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(std::unique_ptr<MCWinCOFFObjectTargetWriter> MOTW,
149                       raw_pwrite_stream &OS);
150 
151   void reset() override {
152     memset(&Header, 0, sizeof(Header));
153     Header.Machine = TargetObjectWriter->getMachine();
154     Sections.clear();
155     Symbols.clear();
156     Strings.clear();
157     SectionMap.clear();
158     SymbolMap.clear();
159     MCObjectWriter::reset();
160   }
161 
162   COFFSymbol *createSymbol(StringRef Name);
163   COFFSymbol *GetOrCreateCOFFSymbol(const MCSymbol *Symbol);
164   COFFSection *createSection(StringRef Name);
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 writeSectionHeaders();
183   void WriteRelocation(const COFF::relocation &R);
184   uint32_t writeSectionContents(MCAssembler &Asm, const MCAsmLayout &Layout,
185                                 const MCSection &MCSec);
186   void writeSection(MCAssembler &Asm, const MCAsmLayout &Layout,
187                     const COFFSection &Sec, const MCSection &MCSec);
188 
189   // MCObjectWriter interface implementation.
190 
191   void executePostLayoutBinding(MCAssembler &Asm,
192                                 const MCAsmLayout &Layout) override;
193 
194   bool isSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
195                                               const MCSymbol &SymA,
196                                               const MCFragment &FB, bool InSet,
197                                               bool IsPCRel) const override;
198 
199   void recordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
200                         const MCFragment *Fragment, const MCFixup &Fixup,
201                         MCValue Target, 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(
227     std::unique_ptr<MCWinCOFFObjectTargetWriter> MOTW, raw_pwrite_stream &OS)
228     : MCObjectWriter(OS, true), TargetObjectWriter(std::move(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   llvm::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   // Don't drop relocations between functions, even if they are in the same text
701   // section. Multiple Visual C++ linker features depend on having the
702   // relocations present. The /INCREMENTAL flag will cause these relocations to
703   // point to thunks, and the /GUARD:CF flag assumes that it can use relocations
704   // to approximate the set of all address taken functions. LLD's implementation
705   // of /GUARD:CF also relies on the existance of these relocations.
706   uint16_t Type = cast<MCSymbolCOFF>(SymA).getType();
707   if ((Type >> COFF::SCT_COMPLEX_TYPE_SHIFT) == COFF::IMAGE_SYM_DTYPE_FUNCTION)
708     return false;
709   return MCObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(Asm, SymA, FB,
710                                                                 InSet, IsPCRel);
711 }
712 
713 void WinCOFFObjectWriter::recordRelocation(MCAssembler &Asm,
714                                            const MCAsmLayout &Layout,
715                                            const MCFragment *Fragment,
716                                            const MCFixup &Fixup, MCValue Target,
717                                            uint64_t &FixedValue) {
718   assert(Target.getSymA() && "Relocation must reference a symbol!");
719 
720   const MCSymbol &A = Target.getSymA()->getSymbol();
721   if (!A.isRegistered()) {
722     Asm.getContext().reportError(Fixup.getLoc(),
723                                       Twine("symbol '") + A.getName() +
724                                           "' can not be undefined");
725     return;
726   }
727   if (A.isTemporary() && A.isUndefined()) {
728     Asm.getContext().reportError(Fixup.getLoc(),
729                                       Twine("assembler label '") + A.getName() +
730                                           "' can not be undefined");
731     return;
732   }
733 
734   MCSection *MCSec = Fragment->getParent();
735 
736   // Mark this symbol as requiring an entry in the symbol table.
737   assert(SectionMap.find(MCSec) != SectionMap.end() &&
738          "Section must already have been defined in executePostLayoutBinding!");
739 
740   COFFSection *Sec = SectionMap[MCSec];
741   const MCSymbolRefExpr *SymB = Target.getSymB();
742 
743   if (SymB) {
744     const MCSymbol *B = &SymB->getSymbol();
745     if (!B->getFragment()) {
746       Asm.getContext().reportError(
747           Fixup.getLoc(),
748           Twine("symbol '") + B->getName() +
749               "' can not be undefined in a subtraction expression");
750       return;
751     }
752 
753     // Offset of the symbol in the section
754     int64_t OffsetOfB = Layout.getSymbolOffset(*B);
755 
756     // Offset of the relocation in the section
757     int64_t OffsetOfRelocation =
758         Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
759 
760     FixedValue = (OffsetOfRelocation - OffsetOfB) + Target.getConstant();
761   } else {
762     FixedValue = Target.getConstant();
763   }
764 
765   COFFRelocation Reloc;
766 
767   Reloc.Data.SymbolTableIndex = 0;
768   Reloc.Data.VirtualAddress = Layout.getFragmentOffset(Fragment);
769 
770   // Turn relocations for temporary symbols into section relocations.
771   if (A.isTemporary()) {
772     MCSection *TargetSection = &A.getSection();
773     assert(
774         SectionMap.find(TargetSection) != SectionMap.end() &&
775         "Section must already have been defined in executePostLayoutBinding!");
776     Reloc.Symb = SectionMap[TargetSection]->Symbol;
777     FixedValue += Layout.getSymbolOffset(A);
778   } else {
779     assert(
780         SymbolMap.find(&A) != SymbolMap.end() &&
781         "Symbol must already have been defined in executePostLayoutBinding!");
782     Reloc.Symb = SymbolMap[&A];
783   }
784 
785   ++Reloc.Symb->Relocations;
786 
787   Reloc.Data.VirtualAddress += Fixup.getOffset();
788   Reloc.Data.Type = TargetObjectWriter->getRelocType(
789       Asm.getContext(), Target, Fixup, SymB, Asm.getBackend());
790 
791   // FIXME: Can anyone explain what this does other than adjust for the size
792   // of the offset?
793   if ((Header.Machine == COFF::IMAGE_FILE_MACHINE_AMD64 &&
794        Reloc.Data.Type == COFF::IMAGE_REL_AMD64_REL32) ||
795       (Header.Machine == COFF::IMAGE_FILE_MACHINE_I386 &&
796        Reloc.Data.Type == COFF::IMAGE_REL_I386_REL32))
797     FixedValue += 4;
798 
799   if (Header.Machine == COFF::IMAGE_FILE_MACHINE_ARMNT) {
800     switch (Reloc.Data.Type) {
801     case COFF::IMAGE_REL_ARM_ABSOLUTE:
802     case COFF::IMAGE_REL_ARM_ADDR32:
803     case COFF::IMAGE_REL_ARM_ADDR32NB:
804     case COFF::IMAGE_REL_ARM_TOKEN:
805     case COFF::IMAGE_REL_ARM_SECTION:
806     case COFF::IMAGE_REL_ARM_SECREL:
807       break;
808     case COFF::IMAGE_REL_ARM_BRANCH11:
809     case COFF::IMAGE_REL_ARM_BLX11:
810     // IMAGE_REL_ARM_BRANCH11 and IMAGE_REL_ARM_BLX11 are only used for
811     // pre-ARMv7, which implicitly rules it out of ARMNT (it would be valid
812     // for Windows CE).
813     case COFF::IMAGE_REL_ARM_BRANCH24:
814     case COFF::IMAGE_REL_ARM_BLX24:
815     case COFF::IMAGE_REL_ARM_MOV32A:
816       // IMAGE_REL_ARM_BRANCH24, IMAGE_REL_ARM_BLX24, IMAGE_REL_ARM_MOV32A are
817       // only used for ARM mode code, which is documented as being unsupported
818       // by Windows on ARM.  Empirical proof indicates that masm is able to
819       // generate the relocations however the rest of the MSVC toolchain is
820       // unable to handle it.
821       llvm_unreachable("unsupported relocation");
822       break;
823     case COFF::IMAGE_REL_ARM_MOV32T:
824       break;
825     case COFF::IMAGE_REL_ARM_BRANCH20T:
826     case COFF::IMAGE_REL_ARM_BRANCH24T:
827     case COFF::IMAGE_REL_ARM_BLX23T:
828       // IMAGE_REL_BRANCH20T, IMAGE_REL_ARM_BRANCH24T, IMAGE_REL_ARM_BLX23T all
829       // perform a 4 byte adjustment to the relocation.  Relative branches are
830       // offset by 4 on ARM, however, because there is no RELA relocations, all
831       // branches are offset by 4.
832       FixedValue = FixedValue + 4;
833       break;
834     }
835   }
836 
837   // The fixed value never makes sense for section indices, ignore it.
838   if (Fixup.getKind() == FK_SecRel_2)
839     FixedValue = 0;
840 
841   if (TargetObjectWriter->recordRelocation(Fixup))
842     Sec->Relocations.push_back(Reloc);
843 }
844 
845 static std::time_t getTime() {
846   std::time_t Now = time(nullptr);
847   if (Now < 0 || !isUInt<32>(Now))
848     return UINT32_MAX;
849   return Now;
850 }
851 
852 // Create .file symbols.
853 void WinCOFFObjectWriter::createFileSymbols(MCAssembler &Asm) {
854   for (const std::string &Name : Asm.getFileNames()) {
855     // round up to calculate the number of auxiliary symbols required
856     unsigned SymbolSize = UseBigObj ? COFF::Symbol32Size : COFF::Symbol16Size;
857     unsigned Count = (Name.size() + SymbolSize - 1) / SymbolSize;
858 
859     COFFSymbol *File = createSymbol(".file");
860     File->Data.SectionNumber = COFF::IMAGE_SYM_DEBUG;
861     File->Data.StorageClass = COFF::IMAGE_SYM_CLASS_FILE;
862     File->Aux.resize(Count);
863 
864     unsigned Offset = 0;
865     unsigned Length = Name.size();
866     for (auto &Aux : File->Aux) {
867       Aux.AuxType = ATFile;
868 
869       if (Length > SymbolSize) {
870         memcpy(&Aux.Aux, Name.c_str() + Offset, SymbolSize);
871         Length = Length - SymbolSize;
872       } else {
873         memcpy(&Aux.Aux, Name.c_str() + Offset, Length);
874         memset((char *)&Aux.Aux + Length, 0, SymbolSize - Length);
875         break;
876       }
877 
878       Offset += SymbolSize;
879     }
880   }
881 }
882 
883 static bool isAssociative(const COFFSection &Section) {
884   return Section.Symbol->Aux[0].Aux.SectionDefinition.Selection ==
885          COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE;
886 }
887 
888 void WinCOFFObjectWriter::assignSectionNumbers() {
889   size_t I = 1;
890   auto Assign = [&](COFFSection &Section) {
891     Section.Number = I;
892     Section.Symbol->Data.SectionNumber = I;
893     Section.Symbol->Aux[0].Aux.SectionDefinition.Number = I;
894     ++I;
895   };
896 
897   // Although it is not explicitly requested by the Microsoft COFF spec,
898   // we should avoid emitting forward associative section references,
899   // because MSVC link.exe as of 2017 cannot handle that.
900   for (const std::unique_ptr<COFFSection> &Section : Sections)
901     if (!isAssociative(*Section))
902       Assign(*Section);
903   for (const std::unique_ptr<COFFSection> &Section : Sections)
904     if (isAssociative(*Section))
905       Assign(*Section);
906 }
907 
908 // Assign file offsets to COFF object file structures.
909 void WinCOFFObjectWriter::assignFileOffsets(MCAssembler &Asm,
910                                             const MCAsmLayout &Layout) {
911   unsigned Offset = getInitialOffset();
912 
913   Offset += UseBigObj ? COFF::Header32Size : COFF::Header16Size;
914   Offset += COFF::SectionSize * Header.NumberOfSections;
915 
916   for (const auto &Section : Asm) {
917     COFFSection *Sec = SectionMap[&Section];
918 
919     if (Sec->Number == -1)
920       continue;
921 
922     Sec->Header.SizeOfRawData = Layout.getSectionAddressSize(&Section);
923 
924     if (IsPhysicalSection(Sec)) {
925       // Align the section data to a four byte boundary.
926       Offset = alignTo(Offset, 4);
927       Sec->Header.PointerToRawData = Offset;
928 
929       Offset += Sec->Header.SizeOfRawData;
930     }
931 
932     if (!Sec->Relocations.empty()) {
933       bool RelocationsOverflow = Sec->Relocations.size() >= 0xffff;
934 
935       if (RelocationsOverflow) {
936         // Signal overflow by setting NumberOfRelocations to max value. Actual
937         // size is found in reloc #0. Microsoft tools understand this.
938         Sec->Header.NumberOfRelocations = 0xffff;
939       } else {
940         Sec->Header.NumberOfRelocations = Sec->Relocations.size();
941       }
942       Sec->Header.PointerToRelocations = Offset;
943 
944       if (RelocationsOverflow) {
945         // Reloc #0 will contain actual count, so make room for it.
946         Offset += COFF::RelocationSize;
947       }
948 
949       Offset += COFF::RelocationSize * Sec->Relocations.size();
950 
951       for (auto &Relocation : Sec->Relocations) {
952         assert(Relocation.Symb->getIndex() != -1);
953         Relocation.Data.SymbolTableIndex = Relocation.Symb->getIndex();
954       }
955     }
956 
957     assert(Sec->Symbol->Aux.size() == 1 &&
958            "Section's symbol must have one aux!");
959     AuxSymbol &Aux = Sec->Symbol->Aux[0];
960     assert(Aux.AuxType == ATSectionDefinition &&
961            "Section's symbol's aux symbol must be a Section Definition!");
962     Aux.Aux.SectionDefinition.Length = Sec->Header.SizeOfRawData;
963     Aux.Aux.SectionDefinition.NumberOfRelocations =
964         Sec->Header.NumberOfRelocations;
965     Aux.Aux.SectionDefinition.NumberOfLinenumbers =
966         Sec->Header.NumberOfLineNumbers;
967   }
968 
969   Header.PointerToSymbolTable = Offset;
970 }
971 
972 void WinCOFFObjectWriter::writeObject(MCAssembler &Asm,
973                                       const MCAsmLayout &Layout) {
974   if (Sections.size() > INT32_MAX)
975     report_fatal_error(
976         "PE COFF object files can't have more than 2147483647 sections");
977 
978   UseBigObj = Sections.size() > COFF::MaxNumberOfSections16;
979   Header.NumberOfSections = Sections.size();
980   Header.NumberOfSymbols = 0;
981 
982   assignSectionNumbers();
983   createFileSymbols(Asm);
984 
985   for (auto &Symbol : Symbols) {
986     // Update section number & offset for symbols that have them.
987     if (Symbol->Section)
988       Symbol->Data.SectionNumber = Symbol->Section->Number;
989     Symbol->setIndex(Header.NumberOfSymbols++);
990     // Update auxiliary symbol info.
991     Symbol->Data.NumberOfAuxSymbols = Symbol->Aux.size();
992     Header.NumberOfSymbols += Symbol->Data.NumberOfAuxSymbols;
993   }
994 
995   // Build string table.
996   for (const auto &S : Sections)
997     if (S->Name.size() > COFF::NameSize)
998       Strings.add(S->Name);
999   for (const auto &S : Symbols)
1000     if (S->Name.size() > COFF::NameSize)
1001       Strings.add(S->Name);
1002   Strings.finalize();
1003 
1004   // Set names.
1005   for (const auto &S : Sections)
1006     SetSectionName(*S);
1007   for (auto &S : Symbols)
1008     SetSymbolName(*S);
1009 
1010   // Fixup weak external references.
1011   for (auto &Symbol : Symbols) {
1012     if (Symbol->Other) {
1013       assert(Symbol->getIndex() != -1);
1014       assert(Symbol->Aux.size() == 1 && "Symbol must contain one aux symbol!");
1015       assert(Symbol->Aux[0].AuxType == ATWeakExternal &&
1016              "Symbol's aux symbol must be a Weak External!");
1017       Symbol->Aux[0].Aux.WeakExternal.TagIndex = Symbol->Other->getIndex();
1018     }
1019   }
1020 
1021   // Fixup associative COMDAT sections.
1022   for (auto &Section : Sections) {
1023     if (Section->Symbol->Aux[0].Aux.SectionDefinition.Selection !=
1024         COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE)
1025       continue;
1026 
1027     const MCSectionCOFF &MCSec = *Section->MCSection;
1028 
1029     const MCSymbol *COMDAT = MCSec.getCOMDATSymbol();
1030     assert(COMDAT);
1031     COFFSymbol *COMDATSymbol = GetOrCreateCOFFSymbol(COMDAT);
1032     assert(COMDATSymbol);
1033     COFFSection *Assoc = COMDATSymbol->Section;
1034     if (!Assoc)
1035       report_fatal_error(
1036           Twine("Missing associated COMDAT section for section ") +
1037           MCSec.getSectionName());
1038 
1039     // Skip this section if the associated section is unused.
1040     if (Assoc->Number == -1)
1041       continue;
1042 
1043     Section->Symbol->Aux[0].Aux.SectionDefinition.Number = Assoc->Number;
1044   }
1045 
1046   assignFileOffsets(Asm, Layout);
1047 
1048   // MS LINK expects to be able to use this timestamp to implement their
1049   // /INCREMENTAL feature.
1050   if (Asm.isIncrementalLinkerCompatible()) {
1051     Header.TimeDateStamp = getTime();
1052   } else {
1053     // Have deterministic output if /INCREMENTAL isn't needed. Also matches GNU.
1054     Header.TimeDateStamp = 0;
1055   }
1056 
1057   // Write it all to disk...
1058   WriteFileHeader(Header);
1059   writeSectionHeaders();
1060 
1061   // Write section contents.
1062   sections::iterator I = Sections.begin();
1063   sections::iterator IE = Sections.end();
1064   MCAssembler::iterator J = Asm.begin();
1065   MCAssembler::iterator JE = Asm.end();
1066   for (; I != IE && J != JE; ++I, ++J)
1067     writeSection(Asm, Layout, **I, *J);
1068 
1069   assert(getStream().tell() == Header.PointerToSymbolTable &&
1070          "Header::PointerToSymbolTable is insane!");
1071 
1072   // Write a symbol table.
1073   for (auto &Symbol : Symbols)
1074     if (Symbol->getIndex() != -1)
1075       WriteSymbol(*Symbol);
1076 
1077   // Write a string table, which completes the entire COFF file.
1078   Strings.write(getStream());
1079 }
1080 
1081 MCWinCOFFObjectTargetWriter::MCWinCOFFObjectTargetWriter(unsigned Machine_)
1082     : Machine(Machine_) {}
1083 
1084 // Pin the vtable to this file.
1085 void MCWinCOFFObjectTargetWriter::anchor() {}
1086 
1087 //------------------------------------------------------------------------------
1088 // WinCOFFObjectWriter factory function
1089 
1090 std::unique_ptr<MCObjectWriter> llvm::createWinCOFFObjectWriter(
1091     std::unique_ptr<MCWinCOFFObjectTargetWriter> MOTW, raw_pwrite_stream &OS) {
1092   return llvm::make_unique<WinCOFFObjectWriter>(std::move(MOTW), OS);
1093 }
1094