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/LEB128.h"
19 #include "llvm/Support/YAMLTraits.h"
20 #include "llvm/Support/raw_ostream.h"
21 
22 #include "llvm/Support/Format.h"
23 
24 using namespace llvm;
25 
26 namespace {
27 
28 class MachOWriter {
29 public:
30   MachOWriter(MachOYAML::Object &Obj) : Obj(Obj), is64Bit(true), fileStart(0) {
31     is64Bit = Obj.Header.magic == MachO::MH_MAGIC_64 ||
32               Obj.Header.magic == MachO::MH_CIGAM_64;
33     memset(reinterpret_cast<void *>(&Header), 0, sizeof(MachO::mach_header_64));
34   }
35 
36   void writeMachO(raw_ostream &OS);
37 
38 private:
39   void writeHeader(raw_ostream &OS);
40   void writeLoadCommands(raw_ostream &OS);
41   void writeSectionData(raw_ostream &OS);
42   void writeRelocations(raw_ostream &OS);
43   void writeLinkEditData(raw_ostream &OS);
44 
45   void writeBindOpcodes(raw_ostream &OS,
46                         std::vector<MachOYAML::BindOpcode> &BindOpcodes);
47   // LinkEdit writers
48   void writeRebaseOpcodes(raw_ostream &OS);
49   void writeBasicBindOpcodes(raw_ostream &OS);
50   void writeWeakBindOpcodes(raw_ostream &OS);
51   void writeLazyBindOpcodes(raw_ostream &OS);
52   void writeNameList(raw_ostream &OS);
53   void writeStringTable(raw_ostream &OS);
54   void 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   MachO::mach_header_64 Header;
63 
64   // Old PPC Object Files didn't have __LINKEDIT segments, the data was just
65   // stuck at the end of the file.
66   bool FoundLinkEditSeg = false;
67 };
68 
69 void MachOWriter::writeMachO(raw_ostream &OS) {
70   fileStart = OS.tell();
71   writeHeader(OS);
72   writeLoadCommands(OS);
73   writeSectionData(OS);
74   writeRelocations(OS);
75   if (!FoundLinkEditSeg)
76     writeLinkEditData(OS);
77 }
78 
79 void MachOWriter::writeHeader(raw_ostream &OS) {
80   Header.magic = Obj.Header.magic;
81   Header.cputype = Obj.Header.cputype;
82   Header.cpusubtype = Obj.Header.cpusubtype;
83   Header.filetype = Obj.Header.filetype;
84   Header.ncmds = Obj.Header.ncmds;
85   Header.sizeofcmds = Obj.Header.sizeofcmds;
86   Header.flags = Obj.Header.flags;
87   Header.reserved = Obj.Header.reserved;
88 
89   if (Obj.IsLittleEndian != sys::IsLittleEndianHost)
90     MachO::swapStruct(Header);
91 
92   auto header_size =
93       is64Bit ? sizeof(MachO::mach_header_64) : sizeof(MachO::mach_header);
94   OS.write((const char *)&Header, header_size);
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 void 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 }
263 
264 void MachOWriter::writeSectionData(raw_ostream &OS) {
265   for (auto &LC : Obj.LoadCommands) {
266     switch (LC.Data.load_command_data.cmd) {
267     case MachO::LC_SEGMENT:
268     case MachO::LC_SEGMENT_64:
269       uint64_t segOff = is64Bit ? LC.Data.segment_command_64_data.fileoff
270                                 : LC.Data.segment_command_data.fileoff;
271       if (0 ==
272           strncmp(&LC.Data.segment_command_data.segname[0], "__LINKEDIT", 16)) {
273         FoundLinkEditSeg = true;
274         writeLinkEditData(OS);
275       }
276       for (auto &Sec : LC.Sections) {
277         ZeroToOffset(OS, Sec.offset);
278         // Zero Fill any data between the end of the last thing we wrote and the
279         // start of this section.
280         assert((OS.tell() - fileStart <= Sec.offset ||
281                 Sec.offset == (uint32_t)0) &&
282                "Wrote too much data somewhere, section offsets don't line up.");
283         if (0 == strncmp(&Sec.segname[0], "__DWARF", 16)) {
284           if (0 == strncmp(&Sec.sectname[0], "__debug_str", 16)) {
285             DWARFYAML::EmitDebugStr(OS, Obj.DWARF);
286           } else if (0 == strncmp(&Sec.sectname[0], "__debug_abbrev", 16)) {
287             DWARFYAML::EmitDebugAbbrev(OS, Obj.DWARF);
288           } else if (0 == strncmp(&Sec.sectname[0], "__debug_aranges", 16)) {
289             DWARFYAML::EmitDebugAranges(OS, Obj.DWARF);
290           } else if (0 == strncmp(&Sec.sectname[0], "__debug_ranges", 16)) {
291             DWARFYAML::EmitDebugRanges(OS, Obj.DWARF);
292           } else if (0 == strncmp(&Sec.sectname[0], "__debug_pubnames", 16)) {
293             DWARFYAML::EmitPubSection(OS, Obj.DWARF.PubNames,
294                                       Obj.IsLittleEndian);
295           } else if (0 == strncmp(&Sec.sectname[0], "__debug_pubtypes", 16)) {
296             DWARFYAML::EmitPubSection(OS, Obj.DWARF.PubTypes,
297                                       Obj.IsLittleEndian);
298           } else if (0 == strncmp(&Sec.sectname[0], "__debug_info", 16)) {
299             DWARFYAML::EmitDebugInfo(OS, Obj.DWARF);
300           } else if (0 == strncmp(&Sec.sectname[0], "__debug_line", 16)) {
301             DWARFYAML::EmitDebugLine(OS, Obj.DWARF);
302           }
303 
304           continue;
305         }
306 
307         // Skip if it's a virtual section.
308         if (MachO::isVirtualSection(Sec.flags & MachO::SECTION_TYPE))
309           continue;
310 
311         if (Sec.content) {
312           yaml::BinaryRef Content = *Sec.content;
313           Content.writeAsBinary(OS);
314           ZeroFillBytes(OS, Sec.size - Content.binary_size());
315         } else {
316           // Fill section data with 0xDEADBEEF.
317           Fill(OS, Sec.size, 0xDEADBEEFu);
318         }
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 }
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   void 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 void UniversalWriter::writeMachO(raw_ostream &OS) {
544   fileStart = OS.tell();
545   if (ObjectFile.MachO) {
546     MachOWriter Writer(*ObjectFile.MachO);
547     Writer.writeMachO(OS);
548     return;
549   }
550 
551   writeFatHeader(OS);
552   writeFatArchs(OS);
553 
554   auto &FatFile = *ObjectFile.FatMachO;
555   assert(FatFile.FatArchs.size() >= FatFile.Slices.size() &&
556          "Cannot write Slices if not decribed in FatArches");
557   for (size_t i = 0; i < FatFile.Slices.size(); i++) {
558     ZeroToOffset(OS, FatFile.FatArchs[i].offset);
559     MachOWriter Writer(FatFile.Slices[i]);
560     Writer.writeMachO(OS);
561 
562     auto SliceEnd = FatFile.FatArchs[i].offset + FatFile.FatArchs[i].size;
563     ZeroToOffset(OS, SliceEnd);
564   }
565 }
566 
567 void UniversalWriter::writeFatHeader(raw_ostream &OS) {
568   auto &FatFile = *ObjectFile.FatMachO;
569   MachO::fat_header header;
570   header.magic = FatFile.Header.magic;
571   header.nfat_arch = FatFile.Header.nfat_arch;
572   if (sys::IsLittleEndianHost)
573     swapStruct(header);
574   OS.write(reinterpret_cast<const char *>(&header), sizeof(MachO::fat_header));
575 }
576 
577 template <typename FatArchType>
578 FatArchType constructFatArch(MachOYAML::FatArch &Arch) {
579   FatArchType FatArch;
580   FatArch.cputype = Arch.cputype;
581   FatArch.cpusubtype = Arch.cpusubtype;
582   FatArch.offset = Arch.offset;
583   FatArch.size = Arch.size;
584   FatArch.align = Arch.align;
585   return FatArch;
586 }
587 
588 template <typename StructType>
589 void writeFatArch(MachOYAML::FatArch &LC, raw_ostream &OS) {}
590 
591 template <>
592 void writeFatArch<MachO::fat_arch>(MachOYAML::FatArch &Arch, raw_ostream &OS) {
593   auto FatArch = constructFatArch<MachO::fat_arch>(Arch);
594   if (sys::IsLittleEndianHost)
595     swapStruct(FatArch);
596   OS.write(reinterpret_cast<const char *>(&FatArch), sizeof(MachO::fat_arch));
597 }
598 
599 template <>
600 void writeFatArch<MachO::fat_arch_64>(MachOYAML::FatArch &Arch,
601                                       raw_ostream &OS) {
602   auto FatArch = constructFatArch<MachO::fat_arch_64>(Arch);
603   FatArch.reserved = Arch.reserved;
604   if (sys::IsLittleEndianHost)
605     swapStruct(FatArch);
606   OS.write(reinterpret_cast<const char *>(&FatArch),
607            sizeof(MachO::fat_arch_64));
608 }
609 
610 void UniversalWriter::writeFatArchs(raw_ostream &OS) {
611   auto &FatFile = *ObjectFile.FatMachO;
612   bool is64Bit = FatFile.Header.magic == MachO::FAT_MAGIC_64;
613   for (auto Arch : FatFile.FatArchs) {
614     if (is64Bit)
615       writeFatArch<MachO::fat_arch_64>(Arch, OS);
616     else
617       writeFatArch<MachO::fat_arch>(Arch, OS);
618   }
619 }
620 
621 void UniversalWriter::ZeroToOffset(raw_ostream &OS, size_t Offset) {
622   auto currOffset = OS.tell() - fileStart;
623   if (currOffset < Offset)
624     ZeroFillBytes(OS, Offset - currOffset);
625 }
626 
627 } // end anonymous namespace
628 
629 namespace llvm {
630 namespace yaml {
631 
632 bool yaml2macho(YamlObjectFile &Doc, raw_ostream &Out, ErrorHandler /*EH*/) {
633   UniversalWriter Writer(Doc);
634   Writer.writeMachO(Out);
635   return true;
636 }
637 
638 } // namespace yaml
639 } // namespace llvm
640