    for (PhdrEntry *p : mainPart->phdrs)
+      if (p->p_type == PT_TLS)
+        Out::tlsPhdr = p;
+  }
+
+  // Some symbols are defined in term of program headers. Now that we
+  // have the headers, we can find out which sections they point to.
+  setReservedSymbolSections();
+
+  finalizeSynthetic(in.bss);
+  finalizeSynthetic(in.bssRelRo);
+  finalizeSynthetic(in.symTabShndx);
+  finalizeSynthetic(in.shStrTab);
+  finalizeSynthetic(in.strTab);
+  finalizeSynthetic(in.got);
+  finalizeSynthetic(in.mipsGot);
+  finalizeSynthetic(in.igotPlt);
+  finalizeSynthetic(in.gotPlt);
+  finalizeSynthetic(in.relaIplt);
+  finalizeSynthetic(in.relaPlt);
+  finalizeSynthetic(in.plt);
+  finalizeSynthetic(in.iplt);
+  finalizeSynthetic(in.ppc32Got2);
+  finalizeSynthetic(in.partIndex);
+
+  // Dynamic section must be the last one in this list and dynamic
+  // symbol table section (dynSymTab) must be the first one.
+  for (Partition &part : partitions) {
+    finalizeSynthetic(part.armExidx);
+    finalizeSynthetic(part.dynSymTab);
+    finalizeSynthetic(part.gnuHashTab);
+    finalizeSynthetic(part.hashTab);
+    finalizeSynthetic(part.verDef);
+    finalizeSynthetic(part.relaDyn);
+    finalizeSynthetic(part.relrDyn);
+    finalizeSynthetic(part.ehFrameHdr);
+    finalizeSynthetic(part.verSym);
+    finalizeSynthetic(part.verNeed);
+    finalizeSynthetic(part.dynamic);
+  }
+
+  if (!script->hasSectionsCommand && !config->relocatable)
+    fixSectionAlignments();
+
+  // SHFLinkOrder processing must be processed after relative section placements are
+  // known but before addresses are allocated.
+  resolveShfLinkOrder();
+  if (errorCount())
+    return;
+
+  // This is used to:
+  // 1) Create "thunks":
+  //    Jump instructions in many ISAs have small displacements, and therefore
+  //    they cannot jump to arbitrary addresses in memory. For example, RISC-V
+  //    JAL instruction can target only +-1 MiB from PC. It is a linker's
+  //    responsibility to create and insert small pieces of code between
+  //    sections to extend the ranges if jump targets are out of range. Such
+  //    code pieces are called "thunks".
+  //
+  //    We add thunks at this stage. We couldn't do this before this point
+  //    because this is the earliest point where we know sizes of sections and
+  //    their layouts (that are needed to determine if jump targets are in
+  //    range).
+  //
+  // 2) Update the sections. We need to generate content that depends on the
+  //    address of InputSections. For example, MIPS GOT section content or
+  //    android packed relocations sections content.
+  //
+  // 3) Assign the final values for the linker script symbols. Linker scripts
+  //    sometimes using forward symbol declarations. We want to set the correct
+  //    values. They also might change after adding the thunks.
+  finalizeAddressDependentContent();
+
+  // finalizeAddressDependentContent may have added local symbols to the static symbol table.
+  finalizeSynthetic(in.symTab);
+  finalizeSynthetic(in.ppc64LongBranchTarget);
+
+  // Fill other section headers. The dynamic table is finalized
+  // at the end because some tags like RELSZ depend on result
+  // of finalizing other sections.
+  for (OutputSection *sec : outputSections)
+    sec->finalize();
+}
+
+// Ensure data sections are not mixed with executable sections when
+// -execute-only is used. -execute-only is a feature to make pages executable
+// but not readable, and the feature is currently supported only on AArch64.
+template <class ELFT> void Writer<ELFT>::checkExecuteOnly() {
+  if (!config->executeOnly)
+    return;
+
+  for (OutputSection *os : outputSections)
+    if (os->flags & SHF_EXECINSTR)
+      for (InputSection *isec : getInputSections(os))
+        if (!(isec->flags & SHF_EXECINSTR))
+          error("cannot place " + toString(isec) + " into " + toString(os->name) +
+                ": -execute-only does not support intermingling data and code");
+}
+
+// The linker is expected to define SECNAME_start and SECNAME_end
+// symbols for a few sections. This function defines them.
+template <class ELFT> void Writer<ELFT>::addStartEndSymbols() {
+  // If a section does not exist, there's ambiguity as to how we
+  // define _start and _end symbols for an init/fini section. Since
+  // the loader assume that the symbols are always defined, we need to
+  // always define them. But what value? The loader iterates over all
+  // pointers between _start and _end to run global ctors/dtors, so if
+  // the section is empty, their symbol values don't actually matter
+  // as long as _start and _end point to the same location.
+  //
+  // That said, we don't want to set the symbols to 0 (which is
+  // probably the simplest value) because that could cause some
+  // program to fail to link due to relocation overflow, if their
+  // program text is above 2 GiB. We use the address of the .text
+  // section instead to prevent that failure.
+  //
+  // In rare situations, the .text section may not exist. If that's the
+  // case, use the image base address as a last resort.
+  OutputSection *Default = findSection(".text");
+  if (!Default)
+    Default = Out::elfHeader;
+
+  auto define = [=](StringRef start, StringRef end, OutputSection *os) {
+    if (os) {
+      addOptionalRegular(start, os, 0);
+      addOptionalRegular(end, os, -1);
+    } else {
+      addOptionalRegular(start, Default, 0);
+      addOptionalRegular(end, Default, 0);
+    }
+  };
+
+  define("__preinit_array_start", "__preinit_array_end", Out::preinitArray);
+  define("__init_array_start", "__init_array_end", Out::initArray);
+  define("__fini_array_start", "__fini_array_end", Out::finiArray);
+
+  if (OutputSection *sec = findSection(".ARM.exidx"))
+    define("__exidx_start", "__exidx_end", sec);
+}
+
+// If a section name is valid as a C identifier (which is rare because of
+// the leading '.'), linkers are expected to define __start_<secname> and
+// __stop_<secname> symbols. They are at beginning and end of the section,
+// respectively. This is not requested by the ELF standard, but GNU ld and
+// gold provide the feature, and used by many programs.
+template <class ELFT>
+void Writer<ELFT>::addStartStopSymbols(OutputSection *sec) {
+  StringRef s = sec->name;
+  if (!isValidCIdentifier(s))
+    return;
+  addOptionalRegular(saver.save("__start_" + s), sec, 0, STV_PROTECTED);
+  addOptionalRegular(saver.save("__stop_" + s), sec, -1, STV_PROTECTED);
+}
+
+static bool needsPtLoad(OutputSection *sec) {
+  if (!(sec->flags & SHF_ALLOC) || sec->noload)
+    return false;
+
+  // Don't allocate VA space for TLS NOBITS sections. The PT_TLS PHDR is
+  // responsible for allocating space for them, not the PT_LOAD that
+  // contains the TLS initialization image.
+  if ((sec->flags & SHF_TLS) && sec->type == SHT_NOBITS)
+    return false;
+  return true;
+}
+
+// Linker scripts are responsible for aligning addresses. Unfortunately, most
+// linker scripts are designed for creating two PT_LOADs only, one RX and one
+// RW. This means that there is no alignment in the RO to RX transition and we
+// cannot create a PT_LOAD there.
+static uint64_t computeFlags(uint64_t flags) {
+  if (config->omagic)
+    return PF_R | PF_W | PF_X;
+  if (config->executeOnly && (flags & PF_X))
+    return flags & ~PF_R;
+  if (config->singleRoRx && !(flags & PF_W))
+    return flags | PF_X;
+  return flags;
+}
+
+// Decide which program headers to create and which sections to include in each
+// one.
+template <class ELFT>
+std::vector<PhdrEntry *> Writer<ELFT>::createPhdrs(Partition &part) {
+  std::vector<PhdrEntry *> ret;
+  auto addHdr = [&](unsigned type, unsigned flags) -> PhdrEntry * {
+    ret.push_back(make<PhdrEntry>(type, flags));
+    return ret.back();
+  };
+
+  unsigned partNo = part.getNumber();
+  bool isMain = partNo == 1;
+
+  // Add the first PT_LOAD segment for regular output sections.
+  uint64_t flags = computeFlags(PF_R);
+  PhdrEntry *load = nullptr;
+
+  // nmagic or omagic output does not have PT_PHDR, PT_INTERP, or the readonly
+  // PT_LOAD.
+  if (!config->nmagic && !config->omagic) {
+    // The first phdr entry is PT_PHDR which describes the program header
+    // itself.
+    if (isMain)
+      addHdr(PT_PHDR, PF_R)->add(Out::programHeaders);
+    else
+      addHdr(PT_PHDR, PF_R)->add(part.programHeaders->getParent());
+
+    // PT_INTERP must be the second entry if exists.
+    if (OutputSection *cmd = findSection(".interp", partNo))
+      addHdr(PT_INTERP, cmd->getPhdrFlags())->add(cmd);
+
+    // Add the headers. We will remove them if they don't fit.
+    // In the other partitions the headers are ordinary sections, so they don't
+    // need to be added here.
+    if (isMain) {
+      load = addHdr(PT_LOAD, flags);
+      load->add(Out::elfHeader);
+      load->add(Out::programHeaders);
+    }
+  }
+
+  // PT_GNU_RELRO includes all sections that should be marked as
+  // read-only by dynamic linker after processing relocations.
+  // Current dynamic loaders only support one PT_GNU_RELRO PHDR, give
+  // an error message if more than one PT_GNU_RELRO PHDR is required.
+  PhdrEntry *relRo = make<PhdrEntry>(PT_GNU_RELRO, PF_R);
+  bool inRelroPhdr = false;
+  OutputSection *relroEnd = nullptr;
+  for (OutputSection *sec : outputSections) {
+    if (sec->partition != partNo || !needsPtLoad(sec))
+      continue;
+    if (isRelroSection(sec)) {
+      inRelroPhdr = true;
+      if (!relroEnd)
+        relRo->add(sec);
+      else
+        error("section: " + sec->name + " is not contiguous with other relro" +
+              " sections");
+    } else if (inRelroPhdr) {
+      inRelroPhdr = false;
+      relroEnd = sec;
+    }
+  }
+
+  for (OutputSection *sec : outputSections) {
+    if (!(sec->flags & SHF_ALLOC))
+      break;
+    if (!needsPtLoad(sec))
+      continue;
+
+    // Normally, sections in partitions other than the current partition are
+    // ignored. But partition number 255 is a special case: it contains the
+    // partition end marker (.part.end). It needs to be added to the main
+    // partition so that a segment is created for it in the main partition,
+    // which will cause the dynamic loader to reserve space for the other
+    // partitions.
+    if (sec->partition != partNo) {
+      if (isMain && sec->partition == 255)
+        addHdr(PT_LOAD, computeFlags(sec->getPhdrFlags()))->add(sec);
+      continue;
+    }
+
+    // Segments are contiguous memory regions that has the same attributes
+    // (e.g. executable or writable). There is one phdr for each segment.
+    // Therefore, we need to create a new phdr when the next section has
+    // different flags or is loaded at a discontiguous address or memory
+    // region using AT or AT> linker script command, respectively. At the same
+    // time, we don't want to create a separate load segment for the headers,
+    // even if the first output section has an AT or AT> attribute.
+    uint64_t newFlags = computeFlags(sec->getPhdrFlags());
+    bool sameLMARegion =
+        load && !sec->lmaExpr && sec->lmaRegion == load->firstSec->lmaRegion;
+    if (!(load && newFlags == flags && sec != relroEnd &&
+          sec->memRegion == load->firstSec->memRegion &&
+          (sameLMARegion || load->lastSec == Out::programHeaders))) {
+      load = addHdr(PT_LOAD, newFlags);
+      flags = newFlags;
+    }
+
+    load->add(sec);
+  }
+
+  // Add a TLS segment if any.
+  PhdrEntry *tlsHdr = make<PhdrEntry>(PT_TLS, PF_R);
+  for (OutputSection *sec : outputSections)
+    if (sec->partition == partNo && sec->flags & SHF_TLS)
+      tlsHdr->add(sec);
+  if (tlsHdr->firstSec)
+    ret.push_back(tlsHdr);
+
+  // Add an entry for .dynamic.
+  if (OutputSection *sec = part.dynamic->getParent())
+    addHdr(PT_DYNAMIC, sec->getPhdrFlags())->add(sec);
+
+  if (relRo->firstSec)
+    ret.push_back(relRo);
+
+  // PT_GNU_EH_FRAME is a special section pointing on .eh_frame_hdr.
+  if (part.ehFrame->isNeeded() && part.ehFrameHdr &&
+      part.ehFrame->getParent() && part.ehFrameHdr->getParent())
+    addHdr(PT_GNU_EH_FRAME, part.ehFrameHdr->getParent()->getPhdrFlags())
+        ->add(part.ehFrameHdr->getParent());
+
+  // PT_OPENBSD_RANDOMIZE is an OpenBSD-specific feature. That makes
+  // the dynamic linker fill the segment with random data.
+  if (OutputSection *cmd = findSection(".openbsd.randomdata", partNo))
+    addHdr(PT_OPENBSD_RANDOMIZE, cmd->getPhdrFlags())->add(cmd);
+
+  if (config->zGnustack != GnuStackKind::None) {
+    // PT_GNU_STACK is a special section to tell the loader to make the
+    // pages for the stack non-executable. If you really want an executable
+    // stack, you can pass -z execstack, but that's not recommended for
+    // security reasons.
+    unsigned perm = PF_R | PF_W;
+    if (config->zGnustack == GnuStackKind::Exec)
+      perm |= PF_X;
+    addHdr(PT_GNU_STACK, perm)->p_memsz = config->zStackSize;
+  }
+
+  // PT_OPENBSD_WXNEEDED is a OpenBSD-specific header to mark the executable
+  // is expected to perform W^X violations, such as calling mprotect(2) or
+  // mmap(2) with PROT_WRITE | PROT_EXEC, which is prohibited by default on
+  // OpenBSD.
+  if (config->zWxneeded)
+    addHdr(PT_OPENBSD_WXNEEDED, PF_X);
+
+  if (OutputSection *cmd = findSection(".note.gnu.property", partNo))
+    addHdr(PT_GNU_PROPERTY, PF_R)->add(cmd);
+
+  // Create one PT_NOTE per a group of contiguous SHT_NOTE sections with the
+  // same alignment.
+  PhdrEntry *note = nullptr;
+  for (OutputSection *sec : outputSections) {
+    if (sec->partition != partNo)
+      continue;
+    if (sec->type == SHT_NOTE && (sec->flags & SHF_ALLOC)) {
+      if (!note || sec->lmaExpr || note->lastSec->alignment != sec->alignment)
+        note = addHdr(PT_NOTE, PF_R);
+      note->add(sec);
+    } else {
+      note = nullptr;
+    }
+  }
+  return ret;
+}
+
+template <class ELFT>
+void Writer<ELFT>::addPhdrForSection(Partition &part, unsigned shType,
+                                     unsigned pType, unsigned pFlags) {
+  unsigned partNo = part.getNumber();
+  auto i = llvm::find_if(outputSections, [=](OutputSection *cmd) {
+    return cmd->partition == partNo && cmd->type == shType;
+  });
+  if (i == outputSections.end())
+    return;
+
+  PhdrEntry *entry = make<PhdrEntry>(pType, pFlags);
+  entry->add(*i);
+  part.phdrs.push_back(entry);
+}
+
+// Place the first section of each PT_LOAD to a different page (of maxPageSize).
+// This is achieved by assigning an alignment expression to addrExpr of each
+// such section.
+template <class ELFT> void Writer<ELFT>::fixSectionAlignments() {
+  const PhdrEntry *prev;
+  auto pageAlign = [&](const PhdrEntry *p) {
+    OutputSection *cmd = p->firstSec;
+    if (cmd && !cmd->addrExpr) {
+      // Prefer advancing to align(dot, maxPageSize) + dot%maxPageSize to avoid
+      // padding in the file contents.
+      //
+      // When -z separate-code is used we must not have any overlap in pages
+      // between an executable segment and a non-executable segment. We align to
+      // the next maximum page size boundary on transitions between executable
+      // and non-executable segments.
+      //
+      // SHT_LLVM_PART_EHDR marks the start of a partition. The partition
+      // sections will be extracted to a separate file. Align to the next
+      // maximum page size boundary so that we can find the ELF header at the
+      // start. We cannot benefit from overlapping p_offset ranges with the
+      // previous segment anyway.
+      if (config->zSeparate == SeparateSegmentKind::Loadable ||
+          (config->zSeparate == SeparateSegmentKind::Code && prev &&
+           (prev->p_flags & PF_X) != (p->p_flags & PF_X)) ||
+          cmd->type == SHT_LLVM_PART_EHDR)
+        cmd->addrExpr = [] {
+          return alignTo(script->getDot(), config->maxPageSize);
+        };
+      // PT_TLS is at the start of the first RW PT_LOAD. If `p` includes PT_TLS,
+      // it must be the RW. Align to p_align(PT_TLS) to make sure
+      // p_vaddr(PT_LOAD)%p_align(PT_LOAD) = 0. Otherwise, if
+      // sh_addralign(.tdata) < sh_addralign(.tbss), we will set p_align(PT_TLS)
+      // to sh_addralign(.tbss), while p_vaddr(PT_TLS)=p_vaddr(PT_LOAD) may not
+      // be congruent to 0 modulo p_align(PT_TLS).
+      //
+      // Technically this is not required, but as of 2019, some dynamic loaders
+      // don't handle p_vaddr%p_align != 0 correctly, e.g. glibc (i386 and
+      // x86-64) doesn't make runtime address congruent to p_vaddr modulo
+      // p_align for dynamic TLS blocks (PR/24606), FreeBSD rtld has the same
+      // bug, musl (TLS Variant 1 architectures) before 1.1.23 handled TLS
+      // blocks correctly. We need to keep the workaround for a while.
+      else if (Out::tlsPhdr && Out::tlsPhdr->firstSec == p->firstSec)
+        cmd->addrExpr = [] {
+          return alignTo(script->getDot(), config->maxPageSize) +
+                 alignTo(script->getDot() % config->maxPageSize,
+                         Out::tlsPhdr->p_align);
+        };
+      else
+        cmd->addrExpr = [] {
+          return alignTo(script->getDot(), config->maxPageSize) +
+                 script->getDot() % config->maxPageSize;
+        };
+    }
+  };
+
+  for (Partition &part : partitions) {
+    prev = nullptr;
+    for (const PhdrEntry *p : part.phdrs)
+      if (p->p_type == PT_LOAD && p->firstSec) {
+        pageAlign(p);
+        prev = p;
+      }
+  }
+}
+
+// Compute an in-file position for a given section. The file offset must be the
+// same with its virtual address modulo the page size, so that the loader can
+// load executables without any address adjustment.
+static uint64_t computeFileOffset(OutputSection *os, uint64_t off) {
+  // The first section in a PT_LOAD has to have congruent offset and address
+  // modulo the maximum page size.
+  if (os->ptLoad && os->ptLoad->firstSec == os)
+    return alignTo(off, os->ptLoad->p_align, os->addr);
+
+  // File offsets are not significant for .bss sections other than the first one
+  // in a PT_LOAD. By convention, we keep section offsets monotonically
+  // increasing rather than setting to zero.
+   if (os->type == SHT_NOBITS)
+     return off;
+
+  // If the section is not in a PT_LOAD, we just have to align it.
+  if (!os->ptLoad)
+    return alignTo(off, os->alignment);
+
+  // If two sections share the same PT_LOAD the file offset is calculated
+  // using this formula: Off2 = Off1 + (VA2 - VA1).
+  OutputSection *first = os->ptLoad->firstSec;
+  return first->offset + os->addr - first->addr;
+}
+
+// Set an in-file position to a given section and returns the end position of
+// the section.
+static uint64_t setFileOffset(OutputSection *os, uint64_t off) {
+  off = computeFileOffset(os, off);
+  os->offset = off;
+
+  if (os->type == SHT_NOBITS)
+    return off;
+  return off + os->size;
+}
+
+template <class ELFT> void Writer<ELFT>::assignFileOffsetsBinary() {
+  uint64_t off = 0;
+  for (OutputSection *sec : outputSections)
+    if (sec->flags & SHF_ALLOC)
+      off = setFileOffset(sec, off);
+  fileSize = alignTo(off, config->wordsize);
+}
+
+static std::string rangeToString(uint64_t addr, uint64_t len) {
+  return "[0x" + utohexstr(addr) + ", 0x" + utohexstr(addr + len - 1) + "]";
+}
+
+// Assign file offsets to output sections.
+template <class ELFT> void Writer<ELFT>::assignFileOffsets() {
+  uint64_t off = 0;
+  off = setFileOffset(Out::elfHeader, off);
+  off = setFileOffset(Out::programHeaders, off);
+
+  PhdrEntry *lastRX = nullptr;
+  for (Partition &part : partitions)
+    for (PhdrEntry *p : part.phdrs)
+      if (p->p_type == PT_LOAD && (p->p_flags & PF_X))
+        lastRX = p;
+
+  for (OutputSection *sec : outputSections) {
+    off = setFileOffset(sec, off);
+
+    // If this is a last section of the last executable segment and that
+    // segment is the last loadable segment, align the offset of the
+    // following section to avoid loading non-segments parts of the file.
+    if (config->zSeparate != SeparateSegmentKind::None && lastRX &&
+        lastRX->lastSec == sec)
+      off = alignTo(off, config->commonPageSize);
+  }
+
+  sectionHeaderOff = alignTo(off, config->wordsize);
+  fileSize = sectionHeaderOff + (outputSections.size() + 1) * sizeof(Elf_Shdr);
+
+  // Our logic assumes that sections have rising VA within the same segment.
+  // With use of linker scripts it is possible to violate this rule and get file
+  // offset overlaps or overflows. That should never happen with a valid script
+  // which does not move the location counter backwards and usually scripts do
+  // not do that. Unfortunately, there are apps in the wild, for example, Linux
+  // kernel, which control segment distribution explicitly and move the counter
+  // backwards, so we have to allow doing that to support linking them. We
+  // perform non-critical checks for overlaps in checkSectionOverlap(), but here
+  // we want to prevent file size overflows because it would crash the linker.
+  for (OutputSection *sec : outputSections) {
+    if (sec->type == SHT_NOBITS)
+      continue;
+    if ((sec->offset > fileSize) || (sec->offset + sec->size > fileSize))
+      error("unable to place section " + sec->name + " at file offset " +
+            rangeToString(sec->offset, sec->size) +
+            "; check your linker script for overflows");
+  }
+}
+
+// Finalize the program headers. We call this function after we assign
+// file offsets and VAs to all sections.
+template <class ELFT> void Writer<ELFT>::setPhdrs(Partition &part) {
+  for (PhdrEntry *p : part.phdrs) {
+    OutputSection *first = p->firstSec;
+    OutputSection *last = p->lastSec;
+
+    if (first) {
+      p->p_filesz = last->offset - first->offset;
+      if (last->type != SHT_NOBITS)
+        p->p_filesz += last->size;
+
+      p->p_memsz = last->addr + last->size - first->addr;
+      p->p_offset = first->offset;
+      p->p_vaddr = first->addr;
+
+      // File offsets in partitions other than the main partition are relative
+      // to the offset of the ELF headers. Perform that adjustment now.
+      if (part.elfHeader)
+        p->p_offset -= part.elfHeader->getParent()->offset;
+
+      if (!p->hasLMA)
+        p->p_paddr = first->getLMA();
+    }
+
+    if (p->p_type == PT_GNU_RELRO) {
+      p->p_align = 1;
+      // musl/glibc ld.so rounds the size down, so we need to round up
+      // to protect the last page. This is a no-op on FreeBSD which always
+      // rounds up.
+      p->p_memsz = alignTo(p->p_offset + p->p_memsz, config->commonPageSize) -
+                   p->p_offset;
+    }
+  }
+}
+
+// A helper struct for checkSectionOverlap.
+namespace {
+struct SectionOffset {
+  OutputSection *sec;
+  uint64_t offset;
+};
+} // namespace
+
+// Check whether sections overlap for a specific address range (file offsets,
+// load and virtual addresses).
+static void checkOverlap(StringRef name, std::vector<SectionOffset> &sections,
+                         bool isVirtualAddr) {
+  llvm::sort(sections, [=](const SectionOffset &a, const SectionOffset &b) {
+    return a.offset < b.offset;
+  });
+
+  // Finding overlap is easy given a vector is sorted by start position.
+  // If an element starts before the end of the previous element, they overlap.
+  for (size_t i = 1, end = sections.size(); i < end; ++i) {
+    SectionOffset a = sections[i - 1];
+    SectionOffset b = sections[i];
+    if (b.offset >= a.offset + a.sec->size)
+      continue;
+
+    // If both sections are in OVERLAY we allow the overlapping of virtual
+    // addresses, because it is what OVERLAY was designed for.
+    if (isVirtualAddr && a.sec->inOverlay && b.sec->inOverlay)
+      continue;
+
+    errorOrWarn("section " + a.sec->name + " " + name +
+                " range overlaps with " + b.sec->name + "\n>>> " + a.sec->name +
+                " range is " + rangeToString(a.offset, a.sec->size) + "\n>>> " +
+                b.sec->name + " range is " +
+                rangeToString(b.offset, b.sec->size));
+  }
+}
+
+// Check for overlapping sections and address overflows.
+//
+// In this function we check that none of the output sections have overlapping
+// file offsets. For SHF_ALLOC sections we also check that the load address
+// ranges and the virtual address ranges don't overlap
+template <class ELFT> void Writer<ELFT>::checkSections() {
+  // First, check that section's VAs fit in available address space for target.
+  for (OutputSection *os : outputSections)
+    if ((os->addr + os->size < os->addr) ||
+        (!ELFT::Is64Bits && os->addr + os->size > UINT32_MAX))
+      errorOrWarn("section " + os->name + " at 0x" + utohexstr(os->addr) +
+                  " of size 0x" + utohexstr(os->size) +
+                  " exceeds available address space");
+
+  // Check for overlapping file offsets. In this case we need to skip any
+  // section marked as SHT_NOBITS. These sections don't actually occupy space in
+  // the file so Sec->Offset + Sec->Size can overlap with others. If --oformat
+  // binary is specified only add SHF_ALLOC sections are added to the output
+  // file so we skip any non-allocated sections in that case.
+  std::vector<SectionOffset> fileOffs;
+  for (OutputSection *sec : outputSections)
+    if (sec->size > 0 && sec->type != SHT_NOBITS &&
+        (!config->oFormatBinary || (sec->flags & SHF_ALLOC)))
+      fileOffs.push_back({sec, sec->offset});
+  checkOverlap("file", fileOffs, false);
+
+  // When linking with -r there is no need to check for overlapping virtual/load
+  // addresses since those addresses will only be assigned when the final
+  // executable/shared object is created.
+  if (config->relocatable)
+    return;
+
+  // Checking for overlapping virtual and load addresses only needs to take
+  // into account SHF_ALLOC sections since others will not be loaded.
+  // Furthermore, we also need to skip SHF_TLS sections since these will be
+  // mapped to other addresses at runtime and can therefore have overlapping
+  // ranges in the file.
+  std::vector<SectionOffset> vmas;
+  for (OutputSection *sec : outputSections)
+    if (sec->size > 0 && (sec->flags & SHF_ALLOC) && !(sec->flags & SHF_TLS))
+      vmas.push_back({sec, sec->addr});
+  checkOverlap("virtual address", vmas, true);
+
+  // Finally, check that the load addresses don't overlap. This will usually be
+  // the same as the virtual addresses but can be different when using a linker
+  // script with AT().
+  std::vector<SectionOffset> lmas;
+  for (OutputSection *sec : outputSections)
+    if (sec->size > 0 && (sec->flags & SHF_ALLOC) && !(sec->flags & SHF_TLS))
+      lmas.push_back({sec, sec->getLMA()});
+  checkOverlap("load address", lmas, false);
+}
+
+// The entry point address is chosen in the following ways.
+//
+// 1. the '-e' entry command-line option;
+// 2. the ENTRY(symbol) command in a linker control script;
+// 3. the value of the symbol _start, if present;
+// 4. the number represented by the entry symbol, if it is a number;
+// 5. the address of the first byte of the .text section, if present;
+// 6. the address 0.
+static uint64_t getEntryAddr() {
+  // Case 1, 2 or 3
+  if (Symbol *b = symtab->find(config->entry))
+    return b->getVA();
+
+  // Case 4
+  uint64_t addr;
+  if (to_integer(config->entry, addr))
+    return addr;
+
+  // Case 5
+  if (OutputSection *sec = findSection(".text")) {
+    if (config->warnMissingEntry)
+      warn("cannot find entry symbol " + config->entry + "; defaulting to 0x" +
+           utohexstr(sec->addr));
+    return sec->addr;
+  }
+
+  // Case 6
+  if (config->warnMissingEntry)
+    warn("cannot find entry symbol " + config->entry +
+         "; not setting start address");
+  return 0;
+}
+
+static uint16_t getELFType() {
+  if (config->isPic)
+    return ET_DYN;
+  if (config->relocatable)
+    return ET_REL;
+  return ET_EXEC;
+}
+
+template <class ELFT> void Writer<ELFT>::writeHeader() {
+  writeEhdr<ELFT>(Out::bufferStart, *mainPart);
+  writePhdrs<ELFT>(Out::bufferStart + sizeof(Elf_Ehdr), *mainPart);
+
+  auto *eHdr = reinterpret_cast<Elf_Ehdr *>(Out::bufferStart);
+  eHdr->e_type = getELFType();
+  eHdr->e_entry = getEntryAddr();
+  eHdr->e_shoff = sectionHeaderOff;
+
+  // Write the section header table.
+  //
+  // The ELF header can only store numbers up to SHN_LORESERVE in the e_shnum
+  // and e_shstrndx fields. When the value of one of these fields exceeds
+  // SHN_LORESERVE ELF requires us to put sentinel values in the ELF header and
+  // use fields in the section header at index 0 to store
+  // the value. The sentinel values and fields are:
+  // e_shnum = 0, SHdrs[0].sh_size = number of sections.
+  // e_shstrndx = SHN_XINDEX, SHdrs[0].sh_link = .shstrtab section index.
+  auto *sHdrs = reinterpret_cast<Elf_Shdr *>(Out::bufferStart + eHdr->e_shoff);
+  size_t num = outputSections.size() + 1;
+  if (num >= SHN_LORESERVE)
+    sHdrs->sh_size = num;
+  else
+    eHdr->e_shnum = num;
+
+  uint32_t strTabIndex = in.shStrTab->getParent()->sectionIndex;
+  if (strTabIndex >= SHN_LORESERVE) {
+    sHdrs->sh_link = strTabIndex;
+    eHdr->e_shstrndx = SHN_XINDEX;
+  } else {
+    eHdr->e_shstrndx = strTabIndex;
+  }
+
+  for (OutputSection *sec : outputSections)
+    sec->writeHeaderTo<ELFT>(++sHdrs);
+}
+
+// Open a result file.
+template <class ELFT> void Writer<ELFT>::openFile() {
+  uint64_t maxSize = config->is64 ? INT64_MAX : UINT32_MAX;
+  if (fileSize != size_t(fileSize) || maxSize < fileSize) {
+    error("output file too large: " + Twine(fileSize) + " bytes");
+    return;
+  }
+
+  unlinkAsync(config->outputFile);
+  unsigned flags = 0;
+  if (!config->relocatable)
+    flags |= FileOutputBuffer::F_executable;
+  if (!config->mmapOutputFile)
+    flags |= FileOutputBuffer::F_no_mmap;
+  Expected<std::unique_ptr<FileOutputBuffer>> bufferOrErr =
+      FileOutputBuffer::create(config->outputFile, fileSize, flags);
+
+  if (!bufferOrErr) {
+    error("failed to open " + config->outputFile + ": " +
+          llvm::toString(bufferOrErr.takeError()));
+    return;
+  }
+  buffer = std::move(*bufferOrErr);
+  Out::bufferStart = buffer->getBufferStart();
+}
+
+template <class ELFT> void Writer<ELFT>::writeSectionsBinary() {
+  for (OutputSection *sec : outputSections)
+    if (sec->flags & SHF_ALLOC)
+      sec->writeTo<ELFT>(Out::bufferStart + sec->offset);
+}
+
+static void fillTrap(uint8_t *i, uint8_t *end) {
+  for (; i + 4 <= end; i += 4)
+    memcpy(i, &target->trapInstr, 4);
+}
+
+// Fill the last page of executable segments with trap instructions
+// instead of leaving them as zero. Even though it is not required by any
+// standard, it is in general a good thing to do for security reasons.
+//
+// We'll leave other pages in segments as-is because the rest will be
+// overwritten by output sections.
+template <class ELFT> void Writer<ELFT>::writeTrapInstr() {
+  for (Partition &part : partitions) {
+    // Fill the last page.
+    for (PhdrEntry *p : part.phdrs)
+      if (p->p_type == PT_LOAD && (p->p_flags & PF_X))
+        fillTrap(Out::bufferStart + alignDown(p->firstSec->offset + p->p_filesz,
+                                              config->commonPageSize),
+                 Out::bufferStart + alignTo(p->firstSec->offset + p->p_filesz,
+                                            config->commonPageSize));
+
+    // Round up the file size of the last segment to the page boundary iff it is
+    // an executable segment to ensure that other tools don't accidentally
+    // trim the instruction padding (e.g. when stripping the file).
+    PhdrEntry *last = nullptr;
+    for (PhdrEntry *p : part.phdrs)
+      if (p->p_type == PT_LOAD)
+        last = p;
+
+    if (last && (last->p_flags & PF_X))
+      last->p_memsz = last->p_filesz =
+          alignTo(last->p_filesz, config->commonPageSize);
+  }
+}
+
+// Write section contents to a mmap'ed file.
+template <class ELFT> void Writer<ELFT>::writeSections() {
+  // In -r or -emit-relocs mode, write the relocation sections first as in
+  // ELf_Rel targets we might find out that we need to modify the relocated
+  // section while doing it.
+  for (OutputSection *sec : outputSections)
+    if (sec->type == SHT_REL || sec->type == SHT_RELA)
+      sec->writeTo<ELFT>(Out::bufferStart + sec->offset);
+
+  for (OutputSection *sec : outputSections)
+    if (sec->type != SHT_REL && sec->type != SHT_RELA)
+      sec->writeTo<ELFT>(Out::bufferStart + sec->offset);
+}
+
+// Split one uint8 array into small pieces of uint8 arrays.
+static std::vector<ArrayRef<uint8_t>> split(ArrayRef<uint8_t> arr,
+                                            size_t chunkSize) {
+  std::vector<ArrayRef<uint8_t>> ret;
+  while (arr.size() > chunkSize) {
+    ret.push_back(arr.take_front(chunkSize));
+    arr = arr.drop_front(chunkSize);
+  }
+  if (!arr.empty())
+    ret.push_back(arr);
+  return ret;
+}
+
+// Computes a hash value of Data using a given hash function.
+// In order to utilize multiple cores, we first split data into 1MB
+// chunks, compute a hash for each chunk, and then compute a hash value
+// of the hash values.
+static void
+computeHash(llvm::MutableArrayRef<uint8_t> hashBuf,
+            llvm::ArrayRef<uint8_t> data,
+            std::function<void(uint8_t *dest, ArrayRef<uint8_t> arr)> hashFn) {
+  std::vector<ArrayRef<uint8_t>> chunks = split(data, 1024 * 1024);
+  std::vector<uint8_t> hashes(chunks.size() * hashBuf.size());
+
+  // Compute hash values.
+  parallelForEachN(0, chunks.size(), [&](size_t i) {
+    hashFn(hashes.data() + i * hashBuf.size(), chunks[i]);
+  });
+
+  // Write to the final output buffer.
+  hashFn(hashBuf.data(), hashes);
+}
+
+template <class ELFT> void Writer<ELFT>::writeBuildId() {
+  if (!mainPart->buildId || !mainPart->buildId->getParent())
+    return;
+
+  if (config->buildId == BuildIdKind::Hexstring) {
+    for (Partition &part : partitions)
+      part.buildId->writeBuildId(config->buildIdVector);
+    return;
+  }
+
+  // Compute a hash of all sections of the output file.
+  size_t hashSize = mainPart->buildId->hashSize;
+  std::vector<uint8_t> buildId(hashSize);
+  llvm::ArrayRef<uint8_t> buf{Out::bufferStart, size_t(fileSize)};
+
+  switch (config->buildId) {
+  case BuildIdKind::Fast:
+    computeHash(buildId, buf, [](uint8_t *dest, ArrayRef<uint8_t> arr) {
+      write64le(dest, xxHash64(arr));
+    });
+    break;
+  case BuildIdKind::Md5:
+    computeHash(buildId, buf, [&](uint8_t *dest, ArrayRef<uint8_t> arr) {
+      memcpy(dest, MD5::hash(arr).data(), hashSize);
+    });
+    break;
+  case BuildIdKind::Sha1:
+    computeHash(buildId, buf, [&](uint8_t *dest, ArrayRef<uint8_t> arr) {
+      memcpy(dest, SHA1::hash(arr).data(), hashSize);
+    });
+    break;
+  case BuildIdKind::Uuid:
+    if (auto ec = llvm::getRandomBytes(buildId.data(), hashSize))
+      error("entropy source failure: " + ec.message());
+    break;
+  default:
+    llvm_unreachable("unknown BuildIdKind");
+  }
+  for (Partition &part : partitions)
+    part.buildId->writeBuildId(buildId);
+}
+
+template void createSyntheticSections<ELF32LE>();
+template void createSyntheticSections<ELF32BE>();
+template void createSyntheticSections<ELF64LE>();
+template void createSyntheticSections<ELF64BE>();
+
+template void writeResult<ELF32LE>();
+template void writeResult<ELF32BE>();
+template void writeResult<ELF64LE>();
+template void writeResult<ELF64BE>();
+
+} // namespace elf
+} // namespace lld