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/STLExtras.h"
16 #include "llvm/ADT/SmallString.h"
17 #include "llvm/ADT/SmallVector.h"
18 #include "llvm/ADT/StringRef.h"
19 #include "llvm/ADT/Twine.h"
20 #include "llvm/BinaryFormat/COFF.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/MCFixup.h"
26 #include "llvm/MC/MCFragment.h"
27 #include "llvm/MC/MCObjectWriter.h"
28 #include "llvm/MC/MCSection.h"
29 #include "llvm/MC/MCSectionCOFF.h"
30 #include "llvm/MC/MCSymbol.h"
31 #include "llvm/MC/MCSymbolCOFF.h"
32 #include "llvm/MC/MCValue.h"
33 #include "llvm/MC/MCWinCOFFObjectWriter.h"
34 #include "llvm/MC/StringTableBuilder.h"
35 #include "llvm/Support/Casting.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 <algorithm>
42 #include <cassert>
43 #include <cstddef>
44 #include <cstdint>
45 #include <cstring>
46 #include <ctime>
47 #include <memory>
48 #include <string>
49 #include <vector>
50 
51 using namespace llvm;
52 using llvm::support::endian::write32le;
53 
54 #define DEBUG_TYPE "WinCOFFObjectWriter"
55 
56 namespace {
57 
58 using name = SmallString<COFF::NameSize>;
59 
60 enum AuxiliaryType {
61   ATFunctionDefinition,
62   ATbfAndefSymbol,
63   ATWeakExternal,
64   ATFile,
65   ATSectionDefinition
66 };
67 
68 struct AuxSymbol {
69   AuxiliaryType AuxType;
70   COFF::Auxiliary Aux;
71 };
72 
73 class COFFSection;
74 
75 class COFFSymbol {
76 public:
77   COFF::symbol Data = {};
78 
79   using AuxiliarySymbols = SmallVector<AuxSymbol, 1>;
80 
81   name Name;
82   int Index;
83   AuxiliarySymbols Aux;
84   COFFSymbol *Other = nullptr;
85   COFFSection *Section = nullptr;
86   int Relocations = 0;
87   const MCSymbol *MC = nullptr;
88 
89   COFFSymbol(StringRef Name) : Name(Name) {}
90 
91   void set_name_offset(uint32_t Offset);
92 
93   int64_t getIndex() const { return Index; }
94   void setIndex(int Value) {
95     Index = Value;
96     if (MC)
97       MC->setIndex(static_cast<uint32_t>(Value));
98   }
99 };
100 
101 // This class contains staging data for a COFF relocation entry.
102 struct COFFRelocation {
103   COFF::relocation Data;
104   COFFSymbol *Symb = nullptr;
105 
106   COFFRelocation() = default;
107 
108   static size_t size() { return COFF::RelocationSize; }
109 };
110 
111 using relocations = std::vector<COFFRelocation>;
112 
113 class COFFSection {
114 public:
115   COFF::section Header = {};
116 
117   std::string Name;
118   int Number;
119   MCSectionCOFF const *MCSection = nullptr;
120   COFFSymbol *Symbol = nullptr;
121   relocations Relocations;
122 
123   COFFSection(StringRef Name) : Name(Name) {}
124 };
125 
126 class WinCOFFObjectWriter : public MCObjectWriter {
127 public:
128   using symbols = std::vector<std::unique_ptr<COFFSymbol>>;
129   using sections = std::vector<std::unique_ptr<COFFSection>>;
130 
131   using symbol_map = DenseMap<MCSymbol const *, COFFSymbol *>;
132   using section_map = DenseMap<MCSection const *, COFFSection *>;
133 
134   std::unique_ptr<MCWinCOFFObjectTargetWriter> TargetObjectWriter;
135 
136   // Root level file contents.
137   COFF::header Header = {};
138   sections Sections;
139   symbols Symbols;
140   StringTableBuilder Strings{StringTableBuilder::WinCOFF};
141 
142   // Maps used during object file creation.
143   section_map SectionMap;
144   symbol_map SymbolMap;
145 
146   bool UseBigObj;
147 
148   WinCOFFObjectWriter(MCWinCOFFObjectTargetWriter *MOTW, raw_pwrite_stream &OS);
149 
150   void reset() override {
151     memset(&Header, 0, sizeof(Header));
152     Header.Machine = TargetObjectWriter->getMachine();
153     Sections.clear();
154     Symbols.clear();
155     Strings.clear();
156     SectionMap.clear();
157     SymbolMap.clear();
158     MCObjectWriter::reset();
159   }
160 
161   COFFSymbol *createSymbol(StringRef Name);
162   COFFSymbol *GetOrCreateCOFFSymbol(const MCSymbol *Symbol);
163   COFFSection *createSection(StringRef Name);
164 
165   void defineSection(MCSectionCOFF const &Sec);
166 
167   COFFSymbol *getLinkedSymbol(const MCSymbol &Symbol);
168   void DefineSymbol(const MCSymbol &Symbol, MCAssembler &Assembler,
169                     const MCAsmLayout &Layout);
170 
171   void SetSymbolName(COFFSymbol &S);
172   void SetSectionName(COFFSection &S);
173 
174   bool IsPhysicalSection(COFFSection *S);
175 
176   // Entity writing methods.
177 
178   void WriteFileHeader(const COFF::header &Header);
179   void WriteSymbol(const COFFSymbol &S);
180   void WriteAuxiliarySymbols(const COFFSymbol::AuxiliarySymbols &S);
181   void writeSectionHeaders();
182   void WriteRelocation(const COFF::relocation &R);
183   uint32_t writeSectionContents(MCAssembler &Asm, const MCAsmLayout &Layout,
184                                 const MCSection &MCSec);
185   void writeSection(MCAssembler &Asm, const MCAsmLayout &Layout,
186                     const COFFSection &Sec, const MCSection &MCSec);
187 
188   // MCObjectWriter interface implementation.
189 
190   void executePostLayoutBinding(MCAssembler &Asm,
191                                 const MCAsmLayout &Layout) override;
192 
193   bool isSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
194                                               const MCSymbol &SymA,
195                                               const MCFragment &FB, bool InSet,
196                                               bool IsPCRel) const override;
197 
198   void recordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
199                         const MCFragment *Fragment, const MCFixup &Fixup,
200                         MCValue Target, bool &IsPCRel,
201                         uint64_t &FixedValue) override;
202 
203   void createFileSymbols(MCAssembler &Asm);
204   void assignSectionNumbers();
205   void assignFileOffsets(MCAssembler &Asm, const MCAsmLayout &Layout);
206 
207   void writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
208 };
209 
210 } // end anonymous namespace
211 
212 //------------------------------------------------------------------------------
213 // Symbol class implementation
214 
215 // In the case that the name does not fit within 8 bytes, the offset
216 // into the string table is stored in the last 4 bytes instead, leaving
217 // the first 4 bytes as 0.
218 void COFFSymbol::set_name_offset(uint32_t Offset) {
219   write32le(Data.Name + 0, 0);
220   write32le(Data.Name + 4, Offset);
221 }
222 
223 //------------------------------------------------------------------------------
224 // WinCOFFObjectWriter class implementation
225 
226 WinCOFFObjectWriter::WinCOFFObjectWriter(MCWinCOFFObjectTargetWriter *MOTW,
227                                          raw_pwrite_stream &OS)
228     : MCObjectWriter(OS, true), TargetObjectWriter(MOTW) {
229   Header.Machine = TargetObjectWriter->getMachine();
230 }
231 
232 COFFSymbol *WinCOFFObjectWriter::createSymbol(StringRef Name) {
233   Symbols.push_back(make_unique<COFFSymbol>(Name));
234   return Symbols.back().get();
235 }
236 
237 COFFSymbol *WinCOFFObjectWriter::GetOrCreateCOFFSymbol(const MCSymbol *Symbol) {
238   COFFSymbol *&Ret = SymbolMap[Symbol];
239   if (!Ret)
240     Ret = createSymbol(Symbol->getName());
241   return Ret;
242 }
243 
244 COFFSection *WinCOFFObjectWriter::createSection(StringRef Name) {
245   Sections.emplace_back(make_unique<COFFSection>(Name));
246   return Sections.back().get();
247 }
248 
249 static uint32_t getAlignment(const MCSectionCOFF &Sec) {
250   switch (Sec.getAlignment()) {
251   case 1:
252     return COFF::IMAGE_SCN_ALIGN_1BYTES;
253   case 2:
254     return COFF::IMAGE_SCN_ALIGN_2BYTES;
255   case 4:
256     return COFF::IMAGE_SCN_ALIGN_4BYTES;
257   case 8:
258     return COFF::IMAGE_SCN_ALIGN_8BYTES;
259   case 16:
260     return COFF::IMAGE_SCN_ALIGN_16BYTES;
261   case 32:
262     return COFF::IMAGE_SCN_ALIGN_32BYTES;
263   case 64:
264     return COFF::IMAGE_SCN_ALIGN_64BYTES;
265   case 128:
266     return COFF::IMAGE_SCN_ALIGN_128BYTES;
267   case 256:
268     return COFF::IMAGE_SCN_ALIGN_256BYTES;
269   case 512:
270     return COFF::IMAGE_SCN_ALIGN_512BYTES;
271   case 1024:
272     return COFF::IMAGE_SCN_ALIGN_1024BYTES;
273   case 2048:
274     return COFF::IMAGE_SCN_ALIGN_2048BYTES;
275   case 4096:
276     return COFF::IMAGE_SCN_ALIGN_4096BYTES;
277   case 8192:
278     return COFF::IMAGE_SCN_ALIGN_8192BYTES;
279   }
280   llvm_unreachable("unsupported section alignment");
281 }
282 
283 /// This function takes a section data object from the assembler
284 /// and creates the associated COFF section staging object.
285 void WinCOFFObjectWriter::defineSection(const MCSectionCOFF &MCSec) {
286   COFFSection *Section = createSection(MCSec.getSectionName());
287   COFFSymbol *Symbol = createSymbol(MCSec.getSectionName());
288   Section->Symbol = Symbol;
289   Symbol->Section = Section;
290   Symbol->Data.StorageClass = COFF::IMAGE_SYM_CLASS_STATIC;
291 
292   // Create a COMDAT symbol if needed.
293   if (MCSec.getSelection() != COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE) {
294     if (const MCSymbol *S = MCSec.getCOMDATSymbol()) {
295       COFFSymbol *COMDATSymbol = GetOrCreateCOFFSymbol(S);
296       if (COMDATSymbol->Section)
297         report_fatal_error("two sections have the same comdat");
298       COMDATSymbol->Section = Section;
299     }
300   }
301 
302   // In this case the auxiliary symbol is a Section Definition.
303   Symbol->Aux.resize(1);
304   Symbol->Aux[0] = {};
305   Symbol->Aux[0].AuxType = ATSectionDefinition;
306   Symbol->Aux[0].Aux.SectionDefinition.Selection = MCSec.getSelection();
307 
308   // Set section alignment.
309   Section->Header.Characteristics = MCSec.getCharacteristics();
310   Section->Header.Characteristics |= getAlignment(MCSec);
311 
312   // Bind internal COFF section to MC section.
313   Section->MCSection = &MCSec;
314   SectionMap[&MCSec] = Section;
315 }
316 
317 static uint64_t getSymbolValue(const MCSymbol &Symbol,
318                                const MCAsmLayout &Layout) {
319   if (Symbol.isCommon() && Symbol.isExternal())
320     return Symbol.getCommonSize();
321 
322   uint64_t Res;
323   if (!Layout.getSymbolOffset(Symbol, Res))
324     return 0;
325 
326   return Res;
327 }
328 
329 COFFSymbol *WinCOFFObjectWriter::getLinkedSymbol(const MCSymbol &Symbol) {
330   if (!Symbol.isVariable())
331     return nullptr;
332 
333   const MCSymbolRefExpr *SymRef =
334       dyn_cast<MCSymbolRefExpr>(Symbol.getVariableValue());
335   if (!SymRef)
336     return nullptr;
337 
338   const MCSymbol &Aliasee = SymRef->getSymbol();
339   if (!Aliasee.isUndefined())
340     return nullptr;
341   return GetOrCreateCOFFSymbol(&Aliasee);
342 }
343 
344 /// This function takes a symbol data object from the assembler
345 /// and creates the associated COFF symbol staging object.
346 void WinCOFFObjectWriter::DefineSymbol(const MCSymbol &MCSym,
347                                        MCAssembler &Assembler,
348                                        const MCAsmLayout &Layout) {
349   COFFSymbol *Sym = GetOrCreateCOFFSymbol(&MCSym);
350   const MCSymbol *Base = Layout.getBaseSymbol(MCSym);
351   COFFSection *Sec = nullptr;
352   if (Base && Base->getFragment()) {
353     Sec = SectionMap[Base->getFragment()->getParent()];
354     if (Sym->Section && Sym->Section != Sec)
355       report_fatal_error("conflicting sections for symbol");
356   }
357 
358   COFFSymbol *Local = nullptr;
359   if (cast<MCSymbolCOFF>(MCSym).isWeakExternal()) {
360     Sym->Data.StorageClass = COFF::IMAGE_SYM_CLASS_WEAK_EXTERNAL;
361 
362     COFFSymbol *WeakDefault = getLinkedSymbol(MCSym);
363     if (!WeakDefault) {
364       std::string WeakName = (".weak." + MCSym.getName() + ".default").str();
365       WeakDefault = createSymbol(WeakName);
366       if (!Sec)
367         WeakDefault->Data.SectionNumber = COFF::IMAGE_SYM_ABSOLUTE;
368       else
369         WeakDefault->Section = Sec;
370       Local = WeakDefault;
371     }
372 
373     Sym->Other = WeakDefault;
374 
375     // Setup the Weak External auxiliary symbol.
376     Sym->Aux.resize(1);
377     memset(&Sym->Aux[0], 0, sizeof(Sym->Aux[0]));
378     Sym->Aux[0].AuxType = ATWeakExternal;
379     Sym->Aux[0].Aux.WeakExternal.TagIndex = 0;
380     Sym->Aux[0].Aux.WeakExternal.Characteristics =
381         COFF::IMAGE_WEAK_EXTERN_SEARCH_LIBRARY;
382   } else {
383     if (!Base)
384       Sym->Data.SectionNumber = COFF::IMAGE_SYM_ABSOLUTE;
385     else
386       Sym->Section = Sec;
387     Local = Sym;
388   }
389 
390   if (Local) {
391     Local->Data.Value = getSymbolValue(MCSym, Layout);
392 
393     const MCSymbolCOFF &SymbolCOFF = cast<MCSymbolCOFF>(MCSym);
394     Local->Data.Type = SymbolCOFF.getType();
395     Local->Data.StorageClass = SymbolCOFF.getClass();
396 
397     // If no storage class was specified in the streamer, define it here.
398     if (Local->Data.StorageClass == COFF::IMAGE_SYM_CLASS_NULL) {
399       bool IsExternal = MCSym.isExternal() ||
400                         (!MCSym.getFragment() && !MCSym.isVariable());
401 
402       Local->Data.StorageClass = IsExternal ? COFF::IMAGE_SYM_CLASS_EXTERNAL
403                                             : COFF::IMAGE_SYM_CLASS_STATIC;
404     }
405   }
406 
407   Sym->MC = &MCSym;
408 }
409 
410 // Maximum offsets for different string table entry encodings.
411 enum : unsigned { Max7DecimalOffset = 9999999U };
412 enum : uint64_t { MaxBase64Offset = 0xFFFFFFFFFULL }; // 64^6, including 0
413 
414 // Encode a string table entry offset in base 64, padded to 6 chars, and
415 // prefixed with a double slash: '//AAAAAA', '//AAAAAB', ...
416 // Buffer must be at least 8 bytes large. No terminating null appended.
417 static void encodeBase64StringEntry(char *Buffer, uint64_t Value) {
418   assert(Value > Max7DecimalOffset && Value <= MaxBase64Offset &&
419          "Illegal section name encoding for value");
420 
421   static const char Alphabet[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
422                                  "abcdefghijklmnopqrstuvwxyz"
423                                  "0123456789+/";
424 
425   Buffer[0] = '/';
426   Buffer[1] = '/';
427 
428   char *Ptr = Buffer + 7;
429   for (unsigned i = 0; i < 6; ++i) {
430     unsigned Rem = Value % 64;
431     Value /= 64;
432     *(Ptr--) = Alphabet[Rem];
433   }
434 }
435 
436 void WinCOFFObjectWriter::SetSectionName(COFFSection &S) {
437   if (S.Name.size() <= COFF::NameSize) {
438     std::memcpy(S.Header.Name, S.Name.c_str(), S.Name.size());
439     return;
440   }
441 
442   uint64_t StringTableEntry = Strings.getOffset(S.Name);
443   if (StringTableEntry <= Max7DecimalOffset) {
444     SmallVector<char, COFF::NameSize> Buffer;
445     Twine('/').concat(Twine(StringTableEntry)).toVector(Buffer);
446     assert(Buffer.size() <= COFF::NameSize && Buffer.size() >= 2);
447     std::memcpy(S.Header.Name, Buffer.data(), Buffer.size());
448     return;
449   }
450   if (StringTableEntry <= MaxBase64Offset) {
451     // Starting with 10,000,000, offsets are encoded as base64.
452     encodeBase64StringEntry(S.Header.Name, StringTableEntry);
453     return;
454   }
455   report_fatal_error("COFF string table is greater than 64 GB.");
456 }
457 
458 void WinCOFFObjectWriter::SetSymbolName(COFFSymbol &S) {
459   if (S.Name.size() > COFF::NameSize)
460     S.set_name_offset(Strings.getOffset(S.Name));
461   else
462     std::memcpy(S.Data.Name, S.Name.c_str(), S.Name.size());
463 }
464 
465 bool WinCOFFObjectWriter::IsPhysicalSection(COFFSection *S) {
466   return (S->Header.Characteristics & COFF::IMAGE_SCN_CNT_UNINITIALIZED_DATA) ==
467          0;
468 }
469 
470 //------------------------------------------------------------------------------
471 // entity writing methods
472 
473 void WinCOFFObjectWriter::WriteFileHeader(const COFF::header &Header) {
474   if (UseBigObj) {
475     writeLE16(COFF::IMAGE_FILE_MACHINE_UNKNOWN);
476     writeLE16(0xFFFF);
477     writeLE16(COFF::BigObjHeader::MinBigObjectVersion);
478     writeLE16(Header.Machine);
479     writeLE32(Header.TimeDateStamp);
480     writeBytes(StringRef(COFF::BigObjMagic, sizeof(COFF::BigObjMagic)));
481     writeLE32(0);
482     writeLE32(0);
483     writeLE32(0);
484     writeLE32(0);
485     writeLE32(Header.NumberOfSections);
486     writeLE32(Header.PointerToSymbolTable);
487     writeLE32(Header.NumberOfSymbols);
488   } else {
489     writeLE16(Header.Machine);
490     writeLE16(static_cast<int16_t>(Header.NumberOfSections));
491     writeLE32(Header.TimeDateStamp);
492     writeLE32(Header.PointerToSymbolTable);
493     writeLE32(Header.NumberOfSymbols);
494     writeLE16(Header.SizeOfOptionalHeader);
495     writeLE16(Header.Characteristics);
496   }
497 }
498 
499 void WinCOFFObjectWriter::WriteSymbol(const COFFSymbol &S) {
500   writeBytes(StringRef(S.Data.Name, COFF::NameSize));
501   writeLE32(S.Data.Value);
502   if (UseBigObj)
503     writeLE32(S.Data.SectionNumber);
504   else
505     writeLE16(static_cast<int16_t>(S.Data.SectionNumber));
506   writeLE16(S.Data.Type);
507   write8(S.Data.StorageClass);
508   write8(S.Data.NumberOfAuxSymbols);
509   WriteAuxiliarySymbols(S.Aux);
510 }
511 
512 void WinCOFFObjectWriter::WriteAuxiliarySymbols(
513     const COFFSymbol::AuxiliarySymbols &S) {
514   for (const AuxSymbol &i : S) {
515     switch (i.AuxType) {
516     case ATFunctionDefinition:
517       writeLE32(i.Aux.FunctionDefinition.TagIndex);
518       writeLE32(i.Aux.FunctionDefinition.TotalSize);
519       writeLE32(i.Aux.FunctionDefinition.PointerToLinenumber);
520       writeLE32(i.Aux.FunctionDefinition.PointerToNextFunction);
521       WriteZeros(sizeof(i.Aux.FunctionDefinition.unused));
522       if (UseBigObj)
523         WriteZeros(COFF::Symbol32Size - COFF::Symbol16Size);
524       break;
525     case ATbfAndefSymbol:
526       WriteZeros(sizeof(i.Aux.bfAndefSymbol.unused1));
527       writeLE16(i.Aux.bfAndefSymbol.Linenumber);
528       WriteZeros(sizeof(i.Aux.bfAndefSymbol.unused2));
529       writeLE32(i.Aux.bfAndefSymbol.PointerToNextFunction);
530       WriteZeros(sizeof(i.Aux.bfAndefSymbol.unused3));
531       if (UseBigObj)
532         WriteZeros(COFF::Symbol32Size - COFF::Symbol16Size);
533       break;
534     case ATWeakExternal:
535       writeLE32(i.Aux.WeakExternal.TagIndex);
536       writeLE32(i.Aux.WeakExternal.Characteristics);
537       WriteZeros(sizeof(i.Aux.WeakExternal.unused));
538       if (UseBigObj)
539         WriteZeros(COFF::Symbol32Size - COFF::Symbol16Size);
540       break;
541     case ATFile:
542       writeBytes(
543           StringRef(reinterpret_cast<const char *>(&i.Aux),
544                     UseBigObj ? COFF::Symbol32Size : COFF::Symbol16Size));
545       break;
546     case ATSectionDefinition:
547       writeLE32(i.Aux.SectionDefinition.Length);
548       writeLE16(i.Aux.SectionDefinition.NumberOfRelocations);
549       writeLE16(i.Aux.SectionDefinition.NumberOfLinenumbers);
550       writeLE32(i.Aux.SectionDefinition.CheckSum);
551       writeLE16(static_cast<int16_t>(i.Aux.SectionDefinition.Number));
552       write8(i.Aux.SectionDefinition.Selection);
553       WriteZeros(sizeof(i.Aux.SectionDefinition.unused));
554       writeLE16(static_cast<int16_t>(i.Aux.SectionDefinition.Number >> 16));
555       if (UseBigObj)
556         WriteZeros(COFF::Symbol32Size - COFF::Symbol16Size);
557       break;
558     }
559   }
560 }
561 
562 // Write the section header.
563 void WinCOFFObjectWriter::writeSectionHeaders() {
564   // Section numbers must be monotonically increasing in the section
565   // header, but our Sections array is not sorted by section number,
566   // so make a copy of Sections and sort it.
567   std::vector<COFFSection *> Arr;
568   for (auto &Section : Sections)
569     Arr.push_back(Section.get());
570   std::sort(Arr.begin(), Arr.end(),
571             [](const COFFSection *A, const COFFSection *B) {
572               return A->Number < B->Number;
573             });
574 
575   for (auto &Section : Arr) {
576     if (Section->Number == -1)
577       continue;
578 
579     COFF::section &S = Section->Header;
580     if (Section->Relocations.size() >= 0xffff)
581       S.Characteristics |= COFF::IMAGE_SCN_LNK_NRELOC_OVFL;
582     writeBytes(StringRef(S.Name, COFF::NameSize));
583     writeLE32(S.VirtualSize);
584     writeLE32(S.VirtualAddress);
585     writeLE32(S.SizeOfRawData);
586     writeLE32(S.PointerToRawData);
587     writeLE32(S.PointerToRelocations);
588     writeLE32(S.PointerToLineNumbers);
589     writeLE16(S.NumberOfRelocations);
590     writeLE16(S.NumberOfLineNumbers);
591     writeLE32(S.Characteristics);
592   }
593 }
594 
595 void WinCOFFObjectWriter::WriteRelocation(const COFF::relocation &R) {
596   writeLE32(R.VirtualAddress);
597   writeLE32(R.SymbolTableIndex);
598   writeLE16(R.Type);
599 }
600 
601 // Write MCSec's contents. What this function does is essentially
602 // "Asm.writeSectionData(&MCSec, Layout)", but it's a bit complicated
603 // because it needs to compute a CRC.
604 uint32_t WinCOFFObjectWriter::writeSectionContents(MCAssembler &Asm,
605                                                    const MCAsmLayout &Layout,
606                                                    const MCSection &MCSec) {
607   // Save the contents of the section to a temporary buffer, we need this
608   // to CRC the data before we dump it into the object file.
609   SmallVector<char, 128> Buf;
610   raw_svector_ostream VecOS(Buf);
611   raw_pwrite_stream &OldStream = getStream();
612 
613   // Redirect the output stream to our buffer and fill our buffer with
614   // the section data.
615   setStream(VecOS);
616   Asm.writeSectionData(&MCSec, Layout);
617 
618   // Reset the stream back to what it was before.
619   setStream(OldStream);
620 
621   // Write the section contents to the object file.
622   getStream() << Buf;
623 
624   // Calculate our CRC with an initial value of '0', this is not how
625   // JamCRC is specified but it aligns with the expected output.
626   JamCRC JC(/*Init=*/0);
627   JC.update(Buf);
628   return JC.getCRC();
629 }
630 
631 void WinCOFFObjectWriter::writeSection(MCAssembler &Asm,
632                                        const MCAsmLayout &Layout,
633                                        const COFFSection &Sec,
634                                        const MCSection &MCSec) {
635   if (Sec.Number == -1)
636     return;
637 
638   // Write the section contents.
639   if (Sec.Header.PointerToRawData != 0) {
640     assert(getStream().tell() <= Sec.Header.PointerToRawData &&
641            "Section::PointerToRawData is insane!");
642 
643     unsigned PaddingSize = Sec.Header.PointerToRawData - getStream().tell();
644     assert(PaddingSize < 4 &&
645            "Should only need at most three bytes of padding!");
646     WriteZeros(PaddingSize);
647 
648     uint32_t CRC = writeSectionContents(Asm, Layout, MCSec);
649 
650     // Update the section definition auxiliary symbol to record the CRC.
651     COFFSection *Sec = SectionMap[&MCSec];
652     COFFSymbol::AuxiliarySymbols &AuxSyms = Sec->Symbol->Aux;
653     assert(AuxSyms.size() == 1 && AuxSyms[0].AuxType == ATSectionDefinition);
654     AuxSymbol &SecDef = AuxSyms[0];
655     SecDef.Aux.SectionDefinition.CheckSum = CRC;
656   }
657 
658   // Write relocations for this section.
659   if (Sec.Relocations.empty()) {
660     assert(Sec.Header.PointerToRelocations == 0 &&
661            "Section::PointerToRelocations is insane!");
662     return;
663   }
664 
665   assert(getStream().tell() == Sec.Header.PointerToRelocations &&
666          "Section::PointerToRelocations is insane!");
667 
668   if (Sec.Relocations.size() >= 0xffff) {
669     // In case of overflow, write actual relocation count as first
670     // relocation. Including the synthetic reloc itself (+ 1).
671     COFF::relocation R;
672     R.VirtualAddress = Sec.Relocations.size() + 1;
673     R.SymbolTableIndex = 0;
674     R.Type = 0;
675     WriteRelocation(R);
676   }
677 
678   for (const auto &Relocation : Sec.Relocations)
679     WriteRelocation(Relocation.Data);
680 }
681 
682 ////////////////////////////////////////////////////////////////////////////////
683 // MCObjectWriter interface implementations
684 
685 void WinCOFFObjectWriter::executePostLayoutBinding(MCAssembler &Asm,
686                                                    const MCAsmLayout &Layout) {
687   // "Define" each section & symbol. This creates section & symbol
688   // entries in the staging area.
689   for (const auto &Section : Asm)
690     defineSection(static_cast<const MCSectionCOFF &>(Section));
691 
692   for (const MCSymbol &Symbol : Asm.symbols())
693     if (!Symbol.isTemporary())
694       DefineSymbol(Symbol, Asm, Layout);
695 }
696 
697 bool WinCOFFObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(
698     const MCAssembler &Asm, const MCSymbol &SymA, const MCFragment &FB,
699     bool InSet, bool IsPCRel) const {
700   // MS LINK expects to be able to replace all references to a function with a
701   // thunk to implement their /INCREMENTAL feature.  Make sure we don't optimize
702   // away any relocations to functions.
703   uint16_t Type = cast<MCSymbolCOFF>(SymA).getType();
704   if (Asm.isIncrementalLinkerCompatible() &&
705       (Type >> COFF::SCT_COMPLEX_TYPE_SHIFT) == COFF::IMAGE_SYM_DTYPE_FUNCTION)
706     return false;
707   return MCObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(Asm, SymA, FB,
708                                                                 InSet, IsPCRel);
709 }
710 
711 void WinCOFFObjectWriter::recordRelocation(
712     MCAssembler &Asm, const MCAsmLayout &Layout, const MCFragment *Fragment,
713     const MCFixup &Fixup, MCValue Target, bool &IsPCRel, uint64_t &FixedValue) {
714   assert(Target.getSymA() && "Relocation must reference a symbol!");
715 
716   const MCSymbol &A = Target.getSymA()->getSymbol();
717   if (!A.isRegistered()) {
718     Asm.getContext().reportError(Fixup.getLoc(),
719                                       Twine("symbol '") + A.getName() +
720                                           "' can not be undefined");
721     return;
722   }
723   if (A.isTemporary() && A.isUndefined()) {
724     Asm.getContext().reportError(Fixup.getLoc(),
725                                       Twine("assembler label '") + A.getName() +
726                                           "' can not be undefined");
727     return;
728   }
729 
730   MCSection *MCSec = Fragment->getParent();
731 
732   // Mark this symbol as requiring an entry in the symbol table.
733   assert(SectionMap.find(MCSec) != SectionMap.end() &&
734          "Section must already have been defined in executePostLayoutBinding!");
735 
736   COFFSection *Sec = SectionMap[MCSec];
737   const MCSymbolRefExpr *SymB = Target.getSymB();
738 
739   if (SymB) {
740     const MCSymbol *B = &SymB->getSymbol();
741     if (!B->getFragment()) {
742       Asm.getContext().reportError(
743           Fixup.getLoc(),
744           Twine("symbol '") + B->getName() +
745               "' can not be undefined in a subtraction expression");
746       return;
747     }
748 
749     // Offset of the symbol in the section
750     int64_t OffsetOfB = Layout.getSymbolOffset(*B);
751 
752     // Offset of the relocation in the section
753     int64_t OffsetOfRelocation =
754         Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
755 
756     FixedValue = (OffsetOfRelocation - OffsetOfB) + Target.getConstant();
757   } else {
758     FixedValue = Target.getConstant();
759   }
760 
761   COFFRelocation Reloc;
762 
763   Reloc.Data.SymbolTableIndex = 0;
764   Reloc.Data.VirtualAddress = Layout.getFragmentOffset(Fragment);
765 
766   // Turn relocations for temporary symbols into section relocations.
767   if (A.isTemporary()) {
768     MCSection *TargetSection = &A.getSection();
769     assert(
770         SectionMap.find(TargetSection) != SectionMap.end() &&
771         "Section must already have been defined in executePostLayoutBinding!");
772     Reloc.Symb = SectionMap[TargetSection]->Symbol;
773     FixedValue += Layout.getSymbolOffset(A);
774   } else {
775     assert(
776         SymbolMap.find(&A) != SymbolMap.end() &&
777         "Symbol must already have been defined in executePostLayoutBinding!");
778     Reloc.Symb = SymbolMap[&A];
779   }
780 
781   ++Reloc.Symb->Relocations;
782 
783   Reloc.Data.VirtualAddress += Fixup.getOffset();
784   Reloc.Data.Type = TargetObjectWriter->getRelocType(
785       Asm.getContext(), Target, Fixup, SymB, Asm.getBackend());
786 
787   // FIXME: Can anyone explain what this does other than adjust for the size
788   // of the offset?
789   if ((Header.Machine == COFF::IMAGE_FILE_MACHINE_AMD64 &&
790        Reloc.Data.Type == COFF::IMAGE_REL_AMD64_REL32) ||
791       (Header.Machine == COFF::IMAGE_FILE_MACHINE_I386 &&
792        Reloc.Data.Type == COFF::IMAGE_REL_I386_REL32))
793     FixedValue += 4;
794 
795   if (Header.Machine == COFF::IMAGE_FILE_MACHINE_ARMNT) {
796     switch (Reloc.Data.Type) {
797     case COFF::IMAGE_REL_ARM_ABSOLUTE:
798     case COFF::IMAGE_REL_ARM_ADDR32:
799     case COFF::IMAGE_REL_ARM_ADDR32NB:
800     case COFF::IMAGE_REL_ARM_TOKEN:
801     case COFF::IMAGE_REL_ARM_SECTION:
802     case COFF::IMAGE_REL_ARM_SECREL:
803       break;
804     case COFF::IMAGE_REL_ARM_BRANCH11:
805     case COFF::IMAGE_REL_ARM_BLX11:
806     // IMAGE_REL_ARM_BRANCH11 and IMAGE_REL_ARM_BLX11 are only used for
807     // pre-ARMv7, which implicitly rules it out of ARMNT (it would be valid
808     // for Windows CE).
809     case COFF::IMAGE_REL_ARM_BRANCH24:
810     case COFF::IMAGE_REL_ARM_BLX24:
811     case COFF::IMAGE_REL_ARM_MOV32A:
812       // IMAGE_REL_ARM_BRANCH24, IMAGE_REL_ARM_BLX24, IMAGE_REL_ARM_MOV32A are
813       // only used for ARM mode code, which is documented as being unsupported
814       // by Windows on ARM.  Empirical proof indicates that masm is able to
815       // generate the relocations however the rest of the MSVC toolchain is
816       // unable to handle it.
817       llvm_unreachable("unsupported relocation");
818       break;
819     case COFF::IMAGE_REL_ARM_MOV32T:
820       break;
821     case COFF::IMAGE_REL_ARM_BRANCH20T:
822     case COFF::IMAGE_REL_ARM_BRANCH24T:
823     case COFF::IMAGE_REL_ARM_BLX23T:
824       // IMAGE_REL_BRANCH20T, IMAGE_REL_ARM_BRANCH24T, IMAGE_REL_ARM_BLX23T all
825       // perform a 4 byte adjustment to the relocation.  Relative branches are
826       // offset by 4 on ARM, however, because there is no RELA relocations, all
827       // branches are offset by 4.
828       FixedValue = FixedValue + 4;
829       break;
830     }
831   }
832 
833   // The fixed value never makes sense for section indices, ignore it.
834   if (Fixup.getKind() == FK_SecRel_2)
835     FixedValue = 0;
836 
837   if (TargetObjectWriter->recordRelocation(Fixup))
838     Sec->Relocations.push_back(Reloc);
839 }
840 
841 static std::time_t getTime() {
842   std::time_t Now = time(nullptr);
843   if (Now < 0 || !isUInt<32>(Now))
844     return UINT32_MAX;
845   return Now;
846 }
847 
848 // Create .file symbols.
849 void WinCOFFObjectWriter::createFileSymbols(MCAssembler &Asm) {
850   for (const std::string &Name : Asm.getFileNames()) {
851     // round up to calculate the number of auxiliary symbols required
852     unsigned SymbolSize = UseBigObj ? COFF::Symbol32Size : COFF::Symbol16Size;
853     unsigned Count = (Name.size() + SymbolSize - 1) / SymbolSize;
854 
855     COFFSymbol *File = createSymbol(".file");
856     File->Data.SectionNumber = COFF::IMAGE_SYM_DEBUG;
857     File->Data.StorageClass = COFF::IMAGE_SYM_CLASS_FILE;
858     File->Aux.resize(Count);
859 
860     unsigned Offset = 0;
861     unsigned Length = Name.size();
862     for (auto &Aux : File->Aux) {
863       Aux.AuxType = ATFile;
864 
865       if (Length > SymbolSize) {
866         memcpy(&Aux.Aux, Name.c_str() + Offset, SymbolSize);
867         Length = Length - SymbolSize;
868       } else {
869         memcpy(&Aux.Aux, Name.c_str() + Offset, Length);
870         memset((char *)&Aux.Aux + Length, 0, SymbolSize - Length);
871         break;
872       }
873 
874       Offset += SymbolSize;
875     }
876   }
877 }
878 
879 static bool isAssociative(const COFFSection &Section) {
880   return Section.Symbol->Aux[0].Aux.SectionDefinition.Selection ==
881          COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE;
882 }
883 
884 void WinCOFFObjectWriter::assignSectionNumbers() {
885   size_t I = 1;
886   auto Assign = [&](COFFSection &Section) {
887     Section.Number = I;
888     Section.Symbol->Data.SectionNumber = I;
889     Section.Symbol->Aux[0].Aux.SectionDefinition.Number = I;
890     ++I;
891   };
892 
893   // Although it is not explicitly requested by the Microsoft COFF spec,
894   // we should avoid emitting forward associative section references,
895   // because MSVC link.exe as of 2017 cannot handle that.
896   for (const std::unique_ptr<COFFSection> &Section : Sections)
897     if (!isAssociative(*Section))
898       Assign(*Section);
899   for (const std::unique_ptr<COFFSection> &Section : Sections)
900     if (isAssociative(*Section))
901       Assign(*Section);
902 }
903 
904 // Assign file offsets to COFF object file structures.
905 void WinCOFFObjectWriter::assignFileOffsets(MCAssembler &Asm,
906                                             const MCAsmLayout &Layout) {
907   unsigned Offset = getInitialOffset();
908 
909   Offset += UseBigObj ? COFF::Header32Size : COFF::Header16Size;
910   Offset += COFF::SectionSize * Header.NumberOfSections;
911 
912   for (const auto &Section : Asm) {
913     COFFSection *Sec = SectionMap[&Section];
914 
915     if (Sec->Number == -1)
916       continue;
917 
918     Sec->Header.SizeOfRawData = Layout.getSectionAddressSize(&Section);
919 
920     if (IsPhysicalSection(Sec)) {
921       // Align the section data to a four byte boundary.
922       Offset = alignTo(Offset, 4);
923       Sec->Header.PointerToRawData = Offset;
924 
925       Offset += Sec->Header.SizeOfRawData;
926     }
927 
928     if (!Sec->Relocations.empty()) {
929       bool RelocationsOverflow = Sec->Relocations.size() >= 0xffff;
930 
931       if (RelocationsOverflow) {
932         // Signal overflow by setting NumberOfRelocations to max value. Actual
933         // size is found in reloc #0. Microsoft tools understand this.
934         Sec->Header.NumberOfRelocations = 0xffff;
935       } else {
936         Sec->Header.NumberOfRelocations = Sec->Relocations.size();
937       }
938       Sec->Header.PointerToRelocations = Offset;
939 
940       if (RelocationsOverflow) {
941         // Reloc #0 will contain actual count, so make room for it.
942         Offset += COFF::RelocationSize;
943       }
944 
945       Offset += COFF::RelocationSize * Sec->Relocations.size();
946 
947       for (auto &Relocation : Sec->Relocations) {
948         assert(Relocation.Symb->getIndex() != -1);
949         Relocation.Data.SymbolTableIndex = Relocation.Symb->getIndex();
950       }
951     }
952 
953     assert(Sec->Symbol->Aux.size() == 1 &&
954            "Section's symbol must have one aux!");
955     AuxSymbol &Aux = Sec->Symbol->Aux[0];
956     assert(Aux.AuxType == ATSectionDefinition &&
957            "Section's symbol's aux symbol must be a Section Definition!");
958     Aux.Aux.SectionDefinition.Length = Sec->Header.SizeOfRawData;
959     Aux.Aux.SectionDefinition.NumberOfRelocations =
960         Sec->Header.NumberOfRelocations;
961     Aux.Aux.SectionDefinition.NumberOfLinenumbers =
962         Sec->Header.NumberOfLineNumbers;
963   }
964 
965   Header.PointerToSymbolTable = Offset;
966 }
967 
968 void WinCOFFObjectWriter::writeObject(MCAssembler &Asm,
969                                       const MCAsmLayout &Layout) {
970   if (Sections.size() > INT32_MAX)
971     report_fatal_error(
972         "PE COFF object files can't have more than 2147483647 sections");
973 
974   UseBigObj = Sections.size() > COFF::MaxNumberOfSections16;
975   Header.NumberOfSections = Sections.size();
976   Header.NumberOfSymbols = 0;
977 
978   assignSectionNumbers();
979   createFileSymbols(Asm);
980 
981   for (auto &Symbol : Symbols) {
982     // Update section number & offset for symbols that have them.
983     if (Symbol->Section)
984       Symbol->Data.SectionNumber = Symbol->Section->Number;
985     Symbol->setIndex(Header.NumberOfSymbols++);
986     // Update auxiliary symbol info.
987     Symbol->Data.NumberOfAuxSymbols = Symbol->Aux.size();
988     Header.NumberOfSymbols += Symbol->Data.NumberOfAuxSymbols;
989   }
990 
991   // Build string table.
992   for (const auto &S : Sections)
993     if (S->Name.size() > COFF::NameSize)
994       Strings.add(S->Name);
995   for (const auto &S : Symbols)
996     if (S->Name.size() > COFF::NameSize)
997       Strings.add(S->Name);
998   Strings.finalize();
999 
1000   // Set names.
1001   for (const auto &S : Sections)
1002     SetSectionName(*S);
1003   for (auto &S : Symbols)
1004     SetSymbolName(*S);
1005 
1006   // Fixup weak external references.
1007   for (auto &Symbol : Symbols) {
1008     if (Symbol->Other) {
1009       assert(Symbol->getIndex() != -1);
1010       assert(Symbol->Aux.size() == 1 && "Symbol must contain one aux symbol!");
1011       assert(Symbol->Aux[0].AuxType == ATWeakExternal &&
1012              "Symbol's aux symbol must be a Weak External!");
1013       Symbol->Aux[0].Aux.WeakExternal.TagIndex = Symbol->Other->getIndex();
1014     }
1015   }
1016 
1017   // Fixup associative COMDAT sections.
1018   for (auto &Section : Sections) {
1019     if (Section->Symbol->Aux[0].Aux.SectionDefinition.Selection !=
1020         COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE)
1021       continue;
1022 
1023     const MCSectionCOFF &MCSec = *Section->MCSection;
1024 
1025     const MCSymbol *COMDAT = MCSec.getCOMDATSymbol();
1026     assert(COMDAT);
1027     COFFSymbol *COMDATSymbol = GetOrCreateCOFFSymbol(COMDAT);
1028     assert(COMDATSymbol);
1029     COFFSection *Assoc = COMDATSymbol->Section;
1030     if (!Assoc)
1031       report_fatal_error(
1032           Twine("Missing associated COMDAT section for section ") +
1033           MCSec.getSectionName());
1034 
1035     // Skip this section if the associated section is unused.
1036     if (Assoc->Number == -1)
1037       continue;
1038 
1039     Section->Symbol->Aux[0].Aux.SectionDefinition.Number = Assoc->Number;
1040   }
1041 
1042   assignFileOffsets(Asm, Layout);
1043 
1044   // MS LINK expects to be able to use this timestamp to implement their
1045   // /INCREMENTAL feature.
1046   if (Asm.isIncrementalLinkerCompatible()) {
1047     Header.TimeDateStamp = getTime();
1048   } else {
1049     // Have deterministic output if /INCREMENTAL isn't needed. Also matches GNU.
1050     Header.TimeDateStamp = 0;
1051   }
1052 
1053   // Write it all to disk...
1054   WriteFileHeader(Header);
1055   writeSectionHeaders();
1056 
1057   // Write section contents.
1058   sections::iterator I = Sections.begin();
1059   sections::iterator IE = Sections.end();
1060   MCAssembler::iterator J = Asm.begin();
1061   MCAssembler::iterator JE = Asm.end();
1062   for (; I != IE && J != JE; ++I, ++J)
1063     writeSection(Asm, Layout, **I, *J);
1064 
1065   assert(getStream().tell() == Header.PointerToSymbolTable &&
1066          "Header::PointerToSymbolTable is insane!");
1067 
1068   // Write a symbol table.
1069   for (auto &Symbol : Symbols)
1070     if (Symbol->getIndex() != -1)
1071       WriteSymbol(*Symbol);
1072 
1073   // Write a string table, which completes the entire COFF file.
1074   Strings.write(getStream());
1075 }
1076 
1077 MCWinCOFFObjectTargetWriter::MCWinCOFFObjectTargetWriter(unsigned Machine_)
1078     : Machine(Machine_) {}
1079 
1080 // Pin the vtable to this file.
1081 void MCWinCOFFObjectTargetWriter::anchor() {}
1082 
1083 //------------------------------------------------------------------------------
1084 // WinCOFFObjectWriter factory function
1085 
1086 MCObjectWriter *
1087 llvm::createWinCOFFObjectWriter(MCWinCOFFObjectTargetWriter *MOTW,
1088                                 raw_pwrite_stream &OS) {
1089   return new WinCOFFObjectWriter(MOTW, OS);
1090 }
1091