/contrib/llvm-project/lld/ELF/InputFiles.cpp

//===- InputFiles.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 "InputFiles.h"
#include "Driver.h"
#include "InputSection.h"
#include "LinkerScript.h"
#include "SymbolTable.h"
#include "Symbols.h"
#include "SyntheticSections.h"
#include "Target.h"
#include "lld/Common/CommonLinkerContext.h"
#include "lld/Common/DWARF.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/CodeGen/Analysis.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/LTO/LTO.h"
#include "llvm/MC/StringTableBuilder.h"
#include "llvm/Object/ELFObjectFile.h"
#include "llvm/Support/ARMAttributeParser.h"
#include "llvm/Support/ARMBuildAttributes.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/RISCVAttributeParser.h"
#include "llvm/Support/TarWriter.h"
#include "llvm/Support/raw_ostream.h"

using namespace llvm;
using namespace llvm::ELF;
using namespace llvm::object;
using namespace llvm::sys;
using namespace llvm::sys::fs;
using namespace llvm::support::endian;
using namespace lld;
using namespace lld::elf;

bool InputFile::isInGroup;
uint32_t InputFile::nextGroupId;

SmallVector<std::unique_ptr<MemoryBuffer>> elf::memoryBuffers;
SmallVector<ArchiveFile *, 0> elf::archiveFiles;
SmallVector<BinaryFile *, 0> elf::binaryFiles;
SmallVector<BitcodeFile *, 0> elf::bitcodeFiles;
SmallVector<BitcodeFile *, 0> elf::lazyBitcodeFiles;
SmallVector<ELFFileBase *, 0> elf::objectFiles;
SmallVector<SharedFile *, 0> elf::sharedFiles;

std::unique_ptr<TarWriter> elf::tar;

// Returns "<internal>", "foo.a(bar.o)" or "baz.o".
std::string lld::toString(const InputFile *f) {
  if (!f)
    return "<internal>";

  if (f->toStringCache.empty()) {
    if (f->archiveName.empty())
      f->toStringCache = f->getName();
    else
      (f->archiveName + "(" + f->getName() + ")").toVector(f->toStringCache);
  }
  return std::string(f->toStringCache);
}

static ELFKind getELFKind(MemoryBufferRef mb, StringRef archiveName) {
  unsigned char size;
  unsigned char endian;
  std::tie(size, endian) = getElfArchType(mb.getBuffer());

  auto report = [&](StringRef msg) {
    StringRef filename = mb.getBufferIdentifier();
    if (archiveName.empty())
      fatal(filename + ": " + msg);
    else
      fatal(archiveName + "(" + filename + "): " + msg);
  };

  if (!mb.getBuffer().startswith(ElfMagic))
    report("not an ELF file");
  if (endian != ELFDATA2LSB && endian != ELFDATA2MSB)
    report("corrupted ELF file: invalid data encoding");
  if (size != ELFCLASS32 && size != ELFCLASS64)
    report("corrupted ELF file: invalid file class");

  size_t bufSize = mb.getBuffer().size();
  if ((size == ELFCLASS32 && bufSize < sizeof(Elf32_Ehdr)) ||
      (size == ELFCLASS64 && bufSize < sizeof(Elf64_Ehdr)))
    report("corrupted ELF file: file is too short");

  if (size == ELFCLASS32)
    return (endian == ELFDATA2LSB) ? ELF32LEKind : ELF32BEKind;
  return (endian == ELFDATA2LSB) ? ELF64LEKind : ELF64BEKind;
}

InputFile::InputFile(Kind k, MemoryBufferRef m)
    : mb(m), groupId(nextGroupId), fileKind(k) {
  // All files within the same --{start,end}-group get the same group ID.
  // Otherwise, a new file will get a new group ID.
  if (!isInGroup)
    ++nextGroupId;
}

Optional<MemoryBufferRef> elf::readFile(StringRef path) {
  llvm::TimeTraceScope timeScope("Load input files", path);

  // The --chroot option changes our virtual root directory.
  // This is useful when you are dealing with files created by --reproduce.
  if (!config->chroot.empty() && path.startswith("/"))
    path = saver().save(config->chroot + path);

  log(path);
  config->dependencyFiles.insert(llvm::CachedHashString(path));

  auto mbOrErr = MemoryBuffer::getFile(path, /*IsText=*/false,
                                       /*RequiresNullTerminator=*/false);
  if (auto ec = mbOrErr.getError()) {
    error("cannot open " + path + ": " + ec.message());
    return None;
  }

  MemoryBufferRef mbref = (*mbOrErr)->getMemBufferRef();
  memoryBuffers.push_back(std::move(*mbOrErr)); // take MB ownership

  if (tar)
    tar->append(relativeToRoot(path), mbref.getBuffer());
  return mbref;
}

// All input object files must be for the same architecture
// (e.g. it does not make sense to link x86 object files with
// MIPS object files.) This function checks for that error.
static bool isCompatible(InputFile *file) {
  if (!file->isElf() && !isa<BitcodeFile>(file))
    return true;

  if (file->ekind == config->ekind && file->emachine == config->emachine) {
    if (config->emachine != EM_MIPS)
      return true;
    if (isMipsN32Abi(file) == config->mipsN32Abi)
      return true;
  }

  StringRef target =
      !config->bfdname.empty() ? config->bfdname : config->emulation;
  if (!target.empty()) {
    error(toString(file) + " is incompatible with " + target);
    return false;
  }

  InputFile *existing = nullptr;
  if (!objectFiles.empty())
    existing = objectFiles[0];
  else if (!sharedFiles.empty())
    existing = sharedFiles[0];
  else if (!bitcodeFiles.empty())
    existing = bitcodeFiles[0];
  std::string with;
  if (existing)
    with = " with " + toString(existing);
  error(toString(file) + " is incompatible" + with);
  return false;
}

template <class ELFT> static void doParseFile(InputFile *file) {
  if (!isCompatible(file))
    return;

  // Binary file
  if (auto *f = dyn_cast<BinaryFile>(file)) {
    binaryFiles.push_back(f);
    f->parse();
    return;
  }

  // .a file
  if (auto *f = dyn_cast<ArchiveFile>(file)) {
    archiveFiles.push_back(f);
    f->parse();
    return;
  }

  // Lazy object file
  if (file->lazy) {
    if (auto *f = dyn_cast<BitcodeFile>(file)) {
      lazyBitcodeFiles.push_back(f);
      f->parseLazy();
    } else {
      cast<ObjFile<ELFT>>(file)->parseLazy();
    }
    return;
  }

  if (config->trace)
    message(toString(file));

  // .so file
  if (auto *f = dyn_cast<SharedFile>(file)) {
    f->parse<ELFT>();
    return;
  }

  // LLVM bitcode file
  if (auto *f = dyn_cast<BitcodeFile>(file)) {
    bitcodeFiles.push_back(f);
    f->parse<ELFT>();
    return;
  }

  // Regular object file
  objectFiles.push_back(cast<ELFFileBase>(file));
  cast<ObjFile<ELFT>>(file)->parse();
}

// Add symbols in File to the symbol table.
void elf::parseFile(InputFile *file) { invokeELFT(doParseFile, file); }

// Concatenates arguments to construct a string representing an error location.
static std::string createFileLineMsg(StringRef path, unsigned line) {
  std::string filename = std::string(path::filename(path));
  std::string lineno = ":" + std::to_string(line);
  if (filename == path)
    return filename + lineno;
  return filename + lineno + " (" + path.str() + lineno + ")";
}

template <class ELFT>
static std::string getSrcMsgAux(ObjFile<ELFT> &file, const Symbol &sym,
                                InputSectionBase &sec, uint64_t offset) {
  // In DWARF, functions and variables are stored to different places.
  // First, lookup a function for a given offset.
  if (Optional<DILineInfo> info = file.getDILineInfo(&sec, offset))
    return createFileLineMsg(info->FileName, info->Line);

  // If it failed, lookup again as a variable.
  if (Optional<std::pair<std::string, unsigned>> fileLine =
          file.getVariableLoc(sym.getName()))
    return createFileLineMsg(fileLine->first, fileLine->second);

  // File.sourceFile contains STT_FILE symbol, and that is a last resort.
  return std::string(file.sourceFile);
}

std::string InputFile::getSrcMsg(const Symbol &sym, InputSectionBase &sec,
                                 uint64_t offset) {
  if (kind() != ObjKind)
    return "";
  switch (config->ekind) {
  default:
    llvm_unreachable("Invalid kind");
  case ELF32LEKind:
    return getSrcMsgAux(cast<ObjFile<ELF32LE>>(*this), sym, sec, offset);
  case ELF32BEKind:
    return getSrcMsgAux(cast<ObjFile<ELF32BE>>(*this), sym, sec, offset);
  case ELF64LEKind:
    return getSrcMsgAux(cast<ObjFile<ELF64LE>>(*this), sym, sec, offset);
  case ELF64BEKind:
    return getSrcMsgAux(cast<ObjFile<ELF64BE>>(*this), sym, sec, offset);
  }
}

StringRef InputFile::getNameForScript() const {
  if (archiveName.empty())
    return getName();

  if (nameForScriptCache.empty())
    nameForScriptCache = (archiveName + Twine(':') + getName()).str();

  return nameForScriptCache;
}

template <class ELFT> DWARFCache *ObjFile<ELFT>::getDwarf() {
  llvm::call_once(initDwarf, [this]() {
    dwarf = std::make_unique<DWARFCache>(std::make_unique<DWARFContext>(
        std::make_unique<LLDDwarfObj<ELFT>>(this), "",
        [&](Error err) { warn(getName() + ": " + toString(std::move(err))); },
        [&](Error warning) {
          warn(getName() + ": " + toString(std::move(warning)));
        }));
  });

  return dwarf.get();
}

// Returns the pair of file name and line number describing location of data
// object (variable, array, etc) definition.
template <class ELFT>
Optional<std::pair<std::string, unsigned>>
ObjFile<ELFT>::getVariableLoc(StringRef name) {
  return getDwarf()->getVariableLoc(name);
}

// Returns source line information for a given offset
// using DWARF debug info.
template <class ELFT>
Optional<DILineInfo> ObjFile<ELFT>::getDILineInfo(InputSectionBase *s,
                                                  uint64_t offset) {
  // Detect SectionIndex for specified section.
  uint64_t sectionIndex = object::SectionedAddress::UndefSection;
  ArrayRef<InputSectionBase *> sections = s->file->getSections();
  for (uint64_t curIndex = 0; curIndex < sections.size(); ++curIndex) {
    if (s == sections[curIndex]) {
      sectionIndex = curIndex;
      break;
    }
  }

  return getDwarf()->getDILineInfo(offset, sectionIndex);
}

ELFFileBase::ELFFileBase(Kind k, MemoryBufferRef mb) : InputFile(k, mb) {
  ekind = getELFKind(mb, "");

  switch (ekind) {
  case ELF32LEKind:
    init<ELF32LE>();
    break;
  case ELF32BEKind:
    init<ELF32BE>();
    break;
  case ELF64LEKind:
    init<ELF64LE>();
    break;
  case ELF64BEKind:
    init<ELF64BE>();
    break;
  default:
    llvm_unreachable("getELFKind");
  }
}

template <typename Elf_Shdr>
static const Elf_Shdr *findSection(ArrayRef<Elf_Shdr> sections, uint32_t type) {
  for (const Elf_Shdr &sec : sections)
    if (sec.sh_type == type)
      return &sec;
  return nullptr;
}

template <class ELFT> void ELFFileBase::init() {
  using Elf_Shdr = typename ELFT::Shdr;
  using Elf_Sym = typename ELFT::Sym;

  // Initialize trivial attributes.
  const ELFFile<ELFT> &obj = getObj<ELFT>();
  emachine = obj.getHeader().e_machine;
  osabi = obj.getHeader().e_ident[llvm::ELF::EI_OSABI];
  abiVersion = obj.getHeader().e_ident[llvm::ELF::EI_ABIVERSION];

  ArrayRef<Elf_Shdr> sections = CHECK(obj.sections(), this);
  elfShdrs = sections.data();
  numELFShdrs = sections.size();

  // Find a symbol table.
  bool isDSO =
      (identify_magic(mb.getBuffer()) == file_magic::elf_shared_object);
  const Elf_Shdr *symtabSec =
      findSection(sections, isDSO ? SHT_DYNSYM : SHT_SYMTAB);

  if (!symtabSec)
    return;

  // Initialize members corresponding to a symbol table.
  firstGlobal = symtabSec->sh_info;

  ArrayRef<Elf_Sym> eSyms = CHECK(obj.symbols(symtabSec), this);
  if (firstGlobal == 0 || firstGlobal > eSyms.size())
    fatal(toString(this) + ": invalid sh_info in symbol table");

  elfSyms = reinterpret_cast<const void *>(eSyms.data());
  numELFSyms = uint32_t(eSyms.size());
  stringTable = CHECK(obj.getStringTableForSymtab(*symtabSec, sections), this);
}

template <class ELFT>
uint32_t ObjFile<ELFT>::getSectionIndex(const Elf_Sym &sym) const {
  return CHECK(
      this->getObj().getSectionIndex(sym, getELFSyms<ELFT>(), shndxTable),
      this);
}

template <class ELFT> void ObjFile<ELFT>::parse(bool ignoreComdats) {
  object::ELFFile<ELFT> obj = this->getObj();
  // Read a section table. justSymbols is usually false.
  if (this->justSymbols)
    initializeJustSymbols();
  else
    initializeSections(ignoreComdats, obj);

  // Read a symbol table.
  initializeSymbols(obj);
}

// Sections with SHT_GROUP and comdat bits define comdat section groups.
// They are identified and deduplicated by group name. This function
// returns a group name.
template <class ELFT>
StringRef ObjFile<ELFT>::getShtGroupSignature(ArrayRef<Elf_Shdr> sections,
                                              const Elf_Shdr &sec) {
  typename ELFT::SymRange symbols = this->getELFSyms<ELFT>();
  if (sec.sh_info >= symbols.size())
    fatal(toString(this) + ": invalid symbol index");
  const typename ELFT::Sym &sym = symbols[sec.sh_info];
  return CHECK(sym.getName(this->stringTable), this);
}

template <class ELFT>
bool ObjFile<ELFT>::shouldMerge(const Elf_Shdr &sec, StringRef name) {
  // On a regular link we don't merge sections if -O0 (default is -O1). This
  // sometimes makes the linker significantly faster, although the output will
  // be bigger.
  //
  // Doing the same for -r would create a problem as it would combine sections
  // with different sh_entsize. One option would be to just copy every SHF_MERGE
  // section as is to the output. While this would produce a valid ELF file with
  // usable SHF_MERGE sections, tools like (llvm-)?dwarfdump get confused when
  // they see two .debug_str. We could have separate logic for combining
  // SHF_MERGE sections based both on their name and sh_entsize, but that seems
  // to be more trouble than it is worth. Instead, we just use the regular (-O1)
  // logic for -r.
  if (config->optimize == 0 && !config->relocatable)
    return false;

  // A mergeable section with size 0 is useless because they don't have
  // any data to merge. A mergeable string section with size 0 can be
  // argued as invalid because it doesn't end with a null character.
  // We'll avoid a mess by handling them as if they were non-mergeable.
  if (sec.sh_size == 0)
    return false;

  // Check for sh_entsize. The ELF spec is not clear about the zero
  // sh_entsize. It says that "the member [sh_entsize] contains 0 if
  // the section does not hold a table of fixed-size entries". We know
  // that Rust 1.13 produces a string mergeable section with a zero
  // sh_entsize. Here we just accept it rather than being picky about it.
  uint64_t entSize = sec.sh_entsize;
  if (entSize == 0)
    return false;
  if (sec.sh_size % entSize)
    fatal(toString(this) + ":(" + name + "): SHF_MERGE section size (" +
          Twine(sec.sh_size) + ") must be a multiple of sh_entsize (" +
          Twine(entSize) + ")");

  if (sec.sh_flags & SHF_WRITE)
    fatal(toString(this) + ":(" + name +
          "): writable SHF_MERGE section is not supported");

  return true;
}

// This is for --just-symbols.
//
// --just-symbols is a very minor feature that allows you to link your
// output against other existing program, so that if you load both your
// program and the other program into memory, your output can refer the
// other program's symbols.
//
// When the option is given, we link "just symbols". The section table is
// initialized with null pointers.
template <class ELFT> void ObjFile<ELFT>::initializeJustSymbols() {
  sections.resize(numELFShdrs);
}

// An ELF object file may contain a `.deplibs` section. If it exists, the
// section contains a list of library specifiers such as `m` for libm. This
// function resolves a given name by finding the first matching library checking
// the various ways that a library can be specified to LLD. This ELF extension
// is a form of autolinking and is called `dependent libraries`. It is currently
// unique to LLVM and lld.
static void addDependentLibrary(StringRef specifier, const InputFile *f) {
  if (!config->dependentLibraries)
    return;
  if (Optional<std::string> s = searchLibraryBaseName(specifier))
    driver->addFile(*s, /*withLOption=*/true);
  else if (Optional<std::string> s = findFromSearchPaths(specifier))
    driver->addFile(*s, /*withLOption=*/true);
  else if (fs::exists(specifier))
    driver->addFile(specifier, /*withLOption=*/false);
  else
    error(toString(f) +
          ": unable to find library from dependent library specifier: " +
          specifier);
}

// Record the membership of a section group so that in the garbage collection
// pass, section group members are kept or discarded as a unit.
template <class ELFT>
static void handleSectionGroup(ArrayRef<InputSectionBase *> sections,
                               ArrayRef<typename ELFT::Word> entries) {
  bool hasAlloc = false;
  for (uint32_t index : entries.slice(1)) {
    if (index >= sections.size())
      return;
    if (InputSectionBase *s = sections[index])
      if (s != &InputSection::discarded && s->flags & SHF_ALLOC)
        hasAlloc = true;
  }

  // If any member has the SHF_ALLOC flag, the whole group is subject to garbage
  // collection. See the comment in markLive(). This rule retains .debug_types
  // and .rela.debug_types.
  if (!hasAlloc)
    return;

  // Connect the members in a circular doubly-linked list via
  // nextInSectionGroup.
  InputSectionBase *head;
  InputSectionBase *prev = nullptr;
  for (uint32_t index : entries.slice(1)) {
    InputSectionBase *s = sections[index];
    if (!s || s == &InputSection::discarded)
      continue;
    if (prev)
      prev->nextInSectionGroup = s;
    else
      head = s;
    prev = s;
  }
  if (prev)
    prev->nextInSectionGroup = head;
}

template <class ELFT>
void ObjFile<ELFT>::initializeSections(bool ignoreComdats,
                                       const llvm::object::ELFFile<ELFT> &obj) {
  ArrayRef<Elf_Shdr> objSections = getELFShdrs<ELFT>();
  StringRef shstrtab = CHECK(obj.getSectionStringTable(objSections), this);
  uint64_t size = objSections.size();
  this->sections.resize(size);

  std::vector<ArrayRef<Elf_Word>> selectedGroups;

  for (size_t i = 0; i != size; ++i) {
    if (this->sections[i] == &InputSection::discarded)
      continue;
    const Elf_Shdr &sec = objSections[i];

    // SHF_EXCLUDE'ed sections are discarded by the linker. However,
    // if -r is given, we'll let the final link discard such sections.
    // This is compatible with GNU.
    if ((sec.sh_flags & SHF_EXCLUDE) && !config->relocatable) {
      if (sec.sh_type == SHT_LLVM_CALL_GRAPH_PROFILE)
        cgProfileSectionIndex = i;
      if (sec.sh_type == SHT_LLVM_ADDRSIG) {
        // We ignore the address-significance table if we know that the object
        // file was created by objcopy or ld -r. This is because these tools
        // will reorder the symbols in the symbol table, invalidating the data
        // in the address-significance table, which refers to symbols by index.
        if (sec.sh_link != 0)
          this->addrsigSec = &sec;
        else if (config->icf == ICFLevel::Safe)
          warn(toString(this) +
               ": --icf=safe conservatively ignores "
               "SHT_LLVM_ADDRSIG [index " +
               Twine(i) +
               "] with sh_link=0 "
               "(likely created using objcopy or ld -r)");
      }
      this->sections[i] = &InputSection::discarded;
      continue;
    }

    switch (sec.sh_type) {
    case SHT_GROUP: {
      // De-duplicate section groups by their signatures.
      StringRef signature = getShtGroupSignature(objSections, sec);
      this->sections[i] = &InputSection::discarded;

      ArrayRef<Elf_Word> entries =
          CHECK(obj.template getSectionContentsAsArray<Elf_Word>(sec), this);
      if (entries.empty())
        fatal(toString(this) + ": empty SHT_GROUP");

      Elf_Word flag = entries[0];
      if (flag && flag != GRP_COMDAT)
        fatal(toString(this) + ": unsupported SHT_GROUP format");

      bool keepGroup =
          (flag & GRP_COMDAT) == 0 || ignoreComdats ||
          symtab->comdatGroups.try_emplace(CachedHashStringRef(signature), this)
              .second;
      if (keepGroup) {
        if (config->relocatable)
          this->sections[i] = createInputSection(
              i, sec, check(obj.getSectionName(sec, shstrtab)));
        selectedGroups.push_back(entries);
        continue;
      }

      // Otherwise, discard group members.
      for (uint32_t secIndex : entries.slice(1)) {
        if (secIndex >= size)
          fatal(toString(this) +
                ": invalid section index in group: " + Twine(secIndex));
        this->sections[secIndex] = &InputSection::discarded;
      }
      break;
    }
    case SHT_SYMTAB_SHNDX:
      shndxTable = CHECK(obj.getSHNDXTable(sec, objSections), this);
      break;
    case SHT_SYMTAB:
    case SHT_STRTAB:
    case SHT_REL:
    case SHT_RELA:
    case SHT_NULL:
      break;
    default:
      this->sections[i] =
          createInputSection(i, sec, check(obj.getSectionName(sec, shstrtab)));
    }
  }

  // We have a second loop. It is used to:
  // 1) handle SHF_LINK_ORDER sections.
  // 2) create SHT_REL[A] sections. In some cases the section header index of a
  //    relocation section may be smaller than that of the relocated section. In
  //    such cases, the relocation section would attempt to reference a target
  //    section that has not yet been created. For simplicity, delay creation of
  //    relocation sections until now.
  for (size_t i = 0; i != size; ++i) {
    if (this->sections[i] == &InputSection::discarded)
      continue;
    const Elf_Shdr &sec = objSections[i];

    if (sec.sh_type == SHT_REL || sec.sh_type == SHT_RELA) {
      // Find a relocation target section and associate this section with that.
      // Target may have been discarded if it is in a different section group
      // and the group is discarded, even though it's a violation of the spec.
      // We handle that situation gracefully by discarding dangling relocation
      // sections.
      const uint32_t info = sec.sh_info;
      InputSectionBase *s = getRelocTarget(i, sec, info);
      if (!s)
        continue;

      // ELF spec allows mergeable sections with relocations, but they are rare,
      // and it is in practice hard to merge such sections by contents, because
      // applying relocations at end of linking changes section contents. So, we
      // simply handle such sections as non-mergeable ones. Degrading like this
      // is acceptable because section merging is optional.
      if (auto *ms = dyn_cast<MergeInputSection>(s)) {
        s = make<InputSection>(ms->file, ms->flags, ms->type, ms->alignment,
                               ms->data(), ms->name);
        sections[info] = s;
      }

      if (s->relSecIdx != 0)
        error(
            toString(s) +
            ": multiple relocation sections to one section are not supported");
      s->relSecIdx = i;

      // Relocation sections are usually removed from the output, so return
      // `nullptr` for the normal case. However, if -r or --emit-relocs is
      // specified, we need to copy them to the output. (Some post link analysis
      // tools specify --emit-relocs to obtain the information.)
      if (config->copyRelocs) {
        auto *isec = make<InputSection>(
            *this, sec, check(obj.getSectionName(sec, shstrtab)));
        // If the relocated section is discarded (due to /DISCARD/ or
        // --gc-sections), the relocation section should be discarded as well.
        s->dependentSections.push_back(isec);
        sections[i] = isec;
      }
      continue;
    }

    // A SHF_LINK_ORDER section with sh_link=0 is handled as if it did not have
    // the flag.
    if (!sec.sh_link || !(sec.sh_flags & SHF_LINK_ORDER))
      continue;

    InputSectionBase *linkSec = nullptr;
    if (sec.sh_link < size)
      linkSec = this->sections[sec.sh_link];
    if (!linkSec)
      fatal(toString(this) + ": invalid sh_link index: " + Twine(sec.sh_link));

    // A SHF_LINK_ORDER section is discarded if its linked-to section is
    // discarded.
    InputSection *isec = cast<InputSection>(this->sections[i]);
    linkSec->dependentSections.push_back(isec);
    if (!isa<InputSection>(linkSec))
      error("a section " + isec->name +
            " with SHF_LINK_ORDER should not refer a non-regular section: " +
            toString(linkSec));
  }

  for (ArrayRef<Elf_Word> entries : selectedGroups)
    handleSectionGroup<ELFT>(this->sections, entries);
}

// For ARM only, to set the EF_ARM_ABI_FLOAT_SOFT or EF_ARM_ABI_FLOAT_HARD
// flag in the ELF Header we need to look at Tag_ABI_VFP_args to find out how
// the input objects have been compiled.
static void updateARMVFPArgs(const ARMAttributeParser &attributes,
                             const InputFile *f) {
  Optional<unsigned> attr =
      attributes.getAttributeValue(ARMBuildAttrs::ABI_VFP_args);
  if (!attr.hasValue())
    // If an ABI tag isn't present then it is implicitly given the value of 0
    // which maps to ARMBuildAttrs::BaseAAPCS. However many assembler files,
    // including some in glibc that don't use FP args (and should have value 3)
    // don't have the attribute so we do not consider an implicit value of 0
    // as a clash.
    return;

  unsigned vfpArgs = attr.getValue();
  ARMVFPArgKind arg;
  switch (vfpArgs) {
  case ARMBuildAttrs::BaseAAPCS:
    arg = ARMVFPArgKind::Base;
    break;
  case ARMBuildAttrs::HardFPAAPCS:
    arg = ARMVFPArgKind::VFP;
    break;
  case ARMBuildAttrs::ToolChainFPPCS:
    // Tool chain specific convention that conforms to neither AAPCS variant.
    arg = ARMVFPArgKind::ToolChain;
    break;
  case ARMBuildAttrs::CompatibleFPAAPCS:
    // Object compatible with all conventions.
    return;
  default:
    error(toString(f) + ": unknown Tag_ABI_VFP_args value: " + Twine(vfpArgs));
    return;
  }
  // Follow ld.bfd and error if there is a mix of calling conventions.
  if (config->armVFPArgs != arg && config->armVFPArgs != ARMVFPArgKind::Default)
    error(toString(f) + ": incompatible Tag_ABI_VFP_args");
  else
    config->armVFPArgs = arg;
}

// The ARM support in lld makes some use of instructions that are not available
// on all ARM architectures. Namely:
// - Use of BLX instruction for interworking between ARM and Thumb state.
// - Use of the extended Thumb branch encoding in relocation.
// - Use of the MOVT/MOVW instructions in Thumb Thunks.
// The ARM Attributes section contains information about the architecture chosen
// at compile time. We follow the convention that if at least one input object
// is compiled with an architecture that supports these features then lld is
// permitted to use them.
static void updateSupportedARMFeatures(const ARMAttributeParser &attributes) {
  Optional<unsigned> attr =
      attributes.getAttributeValue(ARMBuildAttrs::CPU_arch);
  if (!attr.hasValue())
    return;
  auto arch = attr.getValue();
  switch (arch) {
  case ARMBuildAttrs::Pre_v4:
  case ARMBuildAttrs::v4:
  case ARMBuildAttrs::v4T:
    // Architectures prior to v5 do not support BLX instruction
    break;
  case ARMBuildAttrs::v5T:
  case ARMBuildAttrs::v5TE:
  case ARMBuildAttrs::v5TEJ:
  case ARMBuildAttrs::v6:
  case ARMBuildAttrs::v6KZ:
  case ARMBuildAttrs::v6K:
    config->armHasBlx = true;
    // Architectures used in pre-Cortex processors do not support
    // The J1 = 1 J2 = 1 Thumb branch range extension, with the exception
    // of Architecture v6T2 (arm1156t2-s and arm1156t2f-s) that do.
    break;
  default:
    // All other Architectures have BLX and extended branch encoding
    config->armHasBlx = true;
    config->armJ1J2BranchEncoding = true;
    if (arch != ARMBuildAttrs::v6_M && arch != ARMBuildAttrs::v6S_M)
      // All Architectures used in Cortex processors with the exception
      // of v6-M and v6S-M have the MOVT and MOVW instructions.
      config->armHasMovtMovw = true;
    break;
  }
}

// If a source file is compiled with x86 hardware-assisted call flow control
// enabled, the generated object file contains feature flags indicating that
// fact. This function reads the feature flags and returns it.
//
// Essentially we want to read a single 32-bit value in this function, but this
// function is rather complicated because the value is buried deep inside a
// .note.gnu.property section.
//
// The section consists of one or more NOTE records. Each NOTE record consists
// of zero or more type-length-value fields. We want to find a field of a
// certain type. It seems a bit too much to just store a 32-bit value, perhaps
// the ABI is unnecessarily complicated.
template <class ELFT> static uint32_t readAndFeatures(const InputSection &sec) {
  using Elf_Nhdr = typename ELFT::Nhdr;
  using Elf_Note = typename ELFT::Note;

  uint32_t featuresSet = 0;
  ArrayRef<uint8_t> data = sec.data();
  auto reportFatal = [&](const uint8_t *place, const char *msg) {
    fatal(toString(sec.file) + ":(" + sec.name + "+0x" +
          Twine::utohexstr(place - sec.data().data()) + "): " + msg);
  };
  while (!data.empty()) {
    // Read one NOTE record.
    auto *nhdr = reinterpret_cast<const Elf_Nhdr *>(data.data());
    if (data.size() < sizeof(Elf_Nhdr) || data.size() < nhdr->getSize())
      reportFatal(data.data(), "data is too short");

    Elf_Note note(*nhdr);
    if (nhdr->n_type != NT_GNU_PROPERTY_TYPE_0 || note.getName() != "GNU") {
      data = data.slice(nhdr->getSize());
      continue;
    }

    uint32_t featureAndType = config->emachine == EM_AARCH64
                                  ? GNU_PROPERTY_AARCH64_FEATURE_1_AND
                                  : GNU_PROPERTY_X86_FEATURE_1_AND;

    // Read a body of a NOTE record, which consists of type-length-value fields.
    ArrayRef<uint8_t> desc = note.getDesc();
    while (!desc.empty()) {
      const uint8_t *place = desc.data();
      if (desc.size() < 8)
        reportFatal(place, "program property is too short");
      uint32_t type = read32<ELFT::TargetEndianness>(desc.data());
      uint32_t size = read32<ELFT::TargetEndianness>(desc.data() + 4);
      desc = desc.slice(8);
      if (desc.size() < size)
        reportFatal(place, "program property is too short");

      if (type == featureAndType) {
        // We found a FEATURE_1_AND field. There may be more than one of these
        // in a .note.gnu.property section, for a relocatable object we
        // accumulate the bits set.
        if (size < 4)
          reportFatal(place, "FEATURE_1_AND entry is too short");
        featuresSet |= read32<ELFT::TargetEndianness>(desc.data());
      }

      // Padding is present in the note descriptor, if necessary.
      desc = desc.slice(alignTo<(ELFT::Is64Bits ? 8 : 4)>(size));
    }

    // Go to next NOTE record to look for more FEATURE_1_AND descriptions.
    data = data.slice(nhdr->getSize());
  }

  return featuresSet;
}

template <class ELFT>
InputSectionBase *ObjFile<ELFT>::getRelocTarget(uint32_t idx,
                                                const Elf_Shdr &sec,
                                                uint32_t info) {
  if (info < this->sections.size()) {
    InputSectionBase *target = this->sections[info];

    // Strictly speaking, a relocation section must be included in the
    // group of the section it relocates. However, LLVM 3.3 and earlier
    // would fail to do so, so we gracefully handle that case.
    if (target == &InputSection::discarded)
      return nullptr;

    if (target != nullptr)
      return target;
  }

  error(toString(this) + Twine(": relocation section (index ") + Twine(idx) +
        ") has invalid sh_info (" + Twine(info) + ")");
  return nullptr;
}

template <class ELFT>
InputSectionBase *ObjFile<ELFT>::createInputSection(uint32_t idx,
                                                    const Elf_Shdr &sec,
                                                    StringRef name) {
  if (sec.sh_type == SHT_ARM_ATTRIBUTES && config->emachine == EM_ARM) {
    ARMAttributeParser attributes;
    ArrayRef<uint8_t> contents = check(this->getObj().getSectionContents(sec));
    if (Error e = attributes.parse(contents, config->ekind == ELF32LEKind
                                                 ? support::little
                                                 : support::big)) {
      auto *isec = make<InputSection>(*this, sec, name);
      warn(toString(isec) + ": " + llvm::toString(std::move(e)));
    } else {
      updateSupportedARMFeatures(attributes);
      updateARMVFPArgs(attributes, this);

      // FIXME: Retain the first attribute section we see. The eglibc ARM
      // dynamic loaders require the presence of an attribute section for dlopen
      // to work. In a full implementation we would merge all attribute
      // sections.
      if (in.attributes == nullptr) {
        in.attributes = std::make_unique<InputSection>(*this, sec, name);
        return in.attributes.get();
      }
      return &InputSection::discarded;
    }
  }

  if (sec.sh_type == SHT_RISCV_ATTRIBUTES && config->emachine == EM_RISCV) {
    RISCVAttributeParser attributes;
    ArrayRef<uint8_t> contents = check(this->getObj().getSectionContents(sec));
    if (Error e = attributes.parse(contents, support::little)) {
      auto *isec = make<InputSection>(*this, sec, name);
      warn(toString(isec) + ": " + llvm::toString(std::move(e)));
    } else {
      // FIXME: Validate arch tag contains C if and only if EF_RISCV_RVC is
      // present.

      // FIXME: Retain the first attribute section we see. Tools such as
      // llvm-objdump make use of the attribute section to determine which
      // standard extensions to enable. In a full implementation we would merge
      // all attribute sections.
      if (in.attributes == nullptr) {
        in.attributes = std::make_unique<InputSection>(*this, sec, name);
        return in.attributes.get();
      }
      return &InputSection::discarded;
    }
  }

  if (sec.sh_type == SHT_LLVM_DEPENDENT_LIBRARIES && !config->relocatable) {
    ArrayRef<char> data =
        CHECK(this->getObj().template getSectionContentsAsArray<char>(sec), this);
    if (!data.empty() && data.back() != '\0') {
      error(toString(this) +
            ": corrupted dependent libraries section (unterminated string): " +
            name);
      return &InputSection::discarded;
    }
    for (const char *d = data.begin(), *e = data.end(); d < e;) {
      StringRef s(d);
      addDependentLibrary(s, this);
      d += s.size() + 1;
    }
    return &InputSection::discarded;
  }

  if (name.startswith(".n")) {
    // The GNU linker uses .note.GNU-stack section as a marker indicating
    // that the code in the object file does not expect that the stack is
    // executable (in terms of NX bit). If all input files have the marker,
    // the GNU linker adds a PT_GNU_STACK segment to tells the loader to
    // make the stack non-executable. Most object files have this section as
    // of 2017.
    //
    // But making the stack non-executable is a norm today for security
    // reasons. Failure to do so may result in a serious security issue.
    // Therefore, we make LLD always add PT_GNU_STACK unless it is
    // explicitly told to do otherwise (by -z execstack). Because the stack
    // executable-ness is controlled solely by command line options,
    // .note.GNU-stack sections are simply ignored.
    if (name == ".note.GNU-stack")
      return &InputSection::discarded;

    // Object files that use processor features such as Intel Control-Flow
    // Enforcement (CET) or AArch64 Branch Target Identification BTI, use a
    // .note.gnu.property section containing a bitfield of feature bits like the
    // GNU_PROPERTY_X86_FEATURE_1_IBT flag. Read a bitmap containing the flag.
    //
    // Since we merge bitmaps from multiple object files to create a new
    // .note.gnu.property containing a single AND'ed bitmap, we discard an input
    // file's .note.gnu.property section.
    if (name == ".note.gnu.property") {
      this->andFeatures = readAndFeatures<ELFT>(InputSection(*this, sec, name));
      return &InputSection::discarded;
    }

    // Split stacks is a feature to support a discontiguous stack,
    // commonly used in the programming language Go. For the details,
    // see https://gcc.gnu.org/wiki/SplitStacks. An object file compiled
    // for split stack will include a .note.GNU-split-stack section.
    if (name == ".note.GNU-split-stack") {
      if (config->relocatable) {
        error(
            "cannot mix split-stack and non-split-stack in a relocatable link");
        return &InputSection::discarded;
      }
      this->splitStack = true;
      return &InputSection::discarded;
    }

    // An object file cmpiled for split stack, but where some of the
    // functions were compiled with the no_split_stack_attribute will
    // include a .note.GNU-no-split-stack section.
    if (name == ".note.GNU-no-split-stack") {
      this->someNoSplitStack = true;
      return &InputSection::discarded;
    }

    // Strip existing .note.gnu.build-id sections so that the output won't have
    // more than one build-id. This is not usually a problem because input
    // object files normally don't have .build-id sections, but you can create
    // such files by "ld.{bfd,gold,lld} -r --build-id", and we want to guard
    // against it.
    if (name == ".note.gnu.build-id")
      return &InputSection::discarded;
  }

  // The linkonce feature is a sort of proto-comdat. Some glibc i386 object
  // files contain definitions of symbol "__x86.get_pc_thunk.bx" in linkonce
  // sections. Drop those sections to avoid duplicate symbol errors.
  // FIXME: This is glibc PR20543, we should remove this hack once that has been
  // fixed for a while.
  if (name == ".gnu.linkonce.t.__x86.get_pc_thunk.bx" ||
      name == ".gnu.linkonce.t.__i686.get_pc_thunk.bx")
    return &InputSection::discarded;

  // The linker merges EH (exception handling) frames and creates a
  // .eh_frame_hdr section for runtime. So we handle them with a special
  // class. For relocatable outputs, they are just passed through.
  if (name == ".eh_frame" && !config->relocatable)
    return make<EhInputSection>(*this, sec, name);

  if ((sec.sh_flags & SHF_MERGE) && shouldMerge(sec, name))
    return make<MergeInputSection>(*this, sec, name);
  return make<InputSection>(*this, sec, name);
}

// Initialize this->Symbols. this->Symbols is a parallel array as
// its corresponding ELF symbol table.
template <class ELFT>
void ObjFile<ELFT>::initializeSymbols(const object::ELFFile<ELFT> &obj) {
  ArrayRef<InputSectionBase *> sections(this->sections);
  SymbolTable &symtab = *elf::symtab;

  ArrayRef<Elf_Sym> eSyms = this->getELFSyms<ELFT>();
  symbols.resize(eSyms.size());
  SymbolUnion *locals =
      firstGlobal == 0
          ? nullptr
          : getSpecificAllocSingleton<SymbolUnion>().Allocate(firstGlobal);

  for (size_t i = 0, end = firstGlobal; i != end; ++i) {
    const Elf_Sym &eSym = eSyms[i];
    uint32_t secIdx = eSym.st_shndx;
    if (LLVM_UNLIKELY(secIdx == SHN_XINDEX))
      secIdx = check(getExtendedSymbolTableIndex<ELFT>(eSym, i, shndxTable));
    else if (secIdx >= SHN_LORESERVE)
      secIdx = 0;
    if (LLVM_UNLIKELY(secIdx >= sections.size()))
      fatal(toString(this) + ": invalid section index: " + Twine(secIdx));
    if (LLVM_UNLIKELY(eSym.getBinding() != STB_LOCAL))
      error(toString(this) + ": non-local symbol (" + Twine(i) +
            ") found at index < .symtab's sh_info (" + Twine(end) + ")");

    InputSectionBase *sec = sections[secIdx];
    uint8_t type = eSym.getType();
    if (type == STT_FILE)
      sourceFile = CHECK(eSym.getName(stringTable), this);
    if (LLVM_UNLIKELY(stringTable.size() <= eSym.st_name))
      fatal(toString(this) + ": invalid symbol name offset");
    StringRef name(stringTable.data() + eSym.st_name);

    symbols[i] = reinterpret_cast<Symbol *>(locals + i);
    if (eSym.st_shndx == SHN_UNDEF || sec == &InputSection::discarded)
      new (symbols[i]) Undefined(this, name, STB_LOCAL, eSym.st_other, type,
                                 /*discardedSecIdx=*/secIdx);
    else
      new (symbols[i]) Defined(this, name, STB_LOCAL, eSym.st_other, type,
                               eSym.st_value, eSym.st_size, sec);
  }

  // Some entries have been filled by LazyObjFile.
  for (size_t i = firstGlobal, end = eSyms.size(); i != end; ++i)
    if (!symbols[i])
      symbols[i] = symtab.insert(CHECK(eSyms[i].getName(stringTable), this));

  // Perform symbol resolution on non-local symbols.
  SmallVector<unsigned, 32> undefineds;
  for (size_t i = firstGlobal, end = eSyms.size(); i != end; ++i) {
    const Elf_Sym &eSym = eSyms[i];
    uint8_t binding = eSym.getBinding();
    if (LLVM_UNLIKELY(binding == STB_LOCAL)) {
      errorOrWarn(toString(this) + ": STB_LOCAL symbol (" + Twine(i) +
                  ") found at index >= .symtab's sh_info (" +
                  Twine(firstGlobal) + ")");
      continue;
    }
    uint32_t secIdx = eSym.st_shndx;
    if (LLVM_UNLIKELY(secIdx == SHN_XINDEX))
      secIdx = check(getExtendedSymbolTableIndex<ELFT>(eSym, i, shndxTable));
    else if (secIdx >= SHN_LORESERVE)
      secIdx = 0;
    if (LLVM_UNLIKELY(secIdx >= sections.size()))
      fatal(toString(this) + ": invalid section index: " + Twine(secIdx));
    InputSectionBase *sec = sections[secIdx];
    uint8_t stOther = eSym.st_other;
    uint8_t type = eSym.getType();
    uint64_t value = eSym.st_value;
    uint64_t size = eSym.st_size;

    if (eSym.st_shndx == SHN_UNDEF) {
      undefineds.push_back(i);
      continue;
    }

    Symbol *sym = symbols[i];
    const StringRef name = sym->getName();
    if (LLVM_UNLIKELY(eSym.st_shndx == SHN_COMMON)) {
      if (value == 0 || value >= UINT32_MAX)
        fatal(toString(this) + ": common symbol '" + name +
              "' has invalid alignment: " + Twine(value));
      hasCommonSyms = true;
      sym->resolve(
          CommonSymbol{this, name, binding, stOther, type, value, size});
      continue;
    }

    // If a defined symbol is in a discarded section, handle it as if it
    // were an undefined symbol. Such symbol doesn't comply with the
    // standard, but in practice, a .eh_frame often directly refer
    // COMDAT member sections, and if a comdat group is discarded, some
    // defined symbol in a .eh_frame becomes dangling symbols.
    if (sec == &InputSection::discarded) {
      Undefined und{this, name, binding, stOther, type, secIdx};
      // !ArchiveFile::parsed or !LazyObjFile::lazy means that the file
      // containing this object has not finished processing, i.e. this symbol is
      // a result of a lazy symbol extract. We should demote the lazy symbol to
      // an Undefined so that any relocations outside of the group to it will
      // trigger a discarded section error.
      if ((sym->symbolKind == Symbol::LazyArchiveKind &&
           !cast<ArchiveFile>(sym->file)->parsed) ||
          (sym->symbolKind == Symbol::LazyObjectKind && !sym->file->lazy)) {
        sym->replace(und);
        // Prevent LTO from internalizing the symbol in case there is a
        // reference to this symbol from this file.
        sym->isUsedInRegularObj = true;
      } else
        sym->resolve(und);
      continue;
    }

    // Handle global defined symbols.
    if (binding == STB_GLOBAL || binding == STB_WEAK ||
        binding == STB_GNU_UNIQUE) {
      sym->resolve(
          Defined{this, name, binding, stOther, type, value, size, sec});
      continue;
    }

    fatal(toString(this) + ": unexpected binding: " + Twine((int)binding));
  }

  // Undefined symbols (excluding those defined relative to non-prevailing
  // sections) can trigger recursive extract. Process defined symbols first so
  // that the relative order between a defined symbol and an undefined symbol
  // does not change the symbol resolution behavior. In addition, a set of
  // interconnected symbols will all be resolved to the same file, instead of
  // being resolved to different files.
  for (unsigned i : undefineds) {
    const Elf_Sym &eSym = eSyms[i];
    Symbol *sym = symbols[i];
    sym->resolve(Undefined{this, sym->getName(), eSym.getBinding(),
                           eSym.st_other, eSym.getType()});
    sym->referenced = true;
  }
}

ArchiveFile::ArchiveFile(std::unique_ptr<Archive> &&file)
    : InputFile(ArchiveKind, file->getMemoryBufferRef()),
      file(std::move(file)) {}

void ArchiveFile::parse() {
  SymbolTable &symtab = *elf::symtab;
  for (const Archive::Symbol &sym : file->symbols())
    symtab.addSymbol(LazyArchive{*this, sym});

  // Inform a future invocation of ObjFile<ELFT>::initializeSymbols() that this
  // archive has been processed.
  parsed = true;
}

// Returns a buffer pointing to a member file containing a given symbol.
void ArchiveFile::extract(const Archive::Symbol &sym) {
  Archive::Child c =
      CHECK(sym.getMember(), toString(this) +
                                 ": could not get the member for symbol " +
                                 toELFString(sym));

  if (!seen.insert(c.getChildOffset()).second)
    return;

  MemoryBufferRef mb =
      CHECK(c.getMemoryBufferRef(),
            toString(this) +
                ": could not get the buffer for the member defining symbol " +
                toELFString(sym));

  if (tar && c.getParent()->isThin())
    tar->append(relativeToRoot(CHECK(c.getFullName(), this)), mb.getBuffer());

  InputFile *file = createObjectFile(mb, getName(), c.getChildOffset());
  file->groupId = groupId;
  parseFile(file);
}

// The handling of tentative definitions (COMMON symbols) in archives is murky.
// A tentative definition will be promoted to a global definition if there are
// no non-tentative definitions to dominate it. When we hold a tentative
// definition to a symbol and are inspecting archive members for inclusion
// there are 2 ways we can proceed:
//
// 1) Consider the tentative definition a 'real' definition (ie promotion from
//    tentative to real definition has already happened) and not inspect
//    archive members for Global/Weak definitions to replace the tentative
//    definition. An archive member would only be included if it satisfies some
//    other undefined symbol. This is the behavior Gold uses.
//
// 2) Consider the tentative definition as still undefined (ie the promotion to
//    a real definition happens only after all symbol resolution is done).
//    The linker searches archive members for STB_GLOBAL definitions to
//    replace the tentative definition with. This is the behavior used by
//    GNU ld.
//
//  The second behavior is inherited from SysVR4, which based it on the FORTRAN
//  COMMON BLOCK model. This behavior is needed for proper initialization in old
//  (pre F90) FORTRAN code that is packaged into an archive.
//
//  The following functions search archive members for definitions to replace
//  tentative definitions (implementing behavior 2).
static bool isBitcodeNonCommonDef(MemoryBufferRef mb, StringRef symName,
                                  StringRef archiveName) {
  IRSymtabFile symtabFile = check(readIRSymtab(mb));
  for (const irsymtab::Reader::SymbolRef &sym :
       symtabFile.TheReader.symbols()) {
    if (sym.isGlobal() && sym.getName() == symName)
      return !sym.isUndefined() && !sym.isWeak() && !sym.isCommon();
  }
  return false;
}

template <class ELFT>
static bool isNonCommonDef(MemoryBufferRef mb, StringRef symName,
                           StringRef archiveName) {
  ObjFile<ELFT> *obj = make<ObjFile<ELFT>>(mb, archiveName);
  StringRef stringtable = obj->getStringTable();

  for (auto sym : obj->template getGlobalELFSyms<ELFT>()) {
    Expected<StringRef> name = sym.getName(stringtable);
    if (name && name.get() == symName)
      return sym.isDefined() && sym.getBinding() == STB_GLOBAL &&
             !sym.isCommon();
  }
  return false;
}

static bool isNonCommonDef(MemoryBufferRef mb, StringRef symName,
                           StringRef archiveName) {
  switch (getELFKind(mb, archiveName)) {
  case ELF32LEKind:
    return isNonCommonDef<ELF32LE>(mb, symName, archiveName);
  case ELF32BEKind:
    return isNonCommonDef<ELF32BE>(mb, symName, archiveName);
  case ELF64LEKind:
    return isNonCommonDef<ELF64LE>(mb, symName, archiveName);
  case ELF64BEKind:
    return isNonCommonDef<ELF64BE>(mb, symName, archiveName);
  default:
    llvm_unreachable("getELFKind");
  }
}

bool ArchiveFile::shouldExtractForCommon(const Archive::Symbol &sym) {
  Archive::Child c =
      CHECK(sym.getMember(), toString(this) +
                                 ": could not get the member for symbol " +
                                 toELFString(sym));
  MemoryBufferRef mb =
      CHECK(c.getMemoryBufferRef(),
            toString(this) +
                ": could not get the buffer for the member defining symbol " +
                toELFString(sym));

  if (isBitcode(mb))
    return isBitcodeNonCommonDef(mb, sym.getName(), getName());

  return isNonCommonDef(mb, sym.getName(), getName());
}

size_t ArchiveFile::getMemberCount() const {
  size_t count = 0;
  Error err = Error::success();
  for (const Archive::Child &c : file->children(err)) {
    (void)c;
    ++count;
  }
  // This function is used by --print-archive-stats=, where an error does not
  // really matter.
  consumeError(std::move(err));
  return count;
}

unsigned SharedFile::vernauxNum;

// Parse the version definitions in the object file if present, and return a
// vector whose nth element contains a pointer to the Elf_Verdef for version
// identifier n. Version identifiers that are not definitions map to nullptr.
template <typename ELFT>
static SmallVector<const void *, 0>
parseVerdefs(const uint8_t *base, const typename ELFT::Shdr *sec) {
  if (!sec)
    return {};

  // Build the Verdefs array by following the chain of Elf_Verdef objects
  // from the start of the .gnu.version_d section.
  SmallVector<const void *, 0> verd