lib/Object/ArchiveWriter.cpp

   1 //===- ArchiveWriter.cpp - ar File Format implementation --------*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file defines the writeArchive function.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "llvm/Object/ArchiveWriter.h"
  14 #include "llvm/ADT/ArrayRef.h"
  15 #include "llvm/ADT/StringRef.h"
  16 #include "llvm/BinaryFormat/Magic.h"
  17 #include "llvm/IR/LLVMContext.h"
  18 #include "llvm/Object/Archive.h"
  19 #include "llvm/Object/ObjectFile.h"
  20 #include "llvm/Object/SymbolicFile.h"
  21 #include "llvm/Support/EndianStream.h"
  22 #include "llvm/Support/Errc.h"
  23 #include "llvm/Support/ErrorHandling.h"
  24 #include "llvm/Support/Format.h"
  25 #include "llvm/Support/Path.h"
  26 #include "llvm/Support/ToolOutputFile.h"
  27 #include "llvm/Support/raw_ostream.h"
  28
  29 #include <map>
  30
  31 #if !defined(_MSC_VER) && !defined(__MINGW32__)
  32 #include <unistd.h>
  33 #else
  34 #include <io.h>
  35 #endif
  36
  37 using namespace llvm;
  38
  39 NewArchiveMember::NewArchiveMember(MemoryBufferRef BufRef)
  40     : Buf(MemoryBuffer::getMemBuffer(BufRef, false)),
  41       MemberName(BufRef.getBufferIdentifier()) {}
  42
  43 Expected<NewArchiveMember>
  44 NewArchiveMember::getOldMember(const object::Archive::Child &OldMember,
  45                                bool Deterministic) {
  46   Expected<llvm::MemoryBufferRef> BufOrErr = OldMember.getMemoryBufferRef();
  47   if (!BufOrErr)
  48     return BufOrErr.takeError();
  49
  50   NewArchiveMember M;
  51   M.Buf = MemoryBuffer::getMemBuffer(*BufOrErr, false);
  52   M.MemberName = M.Buf->getBufferIdentifier();
  53   if (!Deterministic) {
  54     auto ModTimeOrErr = OldMember.getLastModified();
  55     if (!ModTimeOrErr)
  56       return ModTimeOrErr.takeError();
  57     M.ModTime = ModTimeOrErr.get();
  58     Expected<unsigned> UIDOrErr = OldMember.getUID();
  59     if (!UIDOrErr)
  60       return UIDOrErr.takeError();
  61     M.UID = UIDOrErr.get();
  62     Expected<unsigned> GIDOrErr = OldMember.getGID();
  63     if (!GIDOrErr)
  64       return GIDOrErr.takeError();
  65     M.GID = GIDOrErr.get();
  66     Expected<sys::fs::perms> AccessModeOrErr = OldMember.getAccessMode();
  67     if (!AccessModeOrErr)
  68       return AccessModeOrErr.takeError();
  69     M.Perms = AccessModeOrErr.get();
  70   }
  71   return std::move(M);
  72 }
  73
  74 Expected<NewArchiveMember> NewArchiveMember::getFile(StringRef FileName,
  75                                                      bool Deterministic) {
  76   sys::fs::file_status Status;
  77   int FD;
  78   if (auto EC = sys::fs::openFileForRead(FileName, FD))
  79     return errorCodeToError(EC);
  80   assert(FD != -1);
  81
  82   if (auto EC = sys::fs::status(FD, Status))
  83     return errorCodeToError(EC);
  84
  85   // Opening a directory doesn't make sense. Let it fail.
  86   // Linux cannot open directories with open(2), although
  87   // cygwin and *bsd can.
  88   if (Status.type() == sys::fs::file_type::directory_file)
  89     return errorCodeToError(make_error_code(errc::is_a_directory));
  90
  91   ErrorOr<std::unique_ptr<MemoryBuffer>> MemberBufferOrErr =
  92       MemoryBuffer::getOpenFile(FD, FileName, Status.getSize(), false);
  93   if (!MemberBufferOrErr)
  94     return errorCodeToError(MemberBufferOrErr.getError());
  95
  96   if (close(FD) != 0)
  97     return errorCodeToError(std::error_code(errno, std::generic_category()));
  98
  99   NewArchiveMember M;
 100   M.Buf = std::move(*MemberBufferOrErr);
 101   M.MemberName = M.Buf->getBufferIdentifier();
 102   if (!Deterministic) {
 103     M.ModTime = std::chrono::time_point_cast<std::chrono::seconds>(
 104         Status.getLastModificationTime());
 105     M.UID = Status.getUser();
 106     M.GID = Status.getGroup();
 107     M.Perms = Status.permissions();
 108   }
 109   return std::move(M);
 110 }
 111
 112 template <typename T>
 113 static void printWithSpacePadding(raw_ostream &OS, T Data, unsigned Size) {
 114   uint64_t OldPos = OS.tell();
 115   OS << Data;
 116   unsigned SizeSoFar = OS.tell() - OldPos;
 117   assert(SizeSoFar <= Size && "Data doesn't fit in Size");
 118   OS.indent(Size - SizeSoFar);
 119 }
 120
 121 static bool isDarwin(object::Archive::Kind Kind) {
 122   return Kind == object::Archive::K_DARWIN ||
 123          Kind == object::Archive::K_DARWIN64;
 124 }
 125
 126 static bool isBSDLike(object::Archive::Kind Kind) {
 127   switch (Kind) {
 128   case object::Archive::K_GNU:
 129   case object::Archive::K_GNU64:
 130     return false;
 131   case object::Archive::K_BSD:
 132   case object::Archive::K_DARWIN:
 133   case object::Archive::K_DARWIN64:
 134     return true;
 135   case object::Archive::K_COFF:
 136     break;
 137   }
 138   llvm_unreachable("not supported for writting");
 139 }
 140
 141 template <class T>
 142 static void print(raw_ostream &Out, object::Archive::Kind Kind, T Val) {
 143   support::endian::write(Out, Val,
 144                          isBSDLike(Kind) ? support::little : support::big);
 145 }
 146
 147 static void printRestOfMemberHeader(
 148     raw_ostream &Out, const sys::TimePoint<std::chrono::seconds> &ModTime,
 149     unsigned UID, unsigned GID, unsigned Perms, unsigned Size) {
 150   printWithSpacePadding(Out, sys::toTimeT(ModTime), 12);
 151
 152   // The format has only 6 chars for uid and gid. Truncate if the provided
 153   // values don't fit.
 154   printWithSpacePadding(Out, UID % 1000000, 6);
 155   printWithSpacePadding(Out, GID % 1000000, 6);
 156
 157   printWithSpacePadding(Out, format("%o", Perms), 8);
 158   printWithSpacePadding(Out, Size, 10);
 159   Out << "`\n";
 160 }
 161
 162 static void
 163 printGNUSmallMemberHeader(raw_ostream &Out, StringRef Name,
 164                           const sys::TimePoint<std::chrono::seconds> &ModTime,
 165                           unsigned UID, unsigned GID, unsigned Perms,
 166                           unsigned Size) {
 167   printWithSpacePadding(Out, Twine(Name) + "/", 16);
 168   printRestOfMemberHeader(Out, ModTime, UID, GID, Perms, Size);
 169 }
 170
 171 static void
 172 printBSDMemberHeader(raw_ostream &Out, uint64_t Pos, StringRef Name,
 173                      const sys::TimePoint<std::chrono::seconds> &ModTime,
 174                      unsigned UID, unsigned GID, unsigned Perms,
 175                      unsigned Size) {
 176   uint64_t PosAfterHeader = Pos + 60 + Name.size();
 177   // Pad so that even 64 bit object files are aligned.
 178   unsigned Pad = OffsetToAlignment(PosAfterHeader, 8);
 179   unsigned NameWithPadding = Name.size() + Pad;
 180   printWithSpacePadding(Out, Twine("#1/") + Twine(NameWithPadding), 16);
 181   printRestOfMemberHeader(Out, ModTime, UID, GID, Perms,
 182                           NameWithPadding + Size);
 183   Out << Name;
 184   while (Pad--)
 185     Out.write(uint8_t(0));
 186 }
 187
 188 static bool useStringTable(bool Thin, StringRef Name) {
 189   return Thin || Name.size() >= 16 || Name.contains('/');
 190 }
 191
 192 static bool is64BitKind(object::Archive::Kind Kind) {
 193   switch (Kind) {
 194   case object::Archive::K_GNU:
 195   case object::Archive::K_BSD:
 196   case object::Archive::K_DARWIN:
 197   case object::Archive::K_COFF:
 198     return false;
 199   case object::Archive::K_DARWIN64:
 200   case object::Archive::K_GNU64:
 201     return true;
 202   }
 203   llvm_unreachable("not supported for writting");
 204 }
 205
 206 static void
 207 printMemberHeader(raw_ostream &Out, uint64_t Pos, raw_ostream &StringTable,
 208                   StringMap<uint64_t> &MemberNames, object::Archive::Kind Kind,
 209                   bool Thin, const NewArchiveMember &M,
 210                   sys::TimePoint<std::chrono::seconds> ModTime, unsigned Size) {
 211   if (isBSDLike(Kind))
 212     return printBSDMemberHeader(Out, Pos, M.MemberName, ModTime, M.UID, M.GID,
 213                                 M.Perms, Size);
 214   if (!useStringTable(Thin, M.MemberName))
 215     return printGNUSmallMemberHeader(Out, M.MemberName, ModTime, M.UID, M.GID,
 216                                      M.Perms, Size);
 217   Out << '/';
 218   uint64_t NamePos;
 219   if (Thin) {
 220     NamePos = StringTable.tell();
 221     StringTable << M.MemberName << "/\n";
 222   } else {
 223     auto Insertion = MemberNames.insert({M.MemberName, uint64_t(0)});
 224     if (Insertion.second) {
 225       Insertion.first->second = StringTable.tell();
 226       StringTable << M.MemberName << "/\n";
 227     }
 228     NamePos = Insertion.first->second;
 229   }
 230   printWithSpacePadding(Out, NamePos, 15);
 231   printRestOfMemberHeader(Out, ModTime, M.UID, M.GID, M.Perms, Size);
 232 }
 233
 234 namespace {
 235 struct MemberData {
 236   std::vector<unsigned> Symbols;
 237   std::string Header;
 238   StringRef Data;
 239   StringRef Padding;
 240 };
 241 } // namespace
 242
 243 static MemberData computeStringTable(StringRef Names) {
 244   unsigned Size = Names.size();
 245   unsigned Pad = OffsetToAlignment(Size, 2);
 246   std::string Header;
 247   raw_string_ostream Out(Header);
 248   printWithSpacePadding(Out, "//", 48);
 249   printWithSpacePadding(Out, Size + Pad, 10);
 250   Out << "`\n";
 251   Out.flush();
 252   return {{}, std::move(Header), Names, Pad ? "\n" : ""};
 253 }
 254
 255 static sys::TimePoint<std::chrono::seconds> now(bool Deterministic) {
 256   using namespace std::chrono;
 257
 258   if (!Deterministic)
 259     return time_point_cast<seconds>(system_clock::now());
 260   return sys::TimePoint<seconds>();
 261 }
 262
 263 static bool isArchiveSymbol(const object::BasicSymbolRef &S) {
 264   uint32_t Symflags = S.getFlags();
 265   if (Symflags & object::SymbolRef::SF_FormatSpecific)
 266     return false;
 267   if (!(Symflags & object::SymbolRef::SF_Global))
 268     return false;
 269   if (Symflags & object::SymbolRef::SF_Undefined)
 270     return false;
 271   return true;
 272 }
 273
 274 static void printNBits(raw_ostream &Out, object::Archive::Kind Kind,
 275                        uint64_t Val) {
 276   if (is64BitKind(Kind))
 277     print<uint64_t>(Out, Kind, Val);
 278   else
 279     print<uint32_t>(Out, Kind, Val);
 280 }
 281
 282 static void writeSymbolTable(raw_ostream &Out, object::Archive::Kind Kind,
 283                              bool Deterministic, ArrayRef<MemberData> Members,
 284                              StringRef StringTable) {
 285   // We don't write a symbol table on an archive with no members -- except on
 286   // Darwin, where the linker will abort unless the archive has a symbol table.
 287   if (StringTable.empty() && !isDarwin(Kind))
 288     return;
 289
 290   unsigned NumSyms = 0;
 291   for (const MemberData &M : Members)
 292     NumSyms += M.Symbols.size();
 293
 294   unsigned Size = 0;
 295   unsigned OffsetSize = is64BitKind(Kind) ? sizeof(uint64_t) : sizeof(uint32_t);
 296
 297   Size += OffsetSize; // Number of entries
 298   if (isBSDLike(Kind))
 299     Size += NumSyms * OffsetSize * 2; // Table
 300   else
 301     Size += NumSyms * OffsetSize; // Table
 302   if (isBSDLike(Kind))
 303     Size += OffsetSize; // byte count
 304   Size += StringTable.size();
 305   // ld64 expects the members to be 8-byte aligned for 64-bit content and at
 306   // least 4-byte aligned for 32-bit content.  Opt for the larger encoding
 307   // uniformly.
 308   // We do this for all bsd formats because it simplifies aligning members.
 309   unsigned Alignment = isBSDLike(Kind) ? 8 : 2;
 310   unsigned Pad = OffsetToAlignment(Size, Alignment);
 311   Size += Pad;
 312
 313   if (isBSDLike(Kind)) {
 314     const char *Name = is64BitKind(Kind) ? "__.SYMDEF_64" : "__.SYMDEF";
 315     printBSDMemberHeader(Out, Out.tell(), Name, now(Deterministic), 0, 0, 0,
 316                          Size);
 317   } else {
 318     const char *Name = is64BitKind(Kind) ? "/SYM64" : "";
 319     printGNUSmallMemberHeader(Out, Name, now(Deterministic), 0, 0, 0, Size);
 320   }
 321
 322   uint64_t Pos = Out.tell() + Size;
 323
 324   if (isBSDLike(Kind))
 325     printNBits(Out, Kind, NumSyms * 2 * OffsetSize);
 326   else
 327     printNBits(Out, Kind, NumSyms);
 328
 329   for (const MemberData &M : Members) {
 330     for (unsigned StringOffset : M.Symbols) {
 331       if (isBSDLike(Kind))
 332         printNBits(Out, Kind, StringOffset);
 333       printNBits(Out, Kind, Pos); // member offset
 334     }
 335     Pos += M.Header.size() + M.Data.size() + M.Padding.size();
 336   }
 337
 338   if (isBSDLike(Kind))
 339     // byte count of the string table
 340     printNBits(Out, Kind, StringTable.size());
 341   Out << StringTable;
 342
 343   while (Pad--)
 344     Out.write(uint8_t(0));
 345 }
 346
 347 static Expected<std::vector<unsigned>>
 348 getSymbols(MemoryBufferRef Buf, raw_ostream &SymNames, bool &HasObject) {
 349   std::vector<unsigned> Ret;
 350
 351   // In the scenario when LLVMContext is populated SymbolicFile will contain a
 352   // reference to it, thus SymbolicFile should be destroyed first.
 353   LLVMContext Context;
 354   std::unique_ptr<object::SymbolicFile> Obj;
 355   if (identify_magic(Buf.getBuffer()) == file_magic::bitcode) {
 356     auto ObjOrErr = object::SymbolicFile::createSymbolicFile(
 357         Buf, file_magic::bitcode, &Context);
 358     if (!ObjOrErr) {
 359       // FIXME: check only for "not an object file" errors.
 360       consumeError(ObjOrErr.takeError());
 361       return Ret;
 362     }
 363     Obj = std::move(*ObjOrErr);
 364   } else {
 365     auto ObjOrErr = object::SymbolicFile::createSymbolicFile(Buf);
 366     if (!ObjOrErr) {
 367       // FIXME: check only for "not an object file" errors.
 368       consumeError(ObjOrErr.takeError());
 369       return Ret;
 370     }
 371     Obj = std::move(*ObjOrErr);
 372   }
 373
 374   HasObject = true;
 375   for (const object::BasicSymbolRef &S : Obj->symbols()) {
 376     if (!isArchiveSymbol(S))
 377       continue;
 378     Ret.push_back(SymNames.tell());
 379     if (auto EC = S.printName(SymNames))
 380       return errorCodeToError(EC);
 381     SymNames << '\0';
 382   }
 383   return Ret;
 384 }
 385
 386 static Expected<std::vector<MemberData>>
 387 computeMemberData(raw_ostream &StringTable, raw_ostream &SymNames,
 388                   object::Archive::Kind Kind, bool Thin, bool Deterministic,
 389                   ArrayRef<NewArchiveMember> NewMembers) {
 390   static char PaddingData[8] = {'\n', '\n', '\n', '\n', '\n', '\n', '\n', '\n'};
 391
 392   // This ignores the symbol table, but we only need the value mod 8 and the
 393   // symbol table is aligned to be a multiple of 8 bytes
 394   uint64_t Pos = 0;
 395
 396   std::vector<MemberData> Ret;
 397   bool HasObject = false;
 398
 399   // Deduplicate long member names in the string table and reuse earlier name
 400   // offsets. This especially saves space for COFF Import libraries where all
 401   // members have the same name.
 402   StringMap<uint64_t> MemberNames;
 403
 404   // UniqueTimestamps is a special case to improve debugging on Darwin:
 405   //
 406   // The Darwin linker does not link debug info into the final
 407   // binary. Instead, it emits entries of type N_OSO in in the output
 408   // binary's symbol table, containing references to the linked-in
 409   // object files. Using that reference, the debugger can read the
 410   // debug data directly from the object files. Alternatively, an
 411   // invocation of 'dsymutil' will link the debug data from the object
 412   // files into a dSYM bundle, which can be loaded by the debugger,
 413   // instead of the object files.
 414   //
 415   // For an object file, the N_OSO entries contain the absolute path
 416   // path to the file, and the file's timestamp. For an object
 417   // included in an archive, the path is formatted like
 418   // "/absolute/path/to/archive.a(member.o)", and the timestamp is the
 419   // archive member's timestamp, rather than the archive's timestamp.
 420   //
 421   // However, this doesn't always uniquely identify an object within
 422   // an archive -- an archive file can have multiple entries with the
 423   // same filename. (This will happen commonly if the original object
 424   // files started in different directories.) The only way they get
 425   // distinguished, then, is via the timestamp. But this process is
 426   // unable to find the correct object file in the archive when there
 427   // are two files of the same name and timestamp.
 428   //
 429   // Additionally, timestamp==0 is treated specially, and causes the
 430   // timestamp to be ignored as a match criteria.
 431   //
 432   // That will "usually" work out okay when creating an archive not in
 433   // deterministic timestamp mode, because the objects will probably
 434   // have been created at different timestamps.
 435   //
 436   // To ameliorate this problem, in deterministic archive mode (which
 437   // is the default), on Darwin we will emit a unique non-zero
 438   // timestamp for each entry with a duplicated name. This is still
 439   // deterministic: the only thing affecting that timestamp is the
 440   // order of the files in the resultant archive.
 441   //
 442   // See also the functions that handle the lookup:
 443   // in lldb: ObjectContainerBSDArchive::Archive::FindObject()
 444   // in llvm/tools/dsymutil: BinaryHolder::GetArchiveMemberBuffers().
 445   bool UniqueTimestamps = Deterministic && isDarwin(Kind);
 446   std::map<StringRef, unsigned> FilenameCount;
 447   if (UniqueTimestamps) {
 448     for (const NewArchiveMember &M : NewMembers)
 449       FilenameCount[M.MemberName]++;
 450     for (auto &Entry : FilenameCount)
 451       Entry.second = Entry.second > 1 ? 1 : 0;
 452   }
 453
 454   for (const NewArchiveMember &M : NewMembers) {
 455     std::string Header;
 456     raw_string_ostream Out(Header);
 457
 458     MemoryBufferRef Buf = M.Buf->getMemBufferRef();
 459     StringRef Data = Thin ? "" : Buf.getBuffer();
 460
 461     // ld64 expects the members to be 8-byte aligned for 64-bit content and at
 462     // least 4-byte aligned for 32-bit content.  Opt for the larger encoding
 463     // uniformly.  This matches the behaviour with cctools and ensures that ld64
 464     // is happy with archives that we generate.
 465     unsigned MemberPadding =
 466         isDarwin(Kind) ? OffsetToAlignment(Data.size(), 8) : 0;
 467     unsigned TailPadding = OffsetToAlignment(Data.size() + MemberPadding, 2);
 468     StringRef Padding = StringRef(PaddingData, MemberPadding + TailPadding);
 469
 470     sys::TimePoint<std::chrono::seconds> ModTime;
 471     if (UniqueTimestamps)
 472       // Increment timestamp for each file of a given name.
 473       ModTime = sys::toTimePoint(FilenameCount[M.MemberName]++);
 474     else
 475       ModTime = M.ModTime;
 476     printMemberHeader(Out, Pos, StringTable, MemberNames, Kind, Thin, M,
 477                       ModTime, Buf.getBufferSize() + MemberPadding);
 478     Out.flush();
 479
 480     Expected<std::vector<unsigned>> Symbols =
 481         getSymbols(Buf, SymNames, HasObject);
 482     if (auto E = Symbols.takeError())
 483       return std::move(E);
 484
 485     Pos += Header.size() + Data.size() + Padding.size();
 486     Ret.push_back({std::move(*Symbols), std::move(Header), Data, Padding});
 487   }
 488   // If there are no symbols, emit an empty symbol table, to satisfy Solaris
 489   // tools, older versions of which expect a symbol table in a non-empty
 490   // archive, regardless of whether there are any symbols in it.
 491   if (HasObject && SymNames.tell() == 0)
 492     SymNames << '\0' << '\0' << '\0';
 493   return Ret;
 494 }
 495
 496 namespace llvm {
 497 // Compute the relative path from From to To.
 498 std::string computeArchiveRelativePath(StringRef From, StringRef To) {
 499   if (sys::path::is_absolute(From) || sys::path::is_absolute(To))
 500     return To;
 501
 502   StringRef DirFrom = sys::path::parent_path(From);
 503   auto FromI = sys::path::begin(DirFrom);
 504   auto ToI = sys::path::begin(To);
 505   while (*FromI == *ToI) {
 506     ++FromI;
 507     ++ToI;
 508   }
 509
 510   SmallString<128> Relative;
 511   for (auto FromE = sys::path::end(DirFrom); FromI != FromE; ++FromI)
 512     sys::path::append(Relative, "..");
 513
 514   for (auto ToE = sys::path::end(To); ToI != ToE; ++ToI)
 515     sys::path::append(Relative, *ToI);
 516
 517   // Replace backslashes with slashes so that the path is portable between *nix
 518   // and Windows.
 519   return sys::path::convert_to_slash(Relative);
 520 }
 521
 522 Error writeArchive(StringRef ArcName, ArrayRef<NewArchiveMember> NewMembers,
 523                    bool WriteSymtab, object::Archive::Kind Kind,
 524                    bool Deterministic, bool Thin,
 525                    std::unique_ptr<MemoryBuffer> OldArchiveBuf) {
 526   assert((!Thin || !isBSDLike(Kind)) && "Only the gnu format has a thin mode");
 527
 528   SmallString<0> SymNamesBuf;
 529   raw_svector_ostream SymNames(SymNamesBuf);
 530   SmallString<0> StringTableBuf;
 531   raw_svector_ostream StringTable(StringTableBuf);
 532
 533   Expected<std::vector<MemberData>> DataOrErr = computeMemberData(
 534       StringTable, SymNames, Kind, Thin, Deterministic, NewMembers);
 535   if (Error E = DataOrErr.takeError())
 536     return E;
 537   std::vector<MemberData> &Data = *DataOrErr;
 538
 539   if (!StringTableBuf.empty())
 540     Data.insert(Data.begin(), computeStringTable(StringTableBuf));
 541
 542   // We would like to detect if we need to switch to a 64-bit symbol table.
 543   if (WriteSymtab) {
 544     uint64_t MaxOffset = 0;
 545     uint64_t LastOffset = MaxOffset;
 546     for (const auto &M : Data) {
 547       // Record the start of the member's offset
 548       LastOffset = MaxOffset;
 549       // Account for the size of each part associated with the member.
 550       MaxOffset += M.Header.size() + M.Data.size() + M.Padding.size();
 551       // We assume 32-bit symbols to see if 32-bit symbols are possible or not.
 552       MaxOffset += M.Symbols.size() * 4;
 553     }
 554
 555     // The SYM64 format is used when an archive's member offsets are larger than
 556     // 32-bits can hold. The need for this shift in format is detected by
 557     // writeArchive. To test this we need to generate a file with a member that
 558     // has an offset larger than 32-bits but this demands a very slow test. To
 559     // speed the test up we use this environment variable to pretend like the
 560     // cutoff happens before 32-bits and instead happens at some much smaller
 561     // value.
 562     const char *Sym64Env = std::getenv("SYM64_THRESHOLD");
 563     int Sym64Threshold = 32;
 564     if (Sym64Env)
 565       StringRef(Sym64Env).getAsInteger(10, Sym64Threshold);
 566
 567     // If LastOffset isn't going to fit in a 32-bit varible we need to switch
 568     // to 64-bit. Note that the file can be larger than 4GB as long as the last
 569     // member starts before the 4GB offset.
 570     if (LastOffset >= (1ULL << Sym64Threshold)) {
 571       if (Kind == object::Archive::K_DARWIN)
 572         Kind = object::Archive::K_DARWIN64;
 573       else
 574         Kind = object::Archive::K_GNU64;
 575     }
 576   }
 577
 578   Expected<sys::fs::TempFile> Temp =
 579       sys::fs::TempFile::create(ArcName + ".temp-archive-%%%%%%%.a");
 580   if (!Temp)
 581     return Temp.takeError();
 582
 583   raw_fd_ostream Out(Temp->FD, false);
 584   if (Thin)
 585     Out << "!<thin>\n";
 586   else
 587     Out << "!<arch>\n";
 588
 589   if (WriteSymtab)
 590     writeSymbolTable(Out, Kind, Deterministic, Data, SymNamesBuf);
 591
 592   for (const MemberData &M : Data)
 593     Out << M.Header << M.Data << M.Padding;
 594
 595   Out.flush();
 596
 597   // At this point, we no longer need whatever backing memory
 598   // was used to generate the NewMembers. On Windows, this buffer
 599   // could be a mapped view of the file we want to replace (if
 600   // we're updating an existing archive, say). In that case, the
 601   // rename would still succeed, but it would leave behind a
 602   // temporary file (actually the original file renamed) because
 603   // a file cannot be deleted while there's a handle open on it,
 604   // only renamed. So by freeing this buffer, this ensures that
 605   // the last open handle on the destination file, if any, is
 606   // closed before we attempt to rename.
 607   OldArchiveBuf.reset();
 608
 609   return Temp->keep(ArcName);
 610 }
 611
 612 } // namespace llvm