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/Error.h"
  20 #include "llvm/Object/ObjectFile.h"
  21 #include "llvm/Object/SymbolicFile.h"
  22 #include "llvm/Support/EndianStream.h"
  23 #include "llvm/Support/Errc.h"
  24 #include "llvm/Support/ErrorHandling.h"
  25 #include "llvm/Support/Format.h"
  26 #include "llvm/Support/Path.h"
  27 #include "llvm/Support/ToolOutputFile.h"
  28 #include "llvm/Support/raw_ostream.h"
  29
  30 #include <map>
  31
  32 #if !defined(_MSC_VER) && !defined(__MINGW32__)
  33 #include <unistd.h>
  34 #else
  35 #include <io.h>
  36 #endif
  37
  38 using namespace llvm;
  39
  40 NewArchiveMember::NewArchiveMember(MemoryBufferRef BufRef)
  41     : Buf(MemoryBuffer::getMemBuffer(BufRef, false)),
  42       MemberName(BufRef.getBufferIdentifier()) {}
  43
  44 Expected<NewArchiveMember>
  45 NewArchiveMember::getOldMember(const object::Archive::Child &OldMember,
  46                                bool Deterministic) {
  47   Expected<llvm::MemoryBufferRef> BufOrErr = OldMember.getMemoryBufferRef();
  48   if (!BufOrErr)
  49     return BufOrErr.takeError();
  50
  51   NewArchiveMember M;
  52   M.Buf = MemoryBuffer::getMemBuffer(*BufOrErr, false);
  53   M.MemberName = M.Buf->getBufferIdentifier();
  54   if (!Deterministic) {
  55     auto ModTimeOrErr = OldMember.getLastModified();
  56     if (!ModTimeOrErr)
  57       return ModTimeOrErr.takeError();
  58     M.ModTime = ModTimeOrErr.get();
  59     Expected<unsigned> UIDOrErr = OldMember.getUID();
  60     if (!UIDOrErr)
  61       return UIDOrErr.takeError();
  62     M.UID = UIDOrErr.get();
  63     Expected<unsigned> GIDOrErr = OldMember.getGID();
  64     if (!GIDOrErr)
  65       return GIDOrErr.takeError();
  66     M.GID = GIDOrErr.get();
  67     Expected<sys::fs::perms> AccessModeOrErr = OldMember.getAccessMode();
  68     if (!AccessModeOrErr)
  69       return AccessModeOrErr.takeError();
  70     M.Perms = AccessModeOrErr.get();
  71   }
  72   return std::move(M);
  73 }
  74
  75 Expected<NewArchiveMember> NewArchiveMember::getFile(StringRef FileName,
  76                                                      bool Deterministic) {
  77   sys::fs::file_status Status;
  78   auto FDOrErr = sys::fs::openNativeFileForRead(FileName);
  79   if (!FDOrErr)
  80     return FDOrErr.takeError();
  81   sys::fs::file_t FD = *FDOrErr;
  82   assert(FD != sys::fs::kInvalidFile);
  83
  84   if (auto EC = sys::fs::status(FD, Status))
  85     return errorCodeToError(EC);
  86
  87   // Opening a directory doesn't make sense. Let it fail.
  88   // Linux cannot open directories with open(2), although
  89   // cygwin and *bsd can.
  90   if (Status.type() == sys::fs::file_type::directory_file)
  91     return errorCodeToError(make_error_code(errc::is_a_directory));
  92
  93   ErrorOr<std::unique_ptr<MemoryBuffer>> MemberBufferOrErr =
  94       MemoryBuffer::getOpenFile(FD, FileName, Status.getSize(), false);
  95   if (!MemberBufferOrErr)
  96     return errorCodeToError(MemberBufferOrErr.getError());
  97
  98   if (auto EC = sys::fs::closeFile(FD))
  99     return errorCodeToError(EC);
 100
 101   NewArchiveMember M;
 102   M.Buf = std::move(*MemberBufferOrErr);
 103   M.MemberName = M.Buf->getBufferIdentifier();
 104   if (!Deterministic) {
 105     M.ModTime = std::chrono::time_point_cast<std::chrono::seconds>(
 106         Status.getLastModificationTime());
 107     M.UID = Status.getUser();
 108     M.GID = Status.getGroup();
 109     M.Perms = Status.permissions();
 110   }
 111   return std::move(M);
 112 }
 113
 114 template <typename T>
 115 static void printWithSpacePadding(raw_ostream &OS, T Data, unsigned Size) {
 116   uint64_t OldPos = OS.tell();
 117   OS << Data;
 118   unsigned SizeSoFar = OS.tell() - OldPos;
 119   assert(SizeSoFar <= Size && "Data doesn't fit in Size");
 120   OS.indent(Size - SizeSoFar);
 121 }
 122
 123 static bool isDarwin(object::Archive::Kind Kind) {
 124   return Kind == object::Archive::K_DARWIN ||
 125          Kind == object::Archive::K_DARWIN64;
 126 }
 127
 128 static bool isBSDLike(object::Archive::Kind Kind) {
 129   switch (Kind) {
 130   case object::Archive::K_GNU:
 131   case object::Archive::K_GNU64:
 132     return false;
 133   case object::Archive::K_BSD:
 134   case object::Archive::K_DARWIN:
 135   case object::Archive::K_DARWIN64:
 136     return true;
 137   case object::Archive::K_COFF:
 138     break;
 139   }
 140   llvm_unreachable("not supported for writting");
 141 }
 142
 143 template <class T>
 144 static void print(raw_ostream &Out, object::Archive::Kind Kind, T Val) {
 145   support::endian::write(Out, Val,
 146                          isBSDLike(Kind) ? support::little : support::big);
 147 }
 148
 149 static void printRestOfMemberHeader(
 150     raw_ostream &Out, const sys::TimePoint<std::chrono::seconds> &ModTime,
 151     unsigned UID, unsigned GID, unsigned Perms, uint64_t Size) {
 152   printWithSpacePadding(Out, sys::toTimeT(ModTime), 12);
 153
 154   // The format has only 6 chars for uid and gid. Truncate if the provided
 155   // values don't fit.
 156   printWithSpacePadding(Out, UID % 1000000, 6);
 157   printWithSpacePadding(Out, GID % 1000000, 6);
 158
 159   printWithSpacePadding(Out, format("%o", Perms), 8);
 160   printWithSpacePadding(Out, Size, 10);
 161   Out << "`\n";
 162 }
 163
 164 static void
 165 printGNUSmallMemberHeader(raw_ostream &Out, StringRef Name,
 166                           const sys::TimePoint<std::chrono::seconds> &ModTime,
 167                           unsigned UID, unsigned GID, unsigned Perms,
 168                           uint64_t Size) {
 169   printWithSpacePadding(Out, Twine(Name) + "/", 16);
 170   printRestOfMemberHeader(Out, ModTime, UID, GID, Perms, Size);
 171 }
 172
 173 static void
 174 printBSDMemberHeader(raw_ostream &Out, uint64_t Pos, StringRef Name,
 175                      const sys::TimePoint<std::chrono::seconds> &ModTime,
 176                      unsigned UID, unsigned GID, unsigned Perms, uint64_t Size) {
 177   uint64_t PosAfterHeader = Pos + 60 + Name.size();
 178   // Pad so that even 64 bit object files are aligned.
 179   unsigned Pad = OffsetToAlignment(PosAfterHeader, 8);
 180   unsigned NameWithPadding = Name.size() + Pad;
 181   printWithSpacePadding(Out, Twine("#1/") + Twine(NameWithPadding), 16);
 182   printRestOfMemberHeader(Out, ModTime, UID, GID, Perms,
 183                           NameWithPadding + Size);
 184   Out << Name;
 185   while (Pad--)
 186     Out.write(uint8_t(0));
 187 }
 188
 189 static bool useStringTable(bool Thin, StringRef Name) {
 190   return Thin || Name.size() >= 16 || Name.contains('/');
 191 }
 192
 193 static bool is64BitKind(object::Archive::Kind Kind) {
 194   switch (Kind) {
 195   case object::Archive::K_GNU:
 196   case object::Archive::K_BSD:
 197   case object::Archive::K_DARWIN:
 198   case object::Archive::K_COFF:
 199     return false;
 200   case object::Archive::K_DARWIN64:
 201   case object::Archive::K_GNU64:
 202     return true;
 203   }
 204   llvm_unreachable("not supported for writting");
 205 }
 206
 207 static void
 208 printMemberHeader(raw_ostream &Out, uint64_t Pos, raw_ostream &StringTable,
 209                   StringMap<uint64_t> &MemberNames, object::Archive::Kind Kind,
 210                   bool Thin, const NewArchiveMember &M,
 211                   sys::TimePoint<std::chrono::seconds> ModTime, uint64_t Size) {
 212   if (isBSDLike(Kind))
 213     return printBSDMemberHeader(Out, Pos, M.MemberName, ModTime, M.UID, M.GID,
 214                                 M.Perms, Size);
 215   if (!useStringTable(Thin, M.MemberName))
 216     return printGNUSmallMemberHeader(Out, M.MemberName, ModTime, M.UID, M.GID,
 217                                      M.Perms, Size);
 218   Out << '/';
 219   uint64_t NamePos;
 220   if (Thin) {
 221     NamePos = StringTable.tell();
 222     StringTable << M.MemberName << "/\n";
 223   } else {
 224     auto Insertion = MemberNames.insert({M.MemberName, uint64_t(0)});
 225     if (Insertion.second) {
 226       Insertion.first->second = StringTable.tell();
 227       StringTable << M.MemberName << "/\n";
 228     }
 229     NamePos = Insertion.first->second;
 230   }
 231   printWithSpacePadding(Out, NamePos, 15);
 232   printRestOfMemberHeader(Out, ModTime, M.UID, M.GID, M.Perms, Size);
 233 }
 234
 235 namespace {
 236 struct MemberData {
 237   std::vector<unsigned> Symbols;
 238   std::string Header;
 239   StringRef Data;
 240   StringRef Padding;
 241 };
 242 } // namespace
 243
 244 static MemberData computeStringTable(StringRef Names) {
 245   unsigned Size = Names.size();
 246   unsigned Pad = OffsetToAlignment(Size, 2);
 247   std::string Header;
 248   raw_string_ostream Out(Header);
 249   printWithSpacePadding(Out, "//", 48);
 250   printWithSpacePadding(Out, Size + Pad, 10);
 251   Out << "`\n";
 252   Out.flush();
 253   return {{}, std::move(Header), Names, Pad ? "\n" : ""};
 254 }
 255
 256 static sys::TimePoint<std::chrono::seconds> now(bool Deterministic) {
 257   using namespace std::chrono;
 258
 259   if (!Deterministic)
 260     return time_point_cast<seconds>(system_clock::now());
 261   return sys::TimePoint<seconds>();
 262 }
 263
 264 static bool isArchiveSymbol(const object::BasicSymbolRef &S) {
 265   uint32_t Symflags = S.getFlags();
 266   if (Symflags & object::SymbolRef::SF_FormatSpecific)
 267     return false;
 268   if (!(Symflags & object::SymbolRef::SF_Global))
 269     return false;
 270   if (Symflags & object::SymbolRef::SF_Undefined)
 271     return false;
 272   return true;
 273 }
 274
 275 static void printNBits(raw_ostream &Out, object::Archive::Kind Kind,
 276                        uint64_t Val) {
 277   if (is64BitKind(Kind))
 278     print<uint64_t>(Out, Kind, Val);
 279   else
 280     print<uint32_t>(Out, Kind, Val);
 281 }
 282
 283 static void writeSymbolTable(raw_ostream &Out, object::Archive::Kind Kind,
 284                              bool Deterministic, ArrayRef<MemberData> Members,
 285                              StringRef StringTable) {
 286   // We don't write a symbol table on an archive with no members -- except on
 287   // Darwin, where the linker will abort unless the archive has a symbol table.
 288   if (StringTable.empty() && !isDarwin(Kind))
 289     return;
 290
 291   unsigned NumSyms = 0;
 292   for (const MemberData &M : Members)
 293     NumSyms += M.Symbols.size();
 294
 295   unsigned Size = 0;
 296   unsigned OffsetSize = is64BitKind(Kind) ? sizeof(uint64_t) : sizeof(uint32_t);
 297
 298   Size += OffsetSize; // Number of entries
 299   if (isBSDLike(Kind))
 300     Size += NumSyms * OffsetSize * 2; // Table
 301   else
 302     Size += NumSyms * OffsetSize; // Table
 303   if (isBSDLike(Kind))
 304     Size += OffsetSize; // byte count
 305   Size += StringTable.size();
 306   // ld64 expects the members to be 8-byte aligned for 64-bit content and at
 307   // least 4-byte aligned for 32-bit content.  Opt for the larger encoding
 308   // uniformly.
 309   // We do this for all bsd formats because it simplifies aligning members.
 310   unsigned Alignment = isBSDLike(Kind) ? 8 : 2;
 311   unsigned Pad = OffsetToAlignment(Size, Alignment);
 312   Size += Pad;
 313
 314   if (isBSDLike(Kind)) {
 315     const char *Name = is64BitKind(Kind) ? "__.SYMDEF_64" : "__.SYMDEF";
 316     printBSDMemberHeader(Out, Out.tell(), Name, now(Deterministic), 0, 0, 0,
 317                          Size);
 318   } else {
 319     const char *Name = is64BitKind(Kind) ? "/SYM64" : "";
 320     printGNUSmallMemberHeader(Out, Name, now(Deterministic), 0, 0, 0, Size);
 321   }
 322
 323   uint64_t Pos = Out.tell() + Size;
 324
 325   if (isBSDLike(Kind))
 326     printNBits(Out, Kind, NumSyms * 2 * OffsetSize);
 327   else
 328     printNBits(Out, Kind, NumSyms);
 329
 330   for (const MemberData &M : Members) {
 331     for (unsigned StringOffset : M.Symbols) {
 332       if (isBSDLike(Kind))
 333         printNBits(Out, Kind, StringOffset);
 334       printNBits(Out, Kind, Pos); // member offset
 335     }
 336     Pos += M.Header.size() + M.Data.size() + M.Padding.size();
 337   }
 338
 339   if (isBSDLike(Kind))
 340     // byte count of the string table
 341     printNBits(Out, Kind, StringTable.size());
 342   Out << StringTable;
 343
 344   while (Pad--)
 345     Out.write(uint8_t(0));
 346 }
 347
 348 static Expected<std::vector<unsigned>>
 349 getSymbols(MemoryBufferRef Buf, raw_ostream &SymNames, bool &HasObject) {
 350   std::vector<unsigned> Ret;
 351
 352   // In the scenario when LLVMContext is populated SymbolicFile will contain a
 353   // reference to it, thus SymbolicFile should be destroyed first.
 354   LLVMContext Context;
 355   std::unique_ptr<object::SymbolicFile> Obj;
 356   if (identify_magic(Buf.getBuffer()) == file_magic::bitcode) {
 357     auto ObjOrErr = object::SymbolicFile::createSymbolicFile(
 358         Buf, file_magic::bitcode, &Context);
 359     if (!ObjOrErr) {
 360       // FIXME: check only for "not an object file" errors.
 361       consumeError(ObjOrErr.takeError());
 362       return Ret;
 363     }
 364     Obj = std::move(*ObjOrErr);
 365   } else {
 366     auto ObjOrErr = object::SymbolicFile::createSymbolicFile(Buf);
 367     if (!ObjOrErr) {
 368       // FIXME: check only for "not an object file" errors.
 369       consumeError(ObjOrErr.takeError());
 370       return Ret;
 371     }
 372     Obj = std::move(*ObjOrErr);
 373   }
 374
 375   HasObject = true;
 376   for (const object::BasicSymbolRef &S : Obj->symbols()) {
 377     if (!isArchiveSymbol(S))
 378       continue;
 379     Ret.push_back(SymNames.tell());
 380     if (Error E = S.printName(SymNames))
 381       return std::move(E);
 382     SymNames << '\0';
 383   }
 384   return Ret;
 385 }
 386
 387 static Expected<std::vector<MemberData>>
 388 computeMemberData(raw_ostream &StringTable, raw_ostream &SymNames,
 389                   object::Archive::Kind Kind, bool Thin, bool Deterministic,
 390                   ArrayRef<NewArchiveMember> NewMembers) {
 391   static char PaddingData[8] = {'\n', '\n', '\n', '\n', '\n', '\n', '\n', '\n'};
 392
 393   // This ignores the symbol table, but we only need the value mod 8 and the
 394   // symbol table is aligned to be a multiple of 8 bytes
 395   uint64_t Pos = 0;
 396
 397   std::vector<MemberData> Ret;
 398   bool HasObject = false;
 399
 400   // Deduplicate long member names in the string table and reuse earlier name
 401   // offsets. This especially saves space for COFF Import libraries where all
 402   // members have the same name.
 403   StringMap<uint64_t> MemberNames;
 404
 405   // UniqueTimestamps is a special case to improve debugging on Darwin:
 406   //
 407   // The Darwin linker does not link debug info into the final
 408   // binary. Instead, it emits entries of type N_OSO in in the output
 409   // binary's symbol table, containing references to the linked-in
 410   // object files. Using that reference, the debugger can read the
 411   // debug data directly from the object files. Alternatively, an
 412   // invocation of 'dsymutil' will link the debug data from the object
 413   // files into a dSYM bundle, which can be loaded by the debugger,
 414   // instead of the object files.
 415   //
 416   // For an object file, the N_OSO entries contain the absolute path
 417   // path to the file, and the file's timestamp. For an object
 418   // included in an archive, the path is formatted like
 419   // "/absolute/path/to/archive.a(member.o)", and the timestamp is the
 420   // archive member's timestamp, rather than the archive's timestamp.
 421   //
 422   // However, this doesn't always uniquely identify an object within
 423   // an archive -- an archive file can have multiple entries with the
 424   // same filename. (This will happen commonly if the original object
 425   // files started in different directories.) The only way they get
 426   // distinguished, then, is via the timestamp. But this process is
 427   // unable to find the correct object file in the archive when there
 428   // are two files of the same name and timestamp.
 429   //
 430   // Additionally, timestamp==0 is treated specially, and causes the
 431   // timestamp to be ignored as a match criteria.
 432   //
 433   // That will "usually" work out okay when creating an archive not in
 434   // deterministic timestamp mode, because the objects will probably
 435   // have been created at different timestamps.
 436   //
 437   // To ameliorate this problem, in deterministic archive mode (which
 438   // is the default), on Darwin we will emit a unique non-zero
 439   // timestamp for each entry with a duplicated name. This is still
 440   // deterministic: the only thing affecting that timestamp is the
 441   // order of the files in the resultant archive.
 442   //
 443   // See also the functions that handle the lookup:
 444   // in lldb: ObjectContainerBSDArchive::Archive::FindObject()
 445   // in llvm/tools/dsymutil: BinaryHolder::GetArchiveMemberBuffers().
 446   bool UniqueTimestamps = Deterministic && isDarwin(Kind);
 447   std::map<StringRef, unsigned> FilenameCount;
 448   if (UniqueTimestamps) {
 449     for (const NewArchiveMember &M : NewMembers)
 450       FilenameCount[M.MemberName]++;
 451     for (auto &Entry : FilenameCount)
 452       Entry.second = Entry.second > 1 ? 1 : 0;
 453   }
 454
 455   for (const NewArchiveMember &M : NewMembers) {
 456     std::string Header;
 457     raw_string_ostream Out(Header);
 458
 459     MemoryBufferRef Buf = M.Buf->getMemBufferRef();
 460     StringRef Data = Thin ? "" : Buf.getBuffer();
 461
 462     // ld64 expects the members to be 8-byte aligned for 64-bit content and at
 463     // least 4-byte aligned for 32-bit content.  Opt for the larger encoding
 464     // uniformly.  This matches the behaviour with cctools and ensures that ld64
 465     // is happy with archives that we generate.
 466     unsigned MemberPadding =
 467         isDarwin(Kind) ? OffsetToAlignment(Data.size(), 8) : 0;
 468     unsigned TailPadding = OffsetToAlignment(Data.size() + MemberPadding, 2);
 469     StringRef Padding = StringRef(PaddingData, MemberPadding + TailPadding);
 470
 471     sys::TimePoint<std::chrono::seconds> ModTime;
 472     if (UniqueTimestamps)
 473       // Increment timestamp for each file of a given name.
 474       ModTime = sys::toTimePoint(FilenameCount[M.MemberName]++);
 475     else
 476       ModTime = M.ModTime;
 477
 478     uint64_t Size = Buf.getBufferSize() + MemberPadding;
 479     if (Size > object::Archive::MaxMemberSize) {
 480       std::string StringMsg =
 481           "File " + M.MemberName.str() + " exceeds size limit";
 482       return make_error<object::GenericBinaryError>(
 483           std::move(StringMsg), object::object_error::parse_failed);
 484     }
 485
 486     printMemberHeader(Out, Pos, StringTable, MemberNames, Kind, Thin, M,
 487                       ModTime, Size);
 488     Out.flush();
 489
 490     Expected<std::vector<unsigned>> Symbols =
 491         getSymbols(Buf, SymNames, HasObject);
 492     if (auto E = Symbols.takeError())
 493       return std::move(E);
 494
 495     Pos += Header.size() + Data.size() + Padding.size();
 496     Ret.push_back({std::move(*Symbols), std::move(Header), Data, Padding});
 497   }
 498   // If there are no symbols, emit an empty symbol table, to satisfy Solaris
 499   // tools, older versions of which expect a symbol table in a non-empty
 500   // archive, regardless of whether there are any symbols in it.
 501   if (HasObject && SymNames.tell() == 0)
 502     SymNames << '\0' << '\0' << '\0';
 503   return Ret;
 504 }
 505
 506 namespace llvm {
 507
 508 static ErrorOr<SmallString<128>> canonicalizePath(StringRef P) {
 509   SmallString<128> Ret = P;
 510   std::error_code Err = sys::fs::make_absolute(Ret);
 511   if (Err)
 512     return Err;
 513   sys::path::remove_dots(Ret, /*removedotdot*/ true);
 514   return Ret;
 515 }
 516
 517 // Compute the relative path from From to To.
 518 Expected<std::string> computeArchiveRelativePath(StringRef From, StringRef To) {
 519   ErrorOr<SmallString<128>> PathToOrErr = canonicalizePath(To);
 520   ErrorOr<SmallString<128>> DirFromOrErr = canonicalizePath(From);
 521   if (!PathToOrErr || !DirFromOrErr)
 522     return errorCodeToError(std::error_code(errno, std::generic_category()));
 523
 524   const SmallString<128> &PathTo = *PathToOrErr;
 525   const SmallString<128> &DirFrom = sys::path::parent_path(*DirFromOrErr);
 526
 527   // Can't construct a relative path between different roots
 528   if (sys::path::root_name(PathTo) != sys::path::root_name(DirFrom))
 529     return sys::path::convert_to_slash(PathTo);
 530
 531   // Skip common prefixes
 532   auto FromTo =
 533       std::mismatch(sys::path::begin(DirFrom), sys::path::end(DirFrom),
 534                     sys::path::begin(PathTo));
 535   auto FromI = FromTo.first;
 536   auto ToI = FromTo.second;
 537
 538   // Construct relative path
 539   SmallString<128> Relative;
 540   for (auto FromE = sys::path::end(DirFrom); FromI != FromE; ++FromI)
 541     sys::path::append(Relative, sys::path::Style::posix, "..");
 542
 543   for (auto ToE = sys::path::end(PathTo); ToI != ToE; ++ToI)
 544     sys::path::append(Relative, sys::path::Style::posix, *ToI);
 545
 546   return Relative.str();
 547 }
 548
 549 Error writeArchive(StringRef ArcName, ArrayRef<NewArchiveMember> NewMembers,
 550                    bool WriteSymtab, object::Archive::Kind Kind,
 551                    bool Deterministic, bool Thin,
 552                    std::unique_ptr<MemoryBuffer> OldArchiveBuf) {
 553   assert((!Thin || !isBSDLike(Kind)) && "Only the gnu format has a thin mode");
 554
 555   SmallString<0> SymNamesBuf;
 556   raw_svector_ostream SymNames(SymNamesBuf);
 557   SmallString<0> StringTableBuf;
 558   raw_svector_ostream StringTable(StringTableBuf);
 559
 560   Expected<std::vector<MemberData>> DataOrErr = computeMemberData(
 561       StringTable, SymNames, Kind, Thin, Deterministic, NewMembers);
 562   if (Error E = DataOrErr.takeError())
 563     return E;
 564   std::vector<MemberData> &Data = *DataOrErr;
 565
 566   if (!StringTableBuf.empty())
 567     Data.insert(Data.begin(), computeStringTable(StringTableBuf));
 568
 569   // We would like to detect if we need to switch to a 64-bit symbol table.
 570   if (WriteSymtab) {
 571     uint64_t MaxOffset = 0;
 572     uint64_t LastOffset = MaxOffset;
 573     for (const auto &M : Data) {
 574       // Record the start of the member's offset
 575       LastOffset = MaxOffset;
 576       // Account for the size of each part associated with the member.
 577       MaxOffset += M.Header.size() + M.Data.size() + M.Padding.size();
 578       // We assume 32-bit symbols to see if 32-bit symbols are possible or not.
 579       MaxOffset += M.Symbols.size() * 4;
 580     }
 581
 582     // The SYM64 format is used when an archive's member offsets are larger than
 583     // 32-bits can hold. The need for this shift in format is detected by
 584     // writeArchive. To test this we need to generate a file with a member that
 585     // has an offset larger than 32-bits but this demands a very slow test. To
 586     // speed the test up we use this environment variable to pretend like the
 587     // cutoff happens before 32-bits and instead happens at some much smaller
 588     // value.
 589     const char *Sym64Env = std::getenv("SYM64_THRESHOLD");
 590     int Sym64Threshold = 32;
 591     if (Sym64Env)
 592       StringRef(Sym64Env).getAsInteger(10, Sym64Threshold);
 593
 594     // If LastOffset isn't going to fit in a 32-bit varible we need to switch
 595     // to 64-bit. Note that the file can be larger than 4GB as long as the last
 596     // member starts before the 4GB offset.
 597     if (LastOffset >= (1ULL << Sym64Threshold)) {
 598       if (Kind == object::Archive::K_DARWIN)
 599         Kind = object::Archive::K_DARWIN64;
 600       else
 601         Kind = object::Archive::K_GNU64;
 602     }
 603   }
 604
 605   Expected<sys::fs::TempFile> Temp =
 606       sys::fs::TempFile::create(ArcName + ".temp-archive-%%%%%%%.a");
 607   if (!Temp)
 608     return Temp.takeError();
 609
 610   raw_fd_ostream Out(Temp->FD, false);
 611   if (Thin)
 612     Out << "!<thin>\n";
 613   else
 614     Out << "!<arch>\n";
 615
 616   if (WriteSymtab)
 617     writeSymbolTable(Out, Kind, Deterministic, Data, SymNamesBuf);
 618
 619   for (const MemberData &M : Data)
 620     Out << M.Header << M.Data << M.Padding;
 621
 622   Out.flush();
 623
 624   // At this point, we no longer need whatever backing memory
 625   // was used to generate the NewMembers. On Windows, this buffer
 626   // could be a mapped view of the file we want to replace (if
 627   // we're updating an existing archive, say). In that case, the
 628   // rename would still succeed, but it would leave behind a
 629   // temporary file (actually the original file renamed) because
 630   // a file cannot be deleted while there's a handle open on it,
 631   // only renamed. So by freeing this buffer, this ensures that
 632   // the last open handle on the destination file, if any, is
 633   // closed before we attempt to rename.
 634   OldArchiveBuf.reset();
 635
 636   return Temp->keep(ArcName);
 637 }
 638
 639 } // namespace llvm