ELFObjectWriter.cpp revision 36b56886974eae4f9c5ebc96befd3e7bfe5de338 
1//===- lib/MC/ELFObjectWriter.cpp - ELF File Writer -----------------------===//
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 implements ELF object file writer information.
11//
12//===----------------------------------------------------------------------===//
13
14#include "llvm/MC/MCELFObjectWriter.h"
15#include "llvm/ADT/STLExtras.h"
16#include "llvm/ADT/SmallPtrSet.h"
17#include "llvm/ADT/SmallString.h"
18#include "llvm/ADT/StringMap.h"
19#include "llvm/MC/MCAsmBackend.h"
20#include "llvm/MC/MCAsmLayout.h"
21#include "llvm/MC/MCAssembler.h"
22#include "llvm/MC/MCContext.h"
23#include "llvm/MC/MCELF.h"
24#include "llvm/MC/MCELFSymbolFlags.h"
25#include "llvm/MC/MCExpr.h"
26#include "llvm/MC/MCFixupKindInfo.h"
27#include "llvm/MC/MCObjectWriter.h"
28#include "llvm/MC/MCSectionELF.h"
29#include "llvm/MC/MCValue.h"
30#include "llvm/Support/Debug.h"
31#include "llvm/Support/Endian.h"
32#include "llvm/Support/ELF.h"
33#include "llvm/Support/ErrorHandling.h"
34#include <vector>
35using namespace llvm;
36
37#undef  DEBUG_TYPE
38#define DEBUG_TYPE "reloc-info"
39
40namespace {
41class FragmentWriter {
42  bool IsLittleEndian;
43
44public:
45  FragmentWriter(bool IsLittleEndian);
46  template <typename T> void write(MCDataFragment &F, T Val);
47};
48
49typedef DenseMap<const MCSectionELF *, uint32_t> SectionIndexMapTy;
50
51class SymbolTableWriter {
52  MCAssembler &Asm;
53  FragmentWriter &FWriter;
54  bool Is64Bit;
55  SectionIndexMapTy &SectionIndexMap;
56
57  // The symbol .symtab fragment we are writting to.
58  MCDataFragment *SymtabF;
59
60  // .symtab_shndx fragment we are writting to.
61  MCDataFragment *ShndxF;
62
63  // The numbel of symbols written so far.
64  unsigned NumWritten;
65
66  void createSymtabShndx();
67
68  template <typename T> void write(MCDataFragment &F, T Value);
69
70public:
71  SymbolTableWriter(MCAssembler &Asm, FragmentWriter &FWriter, bool Is64Bit,
72                    SectionIndexMapTy &SectionIndexMap,
73                    MCDataFragment *SymtabF);
74
75  void writeSymbol(uint32_t name, uint8_t info, uint64_t value, uint64_t size,
76                   uint8_t other, uint32_t shndx, bool Reserved);
77};
78
79struct ELFRelocationEntry {
80  uint64_t Offset; // Where is the relocation.
81  bool UseSymbol;  // Relocate with a symbol, not the section.
82  union {
83    const MCSymbol *Symbol;       // The symbol to relocate with.
84    const MCSectionData *Section; // The section to relocate with.
85  };
86  unsigned Type;   // The type of the relocation.
87  uint64_t Addend; // The addend to use.
88
89  ELFRelocationEntry(uint64_t Offset, const MCSymbol *Symbol, unsigned Type,
90                     uint64_t Addend)
91      : Offset(Offset), UseSymbol(true), Symbol(Symbol), Type(Type),
92        Addend(Addend) {}
93
94  ELFRelocationEntry(uint64_t Offset, const MCSectionData *Section,
95                     unsigned Type, uint64_t Addend)
96      : Offset(Offset), UseSymbol(false), Section(Section), Type(Type),
97        Addend(Addend) {}
98};
99
100class ELFObjectWriter : public MCObjectWriter {
101  FragmentWriter FWriter;
102
103  protected:
104
105    static bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind);
106    static bool RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant);
107    static uint64_t SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout);
108    static bool isInSymtab(const MCAssembler &Asm, const MCSymbolData &Data,
109                           bool Used, bool Renamed);
110    static bool isLocal(const MCSymbolData &Data, bool isSignature,
111                        bool isUsedInReloc);
112    static bool IsELFMetaDataSection(const MCSectionData &SD);
113    static uint64_t DataSectionSize(const MCSectionData &SD);
114    static uint64_t GetSectionFileSize(const MCAsmLayout &Layout,
115                                       const MCSectionData &SD);
116    static uint64_t GetSectionAddressSize(const MCAsmLayout &Layout,
117                                          const MCSectionData &SD);
118
119    void WriteDataSectionData(MCAssembler &Asm,
120                              const MCAsmLayout &Layout,
121                              const MCSectionELF &Section);
122
123    /*static bool isFixupKindX86RIPRel(unsigned Kind) {
124      return Kind == X86::reloc_riprel_4byte ||
125        Kind == X86::reloc_riprel_4byte_movq_load;
126    }*/
127
128    /// ELFSymbolData - Helper struct for containing some precomputed
129    /// information on symbols.
130    struct ELFSymbolData {
131      MCSymbolData *SymbolData;
132      uint64_t StringIndex;
133      uint32_t SectionIndex;
134
135      // Support lexicographic sorting.
136      bool operator<(const ELFSymbolData &RHS) const {
137        return SymbolData->getSymbol().getName() <
138               RHS.SymbolData->getSymbol().getName();
139      }
140    };
141
142    /// The target specific ELF writer instance.
143    std::unique_ptr<MCELFObjectTargetWriter> TargetObjectWriter;
144
145    SmallPtrSet<const MCSymbol *, 16> UsedInReloc;
146    SmallPtrSet<const MCSymbol *, 16> WeakrefUsedInReloc;
147    DenseMap<const MCSymbol *, const MCSymbol *> Renames;
148
149    llvm::DenseMap<const MCSectionData *, std::vector<ELFRelocationEntry>>
150    Relocations;
151    DenseMap<const MCSection*, uint64_t> SectionStringTableIndex;
152
153    /// @}
154    /// @name Symbol Table Data
155    /// @{
156
157    SmallString<256> StringTable;
158    std::vector<uint64_t> FileSymbolData;
159    std::vector<ELFSymbolData> LocalSymbolData;
160    std::vector<ELFSymbolData> ExternalSymbolData;
161    std::vector<ELFSymbolData> UndefinedSymbolData;
162
163    /// @}
164
165    bool NeedsGOT;
166
167    // This holds the symbol table index of the last local symbol.
168    unsigned LastLocalSymbolIndex;
169    // This holds the .strtab section index.
170    unsigned StringTableIndex;
171    // This holds the .symtab section index.
172    unsigned SymbolTableIndex;
173
174    unsigned ShstrtabIndex;
175
176
177    // TargetObjectWriter wrappers.
178    bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
179    bool hasRelocationAddend() const {
180      return TargetObjectWriter->hasRelocationAddend();
181    }
182    unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
183                          bool IsPCRel) const {
184      return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel);
185    }
186
187  public:
188    ELFObjectWriter(MCELFObjectTargetWriter *MOTW, raw_ostream &_OS,
189                    bool IsLittleEndian)
190        : MCObjectWriter(_OS, IsLittleEndian), FWriter(IsLittleEndian),
191          TargetObjectWriter(MOTW), NeedsGOT(false) {}
192
193    virtual ~ELFObjectWriter();
194
195    void WriteWord(uint64_t W) {
196      if (is64Bit())
197        Write64(W);
198      else
199        Write32(W);
200    }
201
202    template <typename T> void write(MCDataFragment &F, T Value) {
203      FWriter.write(F, Value);
204    }
205
206    void WriteHeader(const MCAssembler &Asm,
207                     uint64_t SectionDataSize,
208                     unsigned NumberOfSections);
209
210    void WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
211                     const MCAsmLayout &Layout);
212
213    void WriteSymbolTable(MCDataFragment *SymtabF, MCAssembler &Asm,
214                          const MCAsmLayout &Layout,
215                          SectionIndexMapTy &SectionIndexMap);
216
217    bool shouldRelocateWithSymbol(const MCSymbolRefExpr *RefA,
218                                  const MCSymbolData *SD, uint64_t C,
219                                  unsigned Type) const;
220
221    void RecordRelocation(const MCAssembler &Asm, const MCAsmLayout &Layout,
222                          const MCFragment *Fragment, const MCFixup &Fixup,
223                          MCValue Target, bool &IsPCRel,
224                          uint64_t &FixedValue) override;
225
226    uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm,
227                                         const MCSymbol *S);
228
229    // Map from a group section to the signature symbol
230    typedef DenseMap<const MCSectionELF*, const MCSymbol*> GroupMapTy;
231    // Map from a signature symbol to the group section
232    typedef DenseMap<const MCSymbol*, const MCSectionELF*> RevGroupMapTy;
233    // Map from a section to the section with the relocations
234    typedef DenseMap<const MCSectionELF*, const MCSectionELF*> RelMapTy;
235    // Map from a section to its offset
236    typedef DenseMap<const MCSectionELF*, uint64_t> SectionOffsetMapTy;
237
238    /// Compute the symbol table data
239    ///
240    /// \param Asm - The assembler.
241    /// \param SectionIndexMap - Maps a section to its index.
242    /// \param RevGroupMap - Maps a signature symbol to the group section.
243    /// \param NumRegularSections - Number of non-relocation sections.
244    void computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
245                            const SectionIndexMapTy &SectionIndexMap,
246                            RevGroupMapTy RevGroupMap,
247                            unsigned NumRegularSections);
248
249    void ComputeIndexMap(MCAssembler &Asm,
250                         SectionIndexMapTy &SectionIndexMap,
251                         const RelMapTy &RelMap);
252
253    void CreateRelocationSections(MCAssembler &Asm, MCAsmLayout &Layout,
254                                  RelMapTy &RelMap);
255
256    void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout,
257                          const RelMapTy &RelMap);
258
259    void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout,
260                                SectionIndexMapTy &SectionIndexMap,
261                                const RelMapTy &RelMap);
262
263    // Create the sections that show up in the symbol table. Currently
264    // those are the .note.GNU-stack section and the group sections.
265    void CreateIndexedSections(MCAssembler &Asm, MCAsmLayout &Layout,
266                               GroupMapTy &GroupMap,
267                               RevGroupMapTy &RevGroupMap,
268                               SectionIndexMapTy &SectionIndexMap,
269                               const RelMapTy &RelMap);
270
271    void ExecutePostLayoutBinding(MCAssembler &Asm,
272                                  const MCAsmLayout &Layout) override;
273
274    void WriteSectionHeader(MCAssembler &Asm, const GroupMapTy &GroupMap,
275                            const MCAsmLayout &Layout,
276                            const SectionIndexMapTy &SectionIndexMap,
277                            const SectionOffsetMapTy &SectionOffsetMap);
278
279    void ComputeSectionOrder(MCAssembler &Asm,
280                             std::vector<const MCSectionELF*> &Sections);
281
282    void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
283                          uint64_t Address, uint64_t Offset,
284                          uint64_t Size, uint32_t Link, uint32_t Info,
285                          uint64_t Alignment, uint64_t EntrySize);
286
287    void WriteRelocationsFragment(const MCAssembler &Asm,
288                                  MCDataFragment *F,
289                                  const MCSectionData *SD);
290
291    bool
292    IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
293                                           const MCSymbolData &DataA,
294                                           const MCFragment &FB,
295                                           bool InSet,
296                                           bool IsPCRel) const override;
297
298    void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
299    void WriteSection(MCAssembler &Asm,
300                      const SectionIndexMapTy &SectionIndexMap,
301                      uint32_t GroupSymbolIndex,
302                      uint64_t Offset, uint64_t Size, uint64_t Alignment,
303                      const MCSectionELF &Section);
304  };
305}
306
307FragmentWriter::FragmentWriter(bool IsLittleEndian)
308    : IsLittleEndian(IsLittleEndian) {}
309
310template <typename T> void FragmentWriter::write(MCDataFragment &F, T Val) {
311  if (IsLittleEndian)
312    Val = support::endian::byte_swap<T, support::little>(Val);
313  else
314    Val = support::endian::byte_swap<T, support::big>(Val);
315  const char *Start = (const char *)&Val;
316  F.getContents().append(Start, Start + sizeof(T));
317}
318
319void SymbolTableWriter::createSymtabShndx() {
320  if (ShndxF)
321    return;
322
323  MCContext &Ctx = Asm.getContext();
324  const MCSectionELF *SymtabShndxSection =
325      Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0,
326                        SectionKind::getReadOnly(), 4, "");
327  MCSectionData *SymtabShndxSD =
328      &Asm.getOrCreateSectionData(*SymtabShndxSection);
329  SymtabShndxSD->setAlignment(4);
330  ShndxF = new MCDataFragment(SymtabShndxSD);
331  unsigned Index = SectionIndexMap.size() + 1;
332  SectionIndexMap[SymtabShndxSection] = Index;
333
334  for (unsigned I = 0; I < NumWritten; ++I)
335    write(*ShndxF, uint32_t(0));
336}
337
338template <typename T>
339void SymbolTableWriter::write(MCDataFragment &F, T Value) {
340  FWriter.write(F, Value);
341}
342
343SymbolTableWriter::SymbolTableWriter(MCAssembler &Asm, FragmentWriter &FWriter,
344                                     bool Is64Bit,
345                                     SectionIndexMapTy &SectionIndexMap,
346                                     MCDataFragment *SymtabF)
347    : Asm(Asm), FWriter(FWriter), Is64Bit(Is64Bit),
348      SectionIndexMap(SectionIndexMap), SymtabF(SymtabF), ShndxF(nullptr),
349      NumWritten(0) {}
350
351void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
352                                    uint64_t size, uint8_t other,
353                                    uint32_t shndx, bool Reserved) {
354  bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved;
355
356  if (LargeIndex)
357    createSymtabShndx();
358
359  if (ShndxF) {
360    if (LargeIndex)
361      write(*ShndxF, shndx);
362    else
363      write(*ShndxF, uint32_t(0));
364  }
365
366  uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
367
368  raw_svector_ostream OS(SymtabF->getContents());
369
370  if (Is64Bit) {
371    write(*SymtabF, name);  // st_name
372    write(*SymtabF, info);  // st_info
373    write(*SymtabF, other); // st_other
374    write(*SymtabF, Index); // st_shndx
375    write(*SymtabF, value); // st_value
376    write(*SymtabF, size);  // st_size
377  } else {
378    write(*SymtabF, name);            // st_name
379    write(*SymtabF, uint32_t(value)); // st_value
380    write(*SymtabF, uint32_t(size));  // st_size
381    write(*SymtabF, info);            // st_info
382    write(*SymtabF, other);           // st_other
383    write(*SymtabF, Index);           // st_shndx
384  }
385
386  ++NumWritten;
387}
388
389bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
390  const MCFixupKindInfo &FKI =
391    Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
392
393  return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
394}
395
396bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) {
397  switch (Variant) {
398  default:
399    return false;
400  case MCSymbolRefExpr::VK_GOT:
401  case MCSymbolRefExpr::VK_PLT:
402  case MCSymbolRefExpr::VK_GOTPCREL:
403  case MCSymbolRefExpr::VK_GOTOFF:
404  case MCSymbolRefExpr::VK_TPOFF:
405  case MCSymbolRefExpr::VK_TLSGD:
406  case MCSymbolRefExpr::VK_GOTTPOFF:
407  case MCSymbolRefExpr::VK_INDNTPOFF:
408  case MCSymbolRefExpr::VK_NTPOFF:
409  case MCSymbolRefExpr::VK_GOTNTPOFF:
410  case MCSymbolRefExpr::VK_TLSLDM:
411  case MCSymbolRefExpr::VK_DTPOFF:
412  case MCSymbolRefExpr::VK_TLSLD:
413    return true;
414  }
415}
416
417ELFObjectWriter::~ELFObjectWriter()
418{}
419
420// Emit the ELF header.
421void ELFObjectWriter::WriteHeader(const MCAssembler &Asm,
422                                  uint64_t SectionDataSize,
423                                  unsigned NumberOfSections) {
424  // ELF Header
425  // ----------
426  //
427  // Note
428  // ----
429  // emitWord method behaves differently for ELF32 and ELF64, writing
430  // 4 bytes in the former and 8 in the latter.
431
432  Write8(0x7f); // e_ident[EI_MAG0]
433  Write8('E');  // e_ident[EI_MAG1]
434  Write8('L');  // e_ident[EI_MAG2]
435  Write8('F');  // e_ident[EI_MAG3]
436
437  Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
438
439  // e_ident[EI_DATA]
440  Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
441
442  Write8(ELF::EV_CURRENT);        // e_ident[EI_VERSION]
443  // e_ident[EI_OSABI]
444  Write8(TargetObjectWriter->getOSABI());
445  Write8(0);                  // e_ident[EI_ABIVERSION]
446
447  WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
448
449  Write16(ELF::ET_REL);             // e_type
450
451  Write16(TargetObjectWriter->getEMachine()); // e_machine = target
452
453  Write32(ELF::EV_CURRENT);         // e_version
454  WriteWord(0);                    // e_entry, no entry point in .o file
455  WriteWord(0);                    // e_phoff, no program header for .o
456  WriteWord(SectionDataSize + (is64Bit() ? sizeof(ELF::Elf64_Ehdr) :
457            sizeof(ELF::Elf32_Ehdr)));  // e_shoff = sec hdr table off in bytes
458
459  // e_flags = whatever the target wants
460  Write32(Asm.getELFHeaderEFlags());
461
462  // e_ehsize = ELF header size
463  Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
464
465  Write16(0);                  // e_phentsize = prog header entry size
466  Write16(0);                  // e_phnum = # prog header entries = 0
467
468  // e_shentsize = Section header entry size
469  Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
470
471  // e_shnum     = # of section header ents
472  if (NumberOfSections >= ELF::SHN_LORESERVE)
473    Write16(ELF::SHN_UNDEF);
474  else
475    Write16(NumberOfSections);
476
477  // e_shstrndx  = Section # of '.shstrtab'
478  if (ShstrtabIndex >= ELF::SHN_LORESERVE)
479    Write16(ELF::SHN_XINDEX);
480  else
481    Write16(ShstrtabIndex);
482}
483
484uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &OrigData,
485                                      const MCAsmLayout &Layout) {
486  MCSymbolData *Data = &OrigData;
487  if (Data->isCommon() && Data->isExternal())
488    return Data->getCommonAlignment();
489
490  const MCSymbol *Symbol = &Data->getSymbol();
491  bool IsThumbFunc = OrigData.getFlags() & ELF_Other_ThumbFunc;
492
493  uint64_t Res = 0;
494  if (Symbol->isVariable()) {
495    const MCExpr *Expr = Symbol->getVariableValue();
496    MCValue Value;
497    if (!Expr->EvaluateAsRelocatable(Value, &Layout))
498      llvm_unreachable("Invalid expression");
499
500    assert(!Value.getSymB());
501
502    Res = Value.getConstant();
503
504    if (const MCSymbolRefExpr *A = Value.getSymA()) {
505      Symbol = &A->getSymbol();
506      Data = &Layout.getAssembler().getSymbolData(*Symbol);
507    } else {
508      Symbol = 0;
509      Data = 0;
510    }
511  }
512
513  if (IsThumbFunc)
514    Res |= 1;
515
516  if (!Symbol || !Symbol->isInSection())
517    return Res;
518
519  Res += Layout.getSymbolOffset(Data);
520
521  return Res;
522}
523
524void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
525                                               const MCAsmLayout &Layout) {
526  // The presence of symbol versions causes undefined symbols and
527  // versions declared with @@@ to be renamed.
528
529  for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
530         ie = Asm.symbol_end(); it != ie; ++it) {
531    const MCSymbol &Alias = it->getSymbol();
532    const MCSymbol &Symbol = Alias.AliasedSymbol();
533    MCSymbolData &SD = Asm.getSymbolData(Symbol);
534
535    // Not an alias.
536    if (&Symbol == &Alias)
537      continue;
538
539    StringRef AliasName = Alias.getName();
540    size_t Pos = AliasName.find('@');
541    if (Pos == StringRef::npos)
542      continue;
543
544    // Aliases defined with .symvar copy the binding from the symbol they alias.
545    // This is the first place we are able to copy this information.
546    it->setExternal(SD.isExternal());
547    MCELF::SetBinding(*it, MCELF::GetBinding(SD));
548
549    StringRef Rest = AliasName.substr(Pos);
550    if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
551      continue;
552
553    // FIXME: produce a better error message.
554    if (Symbol.isUndefined() && Rest.startswith("@@") &&
555        !Rest.startswith("@@@"))
556      report_fatal_error("A @@ version cannot be undefined");
557
558    Renames.insert(std::make_pair(&Symbol, &Alias));
559  }
560}
561
562static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
563  uint8_t Type = newType;
564
565  // Propagation rules:
566  // IFUNC > FUNC > OBJECT > NOTYPE
567  // TLS_OBJECT > OBJECT > NOTYPE
568  //
569  // dont let the new type degrade the old type
570  switch (origType) {
571  default:
572    break;
573  case ELF::STT_GNU_IFUNC:
574    if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT ||
575        Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS)
576      Type = ELF::STT_GNU_IFUNC;
577    break;
578  case ELF::STT_FUNC:
579    if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
580        Type == ELF::STT_TLS)
581      Type = ELF::STT_FUNC;
582    break;
583  case ELF::STT_OBJECT:
584    if (Type == ELF::STT_NOTYPE)
585      Type = ELF::STT_OBJECT;
586    break;
587  case ELF::STT_TLS:
588    if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
589        Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
590      Type = ELF::STT_TLS;
591    break;
592  }
593
594  return Type;
595}
596
597static const MCSymbol *getBaseSymbol(const MCAsmLayout &Layout,
598                                     const MCSymbol &Symbol) {
599  if (!Symbol.isVariable())
600    return &Symbol;
601
602  const MCExpr *Expr = Symbol.getVariableValue();
603  MCValue Value;
604  if (!Expr->EvaluateAsRelocatable(Value, &Layout))
605    llvm_unreachable("Invalid Expression");
606  assert(!Value.getSymB());
607  const MCSymbolRefExpr *A = Value.getSymA();
608  if (!A)
609    return nullptr;
610  return getBaseSymbol(Layout, A->getSymbol());
611}
612
613void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
614                                  const MCAsmLayout &Layout) {
615  MCSymbolData &OrigData = *MSD.SymbolData;
616  const MCSymbol *Base = getBaseSymbol(Layout, OrigData.getSymbol());
617
618  // This has to be in sync with when computeSymbolTable uses SHN_ABS or
619  // SHN_COMMON.
620  bool IsReserved = !Base || OrigData.isCommon();
621
622  // Binding and Type share the same byte as upper and lower nibbles
623  uint8_t Binding = MCELF::GetBinding(OrigData);
624  uint8_t Type = MCELF::GetType(OrigData);
625  MCSymbolData *BaseSD = nullptr;
626  if (Base) {
627    BaseSD = &Layout.getAssembler().getSymbolData(*Base);
628    Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD));
629  }
630  if (OrigData.getFlags() & ELF_Other_ThumbFunc)
631    Type = ELF::STT_FUNC;
632  uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
633
634  // Other and Visibility share the same byte with Visibility using the lower
635  // 2 bits
636  uint8_t Visibility = MCELF::GetVisibility(OrigData);
637  uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift);
638  Other |= Visibility;
639
640  uint64_t Value = SymbolValue(OrigData, Layout);
641  if (OrigData.getFlags() & ELF_Other_ThumbFunc)
642    Value |= 1;
643  uint64_t Size = 0;
644
645  const MCExpr *ESize = OrigData.getSize();
646  if (!ESize && Base)
647    ESize = BaseSD->getSize();
648
649  if (ESize) {
650    int64_t Res;
651    if (!ESize->EvaluateAsAbsolute(Res, Layout))
652      report_fatal_error("Size expression must be absolute.");
653    Size = Res;
654  }
655
656  // Write out the symbol table entry
657  Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other,
658                     MSD.SectionIndex, IsReserved);
659}
660
661void ELFObjectWriter::WriteSymbolTable(MCDataFragment *SymtabF,
662                                       MCAssembler &Asm,
663                                       const MCAsmLayout &Layout,
664                                       SectionIndexMapTy &SectionIndexMap) {
665  // The string table must be emitted first because we need the index
666  // into the string table for all the symbol names.
667  assert(StringTable.size() && "Missing string table");
668
669  // FIXME: Make sure the start of the symbol table is aligned.
670
671  SymbolTableWriter Writer(Asm, FWriter, is64Bit(), SectionIndexMap, SymtabF);
672
673  // The first entry is the undefined symbol entry.
674  Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
675
676  for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) {
677    Writer.writeSymbol(FileSymbolData[i], ELF::STT_FILE | ELF::STB_LOCAL, 0, 0,
678                       ELF::STV_DEFAULT, ELF::SHN_ABS, true);
679  }
680
681  // Write the symbol table entries.
682  LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1;
683
684  for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
685    ELFSymbolData &MSD = LocalSymbolData[i];
686    WriteSymbol(Writer, MSD, Layout);
687  }
688
689  // Write out a symbol table entry for each regular section.
690  for (MCAssembler::const_iterator i = Asm.begin(), e = Asm.end(); i != e;
691       ++i) {
692    const MCSectionELF &Section =
693      static_cast<const MCSectionELF&>(i->getSection());
694    if (Section.getType() == ELF::SHT_RELA ||
695        Section.getType() == ELF::SHT_REL ||
696        Section.getType() == ELF::SHT_STRTAB ||
697        Section.getType() == ELF::SHT_SYMTAB ||
698        Section.getType() == ELF::SHT_SYMTAB_SHNDX)
699      continue;
700    Writer.writeSymbol(0, ELF::STT_SECTION, 0, 0, ELF::STV_DEFAULT,
701                       SectionIndexMap.lookup(&Section), false);
702    LastLocalSymbolIndex++;
703  }
704
705  for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
706    ELFSymbolData &MSD = ExternalSymbolData[i];
707    MCSymbolData &Data = *MSD.SymbolData;
708    assert(((Data.getFlags() & ELF_STB_Global) ||
709            (Data.getFlags() & ELF_STB_Weak)) &&
710           "External symbol requires STB_GLOBAL or STB_WEAK flag");
711    WriteSymbol(Writer, MSD, Layout);
712    if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
713      LastLocalSymbolIndex++;
714  }
715
716  for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
717    ELFSymbolData &MSD = UndefinedSymbolData[i];
718    MCSymbolData &Data = *MSD.SymbolData;
719    WriteSymbol(Writer, MSD, Layout);
720    if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
721      LastLocalSymbolIndex++;
722  }
723}
724
725// It is always valid to create a relocation with a symbol. It is preferable
726// to use a relocation with a section if that is possible. Using the section
727// allows us to omit some local symbols from the symbol table.
728bool ELFObjectWriter::shouldRelocateWithSymbol(const MCSymbolRefExpr *RefA,
729                                               const MCSymbolData *SD,
730                                               uint64_t C,
731                                               unsigned Type) const {
732  // A PCRel relocation to an absolute value has no symbol (or section). We
733  // represent that with a relocation to a null section.
734  if (!RefA)
735    return false;
736
737  MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
738  switch (Kind) {
739  default:
740    break;
741  // The .odp creation emits a relocation against the symbol ".TOC." which
742  // create a R_PPC64_TOC relocation. However the relocation symbol name
743  // in final object creation should be NULL, since the symbol does not
744  // really exist, it is just the reference to TOC base for the current
745  // object file. Since the symbol is undefined, returning false results
746  // in a relocation with a null section which is the desired result.
747  case MCSymbolRefExpr::VK_PPC_TOCBASE:
748    return false;
749
750  // These VariantKind cause the relocation to refer to something other than
751  // the symbol itself, like a linker generated table. Since the address of
752  // symbol is not relevant, we cannot replace the symbol with the
753  // section and patch the difference in the addend.
754  case MCSymbolRefExpr::VK_GOT:
755  case MCSymbolRefExpr::VK_PLT:
756  case MCSymbolRefExpr::VK_GOTPCREL:
757  case MCSymbolRefExpr::VK_Mips_GOT:
758  case MCSymbolRefExpr::VK_PPC_GOT_LO:
759  case MCSymbolRefExpr::VK_PPC_GOT_HI:
760  case MCSymbolRefExpr::VK_PPC_GOT_HA:
761    return true;
762  }
763
764  // An undefined symbol is not in any section, so the relocation has to point
765  // to the symbol itself.
766  const MCSymbol &Sym = SD->getSymbol();
767  if (Sym.isUndefined())
768    return true;
769
770  unsigned Binding = MCELF::GetBinding(*SD);
771  switch(Binding) {
772  default:
773    llvm_unreachable("Invalid Binding");
774  case ELF::STB_LOCAL:
775    break;
776  case ELF::STB_WEAK:
777    // If the symbol is weak, it might be overridden by a symbol in another
778    // file. The relocation has to point to the symbol so that the linker
779    // can update it.
780    return true;
781  case ELF::STB_GLOBAL:
782    // Global ELF symbols can be preempted by the dynamic linker. The relocation
783    // has to point to the symbol for a reason analogous to the STB_WEAK case.
784    return true;
785  }
786
787  // If a relocation points to a mergeable section, we have to be careful.
788  // If the offset is zero, a relocation with the section will encode the
789  // same information. With a non-zero offset, the situation is different.
790  // For example, a relocation can point 42 bytes past the end of a string.
791  // If we change such a relocation to use the section, the linker would think
792  // that it pointed to another string and subtracting 42 at runtime will
793  // produce the wrong value.
794  auto &Sec = cast<MCSectionELF>(Sym.getSection());
795  unsigned Flags = Sec.getFlags();
796  if (Flags & ELF::SHF_MERGE) {
797    if (C != 0)
798      return true;
799
800    // It looks like gold has a bug (http://sourceware.org/PR16794) and can
801    // only handle section relocations to mergeable sections if using RELA.
802    if (!hasRelocationAddend())
803      return true;
804  }
805
806  // Most TLS relocations use a got, so they need the symbol. Even those that
807  // are just an offset (@tpoff), require a symbol in some linkers (gold,
808  // but not bfd ld).
809  if (Flags & ELF::SHF_TLS)
810    return true;
811
812  if (TargetObjectWriter->needsRelocateWithSymbol(Type))
813    return true;
814  return false;
815}
816
817void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm,
818                                       const MCAsmLayout &Layout,
819                                       const MCFragment *Fragment,
820                                       const MCFixup &Fixup,
821                                       MCValue Target,
822                                       bool &IsPCRel,
823                                       uint64_t &FixedValue) {
824  const MCSectionData *FixupSection = Fragment->getParent();
825  uint64_t C = Target.getConstant();
826  uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
827
828  if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
829    assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
830           "Should not have constructed this");
831
832    // Let A, B and C being the components of Target and R be the location of
833    // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
834    // If it is pcrel, we want to compute (A - B + C - R).
835
836    // In general, ELF has no relocations for -B. It can only represent (A + C)
837    // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
838    // replace B to implement it: (A - R - K + C)
839    if (IsPCRel)
840      Asm.getContext().FatalError(
841          Fixup.getLoc(),
842          "No relocation available to represent this relative expression");
843
844    const MCSymbol &SymB = RefB->getSymbol();
845
846    if (SymB.isUndefined())
847      Asm.getContext().FatalError(
848          Fixup.getLoc(),
849          Twine("symbol '") + SymB.getName() +
850              "' can not be undefined in a subtraction expression");
851
852    assert(!SymB.isAbsolute() && "Should have been folded");
853    const MCSection &SecB = SymB.getSection();
854    if (&SecB != &FixupSection->getSection())
855      Asm.getContext().FatalError(
856          Fixup.getLoc(), "Cannot represent a difference across sections");
857
858    const MCSymbolData &SymBD = Asm.getSymbolData(SymB);
859    uint64_t SymBOffset = Layout.getSymbolOffset(&SymBD);
860    uint64_t K = SymBOffset - FixupOffset;
861    IsPCRel = true;
862    C -= K;
863  }
864
865  // We either rejected the fixup or folded B into C at this point.
866  const MCSymbolRefExpr *RefA = Target.getSymA();
867  const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
868  const MCSymbolData *SymAD = SymA ? &Asm.getSymbolData(*SymA) : nullptr;
869
870  unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
871  bool RelocateWithSymbol = shouldRelocateWithSymbol(RefA, SymAD, C, Type);
872  if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
873    C += Layout.getSymbolOffset(SymAD);
874
875  uint64_t Addend = 0;
876  if (hasRelocationAddend()) {
877    Addend = C;
878    C = 0;
879  }
880
881  FixedValue = C;
882
883  // FIXME: What is this!?!?
884  MCSymbolRefExpr::VariantKind Modifier =
885      RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None;
886  if (RelocNeedsGOT(Modifier))
887    NeedsGOT = true;
888
889  if (!RelocateWithSymbol) {
890    const MCSection *SecA =
891        (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
892    const MCSectionData *SecAD = SecA ? &Asm.getSectionData(*SecA) : nullptr;
893    ELFRelocationEntry Rec(FixupOffset, SecAD, Type, Addend);
894    Relocations[FixupSection].push_back(Rec);
895    return;
896  }
897
898  if (SymA) {
899    if (const MCSymbol *R = Renames.lookup(SymA))
900      SymA = R;
901
902    if (RefA->getKind() == MCSymbolRefExpr::VK_WEAKREF)
903      WeakrefUsedInReloc.insert(SymA);
904    else
905      UsedInReloc.insert(SymA);
906  }
907  ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
908  Relocations[FixupSection].push_back(Rec);
909  return;
910}
911
912
913uint64_t
914ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
915                                             const MCSymbol *S) {
916  MCSymbolData &SD = Asm.getSymbolData(*S);
917  return SD.getIndex();
918}
919
920bool ELFObjectWriter::isInSymtab(const MCAssembler &Asm,
921                                 const MCSymbolData &Data,
922                                 bool Used, bool Renamed) {
923  const MCSymbol &Symbol = Data.getSymbol();
924  if (Symbol.isVariable()) {
925    const MCExpr *Expr = Symbol.getVariableValue();
926    if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
927      if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
928        return false;
929    }
930  }
931
932  if (Used)
933    return true;
934
935  if (Renamed)
936    return false;
937
938  if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
939    return true;
940
941  const MCSymbol &A = Symbol.AliasedSymbol();
942  if (Symbol.isVariable() && !A.isVariable() && A.isUndefined())
943    return false;
944
945  bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
946  if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
947    return false;
948
949  if (Symbol.isTemporary())
950    return false;
951
952  return true;
953}
954
955bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isSignature,
956                              bool isUsedInReloc) {
957  if (Data.isExternal())
958    return false;
959
960  const MCSymbol &Symbol = Data.getSymbol();
961  const MCSymbol &RefSymbol = Symbol.AliasedSymbol();
962
963  if (RefSymbol.isUndefined() && !RefSymbol.isVariable()) {
964    if (isSignature && !isUsedInReloc)
965      return true;
966
967    return false;
968  }
969
970  return true;
971}
972
973void ELFObjectWriter::ComputeIndexMap(MCAssembler &Asm,
974                                      SectionIndexMapTy &SectionIndexMap,
975                                      const RelMapTy &RelMap) {
976  unsigned Index = 1;
977  for (MCAssembler::iterator it = Asm.begin(),
978         ie = Asm.end(); it != ie; ++it) {
979    const MCSectionELF &Section =
980      static_cast<const MCSectionELF &>(it->getSection());
981    if (Section.getType() != ELF::SHT_GROUP)
982      continue;
983    SectionIndexMap[&Section] = Index++;
984  }
985
986  for (MCAssembler::iterator it = Asm.begin(),
987         ie = Asm.end(); it != ie; ++it) {
988    const MCSectionELF &Section =
989      static_cast<const MCSectionELF &>(it->getSection());
990    if (Section.getType() == ELF::SHT_GROUP ||
991        Section.getType() == ELF::SHT_REL ||
992        Section.getType() == ELF::SHT_RELA)
993      continue;
994    SectionIndexMap[&Section] = Index++;
995    const MCSectionELF *RelSection = RelMap.lookup(&Section);
996    if (RelSection)
997      SectionIndexMap[RelSection] = Index++;
998  }
999}
1000
1001void
1002ELFObjectWriter::computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
1003                                    const SectionIndexMapTy &SectionIndexMap,
1004                                    RevGroupMapTy RevGroupMap,
1005                                    unsigned NumRegularSections) {
1006  // FIXME: Is this the correct place to do this?
1007  // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?
1008  if (NeedsGOT) {
1009    StringRef Name = "_GLOBAL_OFFSET_TABLE_";
1010    MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
1011    MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
1012    Data.setExternal(true);
1013    MCELF::SetBinding(Data, ELF::STB_GLOBAL);
1014  }
1015
1016  // Index 0 is always the empty string.
1017  StringMap<uint64_t> StringIndexMap;
1018  StringTable += '\x00';
1019
1020  // FIXME: We could optimize suffixes in strtab in the same way we
1021  // optimize them in shstrtab.
1022
1023  for (MCAssembler::const_file_name_iterator it = Asm.file_names_begin(),
1024                                            ie = Asm.file_names_end();
1025                                            it != ie;
1026                                            ++it) {
1027    StringRef Name = *it;
1028    uint64_t &Entry = StringIndexMap[Name];
1029    if (!Entry) {
1030      Entry = StringTable.size();
1031      StringTable += Name;
1032      StringTable += '\x00';
1033    }
1034    FileSymbolData.push_back(Entry);
1035  }
1036
1037  // Add the data for the symbols.
1038  for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
1039         ie = Asm.symbol_end(); it != ie; ++it) {
1040    const MCSymbol &Symbol = it->getSymbol();
1041
1042    bool Used = UsedInReloc.count(&Symbol);
1043    bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
1044    bool isSignature = RevGroupMap.count(&Symbol);
1045
1046    if (!isInSymtab(Asm, *it,
1047                    Used || WeakrefUsed || isSignature,
1048                    Renames.count(&Symbol)))
1049      continue;
1050
1051    ELFSymbolData MSD;
1052    MSD.SymbolData = it;
1053    const MCSymbol *BaseSymbol = getBaseSymbol(Layout, Symbol);
1054
1055    // Undefined symbols are global, but this is the first place we
1056    // are able to set it.
1057    bool Local = isLocal(*it, isSignature, Used);
1058    if (!Local && MCELF::GetBinding(*it) == ELF::STB_LOCAL) {
1059      assert(BaseSymbol);
1060      MCSymbolData &SD = Asm.getSymbolData(*BaseSymbol);
1061      MCELF::SetBinding(*it, ELF::STB_GLOBAL);
1062      MCELF::SetBinding(SD, ELF::STB_GLOBAL);
1063    }
1064
1065    if (!BaseSymbol) {
1066      MSD.SectionIndex = ELF::SHN_ABS;
1067    } else if (it->isCommon()) {
1068      assert(!Local);
1069      MSD.SectionIndex = ELF::SHN_COMMON;
1070    } else if (BaseSymbol->isUndefined()) {
1071      if (isSignature && !Used)
1072        MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap[&Symbol]);
1073      else
1074        MSD.SectionIndex = ELF::SHN_UNDEF;
1075      if (!Used && WeakrefUsed)
1076        MCELF::SetBinding(*it, ELF::STB_WEAK);
1077    } else {
1078      const MCSectionELF &Section =
1079        static_cast<const MCSectionELF&>(BaseSymbol->getSection());
1080      MSD.SectionIndex = SectionIndexMap.lookup(&Section);
1081      assert(MSD.SectionIndex && "Invalid section index!");
1082    }
1083
1084    // The @@@ in symbol version is replaced with @ in undefined symbols and
1085    // @@ in defined ones.
1086    StringRef Name = Symbol.getName();
1087    SmallString<32> Buf;
1088
1089    size_t Pos = Name.find("@@@");
1090    if (Pos != StringRef::npos) {
1091      Buf += Name.substr(0, Pos);
1092      unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
1093      Buf += Name.substr(Pos + Skip);
1094      Name = Buf;
1095    }
1096
1097    uint64_t &Entry = StringIndexMap[Name];
1098    if (!Entry) {
1099      Entry = StringTable.size();
1100      StringTable += Name;
1101      StringTable += '\x00';
1102    }
1103    MSD.StringIndex = Entry;
1104    if (MSD.SectionIndex == ELF::SHN_UNDEF)
1105      UndefinedSymbolData.push_back(MSD);
1106    else if (Local)
1107      LocalSymbolData.push_back(MSD);
1108    else
1109      ExternalSymbolData.push_back(MSD);
1110  }
1111
1112  // Symbols are required to be in lexicographic order.
1113  array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
1114  array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
1115  array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
1116
1117  // Set the symbol indices. Local symbols must come before all other
1118  // symbols with non-local bindings.
1119  unsigned Index = FileSymbolData.size() + 1;
1120  for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
1121    LocalSymbolData[i].SymbolData->setIndex(Index++);
1122
1123  Index += NumRegularSections;
1124
1125  for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
1126    ExternalSymbolData[i].SymbolData->setIndex(Index++);
1127  for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
1128    UndefinedSymbolData[i].SymbolData->setIndex(Index++);
1129}
1130
1131void ELFObjectWriter::CreateRelocationSections(MCAssembler &Asm,
1132                                               MCAsmLayout &Layout,
1133                                               RelMapTy &RelMap) {
1134  for (MCAssembler::const_iterator it = Asm.begin(),
1135         ie = Asm.end(); it != ie; ++it) {
1136    const MCSectionData &SD = *it;
1137    if (Relocations[&SD].empty())
1138      continue;
1139
1140    MCContext &Ctx = Asm.getContext();
1141    const MCSectionELF &Section =
1142      static_cast<const MCSectionELF&>(SD.getSection());
1143
1144    const StringRef SectionName = Section.getSectionName();
1145    std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
1146    RelaSectionName += SectionName;
1147
1148    unsigned EntrySize;
1149    if (hasRelocationAddend())
1150      EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1151    else
1152      EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1153
1154    unsigned Flags = 0;
1155    StringRef Group = "";
1156    if (Section.getFlags() & ELF::SHF_GROUP) {
1157      Flags = ELF::SHF_GROUP;
1158      Group = Section.getGroup()->getName();
1159    }
1160
1161    const MCSectionELF *RelaSection =
1162      Ctx.getELFSection(RelaSectionName, hasRelocationAddend() ?
1163                        ELF::SHT_RELA : ELF::SHT_REL, Flags,
1164                        SectionKind::getReadOnly(),
1165                        EntrySize, Group);
1166    RelMap[&Section] = RelaSection;
1167    Asm.getOrCreateSectionData(*RelaSection);
1168  }
1169}
1170
1171void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout,
1172                                       const RelMapTy &RelMap) {
1173  for (MCAssembler::const_iterator it = Asm.begin(),
1174         ie = Asm.end(); it != ie; ++it) {
1175    const MCSectionData &SD = *it;
1176    const MCSectionELF &Section =
1177      static_cast<const MCSectionELF&>(SD.getSection());
1178
1179    const MCSectionELF *RelaSection = RelMap.lookup(&Section);
1180    if (!RelaSection)
1181      continue;
1182    MCSectionData &RelaSD = Asm.getOrCreateSectionData(*RelaSection);
1183    RelaSD.setAlignment(is64Bit() ? 8 : 4);
1184
1185    MCDataFragment *F = new MCDataFragment(&RelaSD);
1186    WriteRelocationsFragment(Asm, F, &*it);
1187  }
1188}
1189
1190void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1191                                       uint64_t Flags, uint64_t Address,
1192                                       uint64_t Offset, uint64_t Size,
1193                                       uint32_t Link, uint32_t Info,
1194                                       uint64_t Alignment,
1195                                       uint64_t EntrySize) {
1196  Write32(Name);        // sh_name: index into string table
1197  Write32(Type);        // sh_type
1198  WriteWord(Flags);     // sh_flags
1199  WriteWord(Address);   // sh_addr
1200  WriteWord(Offset);    // sh_offset
1201  WriteWord(Size);      // sh_size
1202  Write32(Link);        // sh_link
1203  Write32(Info);        // sh_info
1204  WriteWord(Alignment); // sh_addralign
1205  WriteWord(EntrySize); // sh_entsize
1206}
1207
1208// ELF doesn't require relocations to be in any order. We sort by the r_offset,
1209// just to match gnu as for easier comparison. The use type is an arbitrary way
1210// of making the sort deterministic.
1211static int cmpRel(const ELFRelocationEntry *AP, const ELFRelocationEntry *BP) {
1212  const ELFRelocationEntry &A = *AP;
1213  const ELFRelocationEntry &B = *BP;
1214  if (A.Offset != B.Offset)
1215    return B.Offset - A.Offset;
1216  if (B.Type != A.Type)
1217    return A.Type - B.Type;
1218  llvm_unreachable("ELFRelocs might be unstable!");
1219}
1220
1221static void sortRelocs(const MCAssembler &Asm,
1222                       std::vector<ELFRelocationEntry> &Relocs) {
1223  array_pod_sort(Relocs.begin(), Relocs.end(), cmpRel);
1224}
1225
1226void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm,
1227                                               MCDataFragment *F,
1228                                               const MCSectionData *SD) {
1229  std::vector<ELFRelocationEntry> &Relocs = Relocations[SD];
1230
1231  sortRelocs(Asm, Relocs);
1232
1233  for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1234    const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1235
1236    unsigned Index;
1237    if (Entry.UseSymbol) {
1238      Index = getSymbolIndexInSymbolTable(Asm, Entry.Symbol);
1239    } else {
1240      const MCSectionData *Sec = Entry.Section;
1241      if (Sec)
1242        Index = Sec->getOrdinal() + FileSymbolData.size() +
1243                LocalSymbolData.size() + 1;
1244      else
1245        Index = 0;
1246    }
1247
1248    if (is64Bit()) {
1249      write(*F, Entry.Offset);
1250      if (TargetObjectWriter->isN64()) {
1251        write(*F, uint32_t(Index));
1252
1253        write(*F, TargetObjectWriter->getRSsym(Entry.Type));
1254        write(*F, TargetObjectWriter->getRType3(Entry.Type));
1255        write(*F, TargetObjectWriter->getRType2(Entry.Type));
1256        write(*F, TargetObjectWriter->getRType(Entry.Type));
1257      } else {
1258        struct ELF::Elf64_Rela ERE64;
1259        ERE64.setSymbolAndType(Index, Entry.Type);
1260        write(*F, ERE64.r_info);
1261      }
1262      if (hasRelocationAddend())
1263        write(*F, Entry.Addend);
1264    } else {
1265      write(*F, uint32_t(Entry.Offset));
1266
1267      struct ELF::Elf32_Rela ERE32;
1268      ERE32.setSymbolAndType(Index, Entry.Type);
1269      write(*F, ERE32.r_info);
1270
1271      if (hasRelocationAddend())
1272        write(*F, uint32_t(Entry.Addend));
1273    }
1274  }
1275}
1276
1277static int compareBySuffix(const MCSectionELF *const *a,
1278                           const MCSectionELF *const *b) {
1279  const StringRef &NameA = (*a)->getSectionName();
1280  const StringRef &NameB = (*b)->getSectionName();
1281  const unsigned sizeA = NameA.size();
1282  const unsigned sizeB = NameB.size();
1283  const unsigned len = std::min(sizeA, sizeB);
1284  for (unsigned int i = 0; i < len; ++i) {
1285    char ca = NameA[sizeA - i - 1];
1286    char cb = NameB[sizeB - i - 1];
1287    if (ca != cb)
1288      return cb - ca;
1289  }
1290
1291  return sizeB - sizeA;
1292}
1293
1294void ELFObjectWriter::CreateMetadataSections(MCAssembler &Asm,
1295                                             MCAsmLayout &Layout,
1296                                             SectionIndexMapTy &SectionIndexMap,
1297                                             const RelMapTy &RelMap) {
1298  MCContext &Ctx = Asm.getContext();
1299  MCDataFragment *F;
1300
1301  unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
1302
1303  // We construct .shstrtab, .symtab and .strtab in this order to match gnu as.
1304  const MCSectionELF *ShstrtabSection =
1305    Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0,
1306                      SectionKind::getReadOnly());
1307  MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection);
1308  ShstrtabSD.setAlignment(1);
1309
1310  const MCSectionELF *SymtabSection =
1311    Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
1312                      SectionKind::getReadOnly(),
1313                      EntrySize, "");
1314  MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
1315  SymtabSD.setAlignment(is64Bit() ? 8 : 4);
1316
1317  const MCSectionELF *StrtabSection;
1318  StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0,
1319                                    SectionKind::getReadOnly());
1320  MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection);
1321  StrtabSD.setAlignment(1);
1322
1323  ComputeIndexMap(Asm, SectionIndexMap, RelMap);
1324
1325  ShstrtabIndex = SectionIndexMap.lookup(ShstrtabSection);
1326  SymbolTableIndex = SectionIndexMap.lookup(SymtabSection);
1327  StringTableIndex = SectionIndexMap.lookup(StrtabSection);
1328
1329  // Symbol table
1330  F = new MCDataFragment(&SymtabSD);
1331  WriteSymbolTable(F, Asm, Layout, SectionIndexMap);
1332
1333  F = new MCDataFragment(&StrtabSD);
1334  F->getContents().append(StringTable.begin(), StringTable.end());
1335
1336  F = new MCDataFragment(&ShstrtabSD);
1337
1338  std::vector<const MCSectionELF*> Sections;
1339  for (MCAssembler::const_iterator it = Asm.begin(),
1340         ie = Asm.end(); it != ie; ++it) {
1341    const MCSectionELF &Section =
1342      static_cast<const MCSectionELF&>(it->getSection());
1343    Sections.push_back(&Section);
1344  }
1345  array_pod_sort(Sections.begin(), Sections.end(), compareBySuffix);
1346
1347  // Section header string table.
1348  //
1349  // The first entry of a string table holds a null character so skip
1350  // section 0.
1351  uint64_t Index = 1;
1352  F->getContents().push_back('\x00');
1353
1354  for (unsigned int I = 0, E = Sections.size(); I != E; ++I) {
1355    const MCSectionELF &Section = *Sections[I];
1356
1357    StringRef Name = Section.getSectionName();
1358    if (I != 0) {
1359      StringRef PreviousName = Sections[I - 1]->getSectionName();
1360      if (PreviousName.endswith(Name)) {
1361        SectionStringTableIndex[&Section] = Index - Name.size() - 1;
1362        continue;
1363      }
1364    }
1365    // Remember the index into the string table so we can write it
1366    // into the sh_name field of the section header table.
1367    SectionStringTableIndex[&Section] = Index;
1368
1369    Index += Name.size() + 1;
1370    F->getContents().append(Name.begin(), Name.end());
1371    F->getContents().push_back('\x00');
1372  }
1373}
1374
1375void ELFObjectWriter::CreateIndexedSections(MCAssembler &Asm,
1376                                            MCAsmLayout &Layout,
1377                                            GroupMapTy &GroupMap,
1378                                            RevGroupMapTy &RevGroupMap,
1379                                            SectionIndexMapTy &SectionIndexMap,
1380                                            const RelMapTy &RelMap) {
1381  // Create the .note.GNU-stack section if needed.
1382  MCContext &Ctx = Asm.getContext();
1383  if (Asm.getNoExecStack()) {
1384    const MCSectionELF *GnuStackSection =
1385      Ctx.getELFSection(".note.GNU-stack", ELF::SHT_PROGBITS, 0,
1386                        SectionKind::getReadOnly());
1387    Asm.getOrCreateSectionData(*GnuStackSection);
1388  }
1389
1390  // Build the groups
1391  for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
1392       it != ie; ++it) {
1393    const MCSectionELF &Section =
1394      static_cast<const MCSectionELF&>(it->getSection());
1395    if (!(Section.getFlags() & ELF::SHF_GROUP))
1396      continue;
1397
1398    const MCSymbol *SignatureSymbol = Section.getGroup();
1399    Asm.getOrCreateSymbolData(*SignatureSymbol);
1400    const MCSectionELF *&Group = RevGroupMap[SignatureSymbol];
1401    if (!Group) {
1402      Group = Ctx.CreateELFGroupSection();
1403      MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1404      Data.setAlignment(4);
1405      MCDataFragment *F = new MCDataFragment(&Data);
1406      write(*F, uint32_t(ELF::GRP_COMDAT));
1407    }
1408    GroupMap[Group] = SignatureSymbol;
1409  }
1410
1411  ComputeIndexMap(Asm, SectionIndexMap, RelMap);
1412
1413  // Add sections to the groups
1414  for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
1415       it != ie; ++it) {
1416    const MCSectionELF &Section =
1417      static_cast<const MCSectionELF&>(it->getSection());
1418    if (!(Section.getFlags() & ELF::SHF_GROUP))
1419      continue;
1420    const MCSectionELF *Group = RevGroupMap[Section.getGroup()];
1421    MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1422    // FIXME: we could use the previous fragment
1423    MCDataFragment *F = new MCDataFragment(&Data);
1424    uint32_t Index = SectionIndexMap.lookup(&Section);
1425    write(*F, Index);
1426  }
1427}
1428
1429void ELFObjectWriter::WriteSection(MCAssembler &Asm,
1430                                   const SectionIndexMapTy &SectionIndexMap,
1431                                   uint32_t GroupSymbolIndex,
1432                                   uint64_t Offset, uint64_t Size,
1433                                   uint64_t Alignment,
1434                                   const MCSectionELF &Section) {
1435  uint64_t sh_link = 0;
1436  uint64_t sh_info = 0;
1437
1438  switch(Section.getType()) {
1439  case ELF::SHT_DYNAMIC:
1440    sh_link = SectionStringTableIndex[&Section];
1441    sh_info = 0;
1442    break;
1443
1444  case ELF::SHT_REL:
1445  case ELF::SHT_RELA: {
1446    const MCSectionELF *SymtabSection;
1447    const MCSectionELF *InfoSection;
1448    SymtabSection = Asm.getContext().getELFSection(".symtab", ELF::SHT_SYMTAB,
1449                                                   0,
1450                                                   SectionKind::getReadOnly());
1451    sh_link = SectionIndexMap.lookup(SymtabSection);
1452    assert(sh_link && ".symtab not found");
1453
1454    // Remove ".rel" and ".rela" prefixes.
1455    unsigned SecNameLen = (Section.getType() == ELF::SHT_REL) ? 4 : 5;
1456    StringRef SectionName = Section.getSectionName().substr(SecNameLen);
1457    StringRef GroupName =
1458        Section.getGroup() ? Section.getGroup()->getName() : "";
1459
1460    InfoSection = Asm.getContext().getELFSection(SectionName, ELF::SHT_PROGBITS,
1461                                                 0, SectionKind::getReadOnly(),
1462                                                 0, GroupName);
1463    sh_info = SectionIndexMap.lookup(InfoSection);
1464    break;
1465  }
1466
1467  case ELF::SHT_SYMTAB:
1468  case ELF::SHT_DYNSYM:
1469    sh_link = StringTableIndex;
1470    sh_info = LastLocalSymbolIndex;
1471    break;
1472
1473  case ELF::SHT_SYMTAB_SHNDX:
1474    sh_link = SymbolTableIndex;
1475    break;
1476
1477  case ELF::SHT_PROGBITS:
1478  case ELF::SHT_STRTAB:
1479  case ELF::SHT_NOBITS:
1480  case ELF::SHT_NOTE:
1481  case ELF::SHT_NULL:
1482  case ELF::SHT_ARM_ATTRIBUTES:
1483  case ELF::SHT_INIT_ARRAY:
1484  case ELF::SHT_FINI_ARRAY:
1485  case ELF::SHT_PREINIT_ARRAY:
1486  case ELF::SHT_X86_64_UNWIND:
1487  case ELF::SHT_MIPS_REGINFO:
1488  case ELF::SHT_MIPS_OPTIONS:
1489    // Nothing to do.
1490    break;
1491
1492  case ELF::SHT_GROUP:
1493    sh_link = SymbolTableIndex;
1494    sh_info = GroupSymbolIndex;
1495    break;
1496
1497  default:
1498    assert(0 && "FIXME: sh_type value not supported!");
1499    break;
1500  }
1501
1502  if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1503      Section.getType() == ELF::SHT_ARM_EXIDX) {
1504    StringRef SecName(Section.getSectionName());
1505    if (SecName == ".ARM.exidx") {
1506      sh_link = SectionIndexMap.lookup(
1507        Asm.getContext().getELFSection(".text",
1508                                       ELF::SHT_PROGBITS,
1509                                       ELF::SHF_EXECINSTR | ELF::SHF_ALLOC,
1510                                       SectionKind::getText()));
1511    } else if (SecName.startswith(".ARM.exidx")) {
1512      StringRef GroupName =
1513          Section.getGroup() ? Section.getGroup()->getName() : "";
1514      sh_link = SectionIndexMap.lookup(Asm.getContext().getELFSection(
1515          SecName.substr(sizeof(".ARM.exidx") - 1), ELF::SHT_PROGBITS,
1516          ELF::SHF_EXECINSTR | ELF::SHF_ALLOC, SectionKind::getText(), 0,
1517          GroupName));
1518    }
1519  }
1520
1521  WriteSecHdrEntry(SectionStringTableIndex[&Section], Section.getType(),
1522                   Section.getFlags(), 0, Offset, Size, sh_link, sh_info,
1523                   Alignment, Section.getEntrySize());
1524}
1525
1526bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) {
1527  return SD.getOrdinal() == ~UINT32_C(0) &&
1528    !SD.getSection().isVirtualSection();
1529}
1530
1531uint64_t ELFObjectWriter::DataSectionSize(const MCSectionData &SD) {
1532  uint64_t Ret = 0;
1533  for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1534       ++i) {
1535    const MCFragment &F = *i;
1536    assert(F.getKind() == MCFragment::FT_Data);
1537    Ret += cast<MCDataFragment>(F).getContents().size();
1538  }
1539  return Ret;
1540}
1541
1542uint64_t ELFObjectWriter::GetSectionFileSize(const MCAsmLayout &Layout,
1543                                             const MCSectionData &SD) {
1544  if (IsELFMetaDataSection(SD))
1545    return DataSectionSize(SD);
1546  return Layout.getSectionFileSize(&SD);
1547}
1548
1549uint64_t ELFObjectWriter::GetSectionAddressSize(const MCAsmLayout &Layout,
1550                                                const MCSectionData &SD) {
1551  if (IsELFMetaDataSection(SD))
1552    return DataSectionSize(SD);
1553  return Layout.getSectionAddressSize(&SD);
1554}
1555
1556void ELFObjectWriter::WriteDataSectionData(MCAssembler &Asm,
1557                                           const MCAsmLayout &Layout,
1558                                           const MCSectionELF &Section) {
1559  const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1560
1561  uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
1562  WriteZeros(Padding);
1563
1564  if (IsELFMetaDataSection(SD)) {
1565    for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1566         ++i) {
1567      const MCFragment &F = *i;
1568      assert(F.getKind() == MCFragment::FT_Data);
1569      WriteBytes(cast<MCDataFragment>(F).getContents());
1570    }
1571  } else {
1572    Asm.writeSectionData(&SD, Layout);
1573  }
1574}
1575
1576void ELFObjectWriter::WriteSectionHeader(MCAssembler &Asm,
1577                                         const GroupMapTy &GroupMap,
1578                                         const MCAsmLayout &Layout,
1579                                      const SectionIndexMapTy &SectionIndexMap,
1580                                   const SectionOffsetMapTy &SectionOffsetMap) {
1581  const unsigned NumSections = Asm.size() + 1;
1582
1583  std::vector<const MCSectionELF*> Sections;
1584  Sections.resize(NumSections - 1);
1585
1586  for (SectionIndexMapTy::const_iterator i=
1587         SectionIndexMap.begin(), e = SectionIndexMap.end(); i != e; ++i) {
1588    const std::pair<const MCSectionELF*, uint32_t> &p = *i;
1589    Sections[p.second - 1] = p.first;
1590  }
1591
1592  // Null section first.
1593  uint64_t FirstSectionSize =
1594    NumSections >= ELF::SHN_LORESERVE ? NumSections : 0;
1595  uint32_t FirstSectionLink =
1596    ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0;
1597  WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0);
1598
1599  for (unsigned i = 0; i < NumSections - 1; ++i) {
1600    const MCSectionELF &Section = *Sections[i];
1601    const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1602    uint32_t GroupSymbolIndex;
1603    if (Section.getType() != ELF::SHT_GROUP)
1604      GroupSymbolIndex = 0;
1605    else
1606      GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm,
1607                                                     GroupMap.lookup(&Section));
1608
1609    uint64_t Size = GetSectionAddressSize(Layout, SD);
1610
1611    WriteSection(Asm, SectionIndexMap, GroupSymbolIndex,
1612                 SectionOffsetMap.lookup(&Section), Size,
1613                 SD.getAlignment(), Section);
1614  }
1615}
1616
1617void ELFObjectWriter::ComputeSectionOrder(MCAssembler &Asm,
1618                                  std::vector<const MCSectionELF*> &Sections) {
1619  for (MCAssembler::iterator it = Asm.begin(),
1620         ie = Asm.end(); it != ie; ++it) {
1621    const MCSectionELF &Section =
1622      static_cast<const MCSectionELF &>(it->getSection());
1623    if (Section.getType() == ELF::SHT_GROUP)
1624      Sections.push_back(&Section);
1625  }
1626
1627  for (MCAssembler::iterator it = Asm.begin(),
1628         ie = Asm.end(); it != ie; ++it) {
1629    const MCSectionELF &Section =
1630      static_cast<const MCSectionELF &>(it->getSection());
1631    if (Section.getType() != ELF::SHT_GROUP &&
1632        Section.getType() != ELF::SHT_REL &&
1633        Section.getType() != ELF::SHT_RELA)
1634      Sections.push_back(&Section);
1635  }
1636
1637  for (MCAssembler::iterator it = Asm.begin(),
1638         ie = Asm.end(); it != ie; ++it) {
1639    const MCSectionELF &Section =
1640      static_cast<const MCSectionELF &>(it->getSection());
1641    if (Section.getType() == ELF::SHT_REL ||
1642        Section.getType() == ELF::SHT_RELA)
1643      Sections.push_back(&Section);
1644  }
1645}
1646
1647void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1648                                  const MCAsmLayout &Layout) {
1649  GroupMapTy GroupMap;
1650  RevGroupMapTy RevGroupMap;
1651  SectionIndexMapTy SectionIndexMap;
1652
1653  unsigned NumUserSections = Asm.size();
1654
1655  DenseMap<const MCSectionELF*, const MCSectionELF*> RelMap;
1656  CreateRelocationSections(Asm, const_cast<MCAsmLayout&>(Layout), RelMap);
1657
1658  const unsigned NumUserAndRelocSections = Asm.size();
1659  CreateIndexedSections(Asm, const_cast<MCAsmLayout&>(Layout), GroupMap,
1660                        RevGroupMap, SectionIndexMap, RelMap);
1661  const unsigned AllSections = Asm.size();
1662  const unsigned NumIndexedSections = AllSections - NumUserAndRelocSections;
1663
1664  unsigned NumRegularSections = NumUserSections + NumIndexedSections;
1665
1666  // Compute symbol table information.
1667  computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap,
1668                     NumRegularSections);
1669
1670  WriteRelocations(Asm, const_cast<MCAsmLayout&>(Layout), RelMap);
1671
1672  CreateMetadataSections(const_cast<MCAssembler&>(Asm),
1673                         const_cast<MCAsmLayout&>(Layout),
1674                         SectionIndexMap,
1675                         RelMap);
1676
1677  uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1678  uint64_t HeaderSize = is64Bit() ? sizeof(ELF::Elf64_Ehdr) :
1679                                    sizeof(ELF::Elf32_Ehdr);
1680  uint64_t FileOff = HeaderSize;
1681
1682  std::vector<const MCSectionELF*> Sections;
1683  ComputeSectionOrder(Asm, Sections);
1684  unsigned NumSections = Sections.size();
1685  SectionOffsetMapTy SectionOffsetMap;
1686  for (unsigned i = 0; i < NumRegularSections + 1; ++i) {
1687    const MCSectionELF &Section = *Sections[i];
1688    const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1689
1690    FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
1691
1692    // Remember the offset into the file for this section.
1693    SectionOffsetMap[&Section] = FileOff;
1694
1695    // Get the size of the section in the output file (including padding).
1696    FileOff += GetSectionFileSize(Layout, SD);
1697  }
1698
1699  FileOff = RoundUpToAlignment(FileOff, NaturalAlignment);
1700
1701  const unsigned SectionHeaderOffset = FileOff - HeaderSize;
1702
1703  uint64_t SectionHeaderEntrySize = is64Bit() ?
1704    sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr);
1705  FileOff += (NumSections + 1) * SectionHeaderEntrySize;
1706
1707  for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) {
1708    const MCSectionELF &Section = *Sections[i];
1709    const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1710
1711    FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
1712
1713    // Remember the offset into the file for this section.
1714    SectionOffsetMap[&Section] = FileOff;
1715
1716    // Get the size of the section in the output file (including padding).
1717    FileOff += GetSectionFileSize(Layout, SD);
1718  }
1719
1720  // Write out the ELF header ...
1721  WriteHeader(Asm, SectionHeaderOffset, NumSections + 1);
1722
1723  // ... then the regular sections ...
1724  // + because of .shstrtab
1725  for (unsigned i = 0; i < NumRegularSections + 1; ++i)
1726    WriteDataSectionData(Asm, Layout, *Sections[i]);
1727
1728  uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1729  WriteZeros(Padding);
1730
1731  // ... then the section header table ...
1732  WriteSectionHeader(Asm, GroupMap, Layout, SectionIndexMap,
1733                     SectionOffsetMap);
1734
1735  // ... and then the remaining sections ...
1736  for (unsigned i = NumRegularSections + 1; i < NumSections; ++i)
1737    WriteDataSectionData(Asm, Layout, *Sections[i]);
1738}
1739
1740bool
1741ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
1742                                                      const MCSymbolData &DataA,
1743                                                      const MCFragment &FB,
1744                                                      bool InSet,
1745                                                      bool IsPCRel) const {
1746  if (DataA.getFlags() & ELF_STB_Weak || MCELF::GetType(DataA) == ELF::STT_GNU_IFUNC)
1747    return false;
1748  return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1749                                                 Asm, DataA, FB,InSet, IsPCRel);
1750}
1751
1752MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1753                                            raw_ostream &OS,
1754                                            bool IsLittleEndian) {
1755  return new ELFObjectWriter(MOTW, OS, IsLittleEndian);
1756}
1757