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/Errc.h"
19 #include "llvm/Support/Error.h"
20 #include "llvm/Support/LEB128.h"
21 #include "llvm/Support/YAMLTraits.h"
22 #include "llvm/Support/raw_ostream.h"
23 
24 #include "llvm/Support/Format.h"
25 
26 using namespace llvm;
27 
28 namespace {
29 
30 class MachOWriter {
31 public:
32   MachOWriter(MachOYAML::Object &Obj) : Obj(Obj), fileStart(0) {
33     is64Bit = Obj.Header.magic == MachO::MH_MAGIC_64 ||
34               Obj.Header.magic == MachO::MH_CIGAM_64;
35     memset(reinterpret_cast<void *>(&Header), 0, sizeof(MachO::mach_header_64));
36   }
37 
38   Error writeMachO(raw_ostream &OS);
39 
40 private:
41   void writeHeader(raw_ostream &OS);
42   void writeLoadCommands(raw_ostream &OS);
43   Error writeSectionData(raw_ostream &OS);
44   void writeRelocations(raw_ostream &OS);
45   void writeLinkEditData(raw_ostream &OS);
46 
47   void writeBindOpcodes(raw_ostream &OS,
48                         std::vector<MachOYAML::BindOpcode> &BindOpcodes);
49   // LinkEdit writers
50   void writeRebaseOpcodes(raw_ostream &OS);
51   void writeBasicBindOpcodes(raw_ostream &OS);
52   void writeWeakBindOpcodes(raw_ostream &OS);
53   void writeLazyBindOpcodes(raw_ostream &OS);
54   void writeNameList(raw_ostream &OS);
55   void writeStringTable(raw_ostream &OS);
56   void writeExportTrie(raw_ostream &OS);
57 
58   void dumpExportEntry(raw_ostream &OS, MachOYAML::ExportEntry &Entry);
59   void ZeroToOffset(raw_ostream &OS, size_t offset);
60 
61   MachOYAML::Object &Obj;
62   bool is64Bit;
63   uint64_t fileStart;
64   MachO::mach_header_64 Header;
65 
66   // Old PPC Object Files didn't have __LINKEDIT segments, the data was just
67   // stuck at the end of the file.
68   bool FoundLinkEditSeg = false;
69 };
70 
71 Error MachOWriter::writeMachO(raw_ostream &OS) {
72   fileStart = OS.tell();
73   writeHeader(OS);
74   writeLoadCommands(OS);
75   if (Error Err = writeSectionData(OS))
76     return Err;
77   writeRelocations(OS);
78   if (!FoundLinkEditSeg)
79     writeLinkEditData(OS);
80   return Error::success();
81 }
82 
83 void MachOWriter::writeHeader(raw_ostream &OS) {
84   Header.magic = Obj.Header.magic;
85   Header.cputype = Obj.Header.cputype;
86   Header.cpusubtype = Obj.Header.cpusubtype;
87   Header.filetype = Obj.Header.filetype;
88   Header.ncmds = Obj.Header.ncmds;
89   Header.sizeofcmds = Obj.Header.sizeofcmds;
90   Header.flags = Obj.Header.flags;
91   Header.reserved = Obj.Header.reserved;
92 
93   if (Obj.IsLittleEndian != sys::IsLittleEndianHost)
94     MachO::swapStruct(Header);
95 
96   auto header_size =
97       is64Bit ? sizeof(MachO::mach_header_64) : sizeof(MachO::mach_header);
98   OS.write((const char *)&Header, header_size);
99 }
100 
101 template <typename SectionType>
102 SectionType constructSection(MachOYAML::Section Sec) {
103   SectionType TempSec;
104   memcpy(reinterpret_cast<void *>(&TempSec.sectname[0]), &Sec.sectname[0], 16);
105   memcpy(reinterpret_cast<void *>(&TempSec.segname[0]), &Sec.segname[0], 16);
106   TempSec.addr = Sec.addr;
107   TempSec.size = Sec.size;
108   TempSec.offset = Sec.offset;
109   TempSec.align = Sec.align;
110   TempSec.reloff = Sec.reloff;
111   TempSec.nreloc = Sec.nreloc;
112   TempSec.flags = Sec.flags;
113   TempSec.reserved1 = Sec.reserved1;
114   TempSec.reserved2 = Sec.reserved2;
115   return TempSec;
116 }
117 
118 template <typename StructType>
119 size_t writeLoadCommandData(MachOYAML::LoadCommand &LC, raw_ostream &OS,
120                             bool IsLittleEndian) {
121   return 0;
122 }
123 
124 template <>
125 size_t writeLoadCommandData<MachO::segment_command>(MachOYAML::LoadCommand &LC,
126                                                     raw_ostream &OS,
127                                                     bool IsLittleEndian) {
128   size_t BytesWritten = 0;
129   for (const auto &Sec : LC.Sections) {
130     auto TempSec = constructSection<MachO::section>(Sec);
131     if (IsLittleEndian != sys::IsLittleEndianHost)
132       MachO::swapStruct(TempSec);
133     OS.write(reinterpret_cast<const char *>(&(TempSec)),
134              sizeof(MachO::section));
135     BytesWritten += sizeof(MachO::section);
136   }
137   return BytesWritten;
138 }
139 
140 template <>
141 size_t writeLoadCommandData<MachO::segment_command_64>(
142     MachOYAML::LoadCommand &LC, raw_ostream &OS, bool IsLittleEndian) {
143   size_t BytesWritten = 0;
144   for (const auto &Sec : LC.Sections) {
145     auto TempSec = constructSection<MachO::section_64>(Sec);
146     TempSec.reserved3 = Sec.reserved3;
147     if (IsLittleEndian != sys::IsLittleEndianHost)
148       MachO::swapStruct(TempSec);
149     OS.write(reinterpret_cast<const char *>(&(TempSec)),
150              sizeof(MachO::section_64));
151     BytesWritten += sizeof(MachO::section_64);
152   }
153   return BytesWritten;
154 }
155 
156 size_t writePayloadString(MachOYAML::LoadCommand &LC, raw_ostream &OS) {
157   size_t BytesWritten = 0;
158   if (!LC.PayloadString.empty()) {
159     OS.write(LC.PayloadString.c_str(), LC.PayloadString.length());
160     BytesWritten = LC.PayloadString.length();
161   }
162   return BytesWritten;
163 }
164 
165 template <>
166 size_t writeLoadCommandData<MachO::dylib_command>(MachOYAML::LoadCommand &LC,
167                                                   raw_ostream &OS,
168                                                   bool IsLittleEndian) {
169   return writePayloadString(LC, OS);
170 }
171 
172 template <>
173 size_t writeLoadCommandData<MachO::dylinker_command>(MachOYAML::LoadCommand &LC,
174                                                      raw_ostream &OS,
175                                                      bool IsLittleEndian) {
176   return writePayloadString(LC, OS);
177 }
178 
179 template <>
180 size_t writeLoadCommandData<MachO::rpath_command>(MachOYAML::LoadCommand &LC,
181                                                   raw_ostream &OS,
182                                                   bool IsLittleEndian) {
183   return writePayloadString(LC, OS);
184 }
185 
186 template <>
187 size_t writeLoadCommandData<MachO::build_version_command>(
188     MachOYAML::LoadCommand &LC, raw_ostream &OS, bool IsLittleEndian) {
189   size_t BytesWritten = 0;
190   for (const auto &T : LC.Tools) {
191     struct MachO::build_tool_version tool = T;
192     if (IsLittleEndian != sys::IsLittleEndianHost)
193       MachO::swapStruct(tool);
194     OS.write(reinterpret_cast<const char *>(&tool),
195              sizeof(MachO::build_tool_version));
196     BytesWritten += sizeof(MachO::build_tool_version);
197   }
198   return BytesWritten;
199 }
200 
201 void ZeroFillBytes(raw_ostream &OS, size_t Size) {
202   std::vector<uint8_t> FillData;
203   FillData.insert(FillData.begin(), Size, 0);
204   OS.write(reinterpret_cast<char *>(FillData.data()), Size);
205 }
206 
207 void Fill(raw_ostream &OS, size_t Size, uint32_t Data) {
208   std::vector<uint32_t> FillData;
209   FillData.insert(FillData.begin(), (Size / 4) + 1, Data);
210   OS.write(reinterpret_cast<char *>(FillData.data()), Size);
211 }
212 
213 void MachOWriter::ZeroToOffset(raw_ostream &OS, size_t Offset) {
214   auto currOffset = OS.tell() - fileStart;
215   if (currOffset < Offset)
216     ZeroFillBytes(OS, Offset - currOffset);
217 }
218 
219 void MachOWriter::writeLoadCommands(raw_ostream &OS) {
220   for (auto &LC : Obj.LoadCommands) {
221     size_t BytesWritten = 0;
222     llvm::MachO::macho_load_command Data = LC.Data;
223 
224 #define HANDLE_LOAD_COMMAND(LCName, LCValue, LCStruct)                         \
225   case MachO::LCName:                                                          \
226     if (Obj.IsLittleEndian != sys::IsLittleEndianHost)                         \
227       MachO::swapStruct(Data.LCStruct##_data);                                 \
228     OS.write(reinterpret_cast<const char *>(&(Data.LCStruct##_data)),          \
229              sizeof(MachO::LCStruct));                                         \
230     BytesWritten = sizeof(MachO::LCStruct);                                    \
231     BytesWritten +=                                                            \
232         writeLoadCommandData<MachO::LCStruct>(LC, OS, Obj.IsLittleEndian);     \
233     break;
234 
235     switch (LC.Data.load_command_data.cmd) {
236     default:
237       if (Obj.IsLittleEndian != sys::IsLittleEndianHost)
238         MachO::swapStruct(Data.load_command_data);
239       OS.write(reinterpret_cast<const char *>(&(Data.load_command_data)),
240                sizeof(MachO::load_command));
241       BytesWritten = sizeof(MachO::load_command);
242       BytesWritten +=
243           writeLoadCommandData<MachO::load_command>(LC, OS, Obj.IsLittleEndian);
244       break;
245 #include "llvm/BinaryFormat/MachO.def"
246     }
247 
248     if (LC.PayloadBytes.size() > 0) {
249       OS.write(reinterpret_cast<const char *>(LC.PayloadBytes.data()),
250                LC.PayloadBytes.size());
251       BytesWritten += LC.PayloadBytes.size();
252     }
253 
254     if (LC.ZeroPadBytes > 0) {
255       ZeroFillBytes(OS, LC.ZeroPadBytes);
256       BytesWritten += LC.ZeroPadBytes;
257     }
258 
259     // Fill remaining bytes with 0. This will only get hit in partially
260     // specified test cases.
261     auto BytesRemaining = LC.Data.load_command_data.cmdsize - BytesWritten;
262     if (BytesRemaining > 0) {
263       ZeroFillBytes(OS, BytesRemaining);
264     }
265   }
266 }
267 
268 Error MachOWriter::writeSectionData(raw_ostream &OS) {
269   for (auto &LC : Obj.LoadCommands) {
270     switch (LC.Data.load_command_data.cmd) {
271     case MachO::LC_SEGMENT:
272     case MachO::LC_SEGMENT_64:
273       uint64_t segOff = is64Bit ? LC.Data.segment_command_64_data.fileoff
274                                 : LC.Data.segment_command_data.fileoff;
275       if (0 ==
276           strncmp(&LC.Data.segment_command_data.segname[0], "__LINKEDIT", 16)) {
277         FoundLinkEditSeg = true;
278         writeLinkEditData(OS);
279       }
280       for (auto &Sec : LC.Sections) {
281         ZeroToOffset(OS, Sec.offset);
282         // Zero Fill any data between the end of the last thing we wrote and the
283         // start of this section.
284         if (OS.tell() - fileStart > Sec.offset && Sec.offset != (uint32_t)0)
285           return createStringError(
286               errc::invalid_argument,
287               "wrote too much data somewhere, section offsets don't line up");
288 
289         StringRef SectName(Sec.sectname,
290                            strnlen(Sec.sectname, sizeof(Sec.sectname)));
291         // If the section's content is specified in the 'DWARF' entry, we will
292         // emit it regardless of the section's segname.
293         if (Obj.DWARF.getNonEmptySectionNames().count(SectName.substr(2))) {
294           if (Sec.content)
295             return createStringError(errc::invalid_argument,
296                                      "cannot specify section '" + SectName +
297                                          "' contents in the 'DWARF' entry and "
298                                          "the 'content' at the same time");
299           auto EmitFunc = DWARFYAML::getDWARFEmitterByName(SectName.substr(2));
300           if (Error Err = EmitFunc(OS, Obj.DWARF))
301             return Err;
302           continue;
303         }
304 
305         // Skip if it's a virtual section.
306         if (MachO::isVirtualSection(Sec.flags & MachO::SECTION_TYPE))
307           continue;
308 
309         if (Sec.content) {
310           yaml::BinaryRef Content = *Sec.content;
311           Content.writeAsBinary(OS);
312           ZeroFillBytes(OS, Sec.size - Content.binary_size());
313         } else {
314           // Fill section data with 0xDEADBEEF.
315           Fill(OS, Sec.size, 0xDEADBEEFu);
316         }
317       }
318       uint64_t segSize = is64Bit ? LC.Data.segment_command_64_data.filesize
319                                  : LC.Data.segment_command_data.filesize;
320       ZeroToOffset(OS, segOff + segSize);
321       break;
322     }
323   }
324 
325   return Error::success();
326 }
327 
328 // The implementation of makeRelocationInfo and makeScatteredRelocationInfo is
329 // consistent with how libObject parses MachO binary files. For the reference
330 // see getStruct, getRelocation, getPlainRelocationPCRel,
331 // getPlainRelocationLength and related methods in MachOObjectFile.cpp
332 static MachO::any_relocation_info
333 makeRelocationInfo(const MachOYAML::Relocation &R, bool IsLE) {
334   assert(!R.is_scattered && "non-scattered relocation expected");
335   MachO::any_relocation_info MRE;
336   MRE.r_word0 = R.address;
337   if (IsLE)
338     MRE.r_word1 = ((unsigned)R.symbolnum << 0) | ((unsigned)R.is_pcrel << 24) |
339                   ((unsigned)R.length << 25) | ((unsigned)R.is_extern << 27) |
340                   ((unsigned)R.type << 28);
341   else
342     MRE.r_word1 = ((unsigned)R.symbolnum << 8) | ((unsigned)R.is_pcrel << 7) |
343                   ((unsigned)R.length << 5) | ((unsigned)R.is_extern << 4) |
344                   ((unsigned)R.type << 0);
345   return MRE;
346 }
347 
348 static MachO::any_relocation_info
349 makeScatteredRelocationInfo(const MachOYAML::Relocation &R) {
350   assert(R.is_scattered && "scattered relocation expected");
351   MachO::any_relocation_info MRE;
352   MRE.r_word0 = (((unsigned)R.address << 0) | ((unsigned)R.type << 24) |
353                  ((unsigned)R.length << 28) | ((unsigned)R.is_pcrel << 30) |
354                  MachO::R_SCATTERED);
355   MRE.r_word1 = R.value;
356   return MRE;
357 }
358 
359 void MachOWriter::writeRelocations(raw_ostream &OS) {
360   for (const MachOYAML::LoadCommand &LC : Obj.LoadCommands) {
361     switch (LC.Data.load_command_data.cmd) {
362     case MachO::LC_SEGMENT:
363     case MachO::LC_SEGMENT_64:
364       for (const MachOYAML::Section &Sec : LC.Sections) {
365         if (Sec.relocations.empty())
366           continue;
367         ZeroToOffset(OS, Sec.reloff);
368         for (const MachOYAML::Relocation &R : Sec.relocations) {
369           MachO::any_relocation_info MRE =
370               R.is_scattered ? makeScatteredRelocationInfo(R)
371                              : makeRelocationInfo(R, Obj.IsLittleEndian);
372           if (Obj.IsLittleEndian != sys::IsLittleEndianHost)
373             MachO::swapStruct(MRE);
374           OS.write(reinterpret_cast<const char *>(&MRE),
375                    sizeof(MachO::any_relocation_info));
376         }
377       }
378     }
379   }
380 }
381 
382 void MachOWriter::writeBindOpcodes(
383     raw_ostream &OS, std::vector<MachOYAML::BindOpcode> &BindOpcodes) {
384 
385   for (auto Opcode : BindOpcodes) {
386     uint8_t OpByte = Opcode.Opcode | Opcode.Imm;
387     OS.write(reinterpret_cast<char *>(&OpByte), 1);
388     for (auto Data : Opcode.ULEBExtraData) {
389       encodeULEB128(Data, OS);
390     }
391     for (auto Data : Opcode.SLEBExtraData) {
392       encodeSLEB128(Data, OS);
393     }
394     if (!Opcode.Symbol.empty()) {
395       OS.write(Opcode.Symbol.data(), Opcode.Symbol.size());
396       OS.write('\0');
397     }
398   }
399 }
400 
401 void MachOWriter::dumpExportEntry(raw_ostream &OS,
402                                   MachOYAML::ExportEntry &Entry) {
403   encodeSLEB128(Entry.TerminalSize, OS);
404   if (Entry.TerminalSize > 0) {
405     encodeSLEB128(Entry.Flags, OS);
406     if (Entry.Flags & MachO::EXPORT_SYMBOL_FLAGS_REEXPORT) {
407       encodeSLEB128(Entry.Other, OS);
408       OS << Entry.ImportName;
409       OS.write('\0');
410     } else {
411       encodeSLEB128(Entry.Address, OS);
412       if (Entry.Flags & MachO::EXPORT_SYMBOL_FLAGS_STUB_AND_RESOLVER)
413         encodeSLEB128(Entry.Other, OS);
414     }
415   }
416   OS.write(static_cast<uint8_t>(Entry.Children.size()));
417   for (auto EE : Entry.Children) {
418     OS << EE.Name;
419     OS.write('\0');
420     encodeSLEB128(EE.NodeOffset, OS);
421   }
422   for (auto EE : Entry.Children)
423     dumpExportEntry(OS, EE);
424 }
425 
426 void MachOWriter::writeExportTrie(raw_ostream &OS) {
427   dumpExportEntry(OS, Obj.LinkEdit.ExportTrie);
428 }
429 
430 template <typename NListType>
431 void writeNListEntry(MachOYAML::NListEntry &NLE, raw_ostream &OS,
432                      bool IsLittleEndian) {
433   NListType ListEntry;
434   ListEntry.n_strx = NLE.n_strx;
435   ListEntry.n_type = NLE.n_type;
436   ListEntry.n_sect = NLE.n_sect;
437   ListEntry.n_desc = NLE.n_desc;
438   ListEntry.n_value = NLE.n_value;
439 
440   if (IsLittleEndian != sys::IsLittleEndianHost)
441     MachO::swapStruct(ListEntry);
442   OS.write(reinterpret_cast<const char *>(&ListEntry), sizeof(NListType));
443 }
444 
445 void MachOWriter::writeLinkEditData(raw_ostream &OS) {
446   typedef void (MachOWriter::*writeHandler)(raw_ostream &);
447   typedef std::pair<uint64_t, writeHandler> writeOperation;
448   std::vector<writeOperation> WriteQueue;
449 
450   MachO::dyld_info_command *DyldInfoOnlyCmd = 0;
451   MachO::symtab_command *SymtabCmd = 0;
452   for (auto &LC : Obj.LoadCommands) {
453     switch (LC.Data.load_command_data.cmd) {
454     case MachO::LC_SYMTAB:
455       SymtabCmd = &LC.Data.symtab_command_data;
456       WriteQueue.push_back(
457           std::make_pair(SymtabCmd->symoff, &MachOWriter::writeNameList));
458       WriteQueue.push_back(
459           std::make_pair(SymtabCmd->stroff, &MachOWriter::writeStringTable));
460       break;
461     case MachO::LC_DYLD_INFO_ONLY:
462       DyldInfoOnlyCmd = &LC.Data.dyld_info_command_data;
463       WriteQueue.push_back(std::make_pair(DyldInfoOnlyCmd->rebase_off,
464                                           &MachOWriter::writeRebaseOpcodes));
465       WriteQueue.push_back(std::make_pair(DyldInfoOnlyCmd->bind_off,
466                                           &MachOWriter::writeBasicBindOpcodes));
467       WriteQueue.push_back(std::make_pair(DyldInfoOnlyCmd->weak_bind_off,
468                                           &MachOWriter::writeWeakBindOpcodes));
469       WriteQueue.push_back(std::make_pair(DyldInfoOnlyCmd->lazy_bind_off,
470                                           &MachOWriter::writeLazyBindOpcodes));
471       WriteQueue.push_back(std::make_pair(DyldInfoOnlyCmd->export_off,
472                                           &MachOWriter::writeExportTrie));
473       break;
474     }
475   }
476 
477   llvm::sort(WriteQueue, [](const writeOperation &a, const writeOperation &b) {
478     return a.first < b.first;
479   });
480 
481   for (auto writeOp : WriteQueue) {
482     ZeroToOffset(OS, writeOp.first);
483     (this->*writeOp.second)(OS);
484   }
485 }
486 
487 void MachOWriter::writeRebaseOpcodes(raw_ostream &OS) {
488   MachOYAML::LinkEditData &LinkEdit = Obj.LinkEdit;
489 
490   for (auto Opcode : LinkEdit.RebaseOpcodes) {
491     uint8_t OpByte = Opcode.Opcode | Opcode.Imm;
492     OS.write(reinterpret_cast<char *>(&OpByte), 1);
493     for (auto Data : Opcode.ExtraData)
494       encodeULEB128(Data, OS);
495   }
496 }
497 
498 void MachOWriter::writeBasicBindOpcodes(raw_ostream &OS) {
499   writeBindOpcodes(OS, Obj.LinkEdit.BindOpcodes);
500 }
501 
502 void MachOWriter::writeWeakBindOpcodes(raw_ostream &OS) {
503   writeBindOpcodes(OS, Obj.LinkEdit.WeakBindOpcodes);
504 }
505 
506 void MachOWriter::writeLazyBindOpcodes(raw_ostream &OS) {
507   writeBindOpcodes(OS, Obj.LinkEdit.LazyBindOpcodes);
508 }
509 
510 void MachOWriter::writeNameList(raw_ostream &OS) {
511   for (auto NLE : Obj.LinkEdit.NameList) {
512     if (is64Bit)
513       writeNListEntry<MachO::nlist_64>(NLE, OS, Obj.IsLittleEndian);
514     else
515       writeNListEntry<MachO::nlist>(NLE, OS, Obj.IsLittleEndian);
516   }
517 }
518 
519 void MachOWriter::writeStringTable(raw_ostream &OS) {
520   for (auto Str : Obj.LinkEdit.StringTable) {
521     OS.write(Str.data(), Str.size());
522     OS.write('\0');
523   }
524 }
525 
526 class UniversalWriter {
527 public:
528   UniversalWriter(yaml::YamlObjectFile &ObjectFile)
529       : ObjectFile(ObjectFile), fileStart(0) {}
530 
531   Error writeMachO(raw_ostream &OS);
532 
533 private:
534   void writeFatHeader(raw_ostream &OS);
535   void writeFatArchs(raw_ostream &OS);
536 
537   void ZeroToOffset(raw_ostream &OS, size_t offset);
538 
539   yaml::YamlObjectFile &ObjectFile;
540   uint64_t fileStart;
541 };
542 
543 Error UniversalWriter::writeMachO(raw_ostream &OS) {
544   fileStart = OS.tell();
545   if (ObjectFile.MachO) {
546     MachOWriter Writer(*ObjectFile.MachO);
547     return Writer.writeMachO(OS);
548   }
549 
550   writeFatHeader(OS);
551   writeFatArchs(OS);
552 
553   auto &FatFile = *ObjectFile.FatMachO;
554   if (FatFile.FatArchs.size() < FatFile.Slices.size())
555     return createStringError(
556         errc::invalid_argument,
557         "cannot write 'Slices' if not described in 'FatArches'");
558 
559   for (size_t i = 0; i < FatFile.Slices.size(); i++) {
560     ZeroToOffset(OS, FatFile.FatArchs[i].offset);
561     MachOWriter Writer(FatFile.Slices[i]);
562     if (Error Err = Writer.writeMachO(OS))
563       return Err;
564 
565     auto SliceEnd = FatFile.FatArchs[i].offset + FatFile.FatArchs[i].size;
566     ZeroToOffset(OS, SliceEnd);
567   }
568 
569   return Error::success();
570 }
571 
572 void UniversalWriter::writeFatHeader(raw_ostream &OS) {
573   auto &FatFile = *ObjectFile.FatMachO;
574   MachO::fat_header header;
575   header.magic = FatFile.Header.magic;
576   header.nfat_arch = FatFile.Header.nfat_arch;
577   if (sys::IsLittleEndianHost)
578     swapStruct(header);
579   OS.write(reinterpret_cast<const char *>(&header), sizeof(MachO::fat_header));
580 }
581 
582 template <typename FatArchType>
583 FatArchType constructFatArch(MachOYAML::FatArch &Arch) {
584   FatArchType FatArch;
585   FatArch.cputype = Arch.cputype;
586   FatArch.cpusubtype = Arch.cpusubtype;
587   FatArch.offset = Arch.offset;
588   FatArch.size = Arch.size;
589   FatArch.align = Arch.align;
590   return FatArch;
591 }
592 
593 template <typename StructType>
594 void writeFatArch(MachOYAML::FatArch &LC, raw_ostream &OS) {}
595 
596 template <>
597 void writeFatArch<MachO::fat_arch>(MachOYAML::FatArch &Arch, raw_ostream &OS) {
598   auto FatArch = constructFatArch<MachO::fat_arch>(Arch);
599   if (sys::IsLittleEndianHost)
600     swapStruct(FatArch);
601   OS.write(reinterpret_cast<const char *>(&FatArch), sizeof(MachO::fat_arch));
602 }
603 
604 template <>
605 void writeFatArch<MachO::fat_arch_64>(MachOYAML::FatArch &Arch,
606                                       raw_ostream &OS) {
607   auto FatArch = constructFatArch<MachO::fat_arch_64>(Arch);
608   FatArch.reserved = Arch.reserved;
609   if (sys::IsLittleEndianHost)
610     swapStruct(FatArch);
611   OS.write(reinterpret_cast<const char *>(&FatArch),
612            sizeof(MachO::fat_arch_64));
613 }
614 
615 void UniversalWriter::writeFatArchs(raw_ostream &OS) {
616   auto &FatFile = *ObjectFile.FatMachO;
617   bool is64Bit = FatFile.Header.magic == MachO::FAT_MAGIC_64;
618   for (auto Arch : FatFile.FatArchs) {
619     if (is64Bit)
620       writeFatArch<MachO::fat_arch_64>(Arch, OS);
621     else
622       writeFatArch<MachO::fat_arch>(Arch, OS);
623   }
624 }
625 
626 void UniversalWriter::ZeroToOffset(raw_ostream &OS, size_t Offset) {
627   auto currOffset = OS.tell() - fileStart;
628   if (currOffset < Offset)
629     ZeroFillBytes(OS, Offset - currOffset);
630 }
631 
632 } // end anonymous namespace
633 
634 namespace llvm {
635 namespace yaml {
636 
637 bool yaml2macho(YamlObjectFile &Doc, raw_ostream &Out, ErrorHandler EH) {
638   UniversalWriter Writer(Doc);
639   if (Error Err = Writer.writeMachO(Out)) {
640     handleAllErrors(std::move(Err),
641                     [&](const ErrorInfoBase &Err) { EH(Err.message()); });
642     return false;
643   }
644   return true;
645 }
646 
647 } // namespace yaml
648 } // namespace llvm
649