path: root/contrib/libs/llvm12/lib/Object/ArchiveWriter.cpp

//===- ArchiveWriter.cpp - ar File Format implementation --------*- C++ -*-===// 
// 
// 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 
// 
//===----------------------------------------------------------------------===// 
// 
// This file defines the writeArchive function. 
// 
//===----------------------------------------------------------------------===// 
 
#include "llvm/Object/ArchiveWriter.h" 
#include "llvm/ADT/ArrayRef.h" 
#include "llvm/ADT/StringMap.h" 
#include "llvm/ADT/StringRef.h" 
#include "llvm/BinaryFormat/Magic.h" 
#include "llvm/IR/LLVMContext.h" 
#include "llvm/Object/Archive.h" 
#include "llvm/Object/Error.h" 
#include "llvm/Object/ObjectFile.h" 
#include "llvm/Object/SymbolicFile.h" 
#include "llvm/Support/Alignment.h" 
#include "llvm/Support/EndianStream.h" 
#include "llvm/Support/Errc.h" 
#include "llvm/Support/ErrorHandling.h" 
#include "llvm/Support/Format.h" 
#include "llvm/Support/Path.h" 
#include "llvm/Support/SmallVectorMemoryBuffer.h"
#include "llvm/Support/ToolOutputFile.h" 
#include "llvm/Support/raw_ostream.h" 
 
#include <map> 
 
#if !defined(_MSC_VER) && !defined(__MINGW32__) 
#include <unistd.h> 
#else 
#include <io.h> 
#endif 
 
using namespace llvm; 
 
NewArchiveMember::NewArchiveMember(MemoryBufferRef BufRef) 
    : Buf(MemoryBuffer::getMemBuffer(BufRef, false)), 
      MemberName(BufRef.getBufferIdentifier()) {} 
 
Expected<NewArchiveMember> 
NewArchiveMember::getOldMember(const object::Archive::Child &OldMember, 
                               bool Deterministic) { 
  Expected<llvm::MemoryBufferRef> BufOrErr = OldMember.getMemoryBufferRef(); 
  if (!BufOrErr) 
    return BufOrErr.takeError(); 
 
  NewArchiveMember M; 
  M.Buf = MemoryBuffer::getMemBuffer(*BufOrErr, false); 
  M.MemberName = M.Buf->getBufferIdentifier(); 
  if (!Deterministic) { 
    auto ModTimeOrErr = OldMember.getLastModified(); 
    if (!ModTimeOrErr) 
      return ModTimeOrErr.takeError(); 
    M.ModTime = ModTimeOrErr.get(); 
    Expected<unsigned> UIDOrErr = OldMember.getUID(); 
    if (!UIDOrErr) 
      return UIDOrErr.takeError(); 
    M.UID = UIDOrErr.get(); 
    Expected<unsigned> GIDOrErr = OldMember.getGID(); 
    if (!GIDOrErr) 
      return GIDOrErr.takeError(); 
    M.GID = GIDOrErr.get(); 
    Expected<sys::fs::perms> AccessModeOrErr = OldMember.getAccessMode(); 
    if (!AccessModeOrErr) 
      return AccessModeOrErr.takeError(); 
    M.Perms = AccessModeOrErr.get(); 
  } 
  return std::move(M); 
} 
 
Expected<NewArchiveMember> NewArchiveMember::getFile(StringRef FileName, 
                                                     bool Deterministic) { 
  sys::fs::file_status Status; 
  auto FDOrErr = sys::fs::openNativeFileForRead(FileName); 
  if (!FDOrErr) 
    return FDOrErr.takeError(); 
  sys::fs::file_t FD = *FDOrErr; 
  assert(FD != sys::fs::kInvalidFile); 
 
  if (auto EC = sys::fs::status(FD, Status)) 
    return errorCodeToError(EC); 
 
  // Opening a directory doesn't make sense. Let it fail. 
  // Linux cannot open directories with open(2), although 
  // cygwin and *bsd can. 
  if (Status.type() == sys::fs::file_type::directory_file) 
    return errorCodeToError(make_error_code(errc::is_a_directory)); 
 
  ErrorOr<std::unique_ptr<MemoryBuffer>> MemberBufferOrErr = 
      MemoryBuffer::getOpenFile(FD, FileName, Status.getSize(), false); 
  if (!MemberBufferOrErr) 
    return errorCodeToError(MemberBufferOrErr.getError()); 
 
  if (auto EC = sys::fs::closeFile(FD)) 
    return errorCodeToError(EC); 
 
  NewArchiveMember M; 
  M.Buf = std::move(*MemberBufferOrErr); 
  M.MemberName = M.Buf->getBufferIdentifier(); 
  if (!Deterministic) { 
    M.ModTime = std::chrono::time_point_cast<std::chrono::seconds>( 
        Status.getLastModificationTime()); 
    M.UID = Status.getUser(); 
    M.GID = Status.getGroup(); 
    M.Perms = Status.permissions(); 
  } 
  return std::move(M); 
} 
 
template <typename T> 
static void printWithSpacePadding(raw_ostream &OS, T Data, unsigned Size) { 
  uint64_t OldPos = OS.tell(); 
  OS << Data; 
  unsigned SizeSoFar = OS.tell() - OldPos; 
  assert(SizeSoFar <= Size && "Data doesn't fit in Size"); 
  OS.indent(Size - SizeSoFar); 
} 
 
static bool isDarwin(object::Archive::Kind Kind) { 
  return Kind == object::Archive::K_DARWIN || 
         Kind == object::Archive::K_DARWIN64; 
} 
 
static bool isBSDLike(object::Archive::Kind Kind) { 
  switch (Kind) { 
  case object::Archive::K_GNU: 
  case object::Archive::K_GNU64: 
    return false; 
  case object::Archive::K_BSD: 
  case object::Archive::K_DARWIN: 
  case object::Archive::K_DARWIN64: 
    return true; 
  case object::Archive::K_COFF: 
    break; 
  } 
  llvm_unreachable("not supported for writting"); 
} 
 
template <class T> 
static void print(raw_ostream &Out, object::Archive::Kind Kind, T Val) { 
  support::endian::write(Out, Val, 
                         isBSDLike(Kind) ? support::little : support::big); 
} 
 
static void printRestOfMemberHeader( 
    raw_ostream &Out, const sys::TimePoint<std::chrono::seconds> &ModTime, 
    unsigned UID, unsigned GID, unsigned Perms, uint64_t Size) { 
  printWithSpacePadding(Out, sys::toTimeT(ModTime), 12); 
 
  // The format has only 6 chars for uid and gid. Truncate if the provided 
  // values don't fit. 
  printWithSpacePadding(Out, UID % 1000000, 6); 
  printWithSpacePadding(Out, GID % 1000000, 6); 
 
  printWithSpacePadding(Out, format("%o", Perms), 8); 
  printWithSpacePadding(Out, Size, 10); 
  Out << "`\n"; 
} 
 
static void 
printGNUSmallMemberHeader(raw_ostream &Out, StringRef Name, 
                          const sys::TimePoint<std::chrono::seconds> &ModTime, 
                          unsigned UID, unsigned GID, unsigned Perms, 
                          uint64_t Size) { 
  printWithSpacePadding(Out, Twine(Name) + "/", 16); 
  printRestOfMemberHeader(Out, ModTime, UID, GID, Perms, Size); 
} 
 
static void 
printBSDMemberHeader(raw_ostream &Out, uint64_t Pos, StringRef Name, 
                     const sys::TimePoint<std::chrono::seconds> &ModTime, 
                     unsigned UID, unsigned GID, unsigned Perms, uint64_t Size) { 
  uint64_t PosAfterHeader = Pos + 60 + Name.size(); 
  // Pad so that even 64 bit object files are aligned. 
  unsigned Pad = offsetToAlignment(PosAfterHeader, Align(8)); 
  unsigned NameWithPadding = Name.size() + Pad; 
  printWithSpacePadding(Out, Twine("#1/") + Twine(NameWithPadding), 16); 
  printRestOfMemberHeader(Out, ModTime, UID, GID, Perms, 
                          NameWithPadding + Size); 
  Out << Name; 
  while (Pad--) 
    Out.write(uint8_t(0)); 
} 
 
static bool useStringTable(bool Thin, StringRef Name) { 
  return Thin || Name.size() >= 16 || Name.contains('/'); 
} 
 
static bool is64BitKind(object::Archive::Kind Kind) { 
  switch (Kind) { 
  case object::Archive::K_GNU: 
  case object::Archive::K_BSD: 
  case object::Archive::K_DARWIN: 
  case object::Archive::K_COFF: 
    return false; 
  case object::Archive::K_DARWIN64: 
  case object::Archive::K_GNU64: 
    return true; 
  } 
  llvm_unreachable("not supported for writting"); 
} 
 
static void 
printMemberHeader(raw_ostream &Out, uint64_t Pos, raw_ostream &StringTable, 
                  StringMap<uint64_t> &MemberNames, object::Archive::Kind Kind, 
                  bool Thin, const NewArchiveMember &M, 
                  sys::TimePoint<std::chrono::seconds> ModTime, uint64_t Size) { 
  if (isBSDLike(Kind)) 
    return printBSDMemberHeader(Out, Pos, M.MemberName, ModTime, M.UID, M.GID, 
                                M.Perms, Size); 
  if (!useStringTable(Thin, M.MemberName)) 
    return printGNUSmallMemberHeader(Out, M.MemberName, ModTime, M.UID, M.GID, 
                                     M.Perms, Size); 
  Out << '/'; 
  uint64_t NamePos; 
  if (Thin) { 
    NamePos = StringTable.tell(); 
    StringTable << M.MemberName << "/\n"; 
  } else { 
    auto Insertion = MemberNames.insert({M.MemberName, uint64_t(0)}); 
    if (Insertion.second) { 
      Insertion.first->second = StringTable.tell(); 
      StringTable << M.MemberName << "/\n"; 
    } 
    NamePos = Insertion.first->second; 
  } 
  printWithSpacePadding(Out, NamePos, 15); 
  printRestOfMemberHeader(Out, ModTime, M.UID, M.GID, M.Perms, Size); 
} 
 
namespace { 
struct MemberData { 
  std::vector<unsigned> Symbols; 
  std::string Header; 
  StringRef Data; 
  StringRef Padding; 
}; 
} // namespace 
 
static MemberData computeStringTable(StringRef Names) { 
  unsigned Size = Names.size(); 
  unsigned Pad = offsetToAlignment(Size, Align(2)); 
  std::string Header; 
  raw_string_ostream Out(Header); 
  printWithSpacePadding(Out, "//", 48); 
  printWithSpacePadding(Out, Size + Pad, 10); 
  Out << "`\n"; 
  Out.flush(); 
  return {{}, std::move(Header), Names, Pad ? "\n" : ""}; 
} 
 
static sys::TimePoint<std::chrono::seconds> now(bool Deterministic) { 
  using namespace std::chrono; 
 
  if (!Deterministic) 
    return time_point_cast<seconds>(system_clock::now()); 
  return sys::TimePoint<seconds>(); 
} 
 
static bool isArchiveSymbol(const object::BasicSymbolRef &S) { 
  Expected<uint32_t> SymFlagsOrErr = S.getFlags(); 
  if (!SymFlagsOrErr) 
    // TODO: Actually report errors helpfully. 
    report_fatal_error(SymFlagsOrErr.takeError()); 
  if (*SymFlagsOrErr & object::SymbolRef::SF_FormatSpecific) 
    return false; 
  if (!(*SymFlagsOrErr & object::SymbolRef::SF_Global)) 
    return false; 
  if (*SymFlagsOrErr & object::SymbolRef::SF_Undefined) 
    return false; 
  return true; 
} 
 
static void printNBits(raw_ostream &Out, object::Archive::Kind Kind, 
                       uint64_t Val) { 
  if (is64BitKind(Kind)) 
    print<uint64_t>(Out, Kind, Val); 
  else 
    print<uint32_t>(Out, Kind, Val); 
} 
 
static uint64_t computeSymbolTableSize(object::Archive::Kind Kind,
                                       uint64_t NumSyms, uint64_t OffsetSize,
                                       StringRef StringTable,
                                       uint32_t *Padding = nullptr) {
  assert((OffsetSize == 4 || OffsetSize == 8) && "Unsupported OffsetSize");
  uint64_t Size = OffsetSize; // Number of entries
  if (isBSDLike(Kind)) 
    Size += NumSyms * OffsetSize * 2; // Table 
  else 
    Size += NumSyms * OffsetSize; // Table 
  if (isBSDLike(Kind)) 
    Size += OffsetSize; // byte count 
  Size += StringTable.size(); 
  // ld64 expects the members to be 8-byte aligned for 64-bit content and at 
  // least 4-byte aligned for 32-bit content.  Opt for the larger encoding 
  // uniformly. 
  // We do this for all bsd formats because it simplifies aligning members. 
  uint32_t Pad = offsetToAlignment(Size, Align(isBSDLike(Kind) ? 8 : 2));
  Size += Pad; 
  if (Padding)
    *Padding = Pad;
  return Size;
}
 
static void writeSymbolTableHeader(raw_ostream &Out, object::Archive::Kind Kind,
                                   bool Deterministic, uint64_t Size) {
  if (isBSDLike(Kind)) { 
    const char *Name = is64BitKind(Kind) ? "__.SYMDEF_64" : "__.SYMDEF"; 
    printBSDMemberHeader(Out, Out.tell(), Name, now(Deterministic), 0, 0, 0, 
                         Size); 
  } else { 
    const char *Name = is64BitKind(Kind) ? "/SYM64" : ""; 
    printGNUSmallMemberHeader(Out, Name, now(Deterministic), 0, 0, 0, Size); 
  } 
}
 
static void writeSymbolTable(raw_ostream &Out, object::Archive::Kind Kind,
                             bool Deterministic, ArrayRef<MemberData> Members,
                             StringRef StringTable) {
  // We don't write a symbol table on an archive with no members -- except on
  // Darwin, where the linker will abort unless the archive has a symbol table.
  if (StringTable.empty() && !isDarwin(Kind))
    return;

  unsigned NumSyms = 0;
  for (const MemberData &M : Members)
    NumSyms += M.Symbols.size();

  uint64_t OffsetSize = is64BitKind(Kind) ? 8 : 4;
  uint32_t Pad;
  uint64_t Size = computeSymbolTableSize(Kind, NumSyms, OffsetSize, StringTable, &Pad);
  writeSymbolTableHeader(Out, Kind, Deterministic, Size);

  uint64_t Pos = Out.tell() + Size; 
 
  if (isBSDLike(Kind)) 
    printNBits(Out, Kind, NumSyms * 2 * OffsetSize); 
  else 
    printNBits(Out, Kind, NumSyms); 
 
  for (const MemberData &M : Members) { 
    for (unsigned StringOffset : M.Symbols) { 
      if (isBSDLike(Kind)) 
        printNBits(Out, Kind, StringOffset); 
      printNBits(Out, Kind, Pos); // member offset 
    } 
    Pos += M.Header.size() + M.Data.size() + M.Padding.size(); 
  } 
 
  if (isBSDLike(Kind)) 
    // byte count of the string table 
    printNBits(Out, Kind, StringTable.size()); 
  Out << StringTable; 
 
  while (Pad--) 
    Out.write(uint8_t(0)); 
} 
 
static Expected<std::vector<unsigned>> 
getSymbols(MemoryBufferRef Buf, raw_ostream &SymNames, bool &HasObject) { 
  std::vector<unsigned> Ret; 
 
  // In the scenario when LLVMContext is populated SymbolicFile will contain a 
  // reference to it, thus SymbolicFile should be destroyed first. 
  LLVMContext Context; 
  std::unique_ptr<object::SymbolicFile> Obj; 

  const file_magic Type = identify_magic(Buf.getBuffer());
  // Treat unsupported file types as having no symbols.
  if (!object::SymbolicFile::isSymbolicFile(Type, &Context))
    return Ret;
  if (Type == file_magic::bitcode) {
    auto ObjOrErr = object::SymbolicFile::createSymbolicFile( 
        Buf, file_magic::bitcode, &Context); 
    if (!ObjOrErr)
      return ObjOrErr.takeError();
    Obj = std::move(*ObjOrErr); 
  } else { 
    auto ObjOrErr = object::SymbolicFile::createSymbolicFile(Buf); 
    if (!ObjOrErr)
      return ObjOrErr.takeError();
    Obj = std::move(*ObjOrErr); 
  } 
 
  HasObject = true; 
  for (const object::BasicSymbolRef &S : Obj->symbols()) { 
    if (!isArchiveSymbol(S)) 
      continue; 
    Ret.push_back(SymNames.tell()); 
    if (Error E = S.printName(SymNames)) 
      return std::move(E); 
    SymNames << '\0'; 
  } 
  return Ret; 
} 
 
static Expected<std::vector<MemberData>> 
computeMemberData(raw_ostream &StringTable, raw_ostream &SymNames, 
                  object::Archive::Kind Kind, bool Thin, bool Deterministic, 
                  bool NeedSymbols, ArrayRef<NewArchiveMember> NewMembers) {
  static char PaddingData[8] = {'\n', '\n', '\n', '\n', '\n', '\n', '\n', '\n'}; 
 
  // This ignores the symbol table, but we only need the value mod 8 and the 
  // symbol table is aligned to be a multiple of 8 bytes 
  uint64_t Pos = 0; 
 
  std::vector<MemberData> Ret; 
  bool HasObject = false; 
 
  // Deduplicate long member names in the string table and reuse earlier name 
  // offsets. This especially saves space for COFF Import libraries where all 
  // members have the same name. 
  StringMap<uint64_t> MemberNames; 
 
  // UniqueTimestamps is a special case to improve debugging on Darwin: 
  // 
  // The Darwin linker does not link debug info into the final 
  // binary. Instead, it emits entries of type N_OSO in in the output 
  // binary's symbol table, containing references to the linked-in 
  // object files. Using that reference, the debugger can read the 
  // debug data directly from the object files. Alternatively, an 
  // invocation of 'dsymutil' will link the debug data from the object 
  // files into a dSYM bundle, which can be loaded by the debugger, 
  // instead of the object files. 
  // 
  // For an object file, the N_OSO entries contain the absolute path 
  // path to the file, and the file's timestamp. For an object 
  // included in an archive, the path is formatted like 
  // "/absolute/path/to/archive.a(member.o)", and the timestamp is the 
  // archive member's timestamp, rather than the archive's timestamp. 
  // 
  // However, this doesn't always uniquely identify an object within 
  // an archive -- an archive file can have multiple entries with the 
  // same filename. (This will happen commonly if the original object 
  // files started in different directories.) The only way they get 
  // distinguished, then, is via the timestamp. But this process is 
  // unable to find the correct object file in the archive when there 
  // are two files of the same name and timestamp. 
  // 
  // Additionally, timestamp==0 is treated specially, and causes the 
  // timestamp to be ignored as a match criteria. 
  // 
  // That will "usually" work out okay when creating an archive not in 
  // deterministic timestamp mode, because the objects will probably 
  // have been created at different timestamps. 
  // 
  // To ameliorate this problem, in deterministic archive mode (which 
  // is the default), on Darwin we will emit a unique non-zero 
  // timestamp for each entry with a duplicated name. This is still 
  // deterministic: the only thing affecting that timestamp is the 
  // order of the files in the resultant archive. 
  // 
  // See also the functions that handle the lookup: 
  // in lldb: ObjectContainerBSDArchive::Archive::FindObject() 
  // in llvm/tools/dsymutil: BinaryHolder::GetArchiveMemberBuffers(). 
  bool UniqueTimestamps = Deterministic && isDarwin(Kind); 
  std::map<StringRef, unsigned> FilenameCount; 
  if (UniqueTimestamps) { 
    for (const NewArchiveMember &M : NewMembers) 
      FilenameCount[M.MemberName]++; 
    for (auto &Entry : FilenameCount) 
      Entry.second = Entry.second > 1 ? 1 : 0; 
  } 
 
  for (const NewArchiveMember &M : NewMembers) { 
    std::string Header; 
    raw_string_ostream Out(Header); 
 
    MemoryBufferRef Buf = M.Buf->getMemBufferRef(); 
    StringRef Data = Thin ? "" : Buf.getBuffer(); 
 
    // ld64 expects the members to be 8-byte aligned for 64-bit content and at 
    // least 4-byte aligned for 32-bit content.  Opt for the larger encoding 
    // uniformly.  This matches the behaviour with cctools and ensures that ld64 
    // is happy with archives that we generate. 
    unsigned MemberPadding = 
        isDarwin(Kind) ? offsetToAlignment(Data.size(), Align(8)) : 0; 
    unsigned TailPadding = 
        offsetToAlignment(Data.size() + MemberPadding, Align(2)); 
    StringRef Padding = StringRef(PaddingData, MemberPadding + TailPadding); 
 
    sys::TimePoint<std::chrono::seconds> ModTime; 
    if (UniqueTimestamps) 
      // Increment timestamp for each file of a given name. 
      ModTime = sys::toTimePoint(FilenameCount[M.MemberName]++); 
    else 
      ModTime = M.ModTime; 
 
    uint64_t Size = Buf.getBufferSize() + MemberPadding; 
    if (Size > object::Archive::MaxMemberSize) { 
      std::string StringMsg = 
          "File " + M.MemberName.str() + " exceeds size limit"; 
      return make_error<object::GenericBinaryError>( 
          std::move(StringMsg), object::object_error::parse_failed); 
    } 
 
    printMemberHeader(Out, Pos, StringTable, MemberNames, Kind, Thin, M, 
                      ModTime, Size); 
    Out.flush(); 
 
    std::vector<unsigned> Symbols;
    if (NeedSymbols) {
      Expected<std::vector<unsigned>> SymbolsOrErr =
          getSymbols(Buf, SymNames, HasObject);
      if (auto E = SymbolsOrErr.takeError())
        return std::move(E);
      Symbols = std::move(*SymbolsOrErr);
    }
 
    Pos += Header.size() + Data.size() + Padding.size(); 
    Ret.push_back({std::move(Symbols), std::move(Header), Data, Padding});
  } 
  // If there are no symbols, emit an empty symbol table, to satisfy Solaris 
  // tools, older versions of which expect a symbol table in a non-empty 
  // archive, regardless of whether there are any symbols in it. 
  if (HasObject && SymNames.tell() == 0) 
    SymNames << '\0' << '\0' << '\0'; 
  return Ret; 
} 
 
namespace llvm { 
 
static ErrorOr<SmallString<128>> canonicalizePath(StringRef P) { 
  SmallString<128> Ret = P; 
  std::error_code Err = sys::fs::make_absolute(Ret); 
  if (Err) 
    return Err; 
  sys::path::remove_dots(Ret, /*removedotdot*/ true); 
  return Ret; 
} 
 
// Compute the relative path from From to To. 
Expected<std::string> computeArchiveRelativePath(StringRef From, StringRef To) { 
  ErrorOr<SmallString<128>> PathToOrErr = canonicalizePath(To); 
  ErrorOr<SmallString<128>> DirFromOrErr = canonicalizePath(From); 
  if (!PathToOrErr || !DirFromOrErr) 
    return errorCodeToError(std::error_code(errno, std::generic_category())); 
 
  const SmallString<128> &PathTo = *PathToOrErr; 
  const SmallString<128> &DirFrom = sys::path::parent_path(*DirFromOrErr); 
 
  // Can't construct a relative path between different roots 
  if (sys::path::root_name(PathTo) != sys::path::root_name(DirFrom)) 
    return sys::path::convert_to_slash(PathTo); 
 
  // Skip common prefixes 
  auto FromTo = 
      std::mismatch(sys::path::begin(DirFrom), sys::path::end(DirFrom), 
                    sys::path::begin(PathTo)); 
  auto FromI = FromTo.first; 
  auto ToI = FromTo.second; 
 
  // Construct relative path 
  SmallString<128> Relative; 
  for (auto FromE = sys::path::end(DirFrom); FromI != FromE; ++FromI) 
    sys::path::append(Relative, sys::path::Style::posix, ".."); 
 
  for (auto ToE = sys::path::end(PathTo); ToI != ToE; ++ToI) 
    sys::path::append(Relative, sys::path::Style::posix, *ToI); 
 
  return std::string(Relative.str()); 
} 
 
static Error writeArchiveToStream(raw_ostream &Out,
                                  ArrayRef<NewArchiveMember> NewMembers,
                                  bool WriteSymtab, object::Archive::Kind Kind,
                                  bool Deterministic, bool Thin) {
  assert((!Thin || !isBSDLike(Kind)) && "Only the gnu format has a thin mode"); 
 
  SmallString<0> SymNamesBuf; 
  raw_svector_ostream SymNames(SymNamesBuf); 
  SmallString<0> StringTableBuf; 
  raw_svector_ostream StringTable(StringTableBuf); 
 
  Expected<std::vector<MemberData>> DataOrErr =
      computeMemberData(StringTable, SymNames, Kind, Thin, Deterministic,
                        WriteSymtab, NewMembers);
  if (Error E = DataOrErr.takeError()) 
    return E; 
  std::vector<MemberData> &Data = *DataOrErr; 
 
  if (!StringTableBuf.empty()) 
    Data.insert(Data.begin(), computeStringTable(StringTableBuf)); 
 
  // We would like to detect if we need to switch to a 64-bit symbol table. 
  if (WriteSymtab) { 
    uint64_t MaxOffset = 8; // For the file signature.
    uint64_t LastOffset = MaxOffset; 
    uint64_t NumSyms = 0;
    for (const auto &M : Data) { 
      // Record the start of the member's offset 
      LastOffset = MaxOffset; 
      // Account for the size of each part associated with the member. 
      MaxOffset += M.Header.size() + M.Data.size() + M.Padding.size(); 
      NumSyms += M.Symbols.size();
    } 
 
    // We assume 32-bit offsets to see if 32-bit symbols are possible or not.
    uint64_t SymtabSize = computeSymbolTableSize(Kind, NumSyms, 4, SymNamesBuf);
    auto computeSymbolTableHeaderSize =
        [=] {
          SmallString<0> TmpBuf;
          raw_svector_ostream Tmp(TmpBuf);
          writeSymbolTableHeader(Tmp, Kind, Deterministic, SymtabSize);
          return TmpBuf.size();
        };
    LastOffset += computeSymbolTableHeaderSize() + SymtabSize;

    // The SYM64 format is used when an archive's member offsets are larger than 
    // 32-bits can hold. The need for this shift in format is detected by 
    // writeArchive. To test this we need to generate a file with a member that 
    // has an offset larger than 32-bits but this demands a very slow test. To 
    // speed the test up we use this environment variable to pretend like the 
    // cutoff happens before 32-bits and instead happens at some much smaller 
    // value. 
    uint64_t Sym64Threshold = 1ULL << 32;
    const char *Sym64Env = std::getenv("SYM64_THRESHOLD"); 
    if (Sym64Env) 
      StringRef(Sym64Env).getAsInteger(10, Sym64Threshold); 
 
    // If LastOffset isn't going to fit in a 32-bit varible we need to switch 
    // to 64-bit. Note that the file can be larger than 4GB as long as the last 
    // member starts before the 4GB offset. 
    if (LastOffset >= Sym64Threshold) {
      if (Kind == object::Archive::K_DARWIN) 
        Kind = object::Archive::K_DARWIN64; 
      else 
        Kind = object::Archive::K_GNU64; 
    } 
  } 
 
  if (Thin) 
    Out << "!<thin>\n"; 
  else 
    Out << "!<arch>\n"; 
 
  if (WriteSymtab) 
    writeSymbolTable(Out, Kind, Deterministic, Data, SymNamesBuf); 
 
  for (const MemberData &M : Data) 
    Out << M.Header << M.Data << M.Padding; 
 
  Out.flush(); 
  return Error::success();
}
 
Error writeArchive(StringRef ArcName, ArrayRef<NewArchiveMember> NewMembers,
                   bool WriteSymtab, object::Archive::Kind Kind,
                   bool Deterministic, bool Thin,
                   std::unique_ptr<MemoryBuffer> OldArchiveBuf) {
  Expected<sys::fs::TempFile> Temp =
      sys::fs::TempFile::create(ArcName + ".temp-archive-%%%%%%%.a");
  if (!Temp)
    return Temp.takeError();
  raw_fd_ostream Out(Temp->FD, false);

  if (Error E = writeArchiveToStream(Out, NewMembers, WriteSymtab, Kind,
                                     Deterministic, Thin)) {
    if (Error DiscardError = Temp->discard())
      return joinErrors(std::move(E), std::move(DiscardError));
    return E;
  }

  // At this point, we no longer need whatever backing memory 
  // was used to generate the NewMembers. On Windows, this buffer 
  // could be a mapped view of the file we want to replace (if 
  // we're updating an existing archive, say). In that case, the 
  // rename would still succeed, but it would leave behind a 
  // temporary file (actually the original file renamed) because 
  // a file cannot be deleted while there's a handle open on it, 
  // only renamed. So by freeing this buffer, this ensures that 
  // the last open handle on the destination file, if any, is 
  // closed before we attempt to rename. 
  OldArchiveBuf.reset(); 
 
  return Temp->keep(ArcName); 
} 
 
Expected<std::unique_ptr<MemoryBuffer>>
writeArchiveToBuffer(ArrayRef<NewArchiveMember> NewMembers, bool WriteSymtab,
                     object::Archive::Kind Kind, bool Deterministic,
                     bool Thin) {
  SmallVector<char, 0> ArchiveBufferVector;
  raw_svector_ostream ArchiveStream(ArchiveBufferVector);

  if (Error E = writeArchiveToStream(ArchiveStream, NewMembers, WriteSymtab,
                                     Kind, Deterministic, Thin))
    return std::move(E);

  return std::make_unique<SmallVectorMemoryBuffer>(
      std::move(ArchiveBufferVector));
}

} // namespace llvm