1 //===-- llvm/MC/WinCOFFObjectWriter.cpp -------------------------*- C++ -*-===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file contains an implementation of a Win32 COFF object file writer.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "llvm/MC/MCWinCOFFObjectWriter.h"
15 #include "llvm/ADT/DenseMap.h"
16 #include "llvm/ADT/STLExtras.h"
17 #include "llvm/ADT/StringMap.h"
18 #include "llvm/ADT/StringRef.h"
19 #include "llvm/ADT/Twine.h"
20 #include "llvm/Config/config.h"
21 #include "llvm/MC/MCAsmLayout.h"
22 #include "llvm/MC/MCAssembler.h"
23 #include "llvm/MC/MCContext.h"
24 #include "llvm/MC/MCExpr.h"
25 #include "llvm/MC/MCObjectFileInfo.h"
26 #include "llvm/MC/MCObjectWriter.h"
27 #include "llvm/MC/MCSection.h"
28 #include "llvm/MC/MCSectionCOFF.h"
29 #include "llvm/MC/MCSymbolCOFF.h"
30 #include "llvm/MC/MCValue.h"
31 #include "llvm/MC/StringTableBuilder.h"
32 #include "llvm/Support/COFF.h"
33 #include "llvm/Support/Debug.h"
34 #include "llvm/Support/Endian.h"
35 #include "llvm/Support/ErrorHandling.h"
36 #include "llvm/Support/JamCRC.h"
37 #include <cstdio>
38 #include <ctime>
39 
40 using namespace llvm;
41 
42 #define DEBUG_TYPE "WinCOFFObjectWriter"
43 
44 namespace {
45 typedef SmallString<COFF::NameSize> name;
46 
47 enum AuxiliaryType {
48   ATFunctionDefinition,
49   ATbfAndefSymbol,
50   ATWeakExternal,
51   ATFile,
52   ATSectionDefinition
53 };
54 
55 struct AuxSymbol {
56   AuxiliaryType AuxType;
57   COFF::Auxiliary Aux;
58 };
59 
60 class COFFSymbol;
61 class COFFSection;
62 
63 class COFFSymbol {
64 public:
65   COFF::symbol Data;
66 
67   typedef SmallVector<AuxSymbol, 1> AuxiliarySymbols;
68 
69   name Name;
70   int Index;
71   AuxiliarySymbols Aux;
72   COFFSymbol *Other;
73   COFFSection *Section;
74   int Relocations;
75 
76   const MCSymbol *MC;
77 
78   COFFSymbol(StringRef name);
79   void set_name_offset(uint32_t Offset);
80 
81   int64_t getIndex() const { return Index; }
82   void setIndex(int Value) {
83     Index = Value;
84     if (MC)
85       MC->setIndex(static_cast<uint32_t>(Value));
86   }
87 };
88 
89 // This class contains staging data for a COFF relocation entry.
90 struct COFFRelocation {
91   COFF::relocation Data;
92   COFFSymbol *Symb;
93 
94   COFFRelocation() : Symb(nullptr) {}
95   static size_t size() { return COFF::RelocationSize; }
96 };
97 
98 typedef std::vector<COFFRelocation> relocations;
99 
100 class COFFSection {
101 public:
102   COFF::section Header;
103 
104   std::string Name;
105   int Number;
106   MCSectionCOFF const *MCSection;
107   COFFSymbol *Symbol;
108   relocations Relocations;
109 
110   COFFSection(StringRef name);
111 };
112 
113 class WinCOFFObjectWriter : public MCObjectWriter {
114 public:
115   typedef std::vector<std::unique_ptr<COFFSymbol>> symbols;
116   typedef std::vector<std::unique_ptr<COFFSection>> sections;
117 
118   typedef DenseMap<MCSymbol const *, COFFSymbol *> symbol_map;
119   typedef DenseMap<MCSection const *, COFFSection *> section_map;
120 
121   std::unique_ptr<MCWinCOFFObjectTargetWriter> TargetObjectWriter;
122 
123   // Root level file contents.
124   COFF::header Header;
125   sections Sections;
126   symbols Symbols;
127   StringTableBuilder Strings{StringTableBuilder::WinCOFF};
128 
129   // Maps used during object file creation.
130   section_map SectionMap;
131   symbol_map SymbolMap;
132 
133   bool UseBigObj;
134 
135   WinCOFFObjectWriter(MCWinCOFFObjectTargetWriter *MOTW, raw_pwrite_stream &OS);
136 
137   void reset() override {
138     memset(&Header, 0, sizeof(Header));
139     Header.Machine = TargetObjectWriter->getMachine();
140     Sections.clear();
141     Symbols.clear();
142     Strings.clear();
143     SectionMap.clear();
144     SymbolMap.clear();
145     MCObjectWriter::reset();
146   }
147 
148   COFFSymbol *createSymbol(StringRef Name);
149   COFFSymbol *GetOrCreateCOFFSymbol(const MCSymbol *Symbol);
150   COFFSection *createSection(StringRef Name);
151 
152   template <typename object_t, typename list_t>
153   object_t *createCOFFEntity(StringRef Name, list_t &List);
154 
155   void defineSection(MCSectionCOFF const &Sec);
156 
157   COFFSymbol *getLinkedSymbol(const MCSymbol &Symbol);
158   void DefineSymbol(const MCSymbol &Symbol, MCAssembler &Assembler,
159                     const MCAsmLayout &Layout);
160 
161   void SetSymbolName(COFFSymbol &S);
162   void SetSectionName(COFFSection &S);
163 
164   bool IsPhysicalSection(COFFSection *S);
165 
166   // Entity writing methods.
167 
168   void WriteFileHeader(const COFF::header &Header);
169   void WriteSymbol(const COFFSymbol &S);
170   void WriteAuxiliarySymbols(const COFFSymbol::AuxiliarySymbols &S);
171   void writeSectionHeader(const COFF::section &S);
172   void WriteRelocation(const COFF::relocation &R);
173 
174   // MCObjectWriter interface implementation.
175 
176   void executePostLayoutBinding(MCAssembler &Asm,
177                                 const MCAsmLayout &Layout) override;
178 
179   bool isSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
180                                               const MCSymbol &SymA,
181                                               const MCFragment &FB, bool InSet,
182                                               bool IsPCRel) const override;
183 
184   bool isWeak(const MCSymbol &Sym) const override;
185 
186   void recordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
187                         const MCFragment *Fragment, const MCFixup &Fixup,
188                         MCValue Target, bool &IsPCRel,
189                         uint64_t &FixedValue) override;
190 
191   void writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
192 };
193 }
194 
195 static inline void write_uint32_le(void *Data, uint32_t Value) {
196   support::endian::write<uint32_t, support::little, support::unaligned>(Data,
197                                                                         Value);
198 }
199 
200 //------------------------------------------------------------------------------
201 // Symbol class implementation
202 
203 COFFSymbol::COFFSymbol(StringRef name)
204     : Name(name.begin(), name.end()), Other(nullptr), Section(nullptr),
205       Relocations(0), MC(nullptr) {
206   memset(&Data, 0, sizeof(Data));
207 }
208 
209 // In the case that the name does not fit within 8 bytes, the offset
210 // into the string table is stored in the last 4 bytes instead, leaving
211 // the first 4 bytes as 0.
212 void COFFSymbol::set_name_offset(uint32_t Offset) {
213   write_uint32_le(Data.Name + 0, 0);
214   write_uint32_le(Data.Name + 4, Offset);
215 }
216 
217 //------------------------------------------------------------------------------
218 // Section class implementation
219 
220 COFFSection::COFFSection(StringRef name)
221     : Name(name), MCSection(nullptr), Symbol(nullptr) {
222   memset(&Header, 0, sizeof(Header));
223 }
224 
225 //------------------------------------------------------------------------------
226 // WinCOFFObjectWriter class implementation
227 
228 WinCOFFObjectWriter::WinCOFFObjectWriter(MCWinCOFFObjectTargetWriter *MOTW,
229                                          raw_pwrite_stream &OS)
230     : MCObjectWriter(OS, true), TargetObjectWriter(MOTW) {
231   memset(&Header, 0, sizeof(Header));
232 
233   Header.Machine = TargetObjectWriter->getMachine();
234 }
235 
236 COFFSymbol *WinCOFFObjectWriter::createSymbol(StringRef Name) {
237   return createCOFFEntity<COFFSymbol>(Name, Symbols);
238 }
239 
240 COFFSymbol *WinCOFFObjectWriter::GetOrCreateCOFFSymbol(const MCSymbol *Symbol) {
241   symbol_map::iterator i = SymbolMap.find(Symbol);
242   if (i != SymbolMap.end())
243     return i->second;
244   COFFSymbol *RetSymbol =
245       createCOFFEntity<COFFSymbol>(Symbol->getName(), Symbols);
246   SymbolMap[Symbol] = RetSymbol;
247   return RetSymbol;
248 }
249 
250 COFFSection *WinCOFFObjectWriter::createSection(StringRef Name) {
251   return createCOFFEntity<COFFSection>(Name, Sections);
252 }
253 
254 /// A template used to lookup or create a symbol/section, and initialize it if
255 /// needed.
256 template <typename object_t, typename list_t>
257 object_t *WinCOFFObjectWriter::createCOFFEntity(StringRef Name, list_t &List) {
258   List.push_back(make_unique<object_t>(Name));
259 
260   return List.back().get();
261 }
262 
263 /// This function takes a section data object from the assembler
264 /// and creates the associated COFF section staging object.
265 void WinCOFFObjectWriter::defineSection(MCSectionCOFF const &Sec) {
266   COFFSection *coff_section = createSection(Sec.getSectionName());
267   COFFSymbol *coff_symbol = createSymbol(Sec.getSectionName());
268   if (Sec.getSelection() != COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE) {
269     if (const MCSymbol *S = Sec.getCOMDATSymbol()) {
270       COFFSymbol *COMDATSymbol = GetOrCreateCOFFSymbol(S);
271       if (COMDATSymbol->Section)
272         report_fatal_error("two sections have the same comdat");
273       COMDATSymbol->Section = coff_section;
274     }
275   }
276 
277   coff_section->Symbol = coff_symbol;
278   coff_symbol->Section = coff_section;
279   coff_symbol->Data.StorageClass = COFF::IMAGE_SYM_CLASS_STATIC;
280 
281   // In this case the auxiliary symbol is a Section Definition.
282   coff_symbol->Aux.resize(1);
283   memset(&coff_symbol->Aux[0], 0, sizeof(coff_symbol->Aux[0]));
284   coff_symbol->Aux[0].AuxType = ATSectionDefinition;
285   coff_symbol->Aux[0].Aux.SectionDefinition.Selection = Sec.getSelection();
286 
287   coff_section->Header.Characteristics = Sec.getCharacteristics();
288 
289   uint32_t &Characteristics = coff_section->Header.Characteristics;
290   switch (Sec.getAlignment()) {
291   case 1:
292     Characteristics |= COFF::IMAGE_SCN_ALIGN_1BYTES;
293     break;
294   case 2:
295     Characteristics |= COFF::IMAGE_SCN_ALIGN_2BYTES;
296     break;
297   case 4:
298     Characteristics |= COFF::IMAGE_SCN_ALIGN_4BYTES;
299     break;
300   case 8:
301     Characteristics |= COFF::IMAGE_SCN_ALIGN_8BYTES;
302     break;
303   case 16:
304     Characteristics |= COFF::IMAGE_SCN_ALIGN_16BYTES;
305     break;
306   case 32:
307     Characteristics |= COFF::IMAGE_SCN_ALIGN_32BYTES;
308     break;
309   case 64:
310     Characteristics |= COFF::IMAGE_SCN_ALIGN_64BYTES;
311     break;
312   case 128:
313     Characteristics |= COFF::IMAGE_SCN_ALIGN_128BYTES;
314     break;
315   case 256:
316     Characteristics |= COFF::IMAGE_SCN_ALIGN_256BYTES;
317     break;
318   case 512:
319     Characteristics |= COFF::IMAGE_SCN_ALIGN_512BYTES;
320     break;
321   case 1024:
322     Characteristics |= COFF::IMAGE_SCN_ALIGN_1024BYTES;
323     break;
324   case 2048:
325     Characteristics |= COFF::IMAGE_SCN_ALIGN_2048BYTES;
326     break;
327   case 4096:
328     Characteristics |= COFF::IMAGE_SCN_ALIGN_4096BYTES;
329     break;
330   case 8192:
331     Characteristics |= COFF::IMAGE_SCN_ALIGN_8192BYTES;
332     break;
333   default:
334     llvm_unreachable("unsupported section alignment");
335   }
336 
337   // Bind internal COFF section to MC section.
338   coff_section->MCSection = &Sec;
339   SectionMap[&Sec] = coff_section;
340 }
341 
342 static uint64_t getSymbolValue(const MCSymbol &Symbol,
343                                const MCAsmLayout &Layout) {
344   if (Symbol.isCommon() && Symbol.isExternal())
345     return Symbol.getCommonSize();
346 
347   uint64_t Res;
348   if (!Layout.getSymbolOffset(Symbol, Res))
349     return 0;
350 
351   return Res;
352 }
353 
354 COFFSymbol *WinCOFFObjectWriter::getLinkedSymbol(const MCSymbol &Symbol) {
355   if (!Symbol.isVariable())
356     return nullptr;
357 
358   const MCSymbolRefExpr *SymRef =
359       dyn_cast<MCSymbolRefExpr>(Symbol.getVariableValue());
360   if (!SymRef)
361     return nullptr;
362 
363   const MCSymbol &Aliasee = SymRef->getSymbol();
364   if (!Aliasee.isUndefined())
365     return nullptr;
366   return GetOrCreateCOFFSymbol(&Aliasee);
367 }
368 
369 /// This function takes a symbol data object from the assembler
370 /// and creates the associated COFF symbol staging object.
371 void WinCOFFObjectWriter::DefineSymbol(const MCSymbol &Symbol,
372                                        MCAssembler &Assembler,
373                                        const MCAsmLayout &Layout) {
374   COFFSymbol *coff_symbol = GetOrCreateCOFFSymbol(&Symbol);
375   const MCSymbol *Base = Layout.getBaseSymbol(Symbol);
376   COFFSection *Sec = nullptr;
377   if (Base && Base->getFragment()) {
378     Sec = SectionMap[Base->getFragment()->getParent()];
379     if (coff_symbol->Section && coff_symbol->Section != Sec)
380       report_fatal_error("conflicting sections for symbol");
381   }
382 
383   COFFSymbol *Local = nullptr;
384   if (cast<MCSymbolCOFF>(Symbol).isWeakExternal()) {
385     coff_symbol->Data.StorageClass = COFF::IMAGE_SYM_CLASS_WEAK_EXTERNAL;
386 
387     COFFSymbol *WeakDefault = getLinkedSymbol(Symbol);
388     if (!WeakDefault) {
389       std::string WeakName = (".weak." + Symbol.getName() + ".default").str();
390       WeakDefault = createSymbol(WeakName);
391       if (!Sec)
392         WeakDefault->Data.SectionNumber = COFF::IMAGE_SYM_ABSOLUTE;
393       else
394         WeakDefault->Section = Sec;
395       Local = WeakDefault;
396     }
397 
398     coff_symbol->Other = WeakDefault;
399 
400     // Setup the Weak External auxiliary symbol.
401     coff_symbol->Aux.resize(1);
402     memset(&coff_symbol->Aux[0], 0, sizeof(coff_symbol->Aux[0]));
403     coff_symbol->Aux[0].AuxType = ATWeakExternal;
404     coff_symbol->Aux[0].Aux.WeakExternal.TagIndex = 0;
405     coff_symbol->Aux[0].Aux.WeakExternal.Characteristics =
406         COFF::IMAGE_WEAK_EXTERN_SEARCH_LIBRARY;
407   } else {
408     if (!Base)
409       coff_symbol->Data.SectionNumber = COFF::IMAGE_SYM_ABSOLUTE;
410     else
411       coff_symbol->Section = Sec;
412     Local = coff_symbol;
413   }
414 
415   if (Local) {
416     Local->Data.Value = getSymbolValue(Symbol, Layout);
417 
418     const MCSymbolCOFF &SymbolCOFF = cast<MCSymbolCOFF>(Symbol);
419     Local->Data.Type = SymbolCOFF.getType();
420     Local->Data.StorageClass = SymbolCOFF.getClass();
421 
422     // If no storage class was specified in the streamer, define it here.
423     if (Local->Data.StorageClass == COFF::IMAGE_SYM_CLASS_NULL) {
424       bool IsExternal = Symbol.isExternal() ||
425                         (!Symbol.getFragment() && !Symbol.isVariable());
426 
427       Local->Data.StorageClass = IsExternal ? COFF::IMAGE_SYM_CLASS_EXTERNAL
428                                             : COFF::IMAGE_SYM_CLASS_STATIC;
429     }
430   }
431 
432   coff_symbol->MC = &Symbol;
433 }
434 
435 // Maximum offsets for different string table entry encodings.
436 enum : unsigned { Max7DecimalOffset = 9999999U };
437 enum : uint64_t { MaxBase64Offset = 0xFFFFFFFFFULL }; // 64^6, including 0
438 
439 // Encode a string table entry offset in base 64, padded to 6 chars, and
440 // prefixed with a double slash: '//AAAAAA', '//AAAAAB', ...
441 // Buffer must be at least 8 bytes large. No terminating null appended.
442 static void encodeBase64StringEntry(char *Buffer, uint64_t Value) {
443   assert(Value > Max7DecimalOffset && Value <= MaxBase64Offset &&
444          "Illegal section name encoding for value");
445 
446   static const char Alphabet[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
447                                  "abcdefghijklmnopqrstuvwxyz"
448                                  "0123456789+/";
449 
450   Buffer[0] = '/';
451   Buffer[1] = '/';
452 
453   char *Ptr = Buffer + 7;
454   for (unsigned i = 0; i < 6; ++i) {
455     unsigned Rem = Value % 64;
456     Value /= 64;
457     *(Ptr--) = Alphabet[Rem];
458   }
459 }
460 
461 void WinCOFFObjectWriter::SetSectionName(COFFSection &S) {
462   if (S.Name.size() > COFF::NameSize) {
463     uint64_t StringTableEntry = Strings.getOffset(S.Name);
464 
465     if (StringTableEntry <= Max7DecimalOffset) {
466       SmallVector<char, COFF::NameSize> Buffer;
467       Twine('/').concat(Twine(StringTableEntry)).toVector(Buffer);
468       assert(Buffer.size() <= COFF::NameSize && Buffer.size() >= 2);
469 
470       std::memcpy(S.Header.Name, Buffer.data(), Buffer.size());
471     } else if (StringTableEntry <= MaxBase64Offset) {
472       // Starting with 10,000,000, offsets are encoded as base64.
473       encodeBase64StringEntry(S.Header.Name, StringTableEntry);
474     } else {
475       report_fatal_error("COFF string table is greater than 64 GB.");
476     }
477   } else {
478     std::memcpy(S.Header.Name, S.Name.c_str(), S.Name.size());
479   }
480 }
481 
482 void WinCOFFObjectWriter::SetSymbolName(COFFSymbol &S) {
483   if (S.Name.size() > COFF::NameSize)
484     S.set_name_offset(Strings.getOffset(S.Name));
485   else
486     std::memcpy(S.Data.Name, S.Name.c_str(), S.Name.size());
487 }
488 
489 bool WinCOFFObjectWriter::IsPhysicalSection(COFFSection *S) {
490   return (S->Header.Characteristics & COFF::IMAGE_SCN_CNT_UNINITIALIZED_DATA) ==
491          0;
492 }
493 
494 //------------------------------------------------------------------------------
495 // entity writing methods
496 
497 void WinCOFFObjectWriter::WriteFileHeader(const COFF::header &Header) {
498   if (UseBigObj) {
499     writeLE16(COFF::IMAGE_FILE_MACHINE_UNKNOWN);
500     writeLE16(0xFFFF);
501     writeLE16(COFF::BigObjHeader::MinBigObjectVersion);
502     writeLE16(Header.Machine);
503     writeLE32(Header.TimeDateStamp);
504     writeBytes(StringRef(COFF::BigObjMagic, sizeof(COFF::BigObjMagic)));
505     writeLE32(0);
506     writeLE32(0);
507     writeLE32(0);
508     writeLE32(0);
509     writeLE32(Header.NumberOfSections);
510     writeLE32(Header.PointerToSymbolTable);
511     writeLE32(Header.NumberOfSymbols);
512   } else {
513     writeLE16(Header.Machine);
514     writeLE16(static_cast<int16_t>(Header.NumberOfSections));
515     writeLE32(Header.TimeDateStamp);
516     writeLE32(Header.PointerToSymbolTable);
517     writeLE32(Header.NumberOfSymbols);
518     writeLE16(Header.SizeOfOptionalHeader);
519     writeLE16(Header.Characteristics);
520   }
521 }
522 
523 void WinCOFFObjectWriter::WriteSymbol(const COFFSymbol &S) {
524   writeBytes(StringRef(S.Data.Name, COFF::NameSize));
525   writeLE32(S.Data.Value);
526   if (UseBigObj)
527     writeLE32(S.Data.SectionNumber);
528   else
529     writeLE16(static_cast<int16_t>(S.Data.SectionNumber));
530   writeLE16(S.Data.Type);
531   write8(S.Data.StorageClass);
532   write8(S.Data.NumberOfAuxSymbols);
533   WriteAuxiliarySymbols(S.Aux);
534 }
535 
536 void WinCOFFObjectWriter::WriteAuxiliarySymbols(
537     const COFFSymbol::AuxiliarySymbols &S) {
538   for (const AuxSymbol &i : S) {
539     switch (i.AuxType) {
540     case ATFunctionDefinition:
541       writeLE32(i.Aux.FunctionDefinition.TagIndex);
542       writeLE32(i.Aux.FunctionDefinition.TotalSize);
543       writeLE32(i.Aux.FunctionDefinition.PointerToLinenumber);
544       writeLE32(i.Aux.FunctionDefinition.PointerToNextFunction);
545       WriteZeros(sizeof(i.Aux.FunctionDefinition.unused));
546       if (UseBigObj)
547         WriteZeros(COFF::Symbol32Size - COFF::Symbol16Size);
548       break;
549     case ATbfAndefSymbol:
550       WriteZeros(sizeof(i.Aux.bfAndefSymbol.unused1));
551       writeLE16(i.Aux.bfAndefSymbol.Linenumber);
552       WriteZeros(sizeof(i.Aux.bfAndefSymbol.unused2));
553       writeLE32(i.Aux.bfAndefSymbol.PointerToNextFunction);
554       WriteZeros(sizeof(i.Aux.bfAndefSymbol.unused3));
555       if (UseBigObj)
556         WriteZeros(COFF::Symbol32Size - COFF::Symbol16Size);
557       break;
558     case ATWeakExternal:
559       writeLE32(i.Aux.WeakExternal.TagIndex);
560       writeLE32(i.Aux.WeakExternal.Characteristics);
561       WriteZeros(sizeof(i.Aux.WeakExternal.unused));
562       if (UseBigObj)
563         WriteZeros(COFF::Symbol32Size - COFF::Symbol16Size);
564       break;
565     case ATFile:
566       writeBytes(
567           StringRef(reinterpret_cast<const char *>(&i.Aux),
568                     UseBigObj ? COFF::Symbol32Size : COFF::Symbol16Size));
569       break;
570     case ATSectionDefinition:
571       writeLE32(i.Aux.SectionDefinition.Length);
572       writeLE16(i.Aux.SectionDefinition.NumberOfRelocations);
573       writeLE16(i.Aux.SectionDefinition.NumberOfLinenumbers);
574       writeLE32(i.Aux.SectionDefinition.CheckSum);
575       writeLE16(static_cast<int16_t>(i.Aux.SectionDefinition.Number));
576       write8(i.Aux.SectionDefinition.Selection);
577       WriteZeros(sizeof(i.Aux.SectionDefinition.unused));
578       writeLE16(static_cast<int16_t>(i.Aux.SectionDefinition.Number >> 16));
579       if (UseBigObj)
580         WriteZeros(COFF::Symbol32Size - COFF::Symbol16Size);
581       break;
582     }
583   }
584 }
585 
586 void WinCOFFObjectWriter::writeSectionHeader(const COFF::section &S) {
587   writeBytes(StringRef(S.Name, COFF::NameSize));
588 
589   writeLE32(S.VirtualSize);
590   writeLE32(S.VirtualAddress);
591   writeLE32(S.SizeOfRawData);
592   writeLE32(S.PointerToRawData);
593   writeLE32(S.PointerToRelocations);
594   writeLE32(S.PointerToLineNumbers);
595   writeLE16(S.NumberOfRelocations);
596   writeLE16(S.NumberOfLineNumbers);
597   writeLE32(S.Characteristics);
598 }
599 
600 void WinCOFFObjectWriter::WriteRelocation(const COFF::relocation &R) {
601   writeLE32(R.VirtualAddress);
602   writeLE32(R.SymbolTableIndex);
603   writeLE16(R.Type);
604 }
605 
606 ////////////////////////////////////////////////////////////////////////////////
607 // MCObjectWriter interface implementations
608 
609 void WinCOFFObjectWriter::executePostLayoutBinding(MCAssembler &Asm,
610                                                    const MCAsmLayout &Layout) {
611   // "Define" each section & symbol. This creates section & symbol
612   // entries in the staging area.
613   for (const auto &Section : Asm)
614     defineSection(static_cast<const MCSectionCOFF &>(Section));
615 
616   for (const MCSymbol &Symbol : Asm.symbols())
617     if (!Symbol.isTemporary())
618       DefineSymbol(Symbol, Asm, Layout);
619 }
620 
621 bool WinCOFFObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(
622     const MCAssembler &Asm, const MCSymbol &SymA, const MCFragment &FB,
623     bool InSet, bool IsPCRel) const {
624   // MS LINK expects to be able to replace all references to a function with a
625   // thunk to implement their /INCREMENTAL feature.  Make sure we don't optimize
626   // away any relocations to functions.
627   uint16_t Type = cast<MCSymbolCOFF>(SymA).getType();
628   if (Asm.isIncrementalLinkerCompatible() &&
629       (Type >> COFF::SCT_COMPLEX_TYPE_SHIFT) == COFF::IMAGE_SYM_DTYPE_FUNCTION)
630     return false;
631   return MCObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(Asm, SymA, FB,
632                                                                 InSet, IsPCRel);
633 }
634 
635 bool WinCOFFObjectWriter::isWeak(const MCSymbol &Sym) const {
636   if (!Sym.isExternal())
637     return false;
638 
639   if (!Sym.isInSection())
640     return false;
641 
642   const auto &Sec = cast<MCSectionCOFF>(Sym.getSection());
643   if (!Sec.getCOMDATSymbol())
644     return false;
645 
646   // It looks like for COFF it is invalid to replace a reference to a global
647   // in a comdat with a reference to a local.
648   // FIXME: Add a specification reference if available.
649   return true;
650 }
651 
652 void WinCOFFObjectWriter::recordRelocation(
653     MCAssembler &Asm, const MCAsmLayout &Layout, const MCFragment *Fragment,
654     const MCFixup &Fixup, MCValue Target, bool &IsPCRel, uint64_t &FixedValue) {
655   assert(Target.getSymA() && "Relocation must reference a symbol!");
656 
657   const MCSymbol &A = Target.getSymA()->getSymbol();
658   if (!A.isRegistered()) {
659     Asm.getContext().reportError(Fixup.getLoc(),
660                                       Twine("symbol '") + A.getName() +
661                                           "' can not be undefined");
662     return;
663   }
664   if (A.isTemporary() && A.isUndefined()) {
665     Asm.getContext().reportError(Fixup.getLoc(),
666                                       Twine("assembler label '") + A.getName() +
667                                           "' can not be undefined");
668     return;
669   }
670 
671   MCSection *Section = Fragment->getParent();
672 
673   // Mark this symbol as requiring an entry in the symbol table.
674   assert(SectionMap.find(Section) != SectionMap.end() &&
675          "Section must already have been defined in executePostLayoutBinding!");
676 
677   COFFSection *coff_section = SectionMap[Section];
678   const MCSymbolRefExpr *SymB = Target.getSymB();
679   bool CrossSection = false;
680 
681   if (SymB) {
682     const MCSymbol *B = &SymB->getSymbol();
683     if (!B->getFragment()) {
684       Asm.getContext().reportError(
685           Fixup.getLoc(),
686           Twine("symbol '") + B->getName() +
687               "' can not be undefined in a subtraction expression");
688       return;
689     }
690 
691     if (!A.getFragment()) {
692       Asm.getContext().reportError(
693           Fixup.getLoc(),
694           Twine("symbol '") + A.getName() +
695               "' can not be undefined in a subtraction expression");
696       return;
697     }
698 
699     CrossSection = &A.getSection() != &B->getSection();
700 
701     // Offset of the symbol in the section
702     int64_t OffsetOfB = Layout.getSymbolOffset(*B);
703 
704     // In the case where we have SymbA and SymB, we just need to store the delta
705     // between the two symbols.  Update FixedValue to account for the delta, and
706     // skip recording the relocation.
707     if (!CrossSection) {
708       int64_t OffsetOfA = Layout.getSymbolOffset(A);
709       FixedValue = (OffsetOfA - OffsetOfB) + Target.getConstant();
710       return;
711     }
712 
713     // Offset of the relocation in the section
714     int64_t OffsetOfRelocation =
715         Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
716 
717     FixedValue = (OffsetOfRelocation - OffsetOfB) + Target.getConstant();
718   } else {
719     FixedValue = Target.getConstant();
720   }
721 
722   COFFRelocation Reloc;
723 
724   Reloc.Data.SymbolTableIndex = 0;
725   Reloc.Data.VirtualAddress = Layout.getFragmentOffset(Fragment);
726 
727   // Turn relocations for temporary symbols into section relocations.
728   if (A.isTemporary() || CrossSection) {
729     MCSection *TargetSection = &A.getSection();
730     assert(
731         SectionMap.find(TargetSection) != SectionMap.end() &&
732         "Section must already have been defined in executePostLayoutBinding!");
733     Reloc.Symb = SectionMap[TargetSection]->Symbol;
734     FixedValue += Layout.getSymbolOffset(A);
735   } else {
736     assert(
737         SymbolMap.find(&A) != SymbolMap.end() &&
738         "Symbol must already have been defined in executePostLayoutBinding!");
739     Reloc.Symb = SymbolMap[&A];
740   }
741 
742   ++Reloc.Symb->Relocations;
743 
744   Reloc.Data.VirtualAddress += Fixup.getOffset();
745   Reloc.Data.Type = TargetObjectWriter->getRelocType(
746       Target, Fixup, CrossSection, Asm.getBackend());
747 
748   // FIXME: Can anyone explain what this does other than adjust for the size
749   // of the offset?
750   if ((Header.Machine == COFF::IMAGE_FILE_MACHINE_AMD64 &&
751        Reloc.Data.Type == COFF::IMAGE_REL_AMD64_REL32) ||
752       (Header.Machine == COFF::IMAGE_FILE_MACHINE_I386 &&
753        Reloc.Data.Type == COFF::IMAGE_REL_I386_REL32))
754     FixedValue += 4;
755 
756   if (Header.Machine == COFF::IMAGE_FILE_MACHINE_ARMNT) {
757     switch (Reloc.Data.Type) {
758     case COFF::IMAGE_REL_ARM_ABSOLUTE:
759     case COFF::IMAGE_REL_ARM_ADDR32:
760     case COFF::IMAGE_REL_ARM_ADDR32NB:
761     case COFF::IMAGE_REL_ARM_TOKEN:
762     case COFF::IMAGE_REL_ARM_SECTION:
763     case COFF::IMAGE_REL_ARM_SECREL:
764       break;
765     case COFF::IMAGE_REL_ARM_BRANCH11:
766     case COFF::IMAGE_REL_ARM_BLX11:
767     // IMAGE_REL_ARM_BRANCH11 and IMAGE_REL_ARM_BLX11 are only used for
768     // pre-ARMv7, which implicitly rules it out of ARMNT (it would be valid
769     // for Windows CE).
770     case COFF::IMAGE_REL_ARM_BRANCH24:
771     case COFF::IMAGE_REL_ARM_BLX24:
772     case COFF::IMAGE_REL_ARM_MOV32A:
773       // IMAGE_REL_ARM_BRANCH24, IMAGE_REL_ARM_BLX24, IMAGE_REL_ARM_MOV32A are
774       // only used for ARM mode code, which is documented as being unsupported
775       // by Windows on ARM.  Empirical proof indicates that masm is able to
776       // generate the relocations however the rest of the MSVC toolchain is
777       // unable to handle it.
778       llvm_unreachable("unsupported relocation");
779       break;
780     case COFF::IMAGE_REL_ARM_MOV32T:
781       break;
782     case COFF::IMAGE_REL_ARM_BRANCH20T:
783     case COFF::IMAGE_REL_ARM_BRANCH24T:
784     case COFF::IMAGE_REL_ARM_BLX23T:
785       // IMAGE_REL_BRANCH20T, IMAGE_REL_ARM_BRANCH24T, IMAGE_REL_ARM_BLX23T all
786       // perform a 4 byte adjustment to the relocation.  Relative branches are
787       // offset by 4 on ARM, however, because there is no RELA relocations, all
788       // branches are offset by 4.
789       FixedValue = FixedValue + 4;
790       break;
791     }
792   }
793 
794   // The fixed value never makes sense for section indices, ignore it.
795   if (Fixup.getKind() == FK_SecRel_2)
796     FixedValue = 0;
797 
798   if (TargetObjectWriter->recordRelocation(Fixup))
799     coff_section->Relocations.push_back(Reloc);
800 }
801 
802 void WinCOFFObjectWriter::writeObject(MCAssembler &Asm,
803                                       const MCAsmLayout &Layout) {
804   size_t SectionsSize = Sections.size();
805   if (SectionsSize > static_cast<size_t>(INT32_MAX))
806     report_fatal_error(
807         "PE COFF object files can't have more than 2147483647 sections");
808 
809   // Assign symbol and section indexes and offsets.
810   int32_t NumberOfSections = static_cast<int32_t>(SectionsSize);
811 
812   UseBigObj = NumberOfSections > COFF::MaxNumberOfSections16;
813 
814   // Assign section numbers.
815   size_t Number = 1;
816   for (const auto &Section : Sections) {
817     Section->Number = Number;
818     Section->Symbol->Data.SectionNumber = Number;
819     Section->Symbol->Aux[0].Aux.SectionDefinition.Number = Number;
820     ++Number;
821   }
822 
823   Header.NumberOfSections = NumberOfSections;
824   Header.NumberOfSymbols = 0;
825 
826   for (const std::string &Name : Asm.getFileNames()) {
827     // round up to calculate the number of auxiliary symbols required
828     unsigned SymbolSize = UseBigObj ? COFF::Symbol32Size : COFF::Symbol16Size;
829     unsigned Count = (Name.size() + SymbolSize - 1) / SymbolSize;
830 
831     COFFSymbol *file = createSymbol(".file");
832     file->Data.SectionNumber = COFF::IMAGE_SYM_DEBUG;
833     file->Data.StorageClass = COFF::IMAGE_SYM_CLASS_FILE;
834     file->Aux.resize(Count);
835 
836     unsigned Offset = 0;
837     unsigned Length = Name.size();
838     for (auto &Aux : file->Aux) {
839       Aux.AuxType = ATFile;
840 
841       if (Length > SymbolSize) {
842         memcpy(&Aux.Aux, Name.c_str() + Offset, SymbolSize);
843         Length = Length - SymbolSize;
844       } else {
845         memcpy(&Aux.Aux, Name.c_str() + Offset, Length);
846         memset((char *)&Aux.Aux + Length, 0, SymbolSize - Length);
847         break;
848       }
849 
850       Offset += SymbolSize;
851     }
852   }
853 
854   for (auto &Symbol : Symbols) {
855     // Update section number & offset for symbols that have them.
856     if (Symbol->Section)
857       Symbol->Data.SectionNumber = Symbol->Section->Number;
858     Symbol->setIndex(Header.NumberOfSymbols++);
859     // Update auxiliary symbol info.
860     Symbol->Data.NumberOfAuxSymbols = Symbol->Aux.size();
861     Header.NumberOfSymbols += Symbol->Data.NumberOfAuxSymbols;
862   }
863 
864   // Build string table.
865   for (const auto &S : Sections)
866     if (S->Name.size() > COFF::NameSize)
867       Strings.add(S->Name);
868   for (const auto &S : Symbols)
869     if (S->Name.size() > COFF::NameSize)
870       Strings.add(S->Name);
871   Strings.finalize();
872 
873   // Set names.
874   for (const auto &S : Sections)
875     SetSectionName(*S);
876   for (auto &S : Symbols)
877     SetSymbolName(*S);
878 
879   // Fixup weak external references.
880   for (auto &Symbol : Symbols) {
881     if (Symbol->Other) {
882       assert(Symbol->getIndex() != -1);
883       assert(Symbol->Aux.size() == 1 && "Symbol must contain one aux symbol!");
884       assert(Symbol->Aux[0].AuxType == ATWeakExternal &&
885              "Symbol's aux symbol must be a Weak External!");
886       Symbol->Aux[0].Aux.WeakExternal.TagIndex = Symbol->Other->getIndex();
887     }
888   }
889 
890   // Fixup associative COMDAT sections.
891   for (auto &Section : Sections) {
892     if (Section->Symbol->Aux[0].Aux.SectionDefinition.Selection !=
893         COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE)
894       continue;
895 
896     const MCSectionCOFF &MCSec = *Section->MCSection;
897 
898     const MCSymbol *COMDAT = MCSec.getCOMDATSymbol();
899     assert(COMDAT);
900     COFFSymbol *COMDATSymbol = GetOrCreateCOFFSymbol(COMDAT);
901     assert(COMDATSymbol);
902     COFFSection *Assoc = COMDATSymbol->Section;
903     if (!Assoc)
904       report_fatal_error(
905           Twine("Missing associated COMDAT section for section ") +
906           MCSec.getSectionName());
907 
908     // Skip this section if the associated section is unused.
909     if (Assoc->Number == -1)
910       continue;
911 
912     Section->Symbol->Aux[0].Aux.SectionDefinition.Number = Assoc->Number;
913   }
914 
915   // Assign file offsets to COFF object file structures.
916 
917   unsigned offset = getInitialOffset();
918 
919   if (UseBigObj)
920     offset += COFF::Header32Size;
921   else
922     offset += COFF::Header16Size;
923   offset += COFF::SectionSize * Header.NumberOfSections;
924 
925   for (const auto &Section : Asm) {
926     COFFSection *Sec = SectionMap[&Section];
927 
928     if (Sec->Number == -1)
929       continue;
930 
931     Sec->Header.SizeOfRawData = Layout.getSectionAddressSize(&Section);
932 
933     if (IsPhysicalSection(Sec)) {
934       // Align the section data to a four byte boundary.
935       offset = alignTo(offset, 4);
936       Sec->Header.PointerToRawData = offset;
937 
938       offset += Sec->Header.SizeOfRawData;
939     }
940 
941     if (Sec->Relocations.size() > 0) {
942       bool RelocationsOverflow = Sec->Relocations.size() >= 0xffff;
943 
944       if (RelocationsOverflow) {
945         // Signal overflow by setting NumberOfRelocations to max value. Actual
946         // size is found in reloc #0. Microsoft tools understand this.
947         Sec->Header.NumberOfRelocations = 0xffff;
948       } else {
949         Sec->Header.NumberOfRelocations = Sec->Relocations.size();
950       }
951       Sec->Header.PointerToRelocations = offset;
952 
953       if (RelocationsOverflow) {
954         // Reloc #0 will contain actual count, so make room for it.
955         offset += COFF::RelocationSize;
956       }
957 
958       offset += COFF::RelocationSize * Sec->Relocations.size();
959 
960       for (auto &Relocation : Sec->Relocations) {
961         assert(Relocation.Symb->getIndex() != -1);
962         Relocation.Data.SymbolTableIndex = Relocation.Symb->getIndex();
963       }
964     }
965 
966     assert(Sec->Symbol->Aux.size() == 1 &&
967            "Section's symbol must have one aux!");
968     AuxSymbol &Aux = Sec->Symbol->Aux[0];
969     assert(Aux.AuxType == ATSectionDefinition &&
970            "Section's symbol's aux symbol must be a Section Definition!");
971     Aux.Aux.SectionDefinition.Length = Sec->Header.SizeOfRawData;
972     Aux.Aux.SectionDefinition.NumberOfRelocations =
973         Sec->Header.NumberOfRelocations;
974     Aux.Aux.SectionDefinition.NumberOfLinenumbers =
975         Sec->Header.NumberOfLineNumbers;
976   }
977 
978   Header.PointerToSymbolTable = offset;
979 
980   // MS LINK expects to be able to use this timestamp to implement their
981   // /INCREMENTAL feature.
982   if (Asm.isIncrementalLinkerCompatible()) {
983     std::time_t Now = time(nullptr);
984     if (Now < 0 || !isUInt<32>(Now))
985       Now = UINT32_MAX;
986     Header.TimeDateStamp = Now;
987   } else {
988     // Have deterministic output if /INCREMENTAL isn't needed. Also matches GNU.
989     Header.TimeDateStamp = 0;
990   }
991 
992   // Write it all to disk...
993   WriteFileHeader(Header);
994 
995   {
996     sections::iterator i, ie;
997     MCAssembler::iterator j, je;
998 
999     for (auto &Section : Sections) {
1000       if (Section->Number != -1) {
1001         if (Section->Relocations.size() >= 0xffff)
1002           Section->Header.Characteristics |= COFF::IMAGE_SCN_LNK_NRELOC_OVFL;
1003         writeSectionHeader(Section->Header);
1004       }
1005     }
1006 
1007     SmallVector<char, 128> SectionContents;
1008     for (i = Sections.begin(), ie = Sections.end(), j = Asm.begin(),
1009         je = Asm.end();
1010          (i != ie) && (j != je); ++i, ++j) {
1011 
1012       if ((*i)->Number == -1)
1013         continue;
1014 
1015       if ((*i)->Header.PointerToRawData != 0) {
1016         assert(getStream().tell() <= (*i)->Header.PointerToRawData &&
1017                "Section::PointerToRawData is insane!");
1018 
1019         unsigned SectionDataPadding =
1020             (*i)->Header.PointerToRawData - getStream().tell();
1021         assert(SectionDataPadding < 4 &&
1022                "Should only need at most three bytes of padding!");
1023 
1024         WriteZeros(SectionDataPadding);
1025 
1026         // Save the contents of the section to a temporary buffer, we need this
1027         // to CRC the data before we dump it into the object file.
1028         SectionContents.clear();
1029         raw_svector_ostream VecOS(SectionContents);
1030         raw_pwrite_stream &OldStream = getStream();
1031         // Redirect the output stream to our buffer.
1032         setStream(VecOS);
1033         // Fill our buffer with the section data.
1034         Asm.writeSectionData(&*j, Layout);
1035         // Reset the stream back to what it was before.
1036         setStream(OldStream);
1037 
1038         // Calculate our CRC with an initial value of '0', this is not how
1039         // JamCRC is specified but it aligns with the expected output.
1040         JamCRC JC(/*Init=*/0x00000000U);
1041         JC.update(SectionContents);
1042 
1043         // Write the section contents to the object file.
1044         getStream() << SectionContents;
1045 
1046         // Update the section definition auxiliary symbol to record the CRC.
1047         COFFSection *Sec = SectionMap[&*j];
1048         COFFSymbol::AuxiliarySymbols &AuxSyms = Sec->Symbol->Aux;
1049         assert(AuxSyms.size() == 1 &&
1050                AuxSyms[0].AuxType == ATSectionDefinition);
1051         AuxSymbol &SecDef = AuxSyms[0];
1052         SecDef.Aux.SectionDefinition.CheckSum = JC.getCRC();
1053       }
1054 
1055       if ((*i)->Relocations.size() > 0) {
1056         assert(getStream().tell() == (*i)->Header.PointerToRelocations &&
1057                "Section::PointerToRelocations is insane!");
1058 
1059         if ((*i)->Relocations.size() >= 0xffff) {
1060           // In case of overflow, write actual relocation count as first
1061           // relocation. Including the synthetic reloc itself (+ 1).
1062           COFF::relocation r;
1063           r.VirtualAddress = (*i)->Relocations.size() + 1;
1064           r.SymbolTableIndex = 0;
1065           r.Type = 0;
1066           WriteRelocation(r);
1067         }
1068 
1069         for (const auto &Relocation : (*i)->Relocations)
1070           WriteRelocation(Relocation.Data);
1071       } else
1072         assert((*i)->Header.PointerToRelocations == 0 &&
1073                "Section::PointerToRelocations is insane!");
1074     }
1075   }
1076 
1077   assert(getStream().tell() == Header.PointerToSymbolTable &&
1078          "Header::PointerToSymbolTable is insane!");
1079 
1080   for (auto &Symbol : Symbols)
1081     if (Symbol->getIndex() != -1)
1082       WriteSymbol(*Symbol);
1083 
1084   Strings.write(getStream());
1085 }
1086 
1087 MCWinCOFFObjectTargetWriter::MCWinCOFFObjectTargetWriter(unsigned Machine_)
1088     : Machine(Machine_) {}
1089 
1090 // Pin the vtable to this file.
1091 void MCWinCOFFObjectTargetWriter::anchor() {}
1092 
1093 //------------------------------------------------------------------------------
1094 // WinCOFFObjectWriter factory function
1095 
1096 MCObjectWriter *
1097 llvm::createWinCOFFObjectWriter(MCWinCOFFObjectTargetWriter *MOTW,
1098                                 raw_pwrite_stream &OS) {
1099   return new WinCOFFObjectWriter(MOTW, OS);
1100 }
1101