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/StringMap.h"
16#include "llvm/ADT/StringRef.h"
17#include "llvm/BinaryFormat/Magic.h"
18#include "llvm/IR/LLVMContext.h"
19#include "llvm/Object/Archive.h"
20#include "llvm/Object/Error.h"
21#include "llvm/Object/ObjectFile.h"
22#include "llvm/Object/SymbolicFile.h"
23#include "llvm/Support/Alignment.h"
24#include "llvm/Support/EndianStream.h"
25#include "llvm/Support/Errc.h"
26#include "llvm/Support/ErrorHandling.h"
27#include "llvm/Support/Format.h"
28#include "llvm/Support/Path.h"
29#include "llvm/Support/ToolOutputFile.h"
30#include "llvm/Support/raw_ostream.h"
31
32#include <map>
33
34#if !defined(_MSC_VER) && !defined(__MINGW32__)
35#include <unistd.h>
36#else
37#include <io.h>
38#endif
39
40using namespace llvm;
41
42NewArchiveMember::NewArchiveMember(MemoryBufferRef BufRef)
43    : Buf(MemoryBuffer::getMemBuffer(BufRef, false)),
44      MemberName(BufRef.getBufferIdentifier()) {}
45
46Expected<NewArchiveMember>
47NewArchiveMember::getOldMember(const object::Archive::Child &OldMember,
48                               bool Deterministic) {
49  Expected<llvm::MemoryBufferRef> BufOrErr = OldMember.getMemoryBufferRef();
50  if (!BufOrErr)
51    return BufOrErr.takeError();
52
53  NewArchiveMember M;
54  M.Buf = MemoryBuffer::getMemBuffer(*BufOrErr, false);
55  M.MemberName = M.Buf->getBufferIdentifier();
56  if (!Deterministic) {
57    auto ModTimeOrErr = OldMember.getLastModified();
58    if (!ModTimeOrErr)
59      return ModTimeOrErr.takeError();
60    M.ModTime = ModTimeOrErr.get();
61    Expected<unsigned> UIDOrErr = OldMember.getUID();
62    if (!UIDOrErr)
63      return UIDOrErr.takeError();
64    M.UID = UIDOrErr.get();
65    Expected<unsigned> GIDOrErr = OldMember.getGID();
66    if (!GIDOrErr)
67      return GIDOrErr.takeError();
68    M.GID = GIDOrErr.get();
69    Expected<sys::fs::perms> AccessModeOrErr = OldMember.getAccessMode();
70    if (!AccessModeOrErr)
71      return AccessModeOrErr.takeError();
72    M.Perms = AccessModeOrErr.get();
73  }
74  return std::move(M);
75}
76
77Expected<NewArchiveMember> NewArchiveMember::getFile(StringRef FileName,
78                                                     bool Deterministic) {
79  sys::fs::file_status Status;
80  auto FDOrErr = sys::fs::openNativeFileForRead(FileName);
81  if (!FDOrErr)
82    return FDOrErr.takeError();
83  sys::fs::file_t FD = *FDOrErr;
84  assert(FD != sys::fs::kInvalidFile);
85
86  if (auto EC = sys::fs::status(FD, Status))
87    return errorCodeToError(EC);
88
89  // Opening a directory doesn't make sense. Let it fail.
90  // Linux cannot open directories with open(2), although
91  // cygwin and *bsd can.
92  if (Status.type() == sys::fs::file_type::directory_file)
93    return errorCodeToError(make_error_code(errc::is_a_directory));
94
95  ErrorOr<std::unique_ptr<MemoryBuffer>> MemberBufferOrErr =
96      MemoryBuffer::getOpenFile(FD, FileName, Status.getSize(), false);
97  if (!MemberBufferOrErr)
98    return errorCodeToError(MemberBufferOrErr.getError());
99
100  if (auto EC = sys::fs::closeFile(FD))
101    return errorCodeToError(EC);
102
103  NewArchiveMember M;
104  M.Buf = std::move(*MemberBufferOrErr);
105  M.MemberName = M.Buf->getBufferIdentifier();
106  if (!Deterministic) {
107    M.ModTime = std::chrono::time_point_cast<std::chrono::seconds>(
108        Status.getLastModificationTime());
109    M.UID = Status.getUser();
110    M.GID = Status.getGroup();
111    M.Perms = Status.permissions();
112  }
113  return std::move(M);
114}
115
116template <typename T>
117static void printWithSpacePadding(raw_ostream &OS, T Data, unsigned Size) {
118  uint64_t OldPos = OS.tell();
119  OS << Data;
120  unsigned SizeSoFar = OS.tell() - OldPos;
121  assert(SizeSoFar <= Size && "Data doesn't fit in Size");
122  OS.indent(Size - SizeSoFar);
123}
124
125static bool isDarwin(object::Archive::Kind Kind) {
126  return Kind == object::Archive::K_DARWIN ||
127         Kind == object::Archive::K_DARWIN64;
128}
129
130static bool isBSDLike(object::Archive::Kind Kind) {
131  switch (Kind) {
132  case object::Archive::K_GNU:
133  case object::Archive::K_GNU64:
134    return false;
135  case object::Archive::K_BSD:
136  case object::Archive::K_DARWIN:
137  case object::Archive::K_DARWIN64:
138    return true;
139  case object::Archive::K_COFF:
140    break;
141  }
142  llvm_unreachable("not supported for writting");
143}
144
145template <class T>
146static void print(raw_ostream &Out, object::Archive::Kind Kind, T Val) {
147  support::endian::write(Out, Val,
148                         isBSDLike(Kind) ? support::little : support::big);
149}
150
151static void printRestOfMemberHeader(
152    raw_ostream &Out, const sys::TimePoint<std::chrono::seconds> &ModTime,
153    unsigned UID, unsigned GID, unsigned Perms, uint64_t Size) {
154  printWithSpacePadding(Out, sys::toTimeT(ModTime), 12);
155
156  // The format has only 6 chars for uid and gid. Truncate if the provided
157  // values don't fit.
158  printWithSpacePadding(Out, UID % 1000000, 6);
159  printWithSpacePadding(Out, GID % 1000000, 6);
160
161  printWithSpacePadding(Out, format("%o", Perms), 8);
162  printWithSpacePadding(Out, Size, 10);
163  Out << "`\n";
164}
165
166static void
167printGNUSmallMemberHeader(raw_ostream &Out, StringRef Name,
168                          const sys::TimePoint<std::chrono::seconds> &ModTime,
169                          unsigned UID, unsigned GID, unsigned Perms,
170                          uint64_t Size) {
171  printWithSpacePadding(Out, Twine(Name) + "/", 16);
172  printRestOfMemberHeader(Out, ModTime, UID, GID, Perms, Size);
173}
174
175static void
176printBSDMemberHeader(raw_ostream &Out, uint64_t Pos, StringRef Name,
177                     const sys::TimePoint<std::chrono::seconds> &ModTime,
178                     unsigned UID, unsigned GID, unsigned Perms, uint64_t Size) {
179  uint64_t PosAfterHeader = Pos + 60 + Name.size();
180  // Pad so that even 64 bit object files are aligned.
181  unsigned Pad = offsetToAlignment(PosAfterHeader, Align(8));
182  unsigned NameWithPadding = Name.size() + Pad;
183  printWithSpacePadding(Out, Twine("#1/") + Twine(NameWithPadding), 16);
184  printRestOfMemberHeader(Out, ModTime, UID, GID, Perms,
185                          NameWithPadding + Size);
186  Out << Name;
187  while (Pad--)
188    Out.write(uint8_t(0));
189}
190
191static bool useStringTable(bool Thin, StringRef Name) {
192  return Thin || Name.size() >= 16 || Name.contains('/');
193}
194
195static bool is64BitKind(object::Archive::Kind Kind) {
196  switch (Kind) {
197  case object::Archive::K_GNU:
198  case object::Archive::K_BSD:
199  case object::Archive::K_DARWIN:
200  case object::Archive::K_COFF:
201    return false;
202  case object::Archive::K_DARWIN64:
203  case object::Archive::K_GNU64:
204    return true;
205  }
206  llvm_unreachable("not supported for writting");
207}
208
209static void
210printMemberHeader(raw_ostream &Out, uint64_t Pos, raw_ostream &StringTable,
211                  StringMap<uint64_t> &MemberNames, object::Archive::Kind Kind,
212                  bool Thin, const NewArchiveMember &M,
213                  sys::TimePoint<std::chrono::seconds> ModTime, uint64_t Size) {
214  if (isBSDLike(Kind))
215    return printBSDMemberHeader(Out, Pos, M.MemberName, ModTime, M.UID, M.GID,
216                                M.Perms, Size);
217  if (!useStringTable(Thin, M.MemberName))
218    return printGNUSmallMemberHeader(Out, M.MemberName, ModTime, M.UID, M.GID,
219                                     M.Perms, Size);
220  Out << '/';
221  uint64_t NamePos;
222  if (Thin) {
223    NamePos = StringTable.tell();
224    StringTable << M.MemberName << "/\n";
225  } else {
226    auto Insertion = MemberNames.insert({M.MemberName, uint64_t(0)});
227    if (Insertion.second) {
228      Insertion.first->second = StringTable.tell();
229      StringTable << M.MemberName << "/\n";
230    }
231    NamePos = Insertion.first->second;
232  }
233  printWithSpacePadding(Out, NamePos, 15);
234  printRestOfMemberHeader(Out, ModTime, M.UID, M.GID, M.Perms, Size);
235}
236
237namespace {
238struct MemberData {
239  std::vector<unsigned> Symbols;
240  std::string Header;
241  StringRef Data;
242  StringRef Padding;
243};
244} // namespace
245
246static MemberData computeStringTable(StringRef Names) {
247  unsigned Size = Names.size();
248  unsigned Pad = offsetToAlignment(Size, Align(2));
249  std::string Header;
250  raw_string_ostream Out(Header);
251  printWithSpacePadding(Out, "//", 48);
252  printWithSpacePadding(Out, Size + Pad, 10);
253  Out << "`\n";
254  Out.flush();
255  return {{}, std::move(Header), Names, Pad ? "\n" : ""};
256}
257
258static sys::TimePoint<std::chrono::seconds> now(bool Deterministic) {
259  using namespace std::chrono;
260
261  if (!Deterministic)
262    return time_point_cast<seconds>(system_clock::now());
263  return sys::TimePoint<seconds>();
264}
265
266static bool isArchiveSymbol(const object::BasicSymbolRef &S) {
267  Expected<uint32_t> SymFlagsOrErr = S.getFlags();
268  if (!SymFlagsOrErr)
269    // TODO: Actually report errors helpfully.
270    report_fatal_error(SymFlagsOrErr.takeError());
271  if (*SymFlagsOrErr & object::SymbolRef::SF_FormatSpecific)
272    return false;
273  if (!(*SymFlagsOrErr & object::SymbolRef::SF_Global))
274    return false;
275  if (*SymFlagsOrErr & object::SymbolRef::SF_Undefined)
276    return false;
277  return true;
278}
279
280static void printNBits(raw_ostream &Out, object::Archive::Kind Kind,
281                       uint64_t Val) {
282  if (is64BitKind(Kind))
283    print<uint64_t>(Out, Kind, Val);
284  else
285    print<uint32_t>(Out, Kind, Val);
286}
287
288static void writeSymbolTable(raw_ostream &Out, object::Archive::Kind Kind,
289                             bool Deterministic, ArrayRef<MemberData> Members,
290                             StringRef StringTable) {
291  // We don't write a symbol table on an archive with no members -- except on
292  // Darwin, where the linker will abort unless the archive has a symbol table.
293  if (StringTable.empty() && !isDarwin(Kind))
294    return;
295
296  unsigned NumSyms = 0;
297  for (const MemberData &M : Members)
298    NumSyms += M.Symbols.size();
299
300  unsigned Size = 0;
301  unsigned OffsetSize = is64BitKind(Kind) ? sizeof(uint64_t) : sizeof(uint32_t);
302
303  Size += OffsetSize; // Number of entries
304  if (isBSDLike(Kind))
305    Size += NumSyms * OffsetSize * 2; // Table
306  else
307    Size += NumSyms * OffsetSize; // Table
308  if (isBSDLike(Kind))
309    Size += OffsetSize; // byte count
310  Size += StringTable.size();
311  // ld64 expects the members to be 8-byte aligned for 64-bit content and at
312  // least 4-byte aligned for 32-bit content.  Opt for the larger encoding
313  // uniformly.
314  // We do this for all bsd formats because it simplifies aligning members.
315  const Align Alignment(isBSDLike(Kind) ? 8 : 2);
316  unsigned Pad = offsetToAlignment(Size, Alignment);
317  Size += Pad;
318
319  if (isBSDLike(Kind)) {
320    const char *Name = is64BitKind(Kind) ? "__.SYMDEF_64" : "__.SYMDEF";
321    printBSDMemberHeader(Out, Out.tell(), Name, now(Deterministic), 0, 0, 0,
322                         Size);
323  } else {
324    const char *Name = is64BitKind(Kind) ? "/SYM64" : "";
325    printGNUSmallMemberHeader(Out, Name, now(Deterministic), 0, 0, 0, Size);
326  }
327
328  uint64_t Pos = Out.tell() + Size;
329
330  if (isBSDLike(Kind))
331    printNBits(Out, Kind, NumSyms * 2 * OffsetSize);
332  else
333    printNBits(Out, Kind, NumSyms);
334
335  for (const MemberData &M : Members) {
336    for (unsigned StringOffset : M.Symbols) {
337      if (isBSDLike(Kind))
338        printNBits(Out, Kind, StringOffset);
339      printNBits(Out, Kind, Pos); // member offset
340    }
341    Pos += M.Header.size() + M.Data.size() + M.Padding.size();
342  }
343
344  if (isBSDLike(Kind))
345    // byte count of the string table
346    printNBits(Out, Kind, StringTable.size());
347  Out << StringTable;
348
349  while (Pad--)
350    Out.write(uint8_t(0));
351}
352
353static Expected<std::vector<unsigned>>
354getSymbols(MemoryBufferRef Buf, raw_ostream &SymNames, bool &HasObject) {
355  std::vector<unsigned> Ret;
356
357  // In the scenario when LLVMContext is populated SymbolicFile will contain a
358  // reference to it, thus SymbolicFile should be destroyed first.
359  LLVMContext Context;
360  std::unique_ptr<object::SymbolicFile> Obj;
361  if (identify_magic(Buf.getBuffer()) == file_magic::bitcode) {
362    auto ObjOrErr = object::SymbolicFile::createSymbolicFile(
363        Buf, file_magic::bitcode, &Context);
364    if (!ObjOrErr) {
365      // FIXME: check only for "not an object file" errors.
366      consumeError(ObjOrErr.takeError());
367      return Ret;
368    }
369    Obj = std::move(*ObjOrErr);
370  } else {
371    auto ObjOrErr = object::SymbolicFile::createSymbolicFile(Buf);
372    if (!ObjOrErr) {
373      // FIXME: check only for "not an object file" errors.
374      consumeError(ObjOrErr.takeError());
375      return Ret;
376    }
377    Obj = std::move(*ObjOrErr);
378  }
379
380  HasObject = true;
381  for (const object::BasicSymbolRef &S : Obj->symbols()) {
382    if (!isArchiveSymbol(S))
383      continue;
384    Ret.push_back(SymNames.tell());
385    if (Error E = S.printName(SymNames))
386      return std::move(E);
387    SymNames << '\0';
388  }
389  return Ret;
390}
391
392static Expected<std::vector<MemberData>>
393computeMemberData(raw_ostream &StringTable, raw_ostream &SymNames,
394                  object::Archive::Kind Kind, bool Thin, bool Deterministic,
395                  ArrayRef<NewArchiveMember> NewMembers) {
396  static char PaddingData[8] = {'\n', '\n', '\n', '\n', '\n', '\n', '\n', '\n'};
397
398  // This ignores the symbol table, but we only need the value mod 8 and the
399  // symbol table is aligned to be a multiple of 8 bytes
400  uint64_t Pos = 0;
401
402  std::vector<MemberData> Ret;
403  bool HasObject = false;
404
405  // Deduplicate long member names in the string table and reuse earlier name
406  // offsets. This especially saves space for COFF Import libraries where all
407  // members have the same name.
408  StringMap<uint64_t> MemberNames;
409
410  // UniqueTimestamps is a special case to improve debugging on Darwin:
411  //
412  // The Darwin linker does not link debug info into the final
413  // binary. Instead, it emits entries of type N_OSO in in the output
414  // binary's symbol table, containing references to the linked-in
415  // object files. Using that reference, the debugger can read the
416  // debug data directly from the object files. Alternatively, an
417  // invocation of 'dsymutil' will link the debug data from the object
418  // files into a dSYM bundle, which can be loaded by the debugger,
419  // instead of the object files.
420  //
421  // For an object file, the N_OSO entries contain the absolute path
422  // path to the file, and the file's timestamp. For an object
423  // included in an archive, the path is formatted like
424  // "/absolute/path/to/archive.a(member.o)", and the timestamp is the
425  // archive member's timestamp, rather than the archive's timestamp.
426  //
427  // However, this doesn't always uniquely identify an object within
428  // an archive -- an archive file can have multiple entries with the
429  // same filename. (This will happen commonly if the original object
430  // files started in different directories.) The only way they get
431  // distinguished, then, is via the timestamp. But this process is
432  // unable to find the correct object file in the archive when there
433  // are two files of the same name and timestamp.
434  //
435  // Additionally, timestamp==0 is treated specially, and causes the
436  // timestamp to be ignored as a match criteria.
437  //
438  // That will "usually" work out okay when creating an archive not in
439  // deterministic timestamp mode, because the objects will probably
440  // have been created at different timestamps.
441  //
442  // To ameliorate this problem, in deterministic archive mode (which
443  // is the default), on Darwin we will emit a unique non-zero
444  // timestamp for each entry with a duplicated name. This is still
445  // deterministic: the only thing affecting that timestamp is the
446  // order of the files in the resultant archive.
447  //
448  // See also the functions that handle the lookup:
449  // in lldb: ObjectContainerBSDArchive::Archive::FindObject()
450  // in llvm/tools/dsymutil: BinaryHolder::GetArchiveMemberBuffers().
451  bool UniqueTimestamps = Deterministic && isDarwin(Kind);
452  std::map<StringRef, unsigned> FilenameCount;
453  if (UniqueTimestamps) {
454    for (const NewArchiveMember &M : NewMembers)
455      FilenameCount[M.MemberName]++;
456    for (auto &Entry : FilenameCount)
457      Entry.second = Entry.second > 1 ? 1 : 0;
458  }
459
460  for (const NewArchiveMember &M : NewMembers) {
461    std::string Header;
462    raw_string_ostream Out(Header);
463
464    MemoryBufferRef Buf = M.Buf->getMemBufferRef();
465    StringRef Data = Thin ? "" : Buf.getBuffer();
466
467    // ld64 expects the members to be 8-byte aligned for 64-bit content and at
468    // least 4-byte aligned for 32-bit content.  Opt for the larger encoding
469    // uniformly.  This matches the behaviour with cctools and ensures that ld64
470    // is happy with archives that we generate.
471    unsigned MemberPadding =
472        isDarwin(Kind) ? offsetToAlignment(Data.size(), Align(8)) : 0;
473    unsigned TailPadding =
474        offsetToAlignment(Data.size() + MemberPadding, Align(2));
475    StringRef Padding = StringRef(PaddingData, MemberPadding + TailPadding);
476
477    sys::TimePoint<std::chrono::seconds> ModTime;
478    if (UniqueTimestamps)
479      // Increment timestamp for each file of a given name.
480      ModTime = sys::toTimePoint(FilenameCount[M.MemberName]++);
481    else
482      ModTime = M.ModTime;
483
484    uint64_t Size = Buf.getBufferSize() + MemberPadding;
485    if (Size > object::Archive::MaxMemberSize) {
486      std::string StringMsg =
487          "File " + M.MemberName.str() + " exceeds size limit";
488      return make_error<object::GenericBinaryError>(
489          std::move(StringMsg), object::object_error::parse_failed);
490    }
491
492    printMemberHeader(Out, Pos, StringTable, MemberNames, Kind, Thin, M,
493                      ModTime, Size);
494    Out.flush();
495
496    Expected<std::vector<unsigned>> Symbols =
497        getSymbols(Buf, SymNames, HasObject);
498    if (auto E = Symbols.takeError())
499      return std::move(E);
500
501    Pos += Header.size() + Data.size() + Padding.size();
502    Ret.push_back({std::move(*Symbols), std::move(Header), Data, Padding});
503  }
504  // If there are no symbols, emit an empty symbol table, to satisfy Solaris
505  // tools, older versions of which expect a symbol table in a non-empty
506  // archive, regardless of whether there are any symbols in it.
507  if (HasObject && SymNames.tell() == 0)
508    SymNames << '\0' << '\0' << '\0';
509  return Ret;
510}
511
512namespace llvm {
513
514static ErrorOr<SmallString<128>> canonicalizePath(StringRef P) {
515  SmallString<128> Ret = P;
516  std::error_code Err = sys::fs::make_absolute(Ret);
517  if (Err)
518    return Err;
519  sys::path::remove_dots(Ret, /*removedotdot*/ true);
520  return Ret;
521}
522
523// Compute the relative path from From to To.
524Expected<std::string> computeArchiveRelativePath(StringRef From, StringRef To) {
525  ErrorOr<SmallString<128>> PathToOrErr = canonicalizePath(To);
526  ErrorOr<SmallString<128>> DirFromOrErr = canonicalizePath(From);
527  if (!PathToOrErr || !DirFromOrErr)
528    return errorCodeToError(std::error_code(errno, std::generic_category()));
529
530  const SmallString<128> &PathTo = *PathToOrErr;
531  const SmallString<128> &DirFrom = sys::path::parent_path(*DirFromOrErr);
532
533  // Can't construct a relative path between different roots
534  if (sys::path::root_name(PathTo) != sys::path::root_name(DirFrom))
535    return sys::path::convert_to_slash(PathTo);
536
537  // Skip common prefixes
538  auto FromTo =
539      std::mismatch(sys::path::begin(DirFrom), sys::path::end(DirFrom),
540                    sys::path::begin(PathTo));
541  auto FromI = FromTo.first;
542  auto ToI = FromTo.second;
543
544  // Construct relative path
545  SmallString<128> Relative;
546  for (auto FromE = sys::path::end(DirFrom); FromI != FromE; ++FromI)
547    sys::path::append(Relative, sys::path::Style::posix, "..");
548
549  for (auto ToE = sys::path::end(PathTo); ToI != ToE; ++ToI)
550    sys::path::append(Relative, sys::path::Style::posix, *ToI);
551
552  return std::string(Relative.str());
553}
554
555Error writeArchive(StringRef ArcName, ArrayRef<NewArchiveMember> NewMembers,
556                   bool WriteSymtab, object::Archive::Kind Kind,
557                   bool Deterministic, bool Thin,
558                   std::unique_ptr<MemoryBuffer> OldArchiveBuf) {
559  assert((!Thin || !isBSDLike(Kind)) && "Only the gnu format has a thin mode");
560
561  SmallString<0> SymNamesBuf;
562  raw_svector_ostream SymNames(SymNamesBuf);
563  SmallString<0> StringTableBuf;
564  raw_svector_ostream StringTable(StringTableBuf);
565
566  Expected<std::vector<MemberData>> DataOrErr = computeMemberData(
567      StringTable, SymNames, Kind, Thin, Deterministic, NewMembers);
568  if (Error E = DataOrErr.takeError())
569    return E;
570  std::vector<MemberData> &Data = *DataOrErr;
571
572  if (!StringTableBuf.empty())
573    Data.insert(Data.begin(), computeStringTable(StringTableBuf));
574
575  // We would like to detect if we need to switch to a 64-bit symbol table.
576  if (WriteSymtab) {
577    uint64_t MaxOffset = 0;
578    uint64_t LastOffset = MaxOffset;
579    for (const auto &M : Data) {
580      // Record the start of the member's offset
581      LastOffset = MaxOffset;
582      // Account for the size of each part associated with the member.
583      MaxOffset += M.Header.size() + M.Data.size() + M.Padding.size();
584      // We assume 32-bit symbols to see if 32-bit symbols are possible or not.
585      MaxOffset += M.Symbols.size() * 4;
586    }
587
588    // The SYM64 format is used when an archive's member offsets are larger than
589    // 32-bits can hold. The need for this shift in format is detected by
590    // writeArchive. To test this we need to generate a file with a member that
591    // has an offset larger than 32-bits but this demands a very slow test. To
592    // speed the test up we use this environment variable to pretend like the
593    // cutoff happens before 32-bits and instead happens at some much smaller
594    // value.
595    const char *Sym64Env = std::getenv("SYM64_THRESHOLD");
596    int Sym64Threshold = 32;
597    if (Sym64Env)
598      StringRef(Sym64Env).getAsInteger(10, Sym64Threshold);
599
600    // If LastOffset isn't going to fit in a 32-bit varible we need to switch
601    // to 64-bit. Note that the file can be larger than 4GB as long as the last
602    // member starts before the 4GB offset.
603    if (LastOffset >= (1ULL << Sym64Threshold)) {
604      if (Kind == object::Archive::K_DARWIN)
605        Kind = object::Archive::K_DARWIN64;
606      else
607        Kind = object::Archive::K_GNU64;
608    }
609  }
610
611  Expected<sys::fs::TempFile> Temp =
612      sys::fs::TempFile::create(ArcName + ".temp-archive-%%%%%%%.a");
613  if (!Temp)
614    return Temp.takeError();
615
616  raw_fd_ostream Out(Temp->FD, false);
617  if (Thin)
618    Out << "!<thin>\n";
619  else
620    Out << "!<arch>\n";
621
622  if (WriteSymtab)
623    writeSymbolTable(Out, Kind, Deterministic, Data, SymNamesBuf);
624
625  for (const MemberData &M : Data)
626    Out << M.Header << M.Data << M.Padding;
627
628  Out.flush();
629
630  // At this point, we no longer need whatever backing memory
631  // was used to generate the NewMembers. On Windows, this buffer
632  // could be a mapped view of the file we want to replace (if
633  // we're updating an existing archive, say). In that case, the
634  // rename would still succeed, but it would leave behind a
635  // temporary file (actually the original file renamed) because
636  // a file cannot be deleted while there's a handle open on it,
637  // only renamed. So by freeing this buffer, this ensures that
638  // the last open handle on the destination file, if any, is
639  // closed before we attempt to rename.
640  OldArchiveBuf.reset();
641
642  return Temp->keep(ArcName);
643}
644
645} // namespace llvm
646