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 "llvm/BinaryFormat/MachO.h"
15 #include "llvm/ObjectYAML/DWARFEmitter.h"
16 #include "llvm/ObjectYAML/ObjectYAML.h"
17 #include "llvm/ObjectYAML/yaml2obj.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 Error MachOWriter::writeSectionData(raw_ostream &OS) {
266   bool FoundLinkEditSeg = false;
267   for (auto &LC : Obj.LoadCommands) {
268     switch (LC.Data.load_command_data.cmd) {
269     case MachO::LC_SEGMENT:
270     case MachO::LC_SEGMENT_64:
271       uint64_t segOff = is64Bit ? LC.Data.segment_command_64_data.fileoff
272                                 : LC.Data.segment_command_data.fileoff;
273       if (0 ==
274           strncmp(&LC.Data.segment_command_data.segname[0], "__LINKEDIT", 16)) {
275         FoundLinkEditSeg = true;
276         if (auto Err = writeLinkEditData(OS))
277           return Err;
278       }
279       for (auto &Sec : LC.Sections) {
280         ZeroToOffset(OS, Sec.offset);
281         // Zero Fill any data between the end of the last thing we wrote and the
282         // start of this section.
283         assert((OS.tell() - fileStart <= Sec.offset ||
284                 Sec.offset == (uint32_t)0) &&
285                "Wrote too much data somewhere, section offsets don't line up.");
286         if (0 == strncmp(&Sec.segname[0], "__DWARF", 16)) {
287           if (0 == strncmp(&Sec.sectname[0], "__debug_str", 16)) {
288             DWARFYAML::EmitDebugStr(OS, Obj.DWARF);
289           } else if (0 == strncmp(&Sec.sectname[0], "__debug_abbrev", 16)) {
290             DWARFYAML::EmitDebugAbbrev(OS, Obj.DWARF);
291           } else if (0 == strncmp(&Sec.sectname[0], "__debug_aranges", 16)) {
292             DWARFYAML::EmitDebugAranges(OS, Obj.DWARF);
293           } else if (0 == strncmp(&Sec.sectname[0], "__debug_pubnames", 16)) {
294             DWARFYAML::EmitPubSection(OS, Obj.DWARF.PubNames,
295                                       Obj.IsLittleEndian);
296           } else if (0 == strncmp(&Sec.sectname[0], "__debug_pubtypes", 16)) {
297             DWARFYAML::EmitPubSection(OS, Obj.DWARF.PubTypes,
298                                       Obj.IsLittleEndian);
299           } else if (0 == strncmp(&Sec.sectname[0], "__debug_info", 16)) {
300             DWARFYAML::EmitDebugInfo(OS, Obj.DWARF);
301           } else if (0 == strncmp(&Sec.sectname[0], "__debug_line", 16)) {
302             DWARFYAML::EmitDebugLine(OS, Obj.DWARF);
303           }
304 
305           continue;
306         }
307 
308         // Skip if it's a virtual section.
309         if (MachO::isVirtualSection(Sec.flags & MachO::SECTION_TYPE))
310           continue;
311 
312         if (Sec.content) {
313           yaml::BinaryRef Content = *Sec.content;
314           Content.writeAsBinary(OS);
315           ZeroFillBytes(OS, Sec.size - Content.binary_size());
316         } else {
317           // Fill section data with 0xDEADBEEF.
318           Fill(OS, Sec.size, 0xDEADBEEFu);
319         }
320       }
321       uint64_t segSize = is64Bit ? LC.Data.segment_command_64_data.filesize
322                                  : LC.Data.segment_command_data.filesize;
323       ZeroToOffset(OS, segOff + segSize);
324       break;
325     }
326   }
327   // Old PPC Object Files didn't have __LINKEDIT segments, the data was just
328   // stuck at the end of the file.
329   if (!FoundLinkEditSeg) {
330     if (auto Err = writeLinkEditData(OS))
331       return Err;
332   }
333   return Error::success();
334 }
335 
336 void MachOWriter::writeBindOpcodes(
337     raw_ostream &OS, std::vector<MachOYAML::BindOpcode> &BindOpcodes) {
338 
339   for (auto Opcode : BindOpcodes) {
340     uint8_t OpByte = Opcode.Opcode | Opcode.Imm;
341     OS.write(reinterpret_cast<char *>(&OpByte), 1);
342     for (auto Data : Opcode.ULEBExtraData) {
343       encodeULEB128(Data, OS);
344     }
345     for (auto Data : Opcode.SLEBExtraData) {
346       encodeSLEB128(Data, OS);
347     }
348     if (!Opcode.Symbol.empty()) {
349       OS.write(Opcode.Symbol.data(), Opcode.Symbol.size());
350       OS.write('\0');
351     }
352   }
353 }
354 
355 void MachOWriter::dumpExportEntry(raw_ostream &OS,
356                                   MachOYAML::ExportEntry &Entry) {
357   encodeSLEB128(Entry.TerminalSize, OS);
358   if (Entry.TerminalSize > 0) {
359     encodeSLEB128(Entry.Flags, OS);
360     if (Entry.Flags & MachO::EXPORT_SYMBOL_FLAGS_REEXPORT) {
361       encodeSLEB128(Entry.Other, OS);
362       OS << Entry.ImportName;
363       OS.write('\0');
364     } else {
365       encodeSLEB128(Entry.Address, OS);
366       if (Entry.Flags & MachO::EXPORT_SYMBOL_FLAGS_STUB_AND_RESOLVER)
367         encodeSLEB128(Entry.Other, OS);
368     }
369   }
370   OS.write(static_cast<uint8_t>(Entry.Children.size()));
371   for (auto EE : Entry.Children) {
372     OS << EE.Name;
373     OS.write('\0');
374     encodeSLEB128(EE.NodeOffset, OS);
375   }
376   for (auto EE : Entry.Children)
377     dumpExportEntry(OS, EE);
378 }
379 
380 Error MachOWriter::writeExportTrie(raw_ostream &OS) {
381   dumpExportEntry(OS, Obj.LinkEdit.ExportTrie);
382   return Error::success();
383 }
384 
385 template <typename NListType>
386 void writeNListEntry(MachOYAML::NListEntry &NLE, raw_ostream &OS,
387                      bool IsLittleEndian) {
388   NListType ListEntry;
389   ListEntry.n_strx = NLE.n_strx;
390   ListEntry.n_type = NLE.n_type;
391   ListEntry.n_sect = NLE.n_sect;
392   ListEntry.n_desc = NLE.n_desc;
393   ListEntry.n_value = NLE.n_value;
394 
395   if (IsLittleEndian != sys::IsLittleEndianHost)
396     MachO::swapStruct(ListEntry);
397   OS.write(reinterpret_cast<const char *>(&ListEntry), sizeof(NListType));
398 }
399 
400 Error MachOWriter::writeLinkEditData(raw_ostream &OS) {
401   typedef Error (MachOWriter::*writeHandler)(raw_ostream &);
402   typedef std::pair<uint64_t, writeHandler> writeOperation;
403   std::vector<writeOperation> WriteQueue;
404 
405   MachO::dyld_info_command *DyldInfoOnlyCmd = 0;
406   MachO::symtab_command *SymtabCmd = 0;
407   for (auto &LC : Obj.LoadCommands) {
408     switch (LC.Data.load_command_data.cmd) {
409     case MachO::LC_SYMTAB:
410       SymtabCmd = &LC.Data.symtab_command_data;
411       WriteQueue.push_back(
412           std::make_pair(SymtabCmd->symoff, &MachOWriter::writeNameList));
413       WriteQueue.push_back(
414           std::make_pair(SymtabCmd->stroff, &MachOWriter::writeStringTable));
415       break;
416     case MachO::LC_DYLD_INFO_ONLY:
417       DyldInfoOnlyCmd = &LC.Data.dyld_info_command_data;
418       WriteQueue.push_back(std::make_pair(DyldInfoOnlyCmd->rebase_off,
419                                           &MachOWriter::writeRebaseOpcodes));
420       WriteQueue.push_back(std::make_pair(DyldInfoOnlyCmd->bind_off,
421                                           &MachOWriter::writeBasicBindOpcodes));
422       WriteQueue.push_back(std::make_pair(DyldInfoOnlyCmd->weak_bind_off,
423                                           &MachOWriter::writeWeakBindOpcodes));
424       WriteQueue.push_back(std::make_pair(DyldInfoOnlyCmd->lazy_bind_off,
425                                           &MachOWriter::writeLazyBindOpcodes));
426       WriteQueue.push_back(std::make_pair(DyldInfoOnlyCmd->export_off,
427                                           &MachOWriter::writeExportTrie));
428       break;
429     }
430   }
431 
432   llvm::sort(WriteQueue, [](const writeOperation &a, const writeOperation &b) {
433     return a.first < b.first;
434   });
435 
436   for (auto writeOp : WriteQueue) {
437     ZeroToOffset(OS, writeOp.first);
438     if (auto Err = (this->*writeOp.second)(OS))
439       return Err;
440   }
441 
442   return Error::success();
443 }
444 
445 Error MachOWriter::writeRebaseOpcodes(raw_ostream &OS) {
446   MachOYAML::LinkEditData &LinkEdit = Obj.LinkEdit;
447 
448   for (auto Opcode : LinkEdit.RebaseOpcodes) {
449     uint8_t OpByte = Opcode.Opcode | Opcode.Imm;
450     OS.write(reinterpret_cast<char *>(&OpByte), 1);
451     for (auto Data : Opcode.ExtraData) {
452       encodeULEB128(Data, OS);
453     }
454   }
455   return Error::success();
456 }
457 
458 Error MachOWriter::writeBasicBindOpcodes(raw_ostream &OS) {
459   writeBindOpcodes(OS, Obj.LinkEdit.BindOpcodes);
460   return Error::success();
461 }
462 
463 Error MachOWriter::writeWeakBindOpcodes(raw_ostream &OS) {
464   writeBindOpcodes(OS, Obj.LinkEdit.WeakBindOpcodes);
465   return Error::success();
466 }
467 
468 Error MachOWriter::writeLazyBindOpcodes(raw_ostream &OS) {
469   writeBindOpcodes(OS, Obj.LinkEdit.LazyBindOpcodes);
470   return Error::success();
471 }
472 
473 Error MachOWriter::writeNameList(raw_ostream &OS) {
474   for (auto NLE : Obj.LinkEdit.NameList) {
475     if (is64Bit)
476       writeNListEntry<MachO::nlist_64>(NLE, OS, Obj.IsLittleEndian);
477     else
478       writeNListEntry<MachO::nlist>(NLE, OS, Obj.IsLittleEndian);
479   }
480   return Error::success();
481 }
482 
483 Error MachOWriter::writeStringTable(raw_ostream &OS) {
484   for (auto Str : Obj.LinkEdit.StringTable) {
485     OS.write(Str.data(), Str.size());
486     OS.write('\0');
487   }
488   return Error::success();
489 }
490 
491 class UniversalWriter {
492 public:
493   UniversalWriter(yaml::YamlObjectFile &ObjectFile)
494       : ObjectFile(ObjectFile), fileStart(0) {}
495 
496   Error writeMachO(raw_ostream &OS);
497 
498 private:
499   Error writeFatHeader(raw_ostream &OS);
500   Error writeFatArchs(raw_ostream &OS);
501 
502   void ZeroToOffset(raw_ostream &OS, size_t offset);
503 
504   yaml::YamlObjectFile &ObjectFile;
505   uint64_t fileStart;
506 };
507 
508 Error UniversalWriter::writeMachO(raw_ostream &OS) {
509   fileStart = OS.tell();
510   if (ObjectFile.MachO) {
511     MachOWriter Writer(*ObjectFile.MachO);
512     return Writer.writeMachO(OS);
513   }
514   if (auto Err = writeFatHeader(OS))
515     return Err;
516   if (auto Err = writeFatArchs(OS))
517     return Err;
518   auto &FatFile = *ObjectFile.FatMachO;
519   assert(FatFile.FatArchs.size() == FatFile.Slices.size());
520   for (size_t i = 0; i < FatFile.Slices.size(); i++) {
521     ZeroToOffset(OS, FatFile.FatArchs[i].offset);
522     MachOWriter Writer(FatFile.Slices[i]);
523     if (auto Err = Writer.writeMachO(OS))
524       return Err;
525     auto SliceEnd = FatFile.FatArchs[i].offset + FatFile.FatArchs[i].size;
526     ZeroToOffset(OS, SliceEnd);
527   }
528   return Error::success();
529 }
530 
531 Error UniversalWriter::writeFatHeader(raw_ostream &OS) {
532   auto &FatFile = *ObjectFile.FatMachO;
533   MachO::fat_header header;
534   header.magic = FatFile.Header.magic;
535   header.nfat_arch = FatFile.Header.nfat_arch;
536   if (sys::IsLittleEndianHost)
537     swapStruct(header);
538   OS.write(reinterpret_cast<const char *>(&header), sizeof(MachO::fat_header));
539   return Error::success();
540 }
541 
542 template <typename FatArchType>
543 FatArchType constructFatArch(MachOYAML::FatArch &Arch) {
544   FatArchType FatArch;
545   FatArch.cputype = Arch.cputype;
546   FatArch.cpusubtype = Arch.cpusubtype;
547   FatArch.offset = Arch.offset;
548   FatArch.size = Arch.size;
549   FatArch.align = Arch.align;
550   return FatArch;
551 }
552 
553 template <typename StructType>
554 void writeFatArch(MachOYAML::FatArch &LC, raw_ostream &OS) {}
555 
556 template <>
557 void writeFatArch<MachO::fat_arch>(MachOYAML::FatArch &Arch, raw_ostream &OS) {
558   auto FatArch = constructFatArch<MachO::fat_arch>(Arch);
559   if (sys::IsLittleEndianHost)
560     swapStruct(FatArch);
561   OS.write(reinterpret_cast<const char *>(&FatArch), sizeof(MachO::fat_arch));
562 }
563 
564 template <>
565 void writeFatArch<MachO::fat_arch_64>(MachOYAML::FatArch &Arch,
566                                       raw_ostream &OS) {
567   auto FatArch = constructFatArch<MachO::fat_arch_64>(Arch);
568   FatArch.reserved = Arch.reserved;
569   if (sys::IsLittleEndianHost)
570     swapStruct(FatArch);
571   OS.write(reinterpret_cast<const char *>(&FatArch),
572            sizeof(MachO::fat_arch_64));
573 }
574 
575 Error UniversalWriter::writeFatArchs(raw_ostream &OS) {
576   auto &FatFile = *ObjectFile.FatMachO;
577   bool is64Bit = FatFile.Header.magic == MachO::FAT_MAGIC_64;
578   for (auto Arch : FatFile.FatArchs) {
579     if (is64Bit)
580       writeFatArch<MachO::fat_arch_64>(Arch, OS);
581     else
582       writeFatArch<MachO::fat_arch>(Arch, OS);
583   }
584 
585   return Error::success();
586 }
587 
588 void UniversalWriter::ZeroToOffset(raw_ostream &OS, size_t Offset) {
589   auto currOffset = OS.tell() - fileStart;
590   if (currOffset < Offset)
591     ZeroFillBytes(OS, Offset - currOffset);
592 }
593 
594 } // end anonymous namespace
595 
596 namespace llvm {
597 namespace yaml {
598 
599 int yaml2macho(YamlObjectFile &Doc, raw_ostream &Out) {
600   UniversalWriter Writer(Doc);
601   if (auto Err = Writer.writeMachO(Out)) {
602     errs() << toString(std::move(Err));
603     return 1;
604   }
605   return 0;
606 }
607 
608 } // namespace yaml
609 } // namespace llvm
610