WinCOFFObjectWriter.cpp revision 360784 
1//===- llvm/MC/WinCOFFObjectWriter.cpp ------------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// This file contains an implementation of a Win32 COFF object file writer.
10//
11//===----------------------------------------------------------------------===//
12
13#include "llvm/ADT/DenseMap.h"
14#include "llvm/ADT/STLExtras.h"
15#include "llvm/ADT/SmallString.h"
16#include "llvm/ADT/SmallVector.h"
17#include "llvm/ADT/StringRef.h"
18#include "llvm/ADT/Twine.h"
19#include "llvm/BinaryFormat/COFF.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/CRC.h"
35#include "llvm/Support/Casting.h"
36#include "llvm/Support/Endian.h"
37#include "llvm/Support/ErrorHandling.h"
38#include "llvm/Support/LEB128.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
51using namespace llvm;
52using llvm::support::endian::write32le;
53
54#define DEBUG_TYPE "WinCOFFObjectWriter"
55
56namespace {
57
58using name = SmallString<COFF::NameSize>;
59
60enum AuxiliaryType {
61  ATWeakExternal,
62  ATFile,
63  ATSectionDefinition
64};
65
66struct AuxSymbol {
67  AuxiliaryType AuxType;
68  COFF::Auxiliary Aux;
69};
70
71class COFFSection;
72
73class COFFSymbol {
74public:
75  COFF::symbol Data = {};
76
77  using AuxiliarySymbols = SmallVector<AuxSymbol, 1>;
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) : Name(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.
100struct COFFRelocation {
101  COFF::relocation Data;
102  COFFSymbol *Symb = nullptr;
103
104  COFFRelocation() = default;
105
106  static size_t size() { return COFF::RelocationSize; }
107};
108
109using relocations = std::vector<COFFRelocation>;
110
111class COFFSection {
112public:
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) : Name(Name) {}
122};
123
124class WinCOFFObjectWriter : public MCObjectWriter {
125public:
126  support::endian::Writer W;
127
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  bool EmitAddrsigSection = false;
149  MCSectionCOFF *AddrsigSection;
150  std::vector<const MCSymbol *> AddrsigSyms;
151
152  WinCOFFObjectWriter(std::unique_ptr<MCWinCOFFObjectTargetWriter> MOTW,
153                      raw_pwrite_stream &OS);
154
155  void reset() override {
156    memset(&Header, 0, sizeof(Header));
157    Header.Machine = TargetObjectWriter->getMachine();
158    Sections.clear();
159    Symbols.clear();
160    Strings.clear();
161    SectionMap.clear();
162    SymbolMap.clear();
163    MCObjectWriter::reset();
164  }
165
166  COFFSymbol *createSymbol(StringRef Name);
167  COFFSymbol *GetOrCreateCOFFSymbol(const MCSymbol *Symbol);
168  COFFSection *createSection(StringRef Name);
169
170  void defineSection(MCSectionCOFF const &Sec);
171
172  COFFSymbol *getLinkedSymbol(const MCSymbol &Symbol);
173  void DefineSymbol(const MCSymbol &Symbol, MCAssembler &Assembler,
174                    const MCAsmLayout &Layout);
175
176  void SetSymbolName(COFFSymbol &S);
177  void SetSectionName(COFFSection &S);
178
179  bool IsPhysicalSection(COFFSection *S);
180
181  // Entity writing methods.
182
183  void WriteFileHeader(const COFF::header &Header);
184  void WriteSymbol(const COFFSymbol &S);
185  void WriteAuxiliarySymbols(const COFFSymbol::AuxiliarySymbols &S);
186  void writeSectionHeaders();
187  void WriteRelocation(const COFF::relocation &R);
188  uint32_t writeSectionContents(MCAssembler &Asm, const MCAsmLayout &Layout,
189                                const MCSection &MCSec);
190  void writeSection(MCAssembler &Asm, const MCAsmLayout &Layout,
191                    const COFFSection &Sec, const MCSection &MCSec);
192
193  // MCObjectWriter interface implementation.
194
195  void executePostLayoutBinding(MCAssembler &Asm,
196                                const MCAsmLayout &Layout) override;
197
198  bool isSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
199                                              const MCSymbol &SymA,
200                                              const MCFragment &FB, bool InSet,
201                                              bool IsPCRel) const override;
202
203  void recordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
204                        const MCFragment *Fragment, const MCFixup &Fixup,
205                        MCValue Target, uint64_t &FixedValue) override;
206
207  void createFileSymbols(MCAssembler &Asm);
208  void assignSectionNumbers();
209  void assignFileOffsets(MCAssembler &Asm, const MCAsmLayout &Layout);
210
211  void emitAddrsigSection() override { EmitAddrsigSection = true; }
212  void addAddrsigSymbol(const MCSymbol *Sym) override {
213    AddrsigSyms.push_back(Sym);
214  }
215
216  uint64_t writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
217};
218
219} // end anonymous namespace
220
221//------------------------------------------------------------------------------
222// Symbol class implementation
223
224// In the case that the name does not fit within 8 bytes, the offset
225// into the string table is stored in the last 4 bytes instead, leaving
226// the first 4 bytes as 0.
227void COFFSymbol::set_name_offset(uint32_t Offset) {
228  write32le(Data.Name + 0, 0);
229  write32le(Data.Name + 4, Offset);
230}
231
232//------------------------------------------------------------------------------
233// WinCOFFObjectWriter class implementation
234
235WinCOFFObjectWriter::WinCOFFObjectWriter(
236    std::unique_ptr<MCWinCOFFObjectTargetWriter> MOTW, raw_pwrite_stream &OS)
237    : W(OS, support::little), TargetObjectWriter(std::move(MOTW)) {
238  Header.Machine = TargetObjectWriter->getMachine();
239}
240
241COFFSymbol *WinCOFFObjectWriter::createSymbol(StringRef Name) {
242  Symbols.push_back(std::make_unique<COFFSymbol>(Name));
243  return Symbols.back().get();
244}
245
246COFFSymbol *WinCOFFObjectWriter::GetOrCreateCOFFSymbol(const MCSymbol *Symbol) {
247  COFFSymbol *&Ret = SymbolMap[Symbol];
248  if (!Ret)
249    Ret = createSymbol(Symbol->getName());
250  return Ret;
251}
252
253COFFSection *WinCOFFObjectWriter::createSection(StringRef Name) {
254  Sections.emplace_back(std::make_unique<COFFSection>(Name));
255  return Sections.back().get();
256}
257
258static uint32_t getAlignment(const MCSectionCOFF &Sec) {
259  switch (Sec.getAlignment()) {
260  case 1:
261    return COFF::IMAGE_SCN_ALIGN_1BYTES;
262  case 2:
263    return COFF::IMAGE_SCN_ALIGN_2BYTES;
264  case 4:
265    return COFF::IMAGE_SCN_ALIGN_4BYTES;
266  case 8:
267    return COFF::IMAGE_SCN_ALIGN_8BYTES;
268  case 16:
269    return COFF::IMAGE_SCN_ALIGN_16BYTES;
270  case 32:
271    return COFF::IMAGE_SCN_ALIGN_32BYTES;
272  case 64:
273    return COFF::IMAGE_SCN_ALIGN_64BYTES;
274  case 128:
275    return COFF::IMAGE_SCN_ALIGN_128BYTES;
276  case 256:
277    return COFF::IMAGE_SCN_ALIGN_256BYTES;
278  case 512:
279    return COFF::IMAGE_SCN_ALIGN_512BYTES;
280  case 1024:
281    return COFF::IMAGE_SCN_ALIGN_1024BYTES;
282  case 2048:
283    return COFF::IMAGE_SCN_ALIGN_2048BYTES;
284  case 4096:
285    return COFF::IMAGE_SCN_ALIGN_4096BYTES;
286  case 8192:
287    return COFF::IMAGE_SCN_ALIGN_8192BYTES;
288  }
289  llvm_unreachable("unsupported section alignment");
290}
291
292/// This function takes a section data object from the assembler
293/// and creates the associated COFF section staging object.
294void WinCOFFObjectWriter::defineSection(const MCSectionCOFF &MCSec) {
295  COFFSection *Section = createSection(MCSec.getSectionName());
296  COFFSymbol *Symbol = createSymbol(MCSec.getSectionName());
297  Section->Symbol = Symbol;
298  Symbol->Section = Section;
299  Symbol->Data.StorageClass = COFF::IMAGE_SYM_CLASS_STATIC;
300
301  // Create a COMDAT symbol if needed.
302  if (MCSec.getSelection() != COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE) {
303    if (const MCSymbol *S = MCSec.getCOMDATSymbol()) {
304      COFFSymbol *COMDATSymbol = GetOrCreateCOFFSymbol(S);
305      if (COMDATSymbol->Section)
306        report_fatal_error("two sections have the same comdat");
307      COMDATSymbol->Section = Section;
308    }
309  }
310
311  // In this case the auxiliary symbol is a Section Definition.
312  Symbol->Aux.resize(1);
313  Symbol->Aux[0] = {};
314  Symbol->Aux[0].AuxType = ATSectionDefinition;
315  Symbol->Aux[0].Aux.SectionDefinition.Selection = MCSec.getSelection();
316
317  // Set section alignment.
318  Section->Header.Characteristics = MCSec.getCharacteristics();
319  Section->Header.Characteristics |= getAlignment(MCSec);
320
321  // Bind internal COFF section to MC section.
322  Section->MCSection = &MCSec;
323  SectionMap[&MCSec] = Section;
324}
325
326static uint64_t getSymbolValue(const MCSymbol &Symbol,
327                               const MCAsmLayout &Layout) {
328  if (Symbol.isCommon() && Symbol.isExternal())
329    return Symbol.getCommonSize();
330
331  uint64_t Res;
332  if (!Layout.getSymbolOffset(Symbol, Res))
333    return 0;
334
335  return Res;
336}
337
338COFFSymbol *WinCOFFObjectWriter::getLinkedSymbol(const MCSymbol &Symbol) {
339  if (!Symbol.isVariable())
340    return nullptr;
341
342  const MCSymbolRefExpr *SymRef =
343      dyn_cast<MCSymbolRefExpr>(Symbol.getVariableValue());
344  if (!SymRef)
345    return nullptr;
346
347  const MCSymbol &Aliasee = SymRef->getSymbol();
348  if (!Aliasee.isUndefined())
349    return nullptr;
350  return GetOrCreateCOFFSymbol(&Aliasee);
351}
352
353/// This function takes a symbol data object from the assembler
354/// and creates the associated COFF symbol staging object.
355void WinCOFFObjectWriter::DefineSymbol(const MCSymbol &MCSym,
356                                       MCAssembler &Assembler,
357                                       const MCAsmLayout &Layout) {
358  COFFSymbol *Sym = GetOrCreateCOFFSymbol(&MCSym);
359  const MCSymbol *Base = Layout.getBaseSymbol(MCSym);
360  COFFSection *Sec = nullptr;
361  if (Base && Base->getFragment()) {
362    Sec = SectionMap[Base->getFragment()->getParent()];
363    if (Sym->Section && Sym->Section != Sec)
364      report_fatal_error("conflicting sections for symbol");
365  }
366
367  COFFSymbol *Local = nullptr;
368  if (cast<MCSymbolCOFF>(MCSym).isWeakExternal()) {
369    Sym->Data.StorageClass = COFF::IMAGE_SYM_CLASS_WEAK_EXTERNAL;
370
371    COFFSymbol *WeakDefault = getLinkedSymbol(MCSym);
372    if (!WeakDefault) {
373      std::string WeakName = (".weak." + MCSym.getName() + ".default").str();
374      WeakDefault = createSymbol(WeakName);
375      if (!Sec)
376        WeakDefault->Data.SectionNumber = COFF::IMAGE_SYM_ABSOLUTE;
377      else
378        WeakDefault->Section = Sec;
379      Local = WeakDefault;
380    }
381
382    Sym->Other = WeakDefault;
383
384    // Setup the Weak External auxiliary symbol.
385    Sym->Aux.resize(1);
386    memset(&Sym->Aux[0], 0, sizeof(Sym->Aux[0]));
387    Sym->Aux[0].AuxType = ATWeakExternal;
388    Sym->Aux[0].Aux.WeakExternal.TagIndex = 0;
389    Sym->Aux[0].Aux.WeakExternal.Characteristics =
390        COFF::IMAGE_WEAK_EXTERN_SEARCH_ALIAS;
391  } else {
392    if (!Base)
393      Sym->Data.SectionNumber = COFF::IMAGE_SYM_ABSOLUTE;
394    else
395      Sym->Section = Sec;
396    Local = Sym;
397  }
398
399  if (Local) {
400    Local->Data.Value = getSymbolValue(MCSym, Layout);
401
402    const MCSymbolCOFF &SymbolCOFF = cast<MCSymbolCOFF>(MCSym);
403    Local->Data.Type = SymbolCOFF.getType();
404    Local->Data.StorageClass = SymbolCOFF.getClass();
405
406    // If no storage class was specified in the streamer, define it here.
407    if (Local->Data.StorageClass == COFF::IMAGE_SYM_CLASS_NULL) {
408      bool IsExternal = MCSym.isExternal() ||
409                        (!MCSym.getFragment() && !MCSym.isVariable());
410
411      Local->Data.StorageClass = IsExternal ? COFF::IMAGE_SYM_CLASS_EXTERNAL
412                                            : COFF::IMAGE_SYM_CLASS_STATIC;
413    }
414  }
415
416  Sym->MC = &MCSym;
417}
418
419// Maximum offsets for different string table entry encodings.
420enum : unsigned { Max7DecimalOffset = 9999999U };
421enum : uint64_t { MaxBase64Offset = 0xFFFFFFFFFULL }; // 64^6, including 0
422
423// Encode a string table entry offset in base 64, padded to 6 chars, and
424// prefixed with a double slash: '//AAAAAA', '//AAAAAB', ...
425// Buffer must be at least 8 bytes large. No terminating null appended.
426static void encodeBase64StringEntry(char *Buffer, uint64_t Value) {
427  assert(Value > Max7DecimalOffset && Value <= MaxBase64Offset &&
428         "Illegal section name encoding for value");
429
430  static const char Alphabet[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
431                                 "abcdefghijklmnopqrstuvwxyz"
432                                 "0123456789+/";
433
434  Buffer[0] = '/';
435  Buffer[1] = '/';
436
437  char *Ptr = Buffer + 7;
438  for (unsigned i = 0; i < 6; ++i) {
439    unsigned Rem = Value % 64;
440    Value /= 64;
441    *(Ptr--) = Alphabet[Rem];
442  }
443}
444
445void WinCOFFObjectWriter::SetSectionName(COFFSection &S) {
446  if (S.Name.size() <= COFF::NameSize) {
447    std::memcpy(S.Header.Name, S.Name.c_str(), S.Name.size());
448    return;
449  }
450
451  uint64_t StringTableEntry = Strings.getOffset(S.Name);
452  if (StringTableEntry <= Max7DecimalOffset) {
453    SmallVector<char, COFF::NameSize> Buffer;
454    Twine('/').concat(Twine(StringTableEntry)).toVector(Buffer);
455    assert(Buffer.size() <= COFF::NameSize && Buffer.size() >= 2);
456    std::memcpy(S.Header.Name, Buffer.data(), Buffer.size());
457    return;
458  }
459  if (StringTableEntry <= MaxBase64Offset) {
460    // Starting with 10,000,000, offsets are encoded as base64.
461    encodeBase64StringEntry(S.Header.Name, StringTableEntry);
462    return;
463  }
464  report_fatal_error("COFF string table is greater than 64 GB.");
465}
466
467void WinCOFFObjectWriter::SetSymbolName(COFFSymbol &S) {
468  if (S.Name.size() > COFF::NameSize)
469    S.set_name_offset(Strings.getOffset(S.Name));
470  else
471    std::memcpy(S.Data.Name, S.Name.c_str(), S.Name.size());
472}
473
474bool WinCOFFObjectWriter::IsPhysicalSection(COFFSection *S) {
475  return (S->Header.Characteristics & COFF::IMAGE_SCN_CNT_UNINITIALIZED_DATA) ==
476         0;
477}
478
479//------------------------------------------------------------------------------
480// entity writing methods
481
482void WinCOFFObjectWriter::WriteFileHeader(const COFF::header &Header) {
483  if (UseBigObj) {
484    W.write<uint16_t>(COFF::IMAGE_FILE_MACHINE_UNKNOWN);
485    W.write<uint16_t>(0xFFFF);
486    W.write<uint16_t>(COFF::BigObjHeader::MinBigObjectVersion);
487    W.write<uint16_t>(Header.Machine);
488    W.write<uint32_t>(Header.TimeDateStamp);
489    W.OS.write(COFF::BigObjMagic, sizeof(COFF::BigObjMagic));
490    W.write<uint32_t>(0);
491    W.write<uint32_t>(0);
492    W.write<uint32_t>(0);
493    W.write<uint32_t>(0);
494    W.write<uint32_t>(Header.NumberOfSections);
495    W.write<uint32_t>(Header.PointerToSymbolTable);
496    W.write<uint32_t>(Header.NumberOfSymbols);
497  } else {
498    W.write<uint16_t>(Header.Machine);
499    W.write<uint16_t>(static_cast<int16_t>(Header.NumberOfSections));
500    W.write<uint32_t>(Header.TimeDateStamp);
501    W.write<uint32_t>(Header.PointerToSymbolTable);
502    W.write<uint32_t>(Header.NumberOfSymbols);
503    W.write<uint16_t>(Header.SizeOfOptionalHeader);
504    W.write<uint16_t>(Header.Characteristics);
505  }
506}
507
508void WinCOFFObjectWriter::WriteSymbol(const COFFSymbol &S) {
509  W.OS.write(S.Data.Name, COFF::NameSize);
510  W.write<uint32_t>(S.Data.Value);
511  if (UseBigObj)
512    W.write<uint32_t>(S.Data.SectionNumber);
513  else
514    W.write<uint16_t>(static_cast<int16_t>(S.Data.SectionNumber));
515  W.write<uint16_t>(S.Data.Type);
516  W.OS << char(S.Data.StorageClass);
517  W.OS << char(S.Data.NumberOfAuxSymbols);
518  WriteAuxiliarySymbols(S.Aux);
519}
520
521void WinCOFFObjectWriter::WriteAuxiliarySymbols(
522    const COFFSymbol::AuxiliarySymbols &S) {
523  for (const AuxSymbol &i : S) {
524    switch (i.AuxType) {
525    case ATWeakExternal:
526      W.write<uint32_t>(i.Aux.WeakExternal.TagIndex);
527      W.write<uint32_t>(i.Aux.WeakExternal.Characteristics);
528      W.OS.write_zeros(sizeof(i.Aux.WeakExternal.unused));
529      if (UseBigObj)
530        W.OS.write_zeros(COFF::Symbol32Size - COFF::Symbol16Size);
531      break;
532    case ATFile:
533      W.OS.write(reinterpret_cast<const char *>(&i.Aux),
534                        UseBigObj ? COFF::Symbol32Size : COFF::Symbol16Size);
535      break;
536    case ATSectionDefinition:
537      W.write<uint32_t>(i.Aux.SectionDefinition.Length);
538      W.write<uint16_t>(i.Aux.SectionDefinition.NumberOfRelocations);
539      W.write<uint16_t>(i.Aux.SectionDefinition.NumberOfLinenumbers);
540      W.write<uint32_t>(i.Aux.SectionDefinition.CheckSum);
541      W.write<uint16_t>(static_cast<int16_t>(i.Aux.SectionDefinition.Number));
542      W.OS << char(i.Aux.SectionDefinition.Selection);
543      W.OS.write_zeros(sizeof(i.Aux.SectionDefinition.unused));
544      W.write<uint16_t>(static_cast<int16_t>(i.Aux.SectionDefinition.Number >> 16));
545      if (UseBigObj)
546        W.OS.write_zeros(COFF::Symbol32Size - COFF::Symbol16Size);
547      break;
548    }
549  }
550}
551
552// Write the section header.
553void WinCOFFObjectWriter::writeSectionHeaders() {
554  // Section numbers must be monotonically increasing in the section
555  // header, but our Sections array is not sorted by section number,
556  // so make a copy of Sections and sort it.
557  std::vector<COFFSection *> Arr;
558  for (auto &Section : Sections)
559    Arr.push_back(Section.get());
560  llvm::sort(Arr, [](const COFFSection *A, const COFFSection *B) {
561    return A->Number < B->Number;
562  });
563
564  for (auto &Section : Arr) {
565    if (Section->Number == -1)
566      continue;
567
568    COFF::section &S = Section->Header;
569    if (Section->Relocations.size() >= 0xffff)
570      S.Characteristics |= COFF::IMAGE_SCN_LNK_NRELOC_OVFL;
571    W.OS.write(S.Name, COFF::NameSize);
572    W.write<uint32_t>(S.VirtualSize);
573    W.write<uint32_t>(S.VirtualAddress);
574    W.write<uint32_t>(S.SizeOfRawData);
575    W.write<uint32_t>(S.PointerToRawData);
576    W.write<uint32_t>(S.PointerToRelocations);
577    W.write<uint32_t>(S.PointerToLineNumbers);
578    W.write<uint16_t>(S.NumberOfRelocations);
579    W.write<uint16_t>(S.NumberOfLineNumbers);
580    W.write<uint32_t>(S.Characteristics);
581  }
582}
583
584void WinCOFFObjectWriter::WriteRelocation(const COFF::relocation &R) {
585  W.write<uint32_t>(R.VirtualAddress);
586  W.write<uint32_t>(R.SymbolTableIndex);
587  W.write<uint16_t>(R.Type);
588}
589
590// Write MCSec's contents. What this function does is essentially
591// "Asm.writeSectionData(&MCSec, Layout)", but it's a bit complicated
592// because it needs to compute a CRC.
593uint32_t WinCOFFObjectWriter::writeSectionContents(MCAssembler &Asm,
594                                                   const MCAsmLayout &Layout,
595                                                   const MCSection &MCSec) {
596  // Save the contents of the section to a temporary buffer, we need this
597  // to CRC the data before we dump it into the object file.
598  SmallVector<char, 128> Buf;
599  raw_svector_ostream VecOS(Buf);
600  Asm.writeSectionData(VecOS, &MCSec, Layout);
601
602  // Write the section contents to the object file.
603  W.OS << Buf;
604
605  // Calculate our CRC with an initial value of '0', this is not how
606  // JamCRC is specified but it aligns with the expected output.
607  JamCRC JC(/*Init=*/0);
608  JC.update(makeArrayRef(reinterpret_cast<uint8_t*>(Buf.data()), Buf.size()));
609  return JC.getCRC();
610}
611
612void WinCOFFObjectWriter::writeSection(MCAssembler &Asm,
613                                       const MCAsmLayout &Layout,
614                                       const COFFSection &Sec,
615                                       const MCSection &MCSec) {
616  if (Sec.Number == -1)
617    return;
618
619  // Write the section contents.
620  if (Sec.Header.PointerToRawData != 0) {
621    assert(W.OS.tell() == Sec.Header.PointerToRawData &&
622           "Section::PointerToRawData is insane!");
623
624    uint32_t CRC = writeSectionContents(Asm, Layout, MCSec);
625
626    // Update the section definition auxiliary symbol to record the CRC.
627    COFFSection *Sec = SectionMap[&MCSec];
628    COFFSymbol::AuxiliarySymbols &AuxSyms = Sec->Symbol->Aux;
629    assert(AuxSyms.size() == 1 && AuxSyms[0].AuxType == ATSectionDefinition);
630    AuxSymbol &SecDef = AuxSyms[0];
631    SecDef.Aux.SectionDefinition.CheckSum = CRC;
632  }
633
634  // Write relocations for this section.
635  if (Sec.Relocations.empty()) {
636    assert(Sec.Header.PointerToRelocations == 0 &&
637           "Section::PointerToRelocations is insane!");
638    return;
639  }
640
641  assert(W.OS.tell() == Sec.Header.PointerToRelocations &&
642         "Section::PointerToRelocations is insane!");
643
644  if (Sec.Relocations.size() >= 0xffff) {
645    // In case of overflow, write actual relocation count as first
646    // relocation. Including the synthetic reloc itself (+ 1).
647    COFF::relocation R;
648    R.VirtualAddress = Sec.Relocations.size() + 1;
649    R.SymbolTableIndex = 0;
650    R.Type = 0;
651    WriteRelocation(R);
652  }
653
654  for (const auto &Relocation : Sec.Relocations)
655    WriteRelocation(Relocation.Data);
656}
657
658////////////////////////////////////////////////////////////////////////////////
659// MCObjectWriter interface implementations
660
661void WinCOFFObjectWriter::executePostLayoutBinding(MCAssembler &Asm,
662                                                   const MCAsmLayout &Layout) {
663  if (EmitAddrsigSection) {
664    AddrsigSection = Asm.getContext().getCOFFSection(
665        ".llvm_addrsig", COFF::IMAGE_SCN_LNK_REMOVE,
666        SectionKind::getMetadata());
667    Asm.registerSection(*AddrsigSection);
668  }
669
670  // "Define" each section & symbol. This creates section & symbol
671  // entries in the staging area.
672  for (const auto &Section : Asm)
673    defineSection(static_cast<const MCSectionCOFF &>(Section));
674
675  for (const MCSymbol &Symbol : Asm.symbols())
676    if (!Symbol.isTemporary())
677      DefineSymbol(Symbol, Asm, Layout);
678}
679
680bool WinCOFFObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(
681    const MCAssembler &Asm, const MCSymbol &SymA, const MCFragment &FB,
682    bool InSet, bool IsPCRel) const {
683  // Don't drop relocations between functions, even if they are in the same text
684  // section. Multiple Visual C++ linker features depend on having the
685  // relocations present. The /INCREMENTAL flag will cause these relocations to
686  // point to thunks, and the /GUARD:CF flag assumes that it can use relocations
687  // to approximate the set of all address taken functions. LLD's implementation
688  // of /GUARD:CF also relies on the existance of these relocations.
689  uint16_t Type = cast<MCSymbolCOFF>(SymA).getType();
690  if ((Type >> COFF::SCT_COMPLEX_TYPE_SHIFT) == COFF::IMAGE_SYM_DTYPE_FUNCTION)
691    return false;
692  return MCObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(Asm, SymA, FB,
693                                                                InSet, IsPCRel);
694}
695
696void WinCOFFObjectWriter::recordRelocation(MCAssembler &Asm,
697                                           const MCAsmLayout &Layout,
698                                           const MCFragment *Fragment,
699                                           const MCFixup &Fixup, MCValue Target,
700                                           uint64_t &FixedValue) {
701  assert(Target.getSymA() && "Relocation must reference a symbol!");
702
703  const MCSymbol &A = Target.getSymA()->getSymbol();
704  if (!A.isRegistered()) {
705    Asm.getContext().reportError(Fixup.getLoc(),
706                                      Twine("symbol '") + A.getName() +
707                                          "' can not be undefined");
708    return;
709  }
710  if (A.isTemporary() && A.isUndefined()) {
711    Asm.getContext().reportError(Fixup.getLoc(),
712                                      Twine("assembler label '") + A.getName() +
713                                          "' can not be undefined");
714    return;
715  }
716
717  MCSection *MCSec = Fragment->getParent();
718
719  // Mark this symbol as requiring an entry in the symbol table.
720  assert(SectionMap.find(MCSec) != SectionMap.end() &&
721         "Section must already have been defined in executePostLayoutBinding!");
722
723  COFFSection *Sec = SectionMap[MCSec];
724  const MCSymbolRefExpr *SymB = Target.getSymB();
725
726  if (SymB) {
727    const MCSymbol *B = &SymB->getSymbol();
728    if (!B->getFragment()) {
729      Asm.getContext().reportError(
730          Fixup.getLoc(),
731          Twine("symbol '") + B->getName() +
732              "' can not be undefined in a subtraction expression");
733      return;
734    }
735
736    // Offset of the symbol in the section
737    int64_t OffsetOfB = Layout.getSymbolOffset(*B);
738
739    // Offset of the relocation in the section
740    int64_t OffsetOfRelocation =
741        Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
742
743    FixedValue = (OffsetOfRelocation - OffsetOfB) + Target.getConstant();
744  } else {
745    FixedValue = Target.getConstant();
746  }
747
748  COFFRelocation Reloc;
749
750  Reloc.Data.SymbolTableIndex = 0;
751  Reloc.Data.VirtualAddress = Layout.getFragmentOffset(Fragment);
752
753  // Turn relocations for temporary symbols into section relocations.
754  if (A.isTemporary()) {
755    MCSection *TargetSection = &A.getSection();
756    assert(
757        SectionMap.find(TargetSection) != SectionMap.end() &&
758        "Section must already have been defined in executePostLayoutBinding!");
759    Reloc.Symb = SectionMap[TargetSection]->Symbol;
760    FixedValue += Layout.getSymbolOffset(A);
761  } else {
762    assert(
763        SymbolMap.find(&A) != SymbolMap.end() &&
764        "Symbol must already have been defined in executePostLayoutBinding!");
765    Reloc.Symb = SymbolMap[&A];
766  }
767
768  ++Reloc.Symb->Relocations;
769
770  Reloc.Data.VirtualAddress += Fixup.getOffset();
771  Reloc.Data.Type = TargetObjectWriter->getRelocType(
772      Asm.getContext(), Target, Fixup, SymB, Asm.getBackend());
773
774  // FIXME: Can anyone explain what this does other than adjust for the size
775  // of the offset?
776  if ((Header.Machine == COFF::IMAGE_FILE_MACHINE_AMD64 &&
777       Reloc.Data.Type == COFF::IMAGE_REL_AMD64_REL32) ||
778      (Header.Machine == COFF::IMAGE_FILE_MACHINE_I386 &&
779       Reloc.Data.Type == COFF::IMAGE_REL_I386_REL32))
780    FixedValue += 4;
781
782  if (Header.Machine == COFF::IMAGE_FILE_MACHINE_ARMNT) {
783    switch (Reloc.Data.Type) {
784    case COFF::IMAGE_REL_ARM_ABSOLUTE:
785    case COFF::IMAGE_REL_ARM_ADDR32:
786    case COFF::IMAGE_REL_ARM_ADDR32NB:
787    case COFF::IMAGE_REL_ARM_TOKEN:
788    case COFF::IMAGE_REL_ARM_SECTION:
789    case COFF::IMAGE_REL_ARM_SECREL:
790      break;
791    case COFF::IMAGE_REL_ARM_BRANCH11:
792    case COFF::IMAGE_REL_ARM_BLX11:
793    // IMAGE_REL_ARM_BRANCH11 and IMAGE_REL_ARM_BLX11 are only used for
794    // pre-ARMv7, which implicitly rules it out of ARMNT (it would be valid
795    // for Windows CE).
796    case COFF::IMAGE_REL_ARM_BRANCH24:
797    case COFF::IMAGE_REL_ARM_BLX24:
798    case COFF::IMAGE_REL_ARM_MOV32A:
799      // IMAGE_REL_ARM_BRANCH24, IMAGE_REL_ARM_BLX24, IMAGE_REL_ARM_MOV32A are
800      // only used for ARM mode code, which is documented as being unsupported
801      // by Windows on ARM.  Empirical proof indicates that masm is able to
802      // generate the relocations however the rest of the MSVC toolchain is
803      // unable to handle it.
804      llvm_unreachable("unsupported relocation");
805      break;
806    case COFF::IMAGE_REL_ARM_MOV32T:
807      break;
808    case COFF::IMAGE_REL_ARM_BRANCH20T:
809    case COFF::IMAGE_REL_ARM_BRANCH24T:
810    case COFF::IMAGE_REL_ARM_BLX23T:
811      // IMAGE_REL_BRANCH20T, IMAGE_REL_ARM_BRANCH24T, IMAGE_REL_ARM_BLX23T all
812      // perform a 4 byte adjustment to the relocation.  Relative branches are
813      // offset by 4 on ARM, however, because there is no RELA relocations, all
814      // branches are offset by 4.
815      FixedValue = FixedValue + 4;
816      break;
817    }
818  }
819
820  // The fixed value never makes sense for section indices, ignore it.
821  if (Fixup.getKind() == FK_SecRel_2)
822    FixedValue = 0;
823
824  if (TargetObjectWriter->recordRelocation(Fixup))
825    Sec->Relocations.push_back(Reloc);
826}
827
828static std::time_t getTime() {
829  std::time_t Now = time(nullptr);
830  if (Now < 0 || !isUInt<32>(Now))
831    return UINT32_MAX;
832  return Now;
833}
834
835// Create .file symbols.
836void WinCOFFObjectWriter::createFileSymbols(MCAssembler &Asm) {
837  for (const std::string &Name : Asm.getFileNames()) {
838    // round up to calculate the number of auxiliary symbols required
839    unsigned SymbolSize = UseBigObj ? COFF::Symbol32Size : COFF::Symbol16Size;
840    unsigned Count = (Name.size() + SymbolSize - 1) / SymbolSize;
841
842    COFFSymbol *File = createSymbol(".file");
843    File->Data.SectionNumber = COFF::IMAGE_SYM_DEBUG;
844    File->Data.StorageClass = COFF::IMAGE_SYM_CLASS_FILE;
845    File->Aux.resize(Count);
846
847    unsigned Offset = 0;
848    unsigned Length = Name.size();
849    for (auto &Aux : File->Aux) {
850      Aux.AuxType = ATFile;
851
852      if (Length > SymbolSize) {
853        memcpy(&Aux.Aux, Name.c_str() + Offset, SymbolSize);
854        Length = Length - SymbolSize;
855      } else {
856        memcpy(&Aux.Aux, Name.c_str() + Offset, Length);
857        memset((char *)&Aux.Aux + Length, 0, SymbolSize - Length);
858        break;
859      }
860
861      Offset += SymbolSize;
862    }
863  }
864}
865
866static bool isAssociative(const COFFSection &Section) {
867  return Section.Symbol->Aux[0].Aux.SectionDefinition.Selection ==
868         COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE;
869}
870
871void WinCOFFObjectWriter::assignSectionNumbers() {
872  size_t I = 1;
873  auto Assign = [&](COFFSection &Section) {
874    Section.Number = I;
875    Section.Symbol->Data.SectionNumber = I;
876    Section.Symbol->Aux[0].Aux.SectionDefinition.Number = I;
877    ++I;
878  };
879
880  // Although it is not explicitly requested by the Microsoft COFF spec,
881  // we should avoid emitting forward associative section references,
882  // because MSVC link.exe as of 2017 cannot handle that.
883  for (const std::unique_ptr<COFFSection> &Section : Sections)
884    if (!isAssociative(*Section))
885      Assign(*Section);
886  for (const std::unique_ptr<COFFSection> &Section : Sections)
887    if (isAssociative(*Section))
888      Assign(*Section);
889}
890
891// Assign file offsets to COFF object file structures.
892void WinCOFFObjectWriter::assignFileOffsets(MCAssembler &Asm,
893                                            const MCAsmLayout &Layout) {
894  unsigned Offset = W.OS.tell();
895
896  Offset += UseBigObj ? COFF::Header32Size : COFF::Header16Size;
897  Offset += COFF::SectionSize * Header.NumberOfSections;
898
899  for (const auto &Section : Asm) {
900    COFFSection *Sec = SectionMap[&Section];
901
902    if (Sec->Number == -1)
903      continue;
904
905    Sec->Header.SizeOfRawData = Layout.getSectionAddressSize(&Section);
906
907    if (IsPhysicalSection(Sec)) {
908      Sec->Header.PointerToRawData = Offset;
909      Offset += Sec->Header.SizeOfRawData;
910    }
911
912    if (!Sec->Relocations.empty()) {
913      bool RelocationsOverflow = Sec->Relocations.size() >= 0xffff;
914
915      if (RelocationsOverflow) {
916        // Signal overflow by setting NumberOfRelocations to max value. Actual
917        // size is found in reloc #0. Microsoft tools understand this.
918        Sec->Header.NumberOfRelocations = 0xffff;
919      } else {
920        Sec->Header.NumberOfRelocations = Sec->Relocations.size();
921      }
922      Sec->Header.PointerToRelocations = Offset;
923
924      if (RelocationsOverflow) {
925        // Reloc #0 will contain actual count, so make room for it.
926        Offset += COFF::RelocationSize;
927      }
928
929      Offset += COFF::RelocationSize * Sec->Relocations.size();
930
931      for (auto &Relocation : Sec->Relocations) {
932        assert(Relocation.Symb->getIndex() != -1);
933        Relocation.Data.SymbolTableIndex = Relocation.Symb->getIndex();
934      }
935    }
936
937    assert(Sec->Symbol->Aux.size() == 1 &&
938           "Section's symbol must have one aux!");
939    AuxSymbol &Aux = Sec->Symbol->Aux[0];
940    assert(Aux.AuxType == ATSectionDefinition &&
941           "Section's symbol's aux symbol must be a Section Definition!");
942    Aux.Aux.SectionDefinition.Length = Sec->Header.SizeOfRawData;
943    Aux.Aux.SectionDefinition.NumberOfRelocations =
944        Sec->Header.NumberOfRelocations;
945    Aux.Aux.SectionDefinition.NumberOfLinenumbers =
946        Sec->Header.NumberOfLineNumbers;
947  }
948
949  Header.PointerToSymbolTable = Offset;
950}
951
952uint64_t WinCOFFObjectWriter::writeObject(MCAssembler &Asm,
953                                          const MCAsmLayout &Layout) {
954  uint64_t StartOffset = W.OS.tell();
955
956  if (Sections.size() > INT32_MAX)
957    report_fatal_error(
958        "PE COFF object files can't have more than 2147483647 sections");
959
960  UseBigObj = Sections.size() > COFF::MaxNumberOfSections16;
961  Header.NumberOfSections = Sections.size();
962  Header.NumberOfSymbols = 0;
963
964  assignSectionNumbers();
965  createFileSymbols(Asm);
966
967  for (auto &Symbol : Symbols) {
968    // Update section number & offset for symbols that have them.
969    if (Symbol->Section)
970      Symbol->Data.SectionNumber = Symbol->Section->Number;
971    Symbol->setIndex(Header.NumberOfSymbols++);
972    // Update auxiliary symbol info.
973    Symbol->Data.NumberOfAuxSymbols = Symbol->Aux.size();
974    Header.NumberOfSymbols += Symbol->Data.NumberOfAuxSymbols;
975  }
976
977  // Build string table.
978  for (const auto &S : Sections)
979    if (S->Name.size() > COFF::NameSize)
980      Strings.add(S->Name);
981  for (const auto &S : Symbols)
982    if (S->Name.size() > COFF::NameSize)
983      Strings.add(S->Name);
984  Strings.finalize();
985
986  // Set names.
987  for (const auto &S : Sections)
988    SetSectionName(*S);
989  for (auto &S : Symbols)
990    SetSymbolName(*S);
991
992  // Fixup weak external references.
993  for (auto &Symbol : Symbols) {
994    if (Symbol->Other) {
995      assert(Symbol->getIndex() != -1);
996      assert(Symbol->Aux.size() == 1 && "Symbol must contain one aux symbol!");
997      assert(Symbol->Aux[0].AuxType == ATWeakExternal &&
998             "Symbol's aux symbol must be a Weak External!");
999      Symbol->Aux[0].Aux.WeakExternal.TagIndex = Symbol->Other->getIndex();
1000    }
1001  }
1002
1003  // Fixup associative COMDAT sections.
1004  for (auto &Section : Sections) {
1005    if (Section->Symbol->Aux[0].Aux.SectionDefinition.Selection !=
1006        COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE)
1007      continue;
1008
1009    const MCSectionCOFF &MCSec = *Section->MCSection;
1010    const MCSymbol *AssocMCSym = MCSec.getCOMDATSymbol();
1011    assert(AssocMCSym);
1012
1013    // It's an error to try to associate with an undefined symbol or a symbol
1014    // without a section.
1015    if (!AssocMCSym->isInSection()) {
1016      Asm.getContext().reportError(
1017          SMLoc(), Twine("cannot make section ") + MCSec.getSectionName() +
1018                       Twine(" associative with sectionless symbol ") +
1019                       AssocMCSym->getName());
1020      continue;
1021    }
1022
1023    const auto *AssocMCSec = cast<MCSectionCOFF>(&AssocMCSym->getSection());
1024    assert(SectionMap.count(AssocMCSec));
1025    COFFSection *AssocSec = SectionMap[AssocMCSec];
1026
1027    // Skip this section if the associated section is unused.
1028    if (AssocSec->Number == -1)
1029      continue;
1030
1031    Section->Symbol->Aux[0].Aux.SectionDefinition.Number = AssocSec->Number;
1032  }
1033
1034  // Create the contents of the .llvm_addrsig section.
1035  if (EmitAddrsigSection) {
1036    auto Frag = new MCDataFragment(AddrsigSection);
1037    Frag->setLayoutOrder(0);
1038    raw_svector_ostream OS(Frag->getContents());
1039    for (const MCSymbol *S : AddrsigSyms) {
1040      if (!S->isTemporary()) {
1041        encodeULEB128(S->getIndex(), OS);
1042        continue;
1043      }
1044
1045      MCSection *TargetSection = &S->getSection();
1046      assert(SectionMap.find(TargetSection) != SectionMap.end() &&
1047             "Section must already have been defined in "
1048             "executePostLayoutBinding!");
1049      encodeULEB128(SectionMap[TargetSection]->Symbol->getIndex(), OS);
1050    }
1051  }
1052
1053  assignFileOffsets(Asm, Layout);
1054
1055  // MS LINK expects to be able to use this timestamp to implement their
1056  // /INCREMENTAL feature.
1057  if (Asm.isIncrementalLinkerCompatible()) {
1058    Header.TimeDateStamp = getTime();
1059  } else {
1060    // Have deterministic output if /INCREMENTAL isn't needed. Also matches GNU.
1061    Header.TimeDateStamp = 0;
1062  }
1063
1064  // Write it all to disk...
1065  WriteFileHeader(Header);
1066  writeSectionHeaders();
1067
1068  // Write section contents.
1069  sections::iterator I = Sections.begin();
1070  sections::iterator IE = Sections.end();
1071  MCAssembler::iterator J = Asm.begin();
1072  MCAssembler::iterator JE = Asm.end();
1073  for (; I != IE && J != JE; ++I, ++J)
1074    writeSection(Asm, Layout, **I, *J);
1075
1076  assert(W.OS.tell() == Header.PointerToSymbolTable &&
1077         "Header::PointerToSymbolTable is insane!");
1078
1079  // Write a symbol table.
1080  for (auto &Symbol : Symbols)
1081    if (Symbol->getIndex() != -1)
1082      WriteSymbol(*Symbol);
1083
1084  // Write a string table, which completes the entire COFF file.
1085  Strings.write(W.OS);
1086
1087  return W.OS.tell() - StartOffset;
1088}
1089
1090MCWinCOFFObjectTargetWriter::MCWinCOFFObjectTargetWriter(unsigned Machine_)
1091    : Machine(Machine_) {}
1092
1093// Pin the vtable to this file.
1094void MCWinCOFFObjectTargetWriter::anchor() {}
1095
1096//------------------------------------------------------------------------------
1097// WinCOFFObjectWriter factory function
1098
1099std::unique_ptr<MCObjectWriter> llvm::createWinCOFFObjectWriter(
1100    std::unique_ptr<MCWinCOFFObjectTargetWriter> MOTW, raw_pwrite_stream &OS) {
1101  return std::make_unique<WinCOFFObjectWriter>(std::move(MOTW), OS);
1102}
1103