1 //===- llvm/MC/WinCOFFObjectWriter.cpp ------------------------------------===//
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/ADT/DenseMap.h"
15 #include "llvm/ADT/SmallString.h"
16 #include "llvm/ADT/SmallVector.h"
17 #include "llvm/ADT/STLExtras.h"
18 #include "llvm/ADT/StringRef.h"
19 #include "llvm/ADT/Twine.h"
20 #include "llvm/MC/MCAsmLayout.h"
21 #include "llvm/MC/MCAssembler.h"
22 #include "llvm/MC/MCContext.h"
23 #include "llvm/MC/MCExpr.h"
24 #include "llvm/MC/MCFixup.h"
25 #include "llvm/MC/MCFragment.h"
26 #include "llvm/MC/MCObjectWriter.h"
27 #include "llvm/MC/MCSection.h"
28 #include "llvm/MC/MCSectionCOFF.h"
29 #include "llvm/MC/MCSymbol.h"
30 #include "llvm/MC/MCSymbolCOFF.h"
31 #include "llvm/MC/MCValue.h"
32 #include "llvm/MC/MCWinCOFFObjectWriter.h"
33 #include "llvm/MC/StringTableBuilder.h"
34 #include "llvm/Support/Casting.h"
35 #include "llvm/Support/COFF.h"
36 #include "llvm/Support/Endian.h"
37 #include "llvm/Support/ErrorHandling.h"
38 #include "llvm/Support/JamCRC.h"
39 #include "llvm/Support/MathExtras.h"
40 #include "llvm/Support/raw_ostream.h"
41 #include <cassert>
42 #include <cstddef>
43 #include <cstdint>
44 #include <cstring>
45 #include <ctime>
46 #include <memory>
47 #include <string>
48 #include <vector>
49 
50 using namespace llvm;
51 
52 #define DEBUG_TYPE "WinCOFFObjectWriter"
53 
54 namespace {
55 
56 typedef SmallString<COFF::NameSize> name;
57 
58 enum AuxiliaryType {
59   ATFunctionDefinition,
60   ATbfAndefSymbol,
61   ATWeakExternal,
62   ATFile,
63   ATSectionDefinition
64 };
65 
66 struct AuxSymbol {
67   AuxiliaryType AuxType;
68   COFF::Auxiliary Aux;
69 };
70 
71 class COFFSection;
72 
73 class COFFSymbol {
74 public:
75   COFF::symbol Data;
76 
77   typedef SmallVector<AuxSymbol, 1> AuxiliarySymbols;
78 
79   name Name;
80   int Index;
81   AuxiliarySymbols Aux;
82   COFFSymbol *Other = nullptr;
83   COFFSection *Section = nullptr;
84   int Relocations = 0;
85   const MCSymbol *MC = nullptr;
86 
87   COFFSymbol(StringRef name);
88 
89   void set_name_offset(uint32_t Offset);
90 
91   int64_t getIndex() const { return Index; }
92   void setIndex(int Value) {
93     Index = Value;
94     if (MC)
95       MC->setIndex(static_cast<uint32_t>(Value));
96   }
97 };
98 
99 // This class contains staging data for a COFF relocation entry.
100 struct COFFRelocation {
101   COFF::relocation Data;
102   COFFSymbol *Symb = nullptr;
103 
104   COFFRelocation() = default;
105 
106   static size_t size() { return COFF::RelocationSize; }
107 };
108 
109 typedef std::vector<COFFRelocation> relocations;
110 
111 class COFFSection {
112 public:
113   COFF::section Header;
114 
115   std::string Name;
116   int Number;
117   MCSectionCOFF const *MCSection = nullptr;
118   COFFSymbol *Symbol = nullptr;
119   relocations Relocations;
120 
121   COFFSection(StringRef name);
122 };
123 
124 class WinCOFFObjectWriter : public MCObjectWriter {
125 public:
126   typedef std::vector<std::unique_ptr<COFFSymbol>> symbols;
127   typedef std::vector<std::unique_ptr<COFFSection>> sections;
128 
129   typedef DenseMap<MCSymbol const *, COFFSymbol *> symbol_map;
130   typedef DenseMap<MCSection const *, COFFSection *> section_map;
131 
132   std::unique_ptr<MCWinCOFFObjectTargetWriter> TargetObjectWriter;
133 
134   // Root level file contents.
135   COFF::header Header;
136   sections Sections;
137   symbols Symbols;
138   StringTableBuilder Strings{StringTableBuilder::WinCOFF};
139 
140   // Maps used during object file creation.
141   section_map SectionMap;
142   symbol_map SymbolMap;
143 
144   bool UseBigObj;
145 
146   WinCOFFObjectWriter(MCWinCOFFObjectTargetWriter *MOTW, raw_pwrite_stream &OS);
147 
148   void reset() override {
149     memset(&Header, 0, sizeof(Header));
150     Header.Machine = TargetObjectWriter->getMachine();
151     Sections.clear();
152     Symbols.clear();
153     Strings.clear();
154     SectionMap.clear();
155     SymbolMap.clear();
156     MCObjectWriter::reset();
157   }
158 
159   COFFSymbol *createSymbol(StringRef Name);
160   COFFSymbol *GetOrCreateCOFFSymbol(const MCSymbol *Symbol);
161   COFFSection *createSection(StringRef Name);
162 
163   template <typename object_t, typename list_t>
164   object_t *createCOFFEntity(StringRef Name, list_t &List);
165 
166   void defineSection(MCSectionCOFF const &Sec);
167 
168   COFFSymbol *getLinkedSymbol(const MCSymbol &Symbol);
169   void DefineSymbol(const MCSymbol &Symbol, MCAssembler &Assembler,
170                     const MCAsmLayout &Layout);
171 
172   void SetSymbolName(COFFSymbol &S);
173   void SetSectionName(COFFSection &S);
174 
175   bool IsPhysicalSection(COFFSection *S);
176 
177   // Entity writing methods.
178 
179   void WriteFileHeader(const COFF::header &Header);
180   void WriteSymbol(const COFFSymbol &S);
181   void WriteAuxiliarySymbols(const COFFSymbol::AuxiliarySymbols &S);
182   void writeSectionHeader(const COFF::section &S);
183   void WriteRelocation(const COFF::relocation &R);
184 
185   // MCObjectWriter interface implementation.
186 
187   void executePostLayoutBinding(MCAssembler &Asm,
188                                 const MCAsmLayout &Layout) override;
189 
190   bool isSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
191                                               const MCSymbol &SymA,
192                                               const MCFragment &FB, bool InSet,
193                                               bool IsPCRel) const override;
194 
195   bool isWeak(const MCSymbol &Sym) const override;
196 
197   void recordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
198                         const MCFragment *Fragment, const MCFixup &Fixup,
199                         MCValue Target, bool &IsPCRel,
200                         uint64_t &FixedValue) override;
201 
202   void writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
203 };
204 
205 } // end anonymous namespace
206 
207 static inline void write_uint32_le(void *Data, uint32_t Value) {
208   support::endian::write<uint32_t, support::little, support::unaligned>(Data,
209                                                                         Value);
210 }
211 
212 //------------------------------------------------------------------------------
213 // Symbol class implementation
214 
215 COFFSymbol::COFFSymbol(StringRef name) : Name(name.begin(), name.end()) {
216   memset(&Data, 0, sizeof(Data));
217 }
218 
219 // In the case that the name does not fit within 8 bytes, the offset
220 // into the string table is stored in the last 4 bytes instead, leaving
221 // the first 4 bytes as 0.
222 void COFFSymbol::set_name_offset(uint32_t Offset) {
223   write_uint32_le(Data.Name + 0, 0);
224   write_uint32_le(Data.Name + 4, Offset);
225 }
226 
227 //------------------------------------------------------------------------------
228 // Section class implementation
229 
230 COFFSection::COFFSection(StringRef name) : Name(name) {
231   memset(&Header, 0, sizeof(Header));
232 }
233 
234 //------------------------------------------------------------------------------
235 // WinCOFFObjectWriter class implementation
236 
237 WinCOFFObjectWriter::WinCOFFObjectWriter(MCWinCOFFObjectTargetWriter *MOTW,
238                                          raw_pwrite_stream &OS)
239     : MCObjectWriter(OS, true), TargetObjectWriter(MOTW) {
240   memset(&Header, 0, sizeof(Header));
241 
242   Header.Machine = TargetObjectWriter->getMachine();
243 }
244 
245 COFFSymbol *WinCOFFObjectWriter::createSymbol(StringRef Name) {
246   return createCOFFEntity<COFFSymbol>(Name, Symbols);
247 }
248 
249 COFFSymbol *WinCOFFObjectWriter::GetOrCreateCOFFSymbol(const MCSymbol *Symbol) {
250   symbol_map::iterator i = SymbolMap.find(Symbol);
251   if (i != SymbolMap.end())
252     return i->second;
253   COFFSymbol *RetSymbol =
254       createCOFFEntity<COFFSymbol>(Symbol->getName(), Symbols);
255   SymbolMap[Symbol] = RetSymbol;
256   return RetSymbol;
257 }
258 
259 COFFSection *WinCOFFObjectWriter::createSection(StringRef Name) {
260   return createCOFFEntity<COFFSection>(Name, Sections);
261 }
262 
263 /// A template used to lookup or create a symbol/section, and initialize it if
264 /// needed.
265 template <typename object_t, typename list_t>
266 object_t *WinCOFFObjectWriter::createCOFFEntity(StringRef Name, list_t &List) {
267   List.push_back(make_unique<object_t>(Name));
268 
269   return List.back().get();
270 }
271 
272 /// This function takes a section data object from the assembler
273 /// and creates the associated COFF section staging object.
274 void WinCOFFObjectWriter::defineSection(MCSectionCOFF const &Sec) {
275   COFFSection *coff_section = createSection(Sec.getSectionName());
276   COFFSymbol *coff_symbol = createSymbol(Sec.getSectionName());
277   if (Sec.getSelection() != COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE) {
278     if (const MCSymbol *S = Sec.getCOMDATSymbol()) {
279       COFFSymbol *COMDATSymbol = GetOrCreateCOFFSymbol(S);
280       if (COMDATSymbol->Section)
281         report_fatal_error("two sections have the same comdat");
282       COMDATSymbol->Section = coff_section;
283     }
284   }
285 
286   coff_section->Symbol = coff_symbol;
287   coff_symbol->Section = coff_section;
288   coff_symbol->Data.StorageClass = COFF::IMAGE_SYM_CLASS_STATIC;
289 
290   // In this case the auxiliary symbol is a Section Definition.
291   coff_symbol->Aux.resize(1);
292   memset(&coff_symbol->Aux[0], 0, sizeof(coff_symbol->Aux[0]));
293   coff_symbol->Aux[0].AuxType = ATSectionDefinition;
294   coff_symbol->Aux[0].Aux.SectionDefinition.Selection = Sec.getSelection();
295 
296   coff_section->Header.Characteristics = Sec.getCharacteristics();
297 
298   uint32_t &Characteristics = coff_section->Header.Characteristics;
299   switch (Sec.getAlignment()) {
300   case 1:
301     Characteristics |= COFF::IMAGE_SCN_ALIGN_1BYTES;
302     break;
303   case 2:
304     Characteristics |= COFF::IMAGE_SCN_ALIGN_2BYTES;
305     break;
306   case 4:
307     Characteristics |= COFF::IMAGE_SCN_ALIGN_4BYTES;
308     break;
309   case 8:
310     Characteristics |= COFF::IMAGE_SCN_ALIGN_8BYTES;
311     break;
312   case 16:
313     Characteristics |= COFF::IMAGE_SCN_ALIGN_16BYTES;
314     break;
315   case 32:
316     Characteristics |= COFF::IMAGE_SCN_ALIGN_32BYTES;
317     break;
318   case 64:
319     Characteristics |= COFF::IMAGE_SCN_ALIGN_64BYTES;
320     break;
321   case 128:
322     Characteristics |= COFF::IMAGE_SCN_ALIGN_128BYTES;
323     break;
324   case 256:
325     Characteristics |= COFF::IMAGE_SCN_ALIGN_256BYTES;
326     break;
327   case 512:
328     Characteristics |= COFF::IMAGE_SCN_ALIGN_512BYTES;
329     break;
330   case 1024:
331     Characteristics |= COFF::IMAGE_SCN_ALIGN_1024BYTES;
332     break;
333   case 2048:
334     Characteristics |= COFF::IMAGE_SCN_ALIGN_2048BYTES;
335     break;
336   case 4096:
337     Characteristics |= COFF::IMAGE_SCN_ALIGN_4096BYTES;
338     break;
339   case 8192:
340     Characteristics |= COFF::IMAGE_SCN_ALIGN_8192BYTES;
341     break;
342   default:
343     llvm_unreachable("unsupported section alignment");
344   }
345 
346   // Bind internal COFF section to MC section.
347   coff_section->MCSection = &Sec;
348   SectionMap[&Sec] = coff_section;
349 }
350 
351 static uint64_t getSymbolValue(const MCSymbol &Symbol,
352                                const MCAsmLayout &Layout) {
353   if (Symbol.isCommon() && Symbol.isExternal())
354     return Symbol.getCommonSize();
355 
356   uint64_t Res;
357   if (!Layout.getSymbolOffset(Symbol, Res))
358     return 0;
359 
360   return Res;
361 }
362 
363 COFFSymbol *WinCOFFObjectWriter::getLinkedSymbol(const MCSymbol &Symbol) {
364   if (!Symbol.isVariable())
365     return nullptr;
366 
367   const MCSymbolRefExpr *SymRef =
368       dyn_cast<MCSymbolRefExpr>(Symbol.getVariableValue());
369   if (!SymRef)
370     return nullptr;
371 
372   const MCSymbol &Aliasee = SymRef->getSymbol();
373   if (!Aliasee.isUndefined())
374     return nullptr;
375   return GetOrCreateCOFFSymbol(&Aliasee);
376 }
377 
378 /// This function takes a symbol data object from the assembler
379 /// and creates the associated COFF symbol staging object.
380 void WinCOFFObjectWriter::DefineSymbol(const MCSymbol &Symbol,
381                                        MCAssembler &Assembler,
382                                        const MCAsmLayout &Layout) {
383   COFFSymbol *coff_symbol = GetOrCreateCOFFSymbol(&Symbol);
384   const MCSymbol *Base = Layout.getBaseSymbol(Symbol);
385   COFFSection *Sec = nullptr;
386   if (Base && Base->getFragment()) {
387     Sec = SectionMap[Base->getFragment()->getParent()];
388     if (coff_symbol->Section && coff_symbol->Section != Sec)
389       report_fatal_error("conflicting sections for symbol");
390   }
391 
392   COFFSymbol *Local = nullptr;
393   if (cast<MCSymbolCOFF>(Symbol).isWeakExternal()) {
394     coff_symbol->Data.StorageClass = COFF::IMAGE_SYM_CLASS_WEAK_EXTERNAL;
395 
396     COFFSymbol *WeakDefault = getLinkedSymbol(Symbol);
397     if (!WeakDefault) {
398       std::string WeakName = (".weak." + Symbol.getName() + ".default").str();
399       WeakDefault = createSymbol(WeakName);
400       if (!Sec)
401         WeakDefault->Data.SectionNumber = COFF::IMAGE_SYM_ABSOLUTE;
402       else
403         WeakDefault->Section = Sec;
404       Local = WeakDefault;
405     }
406 
407     coff_symbol->Other = WeakDefault;
408 
409     // Setup the Weak External auxiliary symbol.
410     coff_symbol->Aux.resize(1);
411     memset(&coff_symbol->Aux[0], 0, sizeof(coff_symbol->Aux[0]));
412     coff_symbol->Aux[0].AuxType = ATWeakExternal;
413     coff_symbol->Aux[0].Aux.WeakExternal.TagIndex = 0;
414     coff_symbol->Aux[0].Aux.WeakExternal.Characteristics =
415         COFF::IMAGE_WEAK_EXTERN_SEARCH_LIBRARY;
416   } else {
417     if (!Base)
418       coff_symbol->Data.SectionNumber = COFF::IMAGE_SYM_ABSOLUTE;
419     else
420       coff_symbol->Section = Sec;
421     Local = coff_symbol;
422   }
423 
424   if (Local) {
425     Local->Data.Value = getSymbolValue(Symbol, Layout);
426 
427     const MCSymbolCOFF &SymbolCOFF = cast<MCSymbolCOFF>(Symbol);
428     Local->Data.Type = SymbolCOFF.getType();
429     Local->Data.StorageClass = SymbolCOFF.getClass();
430 
431     // If no storage class was specified in the streamer, define it here.
432     if (Local->Data.StorageClass == COFF::IMAGE_SYM_CLASS_NULL) {
433       bool IsExternal = Symbol.isExternal() ||
434                         (!Symbol.getFragment() && !Symbol.isVariable());
435 
436       Local->Data.StorageClass = IsExternal ? COFF::IMAGE_SYM_CLASS_EXTERNAL
437                                             : COFF::IMAGE_SYM_CLASS_STATIC;
438     }
439   }
440 
441   coff_symbol->MC = &Symbol;
442 }
443 
444 // Maximum offsets for different string table entry encodings.
445 enum : unsigned { Max7DecimalOffset = 9999999U };
446 enum : uint64_t { MaxBase64Offset = 0xFFFFFFFFFULL }; // 64^6, including 0
447 
448 // Encode a string table entry offset in base 64, padded to 6 chars, and
449 // prefixed with a double slash: '//AAAAAA', '//AAAAAB', ...
450 // Buffer must be at least 8 bytes large. No terminating null appended.
451 static void encodeBase64StringEntry(char *Buffer, uint64_t Value) {
452   assert(Value > Max7DecimalOffset && Value <= MaxBase64Offset &&
453          "Illegal section name encoding for value");
454 
455   static const char Alphabet[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
456                                  "abcdefghijklmnopqrstuvwxyz"
457                                  "0123456789+/";
458 
459   Buffer[0] = '/';
460   Buffer[1] = '/';
461 
462   char *Ptr = Buffer + 7;
463   for (unsigned i = 0; i < 6; ++i) {
464     unsigned Rem = Value % 64;
465     Value /= 64;
466     *(Ptr--) = Alphabet[Rem];
467   }
468 }
469 
470 void WinCOFFObjectWriter::SetSectionName(COFFSection &S) {
471   if (S.Name.size() > COFF::NameSize) {
472     uint64_t StringTableEntry = Strings.getOffset(S.Name);
473 
474     if (StringTableEntry <= Max7DecimalOffset) {
475       SmallVector<char, COFF::NameSize> Buffer;
476       Twine('/').concat(Twine(StringTableEntry)).toVector(Buffer);
477       assert(Buffer.size() <= COFF::NameSize && Buffer.size() >= 2);
478 
479       std::memcpy(S.Header.Name, Buffer.data(), Buffer.size());
480     } else if (StringTableEntry <= MaxBase64Offset) {
481       // Starting with 10,000,000, offsets are encoded as base64.
482       encodeBase64StringEntry(S.Header.Name, StringTableEntry);
483     } else {
484       report_fatal_error("COFF string table is greater than 64 GB.");
485     }
486   } else {
487     std::memcpy(S.Header.Name, S.Name.c_str(), S.Name.size());
488   }
489 }
490 
491 void WinCOFFObjectWriter::SetSymbolName(COFFSymbol &S) {
492   if (S.Name.size() > COFF::NameSize)
493     S.set_name_offset(Strings.getOffset(S.Name));
494   else
495     std::memcpy(S.Data.Name, S.Name.c_str(), S.Name.size());
496 }
497 
498 bool WinCOFFObjectWriter::IsPhysicalSection(COFFSection *S) {
499   return (S->Header.Characteristics & COFF::IMAGE_SCN_CNT_UNINITIALIZED_DATA) ==
500          0;
501 }
502 
503 //------------------------------------------------------------------------------
504 // entity writing methods
505 
506 void WinCOFFObjectWriter::WriteFileHeader(const COFF::header &Header) {
507   if (UseBigObj) {
508     writeLE16(COFF::IMAGE_FILE_MACHINE_UNKNOWN);
509     writeLE16(0xFFFF);
510     writeLE16(COFF::BigObjHeader::MinBigObjectVersion);
511     writeLE16(Header.Machine);
512     writeLE32(Header.TimeDateStamp);
513     writeBytes(StringRef(COFF::BigObjMagic, sizeof(COFF::BigObjMagic)));
514     writeLE32(0);
515     writeLE32(0);
516     writeLE32(0);
517     writeLE32(0);
518     writeLE32(Header.NumberOfSections);
519     writeLE32(Header.PointerToSymbolTable);
520     writeLE32(Header.NumberOfSymbols);
521   } else {
522     writeLE16(Header.Machine);
523     writeLE16(static_cast<int16_t>(Header.NumberOfSections));
524     writeLE32(Header.TimeDateStamp);
525     writeLE32(Header.PointerToSymbolTable);
526     writeLE32(Header.NumberOfSymbols);
527     writeLE16(Header.SizeOfOptionalHeader);
528     writeLE16(Header.Characteristics);
529   }
530 }
531 
532 void WinCOFFObjectWriter::WriteSymbol(const COFFSymbol &S) {
533   writeBytes(StringRef(S.Data.Name, COFF::NameSize));
534   writeLE32(S.Data.Value);
535   if (UseBigObj)
536     writeLE32(S.Data.SectionNumber);
537   else
538     writeLE16(static_cast<int16_t>(S.Data.SectionNumber));
539   writeLE16(S.Data.Type);
540   write8(S.Data.StorageClass);
541   write8(S.Data.NumberOfAuxSymbols);
542   WriteAuxiliarySymbols(S.Aux);
543 }
544 
545 void WinCOFFObjectWriter::WriteAuxiliarySymbols(
546     const COFFSymbol::AuxiliarySymbols &S) {
547   for (const AuxSymbol &i : S) {
548     switch (i.AuxType) {
549     case ATFunctionDefinition:
550       writeLE32(i.Aux.FunctionDefinition.TagIndex);
551       writeLE32(i.Aux.FunctionDefinition.TotalSize);
552       writeLE32(i.Aux.FunctionDefinition.PointerToLinenumber);
553       writeLE32(i.Aux.FunctionDefinition.PointerToNextFunction);
554       WriteZeros(sizeof(i.Aux.FunctionDefinition.unused));
555       if (UseBigObj)
556         WriteZeros(COFF::Symbol32Size - COFF::Symbol16Size);
557       break;
558     case ATbfAndefSymbol:
559       WriteZeros(sizeof(i.Aux.bfAndefSymbol.unused1));
560       writeLE16(i.Aux.bfAndefSymbol.Linenumber);
561       WriteZeros(sizeof(i.Aux.bfAndefSymbol.unused2));
562       writeLE32(i.Aux.bfAndefSymbol.PointerToNextFunction);
563       WriteZeros(sizeof(i.Aux.bfAndefSymbol.unused3));
564       if (UseBigObj)
565         WriteZeros(COFF::Symbol32Size - COFF::Symbol16Size);
566       break;
567     case ATWeakExternal:
568       writeLE32(i.Aux.WeakExternal.TagIndex);
569       writeLE32(i.Aux.WeakExternal.Characteristics);
570       WriteZeros(sizeof(i.Aux.WeakExternal.unused));
571       if (UseBigObj)
572         WriteZeros(COFF::Symbol32Size - COFF::Symbol16Size);
573       break;
574     case ATFile:
575       writeBytes(
576           StringRef(reinterpret_cast<const char *>(&i.Aux),
577                     UseBigObj ? COFF::Symbol32Size : COFF::Symbol16Size));
578       break;
579     case ATSectionDefinition:
580       writeLE32(i.Aux.SectionDefinition.Length);
581       writeLE16(i.Aux.SectionDefinition.NumberOfRelocations);
582       writeLE16(i.Aux.SectionDefinition.NumberOfLinenumbers);
583       writeLE32(i.Aux.SectionDefinition.CheckSum);
584       writeLE16(static_cast<int16_t>(i.Aux.SectionDefinition.Number));
585       write8(i.Aux.SectionDefinition.Selection);
586       WriteZeros(sizeof(i.Aux.SectionDefinition.unused));
587       writeLE16(static_cast<int16_t>(i.Aux.SectionDefinition.Number >> 16));
588       if (UseBigObj)
589         WriteZeros(COFF::Symbol32Size - COFF::Symbol16Size);
590       break;
591     }
592   }
593 }
594 
595 void WinCOFFObjectWriter::writeSectionHeader(const COFF::section &S) {
596   writeBytes(StringRef(S.Name, COFF::NameSize));
597 
598   writeLE32(S.VirtualSize);
599   writeLE32(S.VirtualAddress);
600   writeLE32(S.SizeOfRawData);
601   writeLE32(S.PointerToRawData);
602   writeLE32(S.PointerToRelocations);
603   writeLE32(S.PointerToLineNumbers);
604   writeLE16(S.NumberOfRelocations);
605   writeLE16(S.NumberOfLineNumbers);
606   writeLE32(S.Characteristics);
607 }
608 
609 void WinCOFFObjectWriter::WriteRelocation(const COFF::relocation &R) {
610   writeLE32(R.VirtualAddress);
611   writeLE32(R.SymbolTableIndex);
612   writeLE16(R.Type);
613 }
614 
615 ////////////////////////////////////////////////////////////////////////////////
616 // MCObjectWriter interface implementations
617 
618 void WinCOFFObjectWriter::executePostLayoutBinding(MCAssembler &Asm,
619                                                    const MCAsmLayout &Layout) {
620   // "Define" each section & symbol. This creates section & symbol
621   // entries in the staging area.
622   for (const auto &Section : Asm)
623     defineSection(static_cast<const MCSectionCOFF &>(Section));
624 
625   for (const MCSymbol &Symbol : Asm.symbols())
626     if (!Symbol.isTemporary())
627       DefineSymbol(Symbol, Asm, Layout);
628 }
629 
630 bool WinCOFFObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(
631     const MCAssembler &Asm, const MCSymbol &SymA, const MCFragment &FB,
632     bool InSet, bool IsPCRel) const {
633   // MS LINK expects to be able to replace all references to a function with a
634   // thunk to implement their /INCREMENTAL feature.  Make sure we don't optimize
635   // away any relocations to functions.
636   uint16_t Type = cast<MCSymbolCOFF>(SymA).getType();
637   if (Asm.isIncrementalLinkerCompatible() &&
638       (Type >> COFF::SCT_COMPLEX_TYPE_SHIFT) == COFF::IMAGE_SYM_DTYPE_FUNCTION)
639     return false;
640   return MCObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(Asm, SymA, FB,
641                                                                 InSet, IsPCRel);
642 }
643 
644 bool WinCOFFObjectWriter::isWeak(const MCSymbol &Sym) const {
645   if (!Sym.isExternal())
646     return false;
647 
648   if (!Sym.isInSection())
649     return false;
650 
651   const auto &Sec = cast<MCSectionCOFF>(Sym.getSection());
652   if (!Sec.getCOMDATSymbol())
653     return false;
654 
655   // It looks like for COFF it is invalid to replace a reference to a global
656   // in a comdat with a reference to a local.
657   // FIXME: Add a specification reference if available.
658   return true;
659 }
660 
661 void WinCOFFObjectWriter::recordRelocation(
662     MCAssembler &Asm, const MCAsmLayout &Layout, const MCFragment *Fragment,
663     const MCFixup &Fixup, MCValue Target, bool &IsPCRel, uint64_t &FixedValue) {
664   assert(Target.getSymA() && "Relocation must reference a symbol!");
665 
666   const MCSymbol &A = Target.getSymA()->getSymbol();
667   if (!A.isRegistered()) {
668     Asm.getContext().reportError(Fixup.getLoc(),
669                                       Twine("symbol '") + A.getName() +
670                                           "' can not be undefined");
671     return;
672   }
673   if (A.isTemporary() && A.isUndefined()) {
674     Asm.getContext().reportError(Fixup.getLoc(),
675                                       Twine("assembler label '") + A.getName() +
676                                           "' can not be undefined");
677     return;
678   }
679 
680   MCSection *Section = Fragment->getParent();
681 
682   // Mark this symbol as requiring an entry in the symbol table.
683   assert(SectionMap.find(Section) != SectionMap.end() &&
684          "Section must already have been defined in executePostLayoutBinding!");
685 
686   COFFSection *coff_section = SectionMap[Section];
687   const MCSymbolRefExpr *SymB = Target.getSymB();
688   bool CrossSection = false;
689 
690   if (SymB) {
691     const MCSymbol *B = &SymB->getSymbol();
692     if (!B->getFragment()) {
693       Asm.getContext().reportError(
694           Fixup.getLoc(),
695           Twine("symbol '") + B->getName() +
696               "' can not be undefined in a subtraction expression");
697       return;
698     }
699 
700     if (!A.getFragment()) {
701       Asm.getContext().reportError(
702           Fixup.getLoc(),
703           Twine("symbol '") + A.getName() +
704               "' can not be undefined in a subtraction expression");
705       return;
706     }
707 
708     CrossSection = &A.getSection() != &B->getSection();
709 
710     // Offset of the symbol in the section
711     int64_t OffsetOfB = Layout.getSymbolOffset(*B);
712 
713     // In the case where we have SymbA and SymB, we just need to store the delta
714     // between the two symbols.  Update FixedValue to account for the delta, and
715     // skip recording the relocation.
716     if (!CrossSection) {
717       int64_t OffsetOfA = Layout.getSymbolOffset(A);
718       FixedValue = (OffsetOfA - OffsetOfB) + Target.getConstant();
719       return;
720     }
721 
722     // Offset of the relocation in the section
723     int64_t OffsetOfRelocation =
724         Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
725 
726     FixedValue = (OffsetOfRelocation - OffsetOfB) + Target.getConstant();
727   } else {
728     FixedValue = Target.getConstant();
729   }
730 
731   COFFRelocation Reloc;
732 
733   Reloc.Data.SymbolTableIndex = 0;
734   Reloc.Data.VirtualAddress = Layout.getFragmentOffset(Fragment);
735 
736   // Turn relocations for temporary symbols into section relocations.
737   if (A.isTemporary() || CrossSection) {
738     MCSection *TargetSection = &A.getSection();
739     assert(
740         SectionMap.find(TargetSection) != SectionMap.end() &&
741         "Section must already have been defined in executePostLayoutBinding!");
742     Reloc.Symb = SectionMap[TargetSection]->Symbol;
743     FixedValue += Layout.getSymbolOffset(A);
744   } else {
745     assert(
746         SymbolMap.find(&A) != SymbolMap.end() &&
747         "Symbol must already have been defined in executePostLayoutBinding!");
748     Reloc.Symb = SymbolMap[&A];
749   }
750 
751   ++Reloc.Symb->Relocations;
752 
753   Reloc.Data.VirtualAddress += Fixup.getOffset();
754   Reloc.Data.Type = TargetObjectWriter->getRelocType(
755       Target, Fixup, CrossSection, Asm.getBackend());
756 
757   // FIXME: Can anyone explain what this does other than adjust for the size
758   // of the offset?
759   if ((Header.Machine == COFF::IMAGE_FILE_MACHINE_AMD64 &&
760        Reloc.Data.Type == COFF::IMAGE_REL_AMD64_REL32) ||
761       (Header.Machine == COFF::IMAGE_FILE_MACHINE_I386 &&
762        Reloc.Data.Type == COFF::IMAGE_REL_I386_REL32))
763     FixedValue += 4;
764 
765   if (Header.Machine == COFF::IMAGE_FILE_MACHINE_ARMNT) {
766     switch (Reloc.Data.Type) {
767     case COFF::IMAGE_REL_ARM_ABSOLUTE:
768     case COFF::IMAGE_REL_ARM_ADDR32:
769     case COFF::IMAGE_REL_ARM_ADDR32NB:
770     case COFF::IMAGE_REL_ARM_TOKEN:
771     case COFF::IMAGE_REL_ARM_SECTION:
772     case COFF::IMAGE_REL_ARM_SECREL:
773       break;
774     case COFF::IMAGE_REL_ARM_BRANCH11:
775     case COFF::IMAGE_REL_ARM_BLX11:
776     // IMAGE_REL_ARM_BRANCH11 and IMAGE_REL_ARM_BLX11 are only used for
777     // pre-ARMv7, which implicitly rules it out of ARMNT (it would be valid
778     // for Windows CE).
779     case COFF::IMAGE_REL_ARM_BRANCH24:
780     case COFF::IMAGE_REL_ARM_BLX24:
781     case COFF::IMAGE_REL_ARM_MOV32A:
782       // IMAGE_REL_ARM_BRANCH24, IMAGE_REL_ARM_BLX24, IMAGE_REL_ARM_MOV32A are
783       // only used for ARM mode code, which is documented as being unsupported
784       // by Windows on ARM.  Empirical proof indicates that masm is able to
785       // generate the relocations however the rest of the MSVC toolchain is
786       // unable to handle it.
787       llvm_unreachable("unsupported relocation");
788       break;
789     case COFF::IMAGE_REL_ARM_MOV32T:
790       break;
791     case COFF::IMAGE_REL_ARM_BRANCH20T:
792     case COFF::IMAGE_REL_ARM_BRANCH24T:
793     case COFF::IMAGE_REL_ARM_BLX23T:
794       // IMAGE_REL_BRANCH20T, IMAGE_REL_ARM_BRANCH24T, IMAGE_REL_ARM_BLX23T all
795       // perform a 4 byte adjustment to the relocation.  Relative branches are
796       // offset by 4 on ARM, however, because there is no RELA relocations, all
797       // branches are offset by 4.
798       FixedValue = FixedValue + 4;
799       break;
800     }
801   }
802 
803   // The fixed value never makes sense for section indices, ignore it.
804   if (Fixup.getKind() == FK_SecRel_2)
805     FixedValue = 0;
806 
807   if (TargetObjectWriter->recordRelocation(Fixup))
808     coff_section->Relocations.push_back(Reloc);
809 }
810 
811 void WinCOFFObjectWriter::writeObject(MCAssembler &Asm,
812                                       const MCAsmLayout &Layout) {
813   size_t SectionsSize = Sections.size();
814   if (SectionsSize > static_cast<size_t>(INT32_MAX))
815     report_fatal_error(
816         "PE COFF object files can't have more than 2147483647 sections");
817 
818   // Assign symbol and section indexes and offsets.
819   int32_t NumberOfSections = static_cast<int32_t>(SectionsSize);
820 
821   UseBigObj = NumberOfSections > COFF::MaxNumberOfSections16;
822 
823   // Assign section numbers.
824   size_t Number = 1;
825   for (const auto &Section : Sections) {
826     Section->Number = Number;
827     Section->Symbol->Data.SectionNumber = Number;
828     Section->Symbol->Aux[0].Aux.SectionDefinition.Number = Number;
829     ++Number;
830   }
831 
832   Header.NumberOfSections = NumberOfSections;
833   Header.NumberOfSymbols = 0;
834 
835   for (const std::string &Name : Asm.getFileNames()) {
836     // round up to calculate the number of auxiliary symbols required
837     unsigned SymbolSize = UseBigObj ? COFF::Symbol32Size : COFF::Symbol16Size;
838     unsigned Count = (Name.size() + SymbolSize - 1) / SymbolSize;
839 
840     COFFSymbol *file = createSymbol(".file");
841     file->Data.SectionNumber = COFF::IMAGE_SYM_DEBUG;
842     file->Data.StorageClass = COFF::IMAGE_SYM_CLASS_FILE;
843     file->Aux.resize(Count);
844 
845     unsigned Offset = 0;
846     unsigned Length = Name.size();
847     for (auto &Aux : file->Aux) {
848       Aux.AuxType = ATFile;
849 
850       if (Length > SymbolSize) {
851         memcpy(&Aux.Aux, Name.c_str() + Offset, SymbolSize);
852         Length = Length - SymbolSize;
853       } else {
854         memcpy(&Aux.Aux, Name.c_str() + Offset, Length);
855         memset((char *)&Aux.Aux + Length, 0, SymbolSize - Length);
856         break;
857       }
858 
859       Offset += SymbolSize;
860     }
861   }
862 
863   for (auto &Symbol : Symbols) {
864     // Update section number & offset for symbols that have them.
865     if (Symbol->Section)
866       Symbol->Data.SectionNumber = Symbol->Section->Number;
867     Symbol->setIndex(Header.NumberOfSymbols++);
868     // Update auxiliary symbol info.
869     Symbol->Data.NumberOfAuxSymbols = Symbol->Aux.size();
870     Header.NumberOfSymbols += Symbol->Data.NumberOfAuxSymbols;
871   }
872 
873   // Build string table.
874   for (const auto &S : Sections)
875     if (S->Name.size() > COFF::NameSize)
876       Strings.add(S->Name);
877   for (const auto &S : Symbols)
878     if (S->Name.size() > COFF::NameSize)
879       Strings.add(S->Name);
880   Strings.finalize();
881 
882   // Set names.
883   for (const auto &S : Sections)
884     SetSectionName(*S);
885   for (auto &S : Symbols)
886     SetSymbolName(*S);
887 
888   // Fixup weak external references.
889   for (auto &Symbol : Symbols) {
890     if (Symbol->Other) {
891       assert(Symbol->getIndex() != -1);
892       assert(Symbol->Aux.size() == 1 && "Symbol must contain one aux symbol!");
893       assert(Symbol->Aux[0].AuxType == ATWeakExternal &&
894              "Symbol's aux symbol must be a Weak External!");
895       Symbol->Aux[0].Aux.WeakExternal.TagIndex = Symbol->Other->getIndex();
896     }
897   }
898 
899   // Fixup associative COMDAT sections.
900   for (auto &Section : Sections) {
901     if (Section->Symbol->Aux[0].Aux.SectionDefinition.Selection !=
902         COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE)
903       continue;
904 
905     const MCSectionCOFF &MCSec = *Section->MCSection;
906 
907     const MCSymbol *COMDAT = MCSec.getCOMDATSymbol();
908     assert(COMDAT);
909     COFFSymbol *COMDATSymbol = GetOrCreateCOFFSymbol(COMDAT);
910     assert(COMDATSymbol);
911     COFFSection *Assoc = COMDATSymbol->Section;
912     if (!Assoc)
913       report_fatal_error(
914           Twine("Missing associated COMDAT section for section ") +
915           MCSec.getSectionName());
916 
917     // Skip this section if the associated section is unused.
918     if (Assoc->Number == -1)
919       continue;
920 
921     Section->Symbol->Aux[0].Aux.SectionDefinition.Number = Assoc->Number;
922   }
923 
924   // Assign file offsets to COFF object file structures.
925 
926   unsigned offset = getInitialOffset();
927 
928   if (UseBigObj)
929     offset += COFF::Header32Size;
930   else
931     offset += COFF::Header16Size;
932   offset += COFF::SectionSize * Header.NumberOfSections;
933 
934   for (const auto &Section : Asm) {
935     COFFSection *Sec = SectionMap[&Section];
936 
937     if (Sec->Number == -1)
938       continue;
939 
940     Sec->Header.SizeOfRawData = Layout.getSectionAddressSize(&Section);
941 
942     if (IsPhysicalSection(Sec)) {
943       // Align the section data to a four byte boundary.
944       offset = alignTo(offset, 4);
945       Sec->Header.PointerToRawData = offset;
946 
947       offset += Sec->Header.SizeOfRawData;
948     }
949 
950     if (!Sec->Relocations.empty()) {
951       bool RelocationsOverflow = Sec->Relocations.size() >= 0xffff;
952 
953       if (RelocationsOverflow) {
954         // Signal overflow by setting NumberOfRelocations to max value. Actual
955         // size is found in reloc #0. Microsoft tools understand this.
956         Sec->Header.NumberOfRelocations = 0xffff;
957       } else {
958         Sec->Header.NumberOfRelocations = Sec->Relocations.size();
959       }
960       Sec->Header.PointerToRelocations = offset;
961 
962       if (RelocationsOverflow) {
963         // Reloc #0 will contain actual count, so make room for it.
964         offset += COFF::RelocationSize;
965       }
966 
967       offset += COFF::RelocationSize * Sec->Relocations.size();
968 
969       for (auto &Relocation : Sec->Relocations) {
970         assert(Relocation.Symb->getIndex() != -1);
971         Relocation.Data.SymbolTableIndex = Relocation.Symb->getIndex();
972       }
973     }
974 
975     assert(Sec->Symbol->Aux.size() == 1 &&
976            "Section's symbol must have one aux!");
977     AuxSymbol &Aux = Sec->Symbol->Aux[0];
978     assert(Aux.AuxType == ATSectionDefinition &&
979            "Section's symbol's aux symbol must be a Section Definition!");
980     Aux.Aux.SectionDefinition.Length = Sec->Header.SizeOfRawData;
981     Aux.Aux.SectionDefinition.NumberOfRelocations =
982         Sec->Header.NumberOfRelocations;
983     Aux.Aux.SectionDefinition.NumberOfLinenumbers =
984         Sec->Header.NumberOfLineNumbers;
985   }
986 
987   Header.PointerToSymbolTable = offset;
988 
989   // MS LINK expects to be able to use this timestamp to implement their
990   // /INCREMENTAL feature.
991   if (Asm.isIncrementalLinkerCompatible()) {
992     std::time_t Now = time(nullptr);
993     if (Now < 0 || !isUInt<32>(Now))
994       Now = UINT32_MAX;
995     Header.TimeDateStamp = Now;
996   } else {
997     // Have deterministic output if /INCREMENTAL isn't needed. Also matches GNU.
998     Header.TimeDateStamp = 0;
999   }
1000 
1001   // Write it all to disk...
1002   WriteFileHeader(Header);
1003 
1004   {
1005     sections::iterator i, ie;
1006     MCAssembler::iterator j, je;
1007 
1008     for (auto &Section : Sections) {
1009       if (Section->Number != -1) {
1010         if (Section->Relocations.size() >= 0xffff)
1011           Section->Header.Characteristics |= COFF::IMAGE_SCN_LNK_NRELOC_OVFL;
1012         writeSectionHeader(Section->Header);
1013       }
1014     }
1015 
1016     SmallVector<char, 128> SectionContents;
1017     for (i = Sections.begin(), ie = Sections.end(), j = Asm.begin(),
1018         je = Asm.end();
1019          (i != ie) && (j != je); ++i, ++j) {
1020 
1021       if ((*i)->Number == -1)
1022         continue;
1023 
1024       if ((*i)->Header.PointerToRawData != 0) {
1025         assert(getStream().tell() <= (*i)->Header.PointerToRawData &&
1026                "Section::PointerToRawData is insane!");
1027 
1028         unsigned SectionDataPadding =
1029             (*i)->Header.PointerToRawData - getStream().tell();
1030         assert(SectionDataPadding < 4 &&
1031                "Should only need at most three bytes of padding!");
1032 
1033         WriteZeros(SectionDataPadding);
1034 
1035         // Save the contents of the section to a temporary buffer, we need this
1036         // to CRC the data before we dump it into the object file.
1037         SectionContents.clear();
1038         raw_svector_ostream VecOS(SectionContents);
1039         raw_pwrite_stream &OldStream = getStream();
1040         // Redirect the output stream to our buffer.
1041         setStream(VecOS);
1042         // Fill our buffer with the section data.
1043         Asm.writeSectionData(&*j, Layout);
1044         // Reset the stream back to what it was before.
1045         setStream(OldStream);
1046 
1047         // Calculate our CRC with an initial value of '0', this is not how
1048         // JamCRC is specified but it aligns with the expected output.
1049         JamCRC JC(/*Init=*/0x00000000U);
1050         JC.update(SectionContents);
1051 
1052         // Write the section contents to the object file.
1053         getStream() << SectionContents;
1054 
1055         // Update the section definition auxiliary symbol to record the CRC.
1056         COFFSection *Sec = SectionMap[&*j];
1057         COFFSymbol::AuxiliarySymbols &AuxSyms = Sec->Symbol->Aux;
1058         assert(AuxSyms.size() == 1 &&
1059                AuxSyms[0].AuxType == ATSectionDefinition);
1060         AuxSymbol &SecDef = AuxSyms[0];
1061         SecDef.Aux.SectionDefinition.CheckSum = JC.getCRC();
1062       }
1063 
1064       if (!(*i)->Relocations.empty()) {
1065         assert(getStream().tell() == (*i)->Header.PointerToRelocations &&
1066                "Section::PointerToRelocations is insane!");
1067 
1068         if ((*i)->Relocations.size() >= 0xffff) {
1069           // In case of overflow, write actual relocation count as first
1070           // relocation. Including the synthetic reloc itself (+ 1).
1071           COFF::relocation r;
1072           r.VirtualAddress = (*i)->Relocations.size() + 1;
1073           r.SymbolTableIndex = 0;
1074           r.Type = 0;
1075           WriteRelocation(r);
1076         }
1077 
1078         for (const auto &Relocation : (*i)->Relocations)
1079           WriteRelocation(Relocation.Data);
1080       } else
1081         assert((*i)->Header.PointerToRelocations == 0 &&
1082                "Section::PointerToRelocations is insane!");
1083     }
1084   }
1085 
1086   assert(getStream().tell() == Header.PointerToSymbolTable &&
1087          "Header::PointerToSymbolTable is insane!");
1088 
1089   for (auto &Symbol : Symbols)
1090     if (Symbol->getIndex() != -1)
1091       WriteSymbol(*Symbol);
1092 
1093   Strings.write(getStream());
1094 }
1095 
1096 MCWinCOFFObjectTargetWriter::MCWinCOFFObjectTargetWriter(unsigned Machine_)
1097     : Machine(Machine_) {}
1098 
1099 // Pin the vtable to this file.
1100 void MCWinCOFFObjectTargetWriter::anchor() {}
1101 
1102 //------------------------------------------------------------------------------
1103 // WinCOFFObjectWriter factory function
1104 
1105 MCObjectWriter *
1106 llvm::createWinCOFFObjectWriter(MCWinCOFFObjectTargetWriter *MOTW,
1107                                 raw_pwrite_stream &OS) {
1108   return new WinCOFFObjectWriter(MOTW, OS);
1109 }
1110