tools/yaml2obj/yaml2macho.cpp

   1 //===- yaml2macho - Convert YAML to a Mach object file --------------------===//
   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 /// \file
  10 /// The Mach component of yaml2obj.
  11 ///
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "yaml2obj.h"
  15 #include "llvm/BinaryFormat/MachO.h"
  16 #include "llvm/ObjectYAML/DWARFEmitter.h"
  17 #include "llvm/ObjectYAML/ObjectYAML.h"
  18 #include "llvm/Support/Error.h"
  19 #include "llvm/Support/LEB128.h"
  20 #include "llvm/Support/YAMLTraits.h"
  21 #include "llvm/Support/raw_ostream.h"
  22
  23 #include "llvm/Support/Format.h"
  24
  25 using namespace llvm;
  26
  27 namespace {
  28
  29 class MachOWriter {
  30 public:
  31   MachOWriter(MachOYAML::Object &Obj) : Obj(Obj), is64Bit(true), fileStart(0) {
  32     is64Bit = Obj.Header.magic == MachO::MH_MAGIC_64 ||
  33               Obj.Header.magic == MachO::MH_CIGAM_64;
  34     memset(reinterpret_cast<void *>(&Header), 0, sizeof(MachO::mach_header_64));
  35   }
  36
  37   Error writeMachO(raw_ostream &OS);
  38
  39 private:
  40   Error writeHeader(raw_ostream &OS);
  41   Error writeLoadCommands(raw_ostream &OS);
  42   Error writeSectionData(raw_ostream &OS);
  43   Error writeLinkEditData(raw_ostream &OS);
  44
  45   void writeBindOpcodes(raw_ostream &OS,
  46                         std::vector<MachOYAML::BindOpcode> &BindOpcodes);
  47   // LinkEdit writers
  48   Error writeRebaseOpcodes(raw_ostream &OS);
  49   Error writeBasicBindOpcodes(raw_ostream &OS);
  50   Error writeWeakBindOpcodes(raw_ostream &OS);
  51   Error writeLazyBindOpcodes(raw_ostream &OS);
  52   Error writeNameList(raw_ostream &OS);
  53   Error writeStringTable(raw_ostream &OS);
  54   Error writeExportTrie(raw_ostream &OS);
  55
  56   void dumpExportEntry(raw_ostream &OS, MachOYAML::ExportEntry &Entry);
  57   void ZeroToOffset(raw_ostream &OS, size_t offset);
  58
  59   MachOYAML::Object &Obj;
  60   bool is64Bit;
  61   uint64_t fileStart;
  62
  63   MachO::mach_header_64 Header;
  64 };
  65
  66 Error MachOWriter::writeMachO(raw_ostream &OS) {
  67   fileStart = OS.tell();
  68   if (auto Err = writeHeader(OS))
  69     return Err;
  70   if (auto Err = writeLoadCommands(OS))
  71     return Err;
  72   if (auto Err = writeSectionData(OS))
  73     return Err;
  74   return Error::success();
  75 }
  76
  77 Error MachOWriter::writeHeader(raw_ostream &OS) {
  78   Header.magic = Obj.Header.magic;
  79   Header.cputype = Obj.Header.cputype;
  80   Header.cpusubtype = Obj.Header.cpusubtype;
  81   Header.filetype = Obj.Header.filetype;
  82   Header.ncmds = Obj.Header.ncmds;
  83   Header.sizeofcmds = Obj.Header.sizeofcmds;
  84   Header.flags = Obj.Header.flags;
  85   Header.reserved = Obj.Header.reserved;
  86
  87   if (Obj.IsLittleEndian != sys::IsLittleEndianHost)
  88     MachO::swapStruct(Header);
  89
  90   auto header_size =
  91       is64Bit ? sizeof(MachO::mach_header_64) : sizeof(MachO::mach_header);
  92   OS.write((const char *)&Header, header_size);
  93
  94   return Error::success();
  95 }
  96
  97 template <typename SectionType>
  98 SectionType constructSection(MachOYAML::Section Sec) {
  99   SectionType TempSec;
 100   memcpy(reinterpret_cast<void *>(&TempSec.sectname[0]), &Sec.sectname[0], 16);
 101   memcpy(reinterpret_cast<void *>(&TempSec.segname[0]), &Sec.segname[0], 16);
 102   TempSec.addr = Sec.addr;
 103   TempSec.size = Sec.size;
 104   TempSec.offset = Sec.offset;
 105   TempSec.align = Sec.align;
 106   TempSec.reloff = Sec.reloff;
 107   TempSec.nreloc = Sec.nreloc;
 108   TempSec.flags = Sec.flags;
 109   TempSec.reserved1 = Sec.reserved1;
 110   TempSec.reserved2 = Sec.reserved2;
 111   return TempSec;
 112 }
 113
 114 template <typename StructType>
 115 size_t writeLoadCommandData(MachOYAML::LoadCommand &LC, raw_ostream &OS,
 116                             bool IsLittleEndian) {
 117   return 0;
 118 }
 119
 120 template <>
 121 size_t writeLoadCommandData<MachO::segment_command>(MachOYAML::LoadCommand &LC,
 122                                                     raw_ostream &OS,
 123                                                     bool IsLittleEndian) {
 124   size_t BytesWritten = 0;
 125   for (const auto &Sec : LC.Sections) {
 126     auto TempSec = constructSection<MachO::section>(Sec);
 127     if (IsLittleEndian != sys::IsLittleEndianHost)
 128       MachO::swapStruct(TempSec);
 129     OS.write(reinterpret_cast<const char *>(&(TempSec)),
 130              sizeof(MachO::section));
 131     BytesWritten += sizeof(MachO::section);
 132   }
 133   return BytesWritten;
 134 }
 135
 136 template <>
 137 size_t writeLoadCommandData<MachO::segment_command_64>(
 138     MachOYAML::LoadCommand &LC, raw_ostream &OS, bool IsLittleEndian) {
 139   size_t BytesWritten = 0;
 140   for (const auto &Sec : LC.Sections) {
 141     auto TempSec = constructSection<MachO::section_64>(Sec);
 142     TempSec.reserved3 = Sec.reserved3;
 143     if (IsLittleEndian != sys::IsLittleEndianHost)
 144       MachO::swapStruct(TempSec);
 145     OS.write(reinterpret_cast<const char *>(&(TempSec)),
 146              sizeof(MachO::section_64));
 147     BytesWritten += sizeof(MachO::section_64);
 148   }
 149   return BytesWritten;
 150 }
 151
 152 size_t writePayloadString(MachOYAML::LoadCommand &LC, raw_ostream &OS) {
 153   size_t BytesWritten = 0;
 154   if (!LC.PayloadString.empty()) {
 155     OS.write(LC.PayloadString.c_str(), LC.PayloadString.length());
 156     BytesWritten = LC.PayloadString.length();
 157   }
 158   return BytesWritten;
 159 }
 160
 161 template <>
 162 size_t writeLoadCommandData<MachO::dylib_command>(MachOYAML::LoadCommand &LC,
 163                                                   raw_ostream &OS,
 164                                                   bool IsLittleEndian) {
 165   return writePayloadString(LC, OS);
 166 }
 167
 168 template <>
 169 size_t writeLoadCommandData<MachO::dylinker_command>(MachOYAML::LoadCommand &LC,
 170                                                      raw_ostream &OS,
 171                                                      bool IsLittleEndian) {
 172   return writePayloadString(LC, OS);
 173 }
 174
 175 template <>
 176 size_t writeLoadCommandData<MachO::rpath_command>(MachOYAML::LoadCommand &LC,
 177                                                   raw_ostream &OS,
 178                                                   bool IsLittleEndian) {
 179   return writePayloadString(LC, OS);
 180 }
 181
 182 template <>
 183 size_t writeLoadCommandData<MachO::build_version_command>(
 184     MachOYAML::LoadCommand &LC, raw_ostream &OS, bool IsLittleEndian) {
 185   size_t BytesWritten = 0;
 186   for (const auto &T : LC.Tools) {
 187     struct MachO::build_tool_version tool = T;
 188     if (IsLittleEndian != sys::IsLittleEndianHost)
 189       MachO::swapStruct(tool);
 190     OS.write(reinterpret_cast<const char *>(&tool),
 191              sizeof(MachO::build_tool_version));
 192     BytesWritten += sizeof(MachO::build_tool_version);
 193   }
 194   return BytesWritten;
 195 }
 196
 197 void ZeroFillBytes(raw_ostream &OS, size_t Size) {
 198   std::vector<uint8_t> FillData;
 199   FillData.insert(FillData.begin(), Size, 0);
 200   OS.write(reinterpret_cast<char *>(FillData.data()), Size);
 201 }
 202
 203 void Fill(raw_ostream &OS, size_t Size, uint32_t Data) {
 204   std::vector<uint32_t> FillData;
 205   FillData.insert(FillData.begin(), (Size / 4) + 1, Data);
 206   OS.write(reinterpret_cast<char *>(FillData.data()), Size);
 207 }
 208
 209 void MachOWriter::ZeroToOffset(raw_ostream &OS, size_t Offset) {
 210   auto currOffset = OS.tell() - fileStart;
 211   if (currOffset < Offset)
 212     ZeroFillBytes(OS, Offset - currOffset);
 213 }
 214
 215 Error MachOWriter::writeLoadCommands(raw_ostream &OS) {
 216   for (auto &LC : Obj.LoadCommands) {
 217     size_t BytesWritten = 0;
 218     llvm::MachO::macho_load_command Data = LC.Data;
 219
 220 #define HANDLE_LOAD_COMMAND(LCName, LCValue, LCStruct)                         \
 221   case MachO::LCName:                                                          \
 222     if (Obj.IsLittleEndian != sys::IsLittleEndianHost)                         \
 223       MachO::swapStruct(Data.LCStruct##_data);                                 \
 224     OS.write(reinterpret_cast<const char *>(&(Data.LCStruct##_data)),          \
 225              sizeof(MachO::LCStruct));                                         \
 226     BytesWritten = sizeof(MachO::LCStruct);                                    \
 227     BytesWritten +=                                                            \
 228         writeLoadCommandData<MachO::LCStruct>(LC, OS, Obj.IsLittleEndian);     \
 229     break;
 230
 231     switch (LC.Data.load_command_data.cmd) {
 232     default:
 233       if (Obj.IsLittleEndian != sys::IsLittleEndianHost)
 234         MachO::swapStruct(Data.load_command_data);
 235       OS.write(reinterpret_cast<const char *>(&(Data.load_command_data)),
 236                sizeof(MachO::load_command));
 237       BytesWritten = sizeof(MachO::load_command);
 238       BytesWritten +=
 239           writeLoadCommandData<MachO::load_command>(LC, OS, Obj.IsLittleEndian);
 240       break;
 241 #include "llvm/BinaryFormat/MachO.def"
 242     }
 243
 244     if (LC.PayloadBytes.size() > 0) {
 245       OS.write(reinterpret_cast<const char *>(LC.PayloadBytes.data()),
 246                LC.PayloadBytes.size());
 247       BytesWritten += LC.PayloadBytes.size();
 248     }
 249
 250     if (LC.ZeroPadBytes > 0) {
 251       ZeroFillBytes(OS, LC.ZeroPadBytes);
 252       BytesWritten += LC.ZeroPadBytes;
 253     }
 254
 255     // Fill remaining bytes with 0. This will only get hit in partially
 256     // specified test cases.
 257     auto BytesRemaining = LC.Data.load_command_data.cmdsize - BytesWritten;
 258     if (BytesRemaining > 0) {
 259       ZeroFillBytes(OS, BytesRemaining);
 260     }
 261   }
 262   return Error::success();
 263 }
 264
 265 static bool isVirtualSection(uint8_t type) {
 266   return (type == MachO::S_ZEROFILL ||
 267           type == MachO::S_GB_ZEROFILL ||
 268           type == MachO::S_THREAD_LOCAL_ZEROFILL);
 269 }
 270
 271 Error MachOWriter::writeSectionData(raw_ostream &OS) {
 272   bool FoundLinkEditSeg = false;
 273   for (auto &LC : Obj.LoadCommands) {
 274     switch (LC.Data.load_command_data.cmd) {
 275     case MachO::LC_SEGMENT:
 276     case MachO::LC_SEGMENT_64:
 277       uint64_t segOff = is64Bit ? LC.Data.segment_command_64_data.fileoff
 278                                 : LC.Data.segment_command_data.fileoff;
 279       if (0 == strncmp(&LC.Data.segment_command_data.segname[0], "__LINKEDIT", 16)) {
 280         FoundLinkEditSeg = true;
 281         if (auto Err = writeLinkEditData(OS))
 282           return Err;
 283       }
 284       for (auto &Sec : LC.Sections) {
 285         ZeroToOffset(OS, Sec.offset);
 286         // Zero Fill any data between the end of the last thing we wrote and the
 287         // start of this section.
 288         assert((OS.tell() - fileStart <= Sec.offset ||
 289                 Sec.offset == (uint32_t)0) &&
 290                "Wrote too much data somewhere, section offsets don't line up.");
 291         if (0 == strncmp(&Sec.segname[0], "__DWARF", 16)) {
 292           if (0 == strncmp(&Sec.sectname[0], "__debug_str", 16)) {
 293             DWARFYAML::EmitDebugStr(OS, Obj.DWARF);
 294           } else if (0 == strncmp(&Sec.sectname[0], "__debug_abbrev", 16)) {
 295             DWARFYAML::EmitDebugAbbrev(OS, Obj.DWARF);
 296           } else if (0 == strncmp(&Sec.sectname[0], "__debug_aranges", 16)) {
 297             DWARFYAML::EmitDebugAranges(OS, Obj.DWARF);
 298           } else if (0 == strncmp(&Sec.sectname[0], "__debug_pubnames", 16)) {
 299             DWARFYAML::EmitPubSection(OS, Obj.DWARF.PubNames,
 300                                       Obj.IsLittleEndian);
 301           } else if (0 == strncmp(&Sec.sectname[0], "__debug_pubtypes", 16)) {
 302             DWARFYAML::EmitPubSection(OS, Obj.DWARF.PubTypes,
 303                                       Obj.IsLittleEndian);
 304           } else if (0 == strncmp(&Sec.sectname[0], "__debug_info", 16)) {
 305             DWARFYAML::EmitDebugInfo(OS, Obj.DWARF);
 306           } else if (0 == strncmp(&Sec.sectname[0], "__debug_line", 16)) {
 307             DWARFYAML::EmitDebugLine(OS, Obj.DWARF);
 308           }
 309
 310           continue;
 311         }
 312
 313         // Skip if it's a virtual section.
 314         if (isVirtualSection(Sec.flags & MachO::SECTION_TYPE))
 315           continue;
 316
 317         // Fill section data with 0xDEADBEEF
 318         Fill(OS, Sec.size, 0xDEADBEEFu);
 319       }
 320       uint64_t segSize = is64Bit ? LC.Data.segment_command_64_data.filesize
 321                                  : LC.Data.segment_command_data.filesize;
 322       ZeroToOffset(OS, segOff + segSize);
 323       break;
 324     }
 325   }
 326   // Old PPC Object Files didn't have __LINKEDIT segments, the data was just
 327   // stuck at the end of the file.
 328   if (!FoundLinkEditSeg) {
 329     if (auto Err = writeLinkEditData(OS))
 330       return Err;
 331   }
 332   return Error::success();
 333 }
 334
 335 void MachOWriter::writeBindOpcodes(
 336     raw_ostream &OS, std::vector<MachOYAML::BindOpcode> &BindOpcodes) {
 337
 338   for (auto Opcode : BindOpcodes) {
 339     uint8_t OpByte = Opcode.Opcode | Opcode.Imm;
 340     OS.write(reinterpret_cast<char *>(&OpByte), 1);
 341     for (auto Data : Opcode.ULEBExtraData) {
 342       encodeULEB128(Data, OS);
 343     }
 344     for (auto Data : Opcode.SLEBExtraData) {
 345       encodeSLEB128(Data, OS);
 346     }
 347     if (!Opcode.Symbol.empty()) {
 348       OS.write(Opcode.Symbol.data(), Opcode.Symbol.size());
 349       OS.write('\0');
 350     }
 351   }
 352 }
 353
 354 void MachOWriter::dumpExportEntry(raw_ostream &OS,
 355                                   MachOYAML::ExportEntry &Entry) {
 356   encodeSLEB128(Entry.TerminalSize, OS);
 357   if (Entry.TerminalSize > 0) {
 358     encodeSLEB128(Entry.Flags, OS);
 359     if (Entry.Flags & MachO::EXPORT_SYMBOL_FLAGS_REEXPORT) {
 360       encodeSLEB128(Entry.Other, OS);
 361       OS << Entry.ImportName;
 362       OS.write('\0');
 363     } else {
 364       encodeSLEB128(Entry.Address, OS);
 365       if (Entry.Flags & MachO::EXPORT_SYMBOL_FLAGS_STUB_AND_RESOLVER)
 366         encodeSLEB128(Entry.Other, OS);
 367     }
 368   }
 369   OS.write(static_cast<uint8_t>(Entry.Children.size()));
 370   for (auto EE : Entry.Children) {
 371     OS << EE.Name;
 372     OS.write('\0');
 373     encodeSLEB128(EE.NodeOffset, OS);
 374   }
 375   for (auto EE : Entry.Children)
 376     dumpExportEntry(OS, EE);
 377 }
 378
 379 Error MachOWriter::writeExportTrie(raw_ostream &OS) {
 380   dumpExportEntry(OS, Obj.LinkEdit.ExportTrie);
 381   return Error::success();
 382 }
 383
 384 template <typename NListType>
 385 void writeNListEntry(MachOYAML::NListEntry &NLE, raw_ostream &OS,
 386                      bool IsLittleEndian) {
 387   NListType ListEntry;
 388   ListEntry.n_strx = NLE.n_strx;
 389   ListEntry.n_type = NLE.n_type;
 390   ListEntry.n_sect = NLE.n_sect;
 391   ListEntry.n_desc = NLE.n_desc;
 392   ListEntry.n_value = NLE.n_value;
 393
 394   if (IsLittleEndian != sys::IsLittleEndianHost)
 395     MachO::swapStruct(ListEntry);
 396   OS.write(reinterpret_cast<const char *>(&ListEntry), sizeof(NListType));
 397 }
 398
 399 Error MachOWriter::writeLinkEditData(raw_ostream &OS) {
 400   typedef Error (MachOWriter::*writeHandler)(raw_ostream &);
 401   typedef std::pair<uint64_t, writeHandler> writeOperation;
 402   std::vector<writeOperation> WriteQueue;
 403
 404   MachO::dyld_info_command *DyldInfoOnlyCmd = 0;
 405   MachO::symtab_command *SymtabCmd = 0;
 406   for (auto &LC : Obj.LoadCommands) {
 407     switch (LC.Data.load_command_data.cmd) {
 408     case MachO::LC_SYMTAB:
 409       SymtabCmd = &LC.Data.symtab_command_data;
 410       WriteQueue.push_back(
 411           std::make_pair(SymtabCmd->symoff, &MachOWriter::writeNameList));
 412       WriteQueue.push_back(
 413           std::make_pair(SymtabCmd->stroff, &MachOWriter::writeStringTable));
 414       break;
 415     case MachO::LC_DYLD_INFO_ONLY:
 416       DyldInfoOnlyCmd = &LC.Data.dyld_info_command_data;
 417       WriteQueue.push_back(std::make_pair(DyldInfoOnlyCmd->rebase_off,
 418                                           &MachOWriter::writeRebaseOpcodes));
 419       WriteQueue.push_back(std::make_pair(DyldInfoOnlyCmd->bind_off,
 420                                           &MachOWriter::writeBasicBindOpcodes));
 421       WriteQueue.push_back(std::make_pair(DyldInfoOnlyCmd->weak_bind_off,
 422                                           &MachOWriter::writeWeakBindOpcodes));
 423       WriteQueue.push_back(std::make_pair(DyldInfoOnlyCmd->lazy_bind_off,
 424                                           &MachOWriter::writeLazyBindOpcodes));
 425       WriteQueue.push_back(std::make_pair(DyldInfoOnlyCmd->export_off,
 426                                           &MachOWriter::writeExportTrie));
 427       break;
 428     }
 429   }
 430
 431   llvm::sort(WriteQueue, [](const writeOperation &a, const writeOperation &b) {
 432     return a.first < b.first;
 433   });
 434
 435   for (auto writeOp : WriteQueue) {
 436     ZeroToOffset(OS, writeOp.first);
 437     if (auto Err = (this->*writeOp.second)(OS))
 438       return Err;
 439   }
 440
 441   return Error::success();
 442 }
 443
 444 Error MachOWriter::writeRebaseOpcodes(raw_ostream &OS) {
 445   MachOYAML::LinkEditData &LinkEdit = Obj.LinkEdit;
 446
 447   for (auto Opcode : LinkEdit.RebaseOpcodes) {
 448     uint8_t OpByte = Opcode.Opcode | Opcode.Imm;
 449     OS.write(reinterpret_cast<char *>(&OpByte), 1);
 450     for (auto Data : Opcode.ExtraData) {
 451       encodeULEB128(Data, OS);
 452     }
 453   }
 454   return Error::success();
 455 }
 456
 457 Error MachOWriter::writeBasicBindOpcodes(raw_ostream &OS) {
 458   writeBindOpcodes(OS, Obj.LinkEdit.BindOpcodes);
 459   return Error::success();
 460 }
 461
 462 Error MachOWriter::writeWeakBindOpcodes(raw_ostream &OS) {
 463   writeBindOpcodes(OS, Obj.LinkEdit.WeakBindOpcodes);
 464   return Error::success();
 465 }
 466
 467 Error MachOWriter::writeLazyBindOpcodes(raw_ostream &OS) {
 468   writeBindOpcodes(OS, Obj.LinkEdit.LazyBindOpcodes);
 469   return Error::success();
 470 }
 471
 472 Error MachOWriter::writeNameList(raw_ostream &OS) {
 473   for (auto NLE : Obj.LinkEdit.NameList) {
 474     if (is64Bit)
 475       writeNListEntry<MachO::nlist_64>(NLE, OS, Obj.IsLittleEndian);
 476     else
 477       writeNListEntry<MachO::nlist>(NLE, OS, Obj.IsLittleEndian);
 478   }
 479   return Error::success();
 480 }
 481
 482 Error MachOWriter::writeStringTable(raw_ostream &OS) {
 483   for (auto Str : Obj.LinkEdit.StringTable) {
 484     OS.write(Str.data(), Str.size());
 485     OS.write('\0');
 486   }
 487   return Error::success();
 488 }
 489
 490 class UniversalWriter {
 491 public:
 492   UniversalWriter(yaml::YamlObjectFile &ObjectFile)
 493       : ObjectFile(ObjectFile), fileStart(0) {}
 494
 495   Error writeMachO(raw_ostream &OS);
 496
 497 private:
 498   Error writeFatHeader(raw_ostream &OS);
 499   Error writeFatArchs(raw_ostream &OS);
 500
 501   void ZeroToOffset(raw_ostream &OS, size_t offset);
 502
 503   yaml::YamlObjectFile &ObjectFile;
 504   uint64_t fileStart;
 505 };
 506
 507 Error UniversalWriter::writeMachO(raw_ostream &OS) {
 508   fileStart = OS.tell();
 509   if (ObjectFile.MachO) {
 510     MachOWriter Writer(*ObjectFile.MachO);
 511     return Writer.writeMachO(OS);
 512   }
 513   if (auto Err = writeFatHeader(OS))
 514     return Err;
 515   if (auto Err = writeFatArchs(OS))
 516     return Err;
 517   auto &FatFile = *ObjectFile.FatMachO;
 518   assert(FatFile.FatArchs.size() == FatFile.Slices.size());
 519   for (size_t i = 0; i < FatFile.Slices.size(); i++) {
 520     ZeroToOffset(OS, FatFile.FatArchs[i].offset);
 521     MachOWriter Writer(FatFile.Slices[i]);
 522     if (auto Err = Writer.writeMachO(OS))
 523       return Err;
 524     auto SliceEnd = FatFile.FatArchs[i].offset + FatFile.FatArchs[i].size;
 525     ZeroToOffset(OS, SliceEnd);
 526   }
 527   return Error::success();
 528 }
 529
 530 Error UniversalWriter::writeFatHeader(raw_ostream &OS) {
 531   auto &FatFile = *ObjectFile.FatMachO;
 532   MachO::fat_header header;
 533   header.magic = FatFile.Header.magic;
 534   header.nfat_arch = FatFile.Header.nfat_arch;
 535   if (sys::IsLittleEndianHost)
 536     swapStruct(header);
 537   OS.write(reinterpret_cast<const char *>(&header), sizeof(MachO::fat_header));
 538   return Error::success();
 539 }
 540
 541 template <typename FatArchType>
 542 FatArchType constructFatArch(MachOYAML::FatArch &Arch) {
 543   FatArchType FatArch;
 544   FatArch.cputype = Arch.cputype;
 545   FatArch.cpusubtype = Arch.cpusubtype;
 546   FatArch.offset = Arch.offset;
 547   FatArch.size = Arch.size;
 548   FatArch.align = Arch.align;
 549   return FatArch;
 550 }
 551
 552 template <typename StructType>
 553 void writeFatArch(MachOYAML::FatArch &LC, raw_ostream &OS) {}
 554
 555 template <>
 556 void writeFatArch<MachO::fat_arch>(MachOYAML::FatArch &Arch, raw_ostream &OS) {
 557   auto FatArch = constructFatArch<MachO::fat_arch>(Arch);
 558   if (sys::IsLittleEndianHost)
 559     swapStruct(FatArch);
 560   OS.write(reinterpret_cast<const char *>(&FatArch), sizeof(MachO::fat_arch));
 561 }
 562
 563 template <>
 564 void writeFatArch<MachO::fat_arch_64>(MachOYAML::FatArch &Arch,
 565                                       raw_ostream &OS) {
 566   auto FatArch = constructFatArch<MachO::fat_arch_64>(Arch);
 567   FatArch.reserved = Arch.reserved;
 568   if (sys::IsLittleEndianHost)
 569     swapStruct(FatArch);
 570   OS.write(reinterpret_cast<const char *>(&FatArch),
 571            sizeof(MachO::fat_arch_64));
 572 }
 573
 574 Error UniversalWriter::writeFatArchs(raw_ostream &OS) {
 575   auto &FatFile = *ObjectFile.FatMachO;
 576   bool is64Bit = FatFile.Header.magic == MachO::FAT_MAGIC_64;
 577   for (auto Arch : FatFile.FatArchs) {
 578     if (is64Bit)
 579       writeFatArch<MachO::fat_arch_64>(Arch, OS);
 580     else
 581       writeFatArch<MachO::fat_arch>(Arch, OS);
 582   }
 583
 584   return Error::success();
 585 }
 586
 587 void UniversalWriter::ZeroToOffset(raw_ostream &OS, size_t Offset) {
 588   auto currOffset = OS.tell() - fileStart;
 589   if (currOffset < Offset)
 590     ZeroFillBytes(OS, Offset - currOffset);
 591 }
 592
 593 } // end anonymous namespace
 594
 595 int yaml2macho(yaml::YamlObjectFile &Doc, raw_ostream &Out) {
 596   UniversalWriter Writer(Doc);
 597   if (auto Err = Writer.writeMachO(Out)) {
 598     errs() << toString(std::move(Err));
 599     return 1;
 600   }
 601   return 0;
 602 }