ELFObjectWriter.cpp revision dce4a407a24b04eebc6a376f8e62b41aaa7b071f 
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/MCAsmInfo.h"
21#include "llvm/MC/MCAsmLayout.h"
22#include "llvm/MC/MCAssembler.h"
23#include "llvm/MC/MCContext.h"
24#include "llvm/MC/MCELF.h"
25#include "llvm/MC/MCELFSymbolFlags.h"
26#include "llvm/MC/MCExpr.h"
27#include "llvm/MC/MCFixupKindInfo.h"
28#include "llvm/MC/MCObjectWriter.h"
29#include "llvm/MC/MCSectionELF.h"
30#include "llvm/MC/MCValue.h"
31#include "llvm/Object/StringTableBuilder.h"
32#include "llvm/Support/Compression.h"
33#include "llvm/Support/Debug.h"
34#include "llvm/Support/Endian.h"
35#include "llvm/Support/ELF.h"
36#include "llvm/Support/ErrorHandling.h"
37#include <vector>
38using namespace llvm;
39
40#undef  DEBUG_TYPE
41#define DEBUG_TYPE "reloc-info"
42
43namespace {
44class FragmentWriter {
45  bool IsLittleEndian;
46
47public:
48  FragmentWriter(bool IsLittleEndian);
49  template <typename T> void write(MCDataFragment &F, T Val);
50};
51
52typedef DenseMap<const MCSectionELF *, uint32_t> SectionIndexMapTy;
53
54class SymbolTableWriter {
55  MCAssembler &Asm;
56  FragmentWriter &FWriter;
57  bool Is64Bit;
58  SectionIndexMapTy &SectionIndexMap;
59
60  // The symbol .symtab fragment we are writting to.
61  MCDataFragment *SymtabF;
62
63  // .symtab_shndx fragment we are writting to.
64  MCDataFragment *ShndxF;
65
66  // The numbel of symbols written so far.
67  unsigned NumWritten;
68
69  void createSymtabShndx();
70
71  template <typename T> void write(MCDataFragment &F, T Value);
72
73public:
74  SymbolTableWriter(MCAssembler &Asm, FragmentWriter &FWriter, bool Is64Bit,
75                    SectionIndexMapTy &SectionIndexMap,
76                    MCDataFragment *SymtabF);
77
78  void writeSymbol(uint32_t name, uint8_t info, uint64_t value, uint64_t size,
79                   uint8_t other, uint32_t shndx, bool Reserved);
80};
81
82struct ELFRelocationEntry {
83  uint64_t Offset; // Where is the relocation.
84  bool UseSymbol;  // Relocate with a symbol, not the section.
85  union {
86    const MCSymbol *Symbol;       // The symbol to relocate with.
87    const MCSectionData *Section; // The section to relocate with.
88  };
89  unsigned Type;   // The type of the relocation.
90  uint64_t Addend; // The addend to use.
91
92  ELFRelocationEntry(uint64_t Offset, const MCSymbol *Symbol, unsigned Type,
93                     uint64_t Addend)
94      : Offset(Offset), UseSymbol(true), Symbol(Symbol), Type(Type),
95        Addend(Addend) {}
96
97  ELFRelocationEntry(uint64_t Offset, const MCSectionData *Section,
98                     unsigned Type, uint64_t Addend)
99      : Offset(Offset), UseSymbol(false), Section(Section), Type(Type),
100        Addend(Addend) {}
101};
102
103class ELFObjectWriter : public MCObjectWriter {
104  FragmentWriter FWriter;
105
106  protected:
107
108    static bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind);
109    static bool RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant);
110    static uint64_t SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout);
111    static bool isInSymtab(const MCAsmLayout &Layout, const MCSymbolData &Data,
112                           bool Used, bool Renamed);
113    static bool isLocal(const MCSymbolData &Data, bool isUsedInReloc);
114    static bool IsELFMetaDataSection(const MCSectionData &SD);
115    static uint64_t DataSectionSize(const MCSectionData &SD);
116    static uint64_t GetSectionFileSize(const MCAsmLayout &Layout,
117                                       const MCSectionData &SD);
118    static uint64_t GetSectionAddressSize(const MCAsmLayout &Layout,
119                                          const MCSectionData &SD);
120
121    void WriteDataSectionData(MCAssembler &Asm,
122                              const MCAsmLayout &Layout,
123                              const MCSectionELF &Section);
124
125    /*static bool isFixupKindX86RIPRel(unsigned Kind) {
126      return Kind == X86::reloc_riprel_4byte ||
127        Kind == X86::reloc_riprel_4byte_movq_load;
128    }*/
129
130    /// ELFSymbolData - Helper struct for containing some precomputed
131    /// information on symbols.
132    struct ELFSymbolData {
133      MCSymbolData *SymbolData;
134      uint64_t StringIndex;
135      uint32_t SectionIndex;
136      StringRef Name;
137
138      // Support lexicographic sorting.
139      bool operator<(const ELFSymbolData &RHS) const {
140        return Name < RHS.Name;
141      }
142    };
143
144    /// The target specific ELF writer instance.
145    std::unique_ptr<MCELFObjectTargetWriter> TargetObjectWriter;
146
147    SmallPtrSet<const MCSymbol *, 16> UsedInReloc;
148    SmallPtrSet<const MCSymbol *, 16> WeakrefUsedInReloc;
149    DenseMap<const MCSymbol *, const MCSymbol *> Renames;
150
151    llvm::DenseMap<const MCSectionData *, std::vector<ELFRelocationEntry>>
152    Relocations;
153    StringTableBuilder ShStrTabBuilder;
154
155    /// @}
156    /// @name Symbol Table Data
157    /// @{
158
159    StringTableBuilder StrTabBuilder;
160    std::vector<uint64_t> FileSymbolData;
161    std::vector<ELFSymbolData> LocalSymbolData;
162    std::vector<ELFSymbolData> ExternalSymbolData;
163    std::vector<ELFSymbolData> UndefinedSymbolData;
164
165    /// @}
166
167    bool NeedsGOT;
168
169    // This holds the symbol table index of the last local symbol.
170    unsigned LastLocalSymbolIndex;
171    // This holds the .strtab section index.
172    unsigned StringTableIndex;
173    // This holds the .symtab section index.
174    unsigned SymbolTableIndex;
175
176    unsigned ShstrtabIndex;
177
178
179    // TargetObjectWriter wrappers.
180    bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
181    bool hasRelocationAddend() const {
182      return TargetObjectWriter->hasRelocationAddend();
183    }
184    unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
185                          bool IsPCRel) const {
186      return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel);
187    }
188
189  public:
190    ELFObjectWriter(MCELFObjectTargetWriter *MOTW, raw_ostream &_OS,
191                    bool IsLittleEndian)
192        : MCObjectWriter(_OS, IsLittleEndian), FWriter(IsLittleEndian),
193          TargetObjectWriter(MOTW), NeedsGOT(false) {}
194
195    virtual ~ELFObjectWriter();
196
197    void WriteWord(uint64_t W) {
198      if (is64Bit())
199        Write64(W);
200      else
201        Write32(W);
202    }
203
204    template <typename T> void write(MCDataFragment &F, T Value) {
205      FWriter.write(F, Value);
206    }
207
208    void WriteHeader(const MCAssembler &Asm,
209                     uint64_t SectionDataSize,
210                     unsigned NumberOfSections);
211
212    void WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
213                     const MCAsmLayout &Layout);
214
215    void WriteSymbolTable(MCDataFragment *SymtabF, MCAssembler &Asm,
216                          const MCAsmLayout &Layout,
217                          SectionIndexMapTy &SectionIndexMap);
218
219    bool shouldRelocateWithSymbol(const MCAssembler &Asm,
220                                  const MCSymbolRefExpr *RefA,
221                                  const MCSymbolData *SD, uint64_t C,
222                                  unsigned Type) const;
223
224    void RecordRelocation(const MCAssembler &Asm, const MCAsmLayout &Layout,
225                          const MCFragment *Fragment, const MCFixup &Fixup,
226                          MCValue Target, bool &IsPCRel,
227                          uint64_t &FixedValue) override;
228
229    uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm,
230                                         const MCSymbol *S);
231
232    // Map from a group section to the signature symbol
233    typedef DenseMap<const MCSectionELF*, const MCSymbol*> GroupMapTy;
234    // Map from a signature symbol to the group section
235    typedef DenseMap<const MCSymbol*, const MCSectionELF*> RevGroupMapTy;
236    // Map from a section to the section with the relocations
237    typedef DenseMap<const MCSectionELF*, const MCSectionELF*> RelMapTy;
238    // Map from a section to its offset
239    typedef DenseMap<const MCSectionELF*, uint64_t> SectionOffsetMapTy;
240
241    /// Compute the symbol table data
242    ///
243    /// \param Asm - The assembler.
244    /// \param SectionIndexMap - Maps a section to its index.
245    /// \param RevGroupMap - Maps a signature symbol to the group section.
246    /// \param NumRegularSections - Number of non-relocation sections.
247    void computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
248                            const SectionIndexMapTy &SectionIndexMap,
249                            RevGroupMapTy RevGroupMap,
250                            unsigned NumRegularSections);
251
252    void ComputeIndexMap(MCAssembler &Asm,
253                         SectionIndexMapTy &SectionIndexMap,
254                         const RelMapTy &RelMap);
255
256    void CreateRelocationSections(MCAssembler &Asm, MCAsmLayout &Layout,
257                                  RelMapTy &RelMap);
258
259    void CompressDebugSections(MCAssembler &Asm, MCAsmLayout &Layout);
260
261    void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout,
262                          const RelMapTy &RelMap);
263
264    void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout,
265                                SectionIndexMapTy &SectionIndexMap,
266                                const RelMapTy &RelMap);
267
268    // Create the sections that show up in the symbol table. Currently
269    // those are the .note.GNU-stack section and the group sections.
270    void CreateIndexedSections(MCAssembler &Asm, MCAsmLayout &Layout,
271                               GroupMapTy &GroupMap,
272                               RevGroupMapTy &RevGroupMap,
273                               SectionIndexMapTy &SectionIndexMap,
274                               const RelMapTy &RelMap);
275
276    void ExecutePostLayoutBinding(MCAssembler &Asm,
277                                  const MCAsmLayout &Layout) override;
278
279    void WriteSectionHeader(MCAssembler &Asm, const GroupMapTy &GroupMap,
280                            const MCAsmLayout &Layout,
281                            const SectionIndexMapTy &SectionIndexMap,
282                            const SectionOffsetMapTy &SectionOffsetMap);
283
284    void ComputeSectionOrder(MCAssembler &Asm,
285                             std::vector<const MCSectionELF*> &Sections);
286
287    void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
288                          uint64_t Address, uint64_t Offset,
289                          uint64_t Size, uint32_t Link, uint32_t Info,
290                          uint64_t Alignment, uint64_t EntrySize);
291
292    void WriteRelocationsFragment(const MCAssembler &Asm,
293                                  MCDataFragment *F,
294                                  const MCSectionData *SD);
295
296    bool
297    IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
298                                           const MCSymbolData &DataA,
299                                           const MCFragment &FB,
300                                           bool InSet,
301                                           bool IsPCRel) const override;
302
303    void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
304    void WriteSection(MCAssembler &Asm,
305                      const SectionIndexMapTy &SectionIndexMap,
306                      uint32_t GroupSymbolIndex,
307                      uint64_t Offset, uint64_t Size, uint64_t Alignment,
308                      const MCSectionELF &Section);
309  };
310}
311
312FragmentWriter::FragmentWriter(bool IsLittleEndian)
313    : IsLittleEndian(IsLittleEndian) {}
314
315template <typename T> void FragmentWriter::write(MCDataFragment &F, T Val) {
316  if (IsLittleEndian)
317    Val = support::endian::byte_swap<T, support::little>(Val);
318  else
319    Val = support::endian::byte_swap<T, support::big>(Val);
320  const char *Start = (const char *)&Val;
321  F.getContents().append(Start, Start + sizeof(T));
322}
323
324void SymbolTableWriter::createSymtabShndx() {
325  if (ShndxF)
326    return;
327
328  MCContext &Ctx = Asm.getContext();
329  const MCSectionELF *SymtabShndxSection =
330      Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0,
331                        SectionKind::getReadOnly(), 4, "");
332  MCSectionData *SymtabShndxSD =
333      &Asm.getOrCreateSectionData(*SymtabShndxSection);
334  SymtabShndxSD->setAlignment(4);
335  ShndxF = new MCDataFragment(SymtabShndxSD);
336  unsigned Index = SectionIndexMap.size() + 1;
337  SectionIndexMap[SymtabShndxSection] = Index;
338
339  for (unsigned I = 0; I < NumWritten; ++I)
340    write(*ShndxF, uint32_t(0));
341}
342
343template <typename T>
344void SymbolTableWriter::write(MCDataFragment &F, T Value) {
345  FWriter.write(F, Value);
346}
347
348SymbolTableWriter::SymbolTableWriter(MCAssembler &Asm, FragmentWriter &FWriter,
349                                     bool Is64Bit,
350                                     SectionIndexMapTy &SectionIndexMap,
351                                     MCDataFragment *SymtabF)
352    : Asm(Asm), FWriter(FWriter), Is64Bit(Is64Bit),
353      SectionIndexMap(SectionIndexMap), SymtabF(SymtabF), ShndxF(nullptr),
354      NumWritten(0) {}
355
356void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
357                                    uint64_t size, uint8_t other,
358                                    uint32_t shndx, bool Reserved) {
359  bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved;
360
361  if (LargeIndex)
362    createSymtabShndx();
363
364  if (ShndxF) {
365    if (LargeIndex)
366      write(*ShndxF, shndx);
367    else
368      write(*ShndxF, uint32_t(0));
369  }
370
371  uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
372
373  raw_svector_ostream OS(SymtabF->getContents());
374
375  if (Is64Bit) {
376    write(*SymtabF, name);  // st_name
377    write(*SymtabF, info);  // st_info
378    write(*SymtabF, other); // st_other
379    write(*SymtabF, Index); // st_shndx
380    write(*SymtabF, value); // st_value
381    write(*SymtabF, size);  // st_size
382  } else {
383    write(*SymtabF, name);            // st_name
384    write(*SymtabF, uint32_t(value)); // st_value
385    write(*SymtabF, uint32_t(size));  // st_size
386    write(*SymtabF, info);            // st_info
387    write(*SymtabF, other);           // st_other
388    write(*SymtabF, Index);           // st_shndx
389  }
390
391  ++NumWritten;
392}
393
394bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
395  const MCFixupKindInfo &FKI =
396    Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
397
398  return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
399}
400
401bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) {
402  switch (Variant) {
403  default:
404    return false;
405  case MCSymbolRefExpr::VK_GOT:
406  case MCSymbolRefExpr::VK_PLT:
407  case MCSymbolRefExpr::VK_GOTPCREL:
408  case MCSymbolRefExpr::VK_GOTOFF:
409  case MCSymbolRefExpr::VK_TPOFF:
410  case MCSymbolRefExpr::VK_TLSGD:
411  case MCSymbolRefExpr::VK_GOTTPOFF:
412  case MCSymbolRefExpr::VK_INDNTPOFF:
413  case MCSymbolRefExpr::VK_NTPOFF:
414  case MCSymbolRefExpr::VK_GOTNTPOFF:
415  case MCSymbolRefExpr::VK_TLSLDM:
416  case MCSymbolRefExpr::VK_DTPOFF:
417  case MCSymbolRefExpr::VK_TLSLD:
418    return true;
419  }
420}
421
422ELFObjectWriter::~ELFObjectWriter()
423{}
424
425// Emit the ELF header.
426void ELFObjectWriter::WriteHeader(const MCAssembler &Asm,
427                                  uint64_t SectionDataSize,
428                                  unsigned NumberOfSections) {
429  // ELF Header
430  // ----------
431  //
432  // Note
433  // ----
434  // emitWord method behaves differently for ELF32 and ELF64, writing
435  // 4 bytes in the former and 8 in the latter.
436
437  Write8(0x7f); // e_ident[EI_MAG0]
438  Write8('E');  // e_ident[EI_MAG1]
439  Write8('L');  // e_ident[EI_MAG2]
440  Write8('F');  // e_ident[EI_MAG3]
441
442  Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
443
444  // e_ident[EI_DATA]
445  Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
446
447  Write8(ELF::EV_CURRENT);        // e_ident[EI_VERSION]
448  // e_ident[EI_OSABI]
449  Write8(TargetObjectWriter->getOSABI());
450  Write8(0);                  // e_ident[EI_ABIVERSION]
451
452  WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
453
454  Write16(ELF::ET_REL);             // e_type
455
456  Write16(TargetObjectWriter->getEMachine()); // e_machine = target
457
458  Write32(ELF::EV_CURRENT);         // e_version
459  WriteWord(0);                    // e_entry, no entry point in .o file
460  WriteWord(0);                    // e_phoff, no program header for .o
461  WriteWord(SectionDataSize + (is64Bit() ? sizeof(ELF::Elf64_Ehdr) :
462            sizeof(ELF::Elf32_Ehdr)));  // e_shoff = sec hdr table off in bytes
463
464  // e_flags = whatever the target wants
465  Write32(Asm.getELFHeaderEFlags());
466
467  // e_ehsize = ELF header size
468  Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
469
470  Write16(0);                  // e_phentsize = prog header entry size
471  Write16(0);                  // e_phnum = # prog header entries = 0
472
473  // e_shentsize = Section header entry size
474  Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
475
476  // e_shnum     = # of section header ents
477  if (NumberOfSections >= ELF::SHN_LORESERVE)
478    Write16(ELF::SHN_UNDEF);
479  else
480    Write16(NumberOfSections);
481
482  // e_shstrndx  = Section # of '.shstrtab'
483  if (ShstrtabIndex >= ELF::SHN_LORESERVE)
484    Write16(ELF::SHN_XINDEX);
485  else
486    Write16(ShstrtabIndex);
487}
488
489uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &Data,
490                                      const MCAsmLayout &Layout) {
491  if (Data.isCommon() && Data.isExternal())
492    return Data.getCommonAlignment();
493
494  uint64_t Res;
495  if (!Layout.getSymbolOffset(&Data, Res))
496    return 0;
497
498  if (Layout.getAssembler().isThumbFunc(&Data.getSymbol()))
499    Res |= 1;
500
501  return Res;
502}
503
504void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
505                                               const MCAsmLayout &Layout) {
506  // The presence of symbol versions causes undefined symbols and
507  // versions declared with @@@ to be renamed.
508
509  for (MCSymbolData &OriginalData : Asm.symbols()) {
510    const MCSymbol &Alias = OriginalData.getSymbol();
511
512    // Not an alias.
513    if (!Alias.isVariable())
514      continue;
515    auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
516    if (!Ref)
517      continue;
518    const MCSymbol &Symbol = Ref->getSymbol();
519    MCSymbolData &SD = Asm.getSymbolData(Symbol);
520
521    StringRef AliasName = Alias.getName();
522    size_t Pos = AliasName.find('@');
523    if (Pos == StringRef::npos)
524      continue;
525
526    // Aliases defined with .symvar copy the binding from the symbol they alias.
527    // This is the first place we are able to copy this information.
528    OriginalData.setExternal(SD.isExternal());
529    MCELF::SetBinding(OriginalData, MCELF::GetBinding(SD));
530
531    StringRef Rest = AliasName.substr(Pos);
532    if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
533      continue;
534
535    // FIXME: produce a better error message.
536    if (Symbol.isUndefined() && Rest.startswith("@@") &&
537        !Rest.startswith("@@@"))
538      report_fatal_error("A @@ version cannot be undefined");
539
540    Renames.insert(std::make_pair(&Symbol, &Alias));
541  }
542}
543
544static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
545  uint8_t Type = newType;
546
547  // Propagation rules:
548  // IFUNC > FUNC > OBJECT > NOTYPE
549  // TLS_OBJECT > OBJECT > NOTYPE
550  //
551  // dont let the new type degrade the old type
552  switch (origType) {
553  default:
554    break;
555  case ELF::STT_GNU_IFUNC:
556    if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT ||
557        Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS)
558      Type = ELF::STT_GNU_IFUNC;
559    break;
560  case ELF::STT_FUNC:
561    if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
562        Type == ELF::STT_TLS)
563      Type = ELF::STT_FUNC;
564    break;
565  case ELF::STT_OBJECT:
566    if (Type == ELF::STT_NOTYPE)
567      Type = ELF::STT_OBJECT;
568    break;
569  case ELF::STT_TLS:
570    if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
571        Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
572      Type = ELF::STT_TLS;
573    break;
574  }
575
576  return Type;
577}
578
579void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
580                                  const MCAsmLayout &Layout) {
581  MCSymbolData &OrigData = *MSD.SymbolData;
582  assert((!OrigData.getFragment() ||
583          (&OrigData.getFragment()->getParent()->getSection() ==
584           &OrigData.getSymbol().getSection())) &&
585         "The symbol's section doesn't match the fragment's symbol");
586  const MCSymbol *Base = Layout.getBaseSymbol(OrigData.getSymbol());
587
588  // This has to be in sync with when computeSymbolTable uses SHN_ABS or
589  // SHN_COMMON.
590  bool IsReserved = !Base || OrigData.isCommon();
591
592  // Binding and Type share the same byte as upper and lower nibbles
593  uint8_t Binding = MCELF::GetBinding(OrigData);
594  uint8_t Type = MCELF::GetType(OrigData);
595  MCSymbolData *BaseSD = nullptr;
596  if (Base) {
597    BaseSD = &Layout.getAssembler().getSymbolData(*Base);
598    Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD));
599  }
600  uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
601
602  // Other and Visibility share the same byte with Visibility using the lower
603  // 2 bits
604  uint8_t Visibility = MCELF::GetVisibility(OrigData);
605  uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift);
606  Other |= Visibility;
607
608  uint64_t Value = SymbolValue(OrigData, Layout);
609  uint64_t Size = 0;
610
611  const MCExpr *ESize = OrigData.getSize();
612  if (!ESize && Base)
613    ESize = BaseSD->getSize();
614
615  if (ESize) {
616    int64_t Res;
617    if (!ESize->EvaluateAsAbsolute(Res, Layout))
618      report_fatal_error("Size expression must be absolute.");
619    Size = Res;
620  }
621
622  // Write out the symbol table entry
623  Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other,
624                     MSD.SectionIndex, IsReserved);
625}
626
627void ELFObjectWriter::WriteSymbolTable(MCDataFragment *SymtabF,
628                                       MCAssembler &Asm,
629                                       const MCAsmLayout &Layout,
630                                       SectionIndexMapTy &SectionIndexMap) {
631  // The string table must be emitted first because we need the index
632  // into the string table for all the symbol names.
633
634  // FIXME: Make sure the start of the symbol table is aligned.
635
636  SymbolTableWriter Writer(Asm, FWriter, is64Bit(), SectionIndexMap, SymtabF);
637
638  // The first entry is the undefined symbol entry.
639  Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
640
641  for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) {
642    Writer.writeSymbol(FileSymbolData[i], ELF::STT_FILE | ELF::STB_LOCAL, 0, 0,
643                       ELF::STV_DEFAULT, ELF::SHN_ABS, true);
644  }
645
646  // Write the symbol table entries.
647  LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1;
648
649  for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
650    ELFSymbolData &MSD = LocalSymbolData[i];
651    WriteSymbol(Writer, MSD, Layout);
652  }
653
654  // Write out a symbol table entry for each regular section.
655  for (MCAssembler::const_iterator i = Asm.begin(), e = Asm.end(); i != e;
656       ++i) {
657    const MCSectionELF &Section =
658      static_cast<const MCSectionELF&>(i->getSection());
659    if (Section.getType() == ELF::SHT_RELA ||
660        Section.getType() == ELF::SHT_REL ||
661        Section.getType() == ELF::SHT_STRTAB ||
662        Section.getType() == ELF::SHT_SYMTAB ||
663        Section.getType() == ELF::SHT_SYMTAB_SHNDX)
664      continue;
665    Writer.writeSymbol(0, ELF::STT_SECTION, 0, 0, ELF::STV_DEFAULT,
666                       SectionIndexMap.lookup(&Section), false);
667    LastLocalSymbolIndex++;
668  }
669
670  for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
671    ELFSymbolData &MSD = ExternalSymbolData[i];
672    MCSymbolData &Data = *MSD.SymbolData;
673    assert(((Data.getFlags() & ELF_STB_Global) ||
674            (Data.getFlags() & ELF_STB_Weak)) &&
675           "External symbol requires STB_GLOBAL or STB_WEAK flag");
676    WriteSymbol(Writer, MSD, Layout);
677    if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
678      LastLocalSymbolIndex++;
679  }
680
681  for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
682    ELFSymbolData &MSD = UndefinedSymbolData[i];
683    MCSymbolData &Data = *MSD.SymbolData;
684    WriteSymbol(Writer, MSD, Layout);
685    if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
686      LastLocalSymbolIndex++;
687  }
688}
689
690// It is always valid to create a relocation with a symbol. It is preferable
691// to use a relocation with a section if that is possible. Using the section
692// allows us to omit some local symbols from the symbol table.
693bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
694                                               const MCSymbolRefExpr *RefA,
695                                               const MCSymbolData *SD,
696                                               uint64_t C,
697                                               unsigned Type) const {
698  // A PCRel relocation to an absolute value has no symbol (or section). We
699  // represent that with a relocation to a null section.
700  if (!RefA)
701    return false;
702
703  MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
704  switch (Kind) {
705  default:
706    break;
707  // The .odp creation emits a relocation against the symbol ".TOC." which
708  // create a R_PPC64_TOC relocation. However the relocation symbol name
709  // in final object creation should be NULL, since the symbol does not
710  // really exist, it is just the reference to TOC base for the current
711  // object file. Since the symbol is undefined, returning false results
712  // in a relocation with a null section which is the desired result.
713  case MCSymbolRefExpr::VK_PPC_TOCBASE:
714    return false;
715
716  // These VariantKind cause the relocation to refer to something other than
717  // the symbol itself, like a linker generated table. Since the address of
718  // symbol is not relevant, we cannot replace the symbol with the
719  // section and patch the difference in the addend.
720  case MCSymbolRefExpr::VK_GOT:
721  case MCSymbolRefExpr::VK_PLT:
722  case MCSymbolRefExpr::VK_GOTPCREL:
723  case MCSymbolRefExpr::VK_Mips_GOT:
724  case MCSymbolRefExpr::VK_PPC_GOT_LO:
725  case MCSymbolRefExpr::VK_PPC_GOT_HI:
726  case MCSymbolRefExpr::VK_PPC_GOT_HA:
727    return true;
728  }
729
730  // An undefined symbol is not in any section, so the relocation has to point
731  // to the symbol itself.
732  const MCSymbol &Sym = SD->getSymbol();
733  if (Sym.isUndefined())
734    return true;
735
736  unsigned Binding = MCELF::GetBinding(*SD);
737  switch(Binding) {
738  default:
739    llvm_unreachable("Invalid Binding");
740  case ELF::STB_LOCAL:
741    break;
742  case ELF::STB_WEAK:
743    // If the symbol is weak, it might be overridden by a symbol in another
744    // file. The relocation has to point to the symbol so that the linker
745    // can update it.
746    return true;
747  case ELF::STB_GLOBAL:
748    // Global ELF symbols can be preempted by the dynamic linker. The relocation
749    // has to point to the symbol for a reason analogous to the STB_WEAK case.
750    return true;
751  }
752
753  // If a relocation points to a mergeable section, we have to be careful.
754  // If the offset is zero, a relocation with the section will encode the
755  // same information. With a non-zero offset, the situation is different.
756  // For example, a relocation can point 42 bytes past the end of a string.
757  // If we change such a relocation to use the section, the linker would think
758  // that it pointed to another string and subtracting 42 at runtime will
759  // produce the wrong value.
760  auto &Sec = cast<MCSectionELF>(Sym.getSection());
761  unsigned Flags = Sec.getFlags();
762  if (Flags & ELF::SHF_MERGE) {
763    if (C != 0)
764      return true;
765
766    // It looks like gold has a bug (http://sourceware.org/PR16794) and can
767    // only handle section relocations to mergeable sections if using RELA.
768    if (!hasRelocationAddend())
769      return true;
770  }
771
772  // Most TLS relocations use a got, so they need the symbol. Even those that
773  // are just an offset (@tpoff), require a symbol in some linkers (gold,
774  // but not bfd ld).
775  if (Flags & ELF::SHF_TLS)
776    return true;
777
778  // If the symbol is a thumb function the final relocation must set the lowest
779  // bit. With a symbol that is done by just having the symbol have that bit
780  // set, so we would lose the bit if we relocated with the section.
781  // FIXME: We could use the section but add the bit to the relocation value.
782  if (Asm.isThumbFunc(&Sym))
783    return true;
784
785  if (TargetObjectWriter->needsRelocateWithSymbol(Type))
786    return true;
787  return false;
788}
789
790static const MCSymbol *getWeakRef(const MCSymbolRefExpr &Ref) {
791  const MCSymbol &Sym = Ref.getSymbol();
792
793  if (Ref.getKind() == MCSymbolRefExpr::VK_WEAKREF)
794    return &Sym;
795
796  if (!Sym.isVariable())
797    return nullptr;
798
799  const MCExpr *Expr = Sym.getVariableValue();
800  const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr);
801  if (!Inner)
802    return nullptr;
803
804  if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
805    return &Inner->getSymbol();
806  return nullptr;
807}
808
809void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm,
810                                       const MCAsmLayout &Layout,
811                                       const MCFragment *Fragment,
812                                       const MCFixup &Fixup,
813                                       MCValue Target,
814                                       bool &IsPCRel,
815                                       uint64_t &FixedValue) {
816  const MCSectionData *FixupSection = Fragment->getParent();
817  uint64_t C = Target.getConstant();
818  uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
819
820  if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
821    assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
822           "Should not have constructed this");
823
824    // Let A, B and C being the components of Target and R be the location of
825    // the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
826    // If it is pcrel, we want to compute (A - B + C - R).
827
828    // In general, ELF has no relocations for -B. It can only represent (A + C)
829    // or (A + C - R). If B = R + K and the relocation is not pcrel, we can
830    // replace B to implement it: (A - R - K + C)
831    if (IsPCRel)
832      Asm.getContext().FatalError(
833          Fixup.getLoc(),
834          "No relocation available to represent this relative expression");
835
836    const MCSymbol &SymB = RefB->getSymbol();
837
838    if (SymB.isUndefined())
839      Asm.getContext().FatalError(
840          Fixup.getLoc(),
841          Twine("symbol '") + SymB.getName() +
842              "' can not be undefined in a subtraction expression");
843
844    assert(!SymB.isAbsolute() && "Should have been folded");
845    const MCSection &SecB = SymB.getSection();
846    if (&SecB != &FixupSection->getSection())
847      Asm.getContext().FatalError(
848          Fixup.getLoc(), "Cannot represent a difference across sections");
849
850    const MCSymbolData &SymBD = Asm.getSymbolData(SymB);
851    uint64_t SymBOffset = Layout.getSymbolOffset(&SymBD);
852    uint64_t K = SymBOffset - FixupOffset;
853    IsPCRel = true;
854    C -= K;
855  }
856
857  // We either rejected the fixup or folded B into C at this point.
858  const MCSymbolRefExpr *RefA = Target.getSymA();
859  const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
860  const MCSymbolData *SymAD = SymA ? &Asm.getSymbolData(*SymA) : nullptr;
861
862  unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
863  bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymAD, C, Type);
864  if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
865    C += Layout.getSymbolOffset(SymAD);
866
867  uint64_t Addend = 0;
868  if (hasRelocationAddend()) {
869    Addend = C;
870    C = 0;
871  }
872
873  FixedValue = C;
874
875  // FIXME: What is this!?!?
876  MCSymbolRefExpr::VariantKind Modifier =
877      RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None;
878  if (RelocNeedsGOT(Modifier))
879    NeedsGOT = true;
880
881  if (!RelocateWithSymbol) {
882    const MCSection *SecA =
883        (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
884    const MCSectionData *SecAD = SecA ? &Asm.getSectionData(*SecA) : nullptr;
885    ELFRelocationEntry Rec(FixupOffset, SecAD, Type, Addend);
886    Relocations[FixupSection].push_back(Rec);
887    return;
888  }
889
890  if (SymA) {
891    if (const MCSymbol *R = Renames.lookup(SymA))
892      SymA = R;
893
894    if (const MCSymbol *WeakRef = getWeakRef(*RefA))
895      WeakrefUsedInReloc.insert(WeakRef);
896    else
897      UsedInReloc.insert(SymA);
898  }
899  ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
900  Relocations[FixupSection].push_back(Rec);
901  return;
902}
903
904
905uint64_t
906ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
907                                             const MCSymbol *S) {
908  const MCSymbolData &SD = Asm.getSymbolData(*S);
909  return SD.getIndex();
910}
911
912bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
913                                 const MCSymbolData &Data, bool Used,
914                                 bool Renamed) {
915  const MCSymbol &Symbol = Data.getSymbol();
916  if (Symbol.isVariable()) {
917    const MCExpr *Expr = Symbol.getVariableValue();
918    if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
919      if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
920        return false;
921    }
922  }
923
924  if (Used)
925    return true;
926
927  if (Renamed)
928    return false;
929
930  if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
931    return true;
932
933  if (Symbol.isVariable()) {
934    const MCSymbol *Base = Layout.getBaseSymbol(Symbol);
935    if (Base && Base->isUndefined())
936      return false;
937  }
938
939  bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
940  if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
941    return false;
942
943  if (Symbol.isTemporary())
944    return false;
945
946  return true;
947}
948
949bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isUsedInReloc) {
950  if (Data.isExternal())
951    return false;
952
953  const MCSymbol &Symbol = Data.getSymbol();
954  if (Symbol.isDefined())
955    return true;
956
957  if (isUsedInReloc)
958    return false;
959
960  return true;
961}
962
963void ELFObjectWriter::ComputeIndexMap(MCAssembler &Asm,
964                                      SectionIndexMapTy &SectionIndexMap,
965                                      const RelMapTy &RelMap) {
966  unsigned Index = 1;
967  for (MCAssembler::iterator it = Asm.begin(),
968         ie = Asm.end(); it != ie; ++it) {
969    const MCSectionELF &Section =
970      static_cast<const MCSectionELF &>(it->getSection());
971    if (Section.getType() != ELF::SHT_GROUP)
972      continue;
973    SectionIndexMap[&Section] = Index++;
974  }
975
976  for (MCAssembler::iterator it = Asm.begin(),
977         ie = Asm.end(); it != ie; ++it) {
978    const MCSectionELF &Section =
979      static_cast<const MCSectionELF &>(it->getSection());
980    if (Section.getType() == ELF::SHT_GROUP ||
981        Section.getType() == ELF::SHT_REL ||
982        Section.getType() == ELF::SHT_RELA)
983      continue;
984    SectionIndexMap[&Section] = Index++;
985    const MCSectionELF *RelSection = RelMap.lookup(&Section);
986    if (RelSection)
987      SectionIndexMap[RelSection] = Index++;
988  }
989}
990
991void
992ELFObjectWriter::computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
993                                    const SectionIndexMapTy &SectionIndexMap,
994                                    RevGroupMapTy RevGroupMap,
995                                    unsigned NumRegularSections) {
996  // FIXME: Is this the correct place to do this?
997  // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?
998  if (NeedsGOT) {
999    StringRef Name = "_GLOBAL_OFFSET_TABLE_";
1000    MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
1001    MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
1002    Data.setExternal(true);
1003    MCELF::SetBinding(Data, ELF::STB_GLOBAL);
1004  }
1005
1006  // Add the data for the symbols.
1007  for (MCSymbolData &SD : Asm.symbols()) {
1008    const MCSymbol &Symbol = SD.getSymbol();
1009
1010    bool Used = UsedInReloc.count(&Symbol);
1011    bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
1012    bool isSignature = RevGroupMap.count(&Symbol);
1013
1014    if (!isInSymtab(Layout, SD,
1015                    Used || WeakrefUsed || isSignature,
1016                    Renames.count(&Symbol)))
1017      continue;
1018
1019    ELFSymbolData MSD;
1020    MSD.SymbolData = &SD;
1021    const MCSymbol *BaseSymbol = Layout.getBaseSymbol(Symbol);
1022
1023    // Undefined symbols are global, but this is the first place we
1024    // are able to set it.
1025    bool Local = isLocal(SD, Used);
1026    if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) {
1027      assert(BaseSymbol);
1028      MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol);
1029      MCELF::SetBinding(SD, ELF::STB_GLOBAL);
1030      MCELF::SetBinding(BaseData, ELF::STB_GLOBAL);
1031    }
1032
1033    if (!BaseSymbol) {
1034      MSD.SectionIndex = ELF::SHN_ABS;
1035    } else if (SD.isCommon()) {
1036      assert(!Local);
1037      MSD.SectionIndex = ELF::SHN_COMMON;
1038    } else if (BaseSymbol->isUndefined()) {
1039      if (isSignature && !Used)
1040        MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap[&Symbol]);
1041      else
1042        MSD.SectionIndex = ELF::SHN_UNDEF;
1043      if (!Used && WeakrefUsed)
1044        MCELF::SetBinding(SD, ELF::STB_WEAK);
1045    } else {
1046      const MCSectionELF &Section =
1047        static_cast<const MCSectionELF&>(BaseSymbol->getSection());
1048      MSD.SectionIndex = SectionIndexMap.lookup(&Section);
1049      assert(MSD.SectionIndex && "Invalid section index!");
1050    }
1051
1052    // The @@@ in symbol version is replaced with @ in undefined symbols and
1053    // @@ in defined ones.
1054    StringRef Name = Symbol.getName();
1055    SmallString<32> Buf;
1056    size_t Pos = Name.find("@@@");
1057    if (Pos != StringRef::npos) {
1058      Buf += Name.substr(0, Pos);
1059      unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
1060      Buf += Name.substr(Pos + Skip);
1061      Name = Buf;
1062    }
1063    MSD.Name = StrTabBuilder.add(Name);
1064
1065    if (MSD.SectionIndex == ELF::SHN_UNDEF)
1066      UndefinedSymbolData.push_back(MSD);
1067    else if (Local)
1068      LocalSymbolData.push_back(MSD);
1069    else
1070      ExternalSymbolData.push_back(MSD);
1071  }
1072
1073  for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1074    StrTabBuilder.add(*i);
1075
1076  StrTabBuilder.finalize();
1077
1078  for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
1079    FileSymbolData.push_back(StrTabBuilder.getOffset(*i));
1080
1081  for (ELFSymbolData& MSD : LocalSymbolData)
1082    MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1083  for (ELFSymbolData& MSD : ExternalSymbolData)
1084    MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1085  for (ELFSymbolData& MSD : UndefinedSymbolData)
1086    MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
1087
1088  // Symbols are required to be in lexicographic order.
1089  array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
1090  array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
1091  array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
1092
1093  // Set the symbol indices. Local symbols must come before all other
1094  // symbols with non-local bindings.
1095  unsigned Index = FileSymbolData.size() + 1;
1096  for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
1097    LocalSymbolData[i].SymbolData->setIndex(Index++);
1098
1099  Index += NumRegularSections;
1100
1101  for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
1102    ExternalSymbolData[i].SymbolData->setIndex(Index++);
1103  for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
1104    UndefinedSymbolData[i].SymbolData->setIndex(Index++);
1105}
1106
1107void ELFObjectWriter::CreateRelocationSections(MCAssembler &Asm,
1108                                               MCAsmLayout &Layout,
1109                                               RelMapTy &RelMap) {
1110  for (MCAssembler::const_iterator it = Asm.begin(),
1111         ie = Asm.end(); it != ie; ++it) {
1112    const MCSectionData &SD = *it;
1113    if (Relocations[&SD].empty())
1114      continue;
1115
1116    MCContext &Ctx = Asm.getContext();
1117    const MCSectionELF &Section =
1118      static_cast<const MCSectionELF&>(SD.getSection());
1119
1120    const StringRef SectionName = Section.getSectionName();
1121    std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
1122    RelaSectionName += SectionName;
1123
1124    unsigned EntrySize;
1125    if (hasRelocationAddend())
1126      EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1127    else
1128      EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1129
1130    unsigned Flags = 0;
1131    StringRef Group = "";
1132    if (Section.getFlags() & ELF::SHF_GROUP) {
1133      Flags = ELF::SHF_GROUP;
1134      Group = Section.getGroup()->getName();
1135    }
1136
1137    const MCSectionELF *RelaSection =
1138      Ctx.getELFSection(RelaSectionName, hasRelocationAddend() ?
1139                        ELF::SHT_RELA : ELF::SHT_REL, Flags,
1140                        SectionKind::getReadOnly(),
1141                        EntrySize, Group);
1142    RelMap[&Section] = RelaSection;
1143    Asm.getOrCreateSectionData(*RelaSection);
1144  }
1145}
1146
1147static SmallVector<char, 128>
1148getUncompressedData(MCAsmLayout &Layout,
1149                    MCSectionData::FragmentListType &Fragments) {
1150  SmallVector<char, 128> UncompressedData;
1151  for (const MCFragment &F : Fragments) {
1152    const SmallVectorImpl<char> *Contents;
1153    switch (F.getKind()) {
1154    case MCFragment::FT_Data:
1155      Contents = &cast<MCDataFragment>(F).getContents();
1156      break;
1157    case MCFragment::FT_Dwarf:
1158      Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
1159      break;
1160    case MCFragment::FT_DwarfFrame:
1161      Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
1162      break;
1163    default:
1164      llvm_unreachable(
1165          "Not expecting any other fragment types in a debug_* section");
1166    }
1167    UncompressedData.append(Contents->begin(), Contents->end());
1168  }
1169  return UncompressedData;
1170}
1171
1172// Include the debug info compression header:
1173// "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
1174// useful for consumers to preallocate a buffer to decompress into.
1175static bool
1176prependCompressionHeader(uint64_t Size,
1177                         SmallVectorImpl<char> &CompressedContents) {
1178  static const StringRef Magic = "ZLIB";
1179  if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size())
1180    return false;
1181  if (sys::IsLittleEndianHost)
1182    Size = sys::SwapByteOrder(Size);
1183  CompressedContents.insert(CompressedContents.begin(),
1184                            Magic.size() + sizeof(Size), 0);
1185  std::copy(Magic.begin(), Magic.end(), CompressedContents.begin());
1186  std::copy(reinterpret_cast<char *>(&Size),
1187            reinterpret_cast<char *>(&Size + 1),
1188            CompressedContents.begin() + Magic.size());
1189  return true;
1190}
1191
1192// Return a single fragment containing the compressed contents of the whole
1193// section. Null if the section was not compressed for any reason.
1194static std::unique_ptr<MCDataFragment>
1195getCompressedFragment(MCAsmLayout &Layout,
1196                      MCSectionData::FragmentListType &Fragments) {
1197  std::unique_ptr<MCDataFragment> CompressedFragment(new MCDataFragment());
1198
1199  // Gather the uncompressed data from all the fragments, recording the
1200  // alignment fragment, if seen, and any fixups.
1201  SmallVector<char, 128> UncompressedData =
1202      getUncompressedData(Layout, Fragments);
1203
1204  SmallVectorImpl<char> &CompressedContents = CompressedFragment->getContents();
1205
1206  zlib::Status Success = zlib::compress(
1207      StringRef(UncompressedData.data(), UncompressedData.size()),
1208      CompressedContents);
1209  if (Success != zlib::StatusOK)
1210    return nullptr;
1211
1212  if (!prependCompressionHeader(UncompressedData.size(), CompressedContents))
1213    return nullptr;
1214
1215  return CompressedFragment;
1216}
1217
1218typedef DenseMap<const MCSectionData *, std::vector<MCSymbolData *>>
1219DefiningSymbolMap;
1220
1221static void UpdateSymbols(const MCAsmLayout &Layout,
1222                          const std::vector<MCSymbolData *> &Symbols,
1223                          MCFragment &NewFragment) {
1224  for (MCSymbolData *Sym : Symbols) {
1225    Sym->setOffset(Sym->getOffset() +
1226                   Layout.getFragmentOffset(Sym->getFragment()));
1227    Sym->setFragment(&NewFragment);
1228  }
1229}
1230
1231static void CompressDebugSection(MCAssembler &Asm, MCAsmLayout &Layout,
1232                                 const DefiningSymbolMap &DefiningSymbols,
1233                                 const MCSectionELF &Section,
1234                                 MCSectionData &SD) {
1235  StringRef SectionName = Section.getSectionName();
1236  MCSectionData::FragmentListType &Fragments = SD.getFragmentList();
1237
1238  std::unique_ptr<MCDataFragment> CompressedFragment =
1239      getCompressedFragment(Layout, Fragments);
1240
1241  // Leave the section as-is if the fragments could not be compressed.
1242  if (!CompressedFragment)
1243    return;
1244
1245  // Update the fragment+offsets of any symbols referring to fragments in this
1246  // section to refer to the new fragment.
1247  auto I = DefiningSymbols.find(&SD);
1248  if (I != DefiningSymbols.end())
1249    UpdateSymbols(Layout, I->second, *CompressedFragment);
1250
1251  // Invalidate the layout for the whole section since it will have new and
1252  // different fragments now.
1253  Layout.invalidateFragmentsFrom(&Fragments.front());
1254  Fragments.clear();
1255
1256  // Complete the initialization of the new fragment
1257  CompressedFragment->setParent(&SD);
1258  CompressedFragment->setLayoutOrder(0);
1259  Fragments.push_back(CompressedFragment.release());
1260
1261  // Rename from .debug_* to .zdebug_*
1262  Asm.getContext().renameELFSection(&Section,
1263                                    (".z" + SectionName.drop_front(1)).str());
1264}
1265
1266void ELFObjectWriter::CompressDebugSections(MCAssembler &Asm,
1267                                            MCAsmLayout &Layout) {
1268  if (!Asm.getContext().getAsmInfo()->compressDebugSections())
1269    return;
1270
1271  DefiningSymbolMap DefiningSymbols;
1272
1273  for (MCSymbolData &SD : Asm.symbols())
1274    if (MCFragment *F = SD.getFragment())
1275      DefiningSymbols[F->getParent()].push_back(&SD);
1276
1277  for (MCSectionData &SD : Asm) {
1278    const MCSectionELF &Section =
1279        static_cast<const MCSectionELF &>(SD.getSection());
1280    StringRef SectionName = Section.getSectionName();
1281
1282    // Compressing debug_frame requires handling alignment fragments which is
1283    // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
1284    // for writing to arbitrary buffers) for little benefit.
1285    if (!SectionName.startswith(".debug_") || SectionName == ".debug_frame")
1286      continue;
1287
1288    CompressDebugSection(Asm, Layout, DefiningSymbols, Section, SD);
1289  }
1290}
1291
1292void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout,
1293                                       const RelMapTy &RelMap) {
1294  for (MCAssembler::const_iterator it = Asm.begin(),
1295         ie = Asm.end(); it != ie; ++it) {
1296    const MCSectionData &SD = *it;
1297    const MCSectionELF &Section =
1298      static_cast<const MCSectionELF&>(SD.getSection());
1299
1300    const MCSectionELF *RelaSection = RelMap.lookup(&Section);
1301    if (!RelaSection)
1302      continue;
1303    MCSectionData &RelaSD = Asm.getOrCreateSectionData(*RelaSection);
1304    RelaSD.setAlignment(is64Bit() ? 8 : 4);
1305
1306    MCDataFragment *F = new MCDataFragment(&RelaSD);
1307    WriteRelocationsFragment(Asm, F, &*it);
1308  }
1309}
1310
1311void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1312                                       uint64_t Flags, uint64_t Address,
1313                                       uint64_t Offset, uint64_t Size,
1314                                       uint32_t Link, uint32_t Info,
1315                                       uint64_t Alignment,
1316                                       uint64_t EntrySize) {
1317  Write32(Name);        // sh_name: index into string table
1318  Write32(Type);        // sh_type
1319  WriteWord(Flags);     // sh_flags
1320  WriteWord(Address);   // sh_addr
1321  WriteWord(Offset);    // sh_offset
1322  WriteWord(Size);      // sh_size
1323  Write32(Link);        // sh_link
1324  Write32(Info);        // sh_info
1325  WriteWord(Alignment); // sh_addralign
1326  WriteWord(EntrySize); // sh_entsize
1327}
1328
1329// ELF doesn't require relocations to be in any order. We sort by the r_offset,
1330// just to match gnu as for easier comparison. The use type is an arbitrary way
1331// of making the sort deterministic.
1332static int cmpRel(const ELFRelocationEntry *AP, const ELFRelocationEntry *BP) {
1333  const ELFRelocationEntry &A = *AP;
1334  const ELFRelocationEntry &B = *BP;
1335  if (A.Offset != B.Offset)
1336    return B.Offset - A.Offset;
1337  if (B.Type != A.Type)
1338    return A.Type - B.Type;
1339  llvm_unreachable("ELFRelocs might be unstable!");
1340}
1341
1342static void sortRelocs(const MCAssembler &Asm,
1343                       std::vector<ELFRelocationEntry> &Relocs) {
1344  array_pod_sort(Relocs.begin(), Relocs.end(), cmpRel);
1345}
1346
1347void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm,
1348                                               MCDataFragment *F,
1349                                               const MCSectionData *SD) {
1350  std::vector<ELFRelocationEntry> &Relocs = Relocations[SD];
1351
1352  sortRelocs(Asm, Relocs);
1353
1354  for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1355    const ELFRelocationEntry &Entry = Relocs[e - i - 1];
1356
1357    unsigned Index;
1358    if (Entry.UseSymbol) {
1359      Index = getSymbolIndexInSymbolTable(Asm, Entry.Symbol);
1360    } else {
1361      const MCSectionData *Sec = Entry.Section;
1362      if (Sec)
1363        Index = Sec->getOrdinal() + FileSymbolData.size() +
1364                LocalSymbolData.size() + 1;
1365      else
1366        Index = 0;
1367    }
1368
1369    if (is64Bit()) {
1370      write(*F, Entry.Offset);
1371      if (TargetObjectWriter->isN64()) {
1372        write(*F, uint32_t(Index));
1373
1374        write(*F, TargetObjectWriter->getRSsym(Entry.Type));
1375        write(*F, TargetObjectWriter->getRType3(Entry.Type));
1376        write(*F, TargetObjectWriter->getRType2(Entry.Type));
1377        write(*F, TargetObjectWriter->getRType(Entry.Type));
1378      } else {
1379        struct ELF::Elf64_Rela ERE64;
1380        ERE64.setSymbolAndType(Index, Entry.Type);
1381        write(*F, ERE64.r_info);
1382      }
1383      if (hasRelocationAddend())
1384        write(*F, Entry.Addend);
1385    } else {
1386      write(*F, uint32_t(Entry.Offset));
1387
1388      struct ELF::Elf32_Rela ERE32;
1389      ERE32.setSymbolAndType(Index, Entry.Type);
1390      write(*F, ERE32.r_info);
1391
1392      if (hasRelocationAddend())
1393        write(*F, uint32_t(Entry.Addend));
1394    }
1395  }
1396}
1397
1398void ELFObjectWriter::CreateMetadataSections(MCAssembler &Asm,
1399                                             MCAsmLayout &Layout,
1400                                             SectionIndexMapTy &SectionIndexMap,
1401                                             const RelMapTy &RelMap) {
1402  MCContext &Ctx = Asm.getContext();
1403  MCDataFragment *F;
1404
1405  unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
1406
1407  // We construct .shstrtab, .symtab and .strtab in this order to match gnu as.
1408  const MCSectionELF *ShstrtabSection =
1409    Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0,
1410                      SectionKind::getReadOnly());
1411  MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection);
1412  ShstrtabSD.setAlignment(1);
1413
1414  const MCSectionELF *SymtabSection =
1415    Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
1416                      SectionKind::getReadOnly(),
1417                      EntrySize, "");
1418  MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
1419  SymtabSD.setAlignment(is64Bit() ? 8 : 4);
1420
1421  const MCSectionELF *StrtabSection;
1422  StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0,
1423                                    SectionKind::getReadOnly());
1424  MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection);
1425  StrtabSD.setAlignment(1);
1426
1427  ComputeIndexMap(Asm, SectionIndexMap, RelMap);
1428
1429  ShstrtabIndex = SectionIndexMap.lookup(ShstrtabSection);
1430  SymbolTableIndex = SectionIndexMap.lookup(SymtabSection);
1431  StringTableIndex = SectionIndexMap.lookup(StrtabSection);
1432
1433  // Symbol table
1434  F = new MCDataFragment(&SymtabSD);
1435  WriteSymbolTable(F, Asm, Layout, SectionIndexMap);
1436
1437  F = new MCDataFragment(&StrtabSD);
1438  F->getContents().append(StrTabBuilder.data().begin(),
1439                          StrTabBuilder.data().end());
1440
1441  F = new MCDataFragment(&ShstrtabSD);
1442
1443  // Section header string table.
1444  for (auto it = Asm.begin(), ie = Asm.end(); it != ie; ++it) {
1445    const MCSectionELF &Section =
1446      static_cast<const MCSectionELF&>(it->getSection());
1447    ShStrTabBuilder.add(Section.getSectionName());
1448  }
1449  ShStrTabBuilder.finalize();
1450  F->getContents().append(ShStrTabBuilder.data().begin(),
1451                          ShStrTabBuilder.data().end());
1452}
1453
1454void ELFObjectWriter::CreateIndexedSections(MCAssembler &Asm,
1455                                            MCAsmLayout &Layout,
1456                                            GroupMapTy &GroupMap,
1457                                            RevGroupMapTy &RevGroupMap,
1458                                            SectionIndexMapTy &SectionIndexMap,
1459                                            const RelMapTy &RelMap) {
1460  // Create the .note.GNU-stack section if needed.
1461  MCContext &Ctx = Asm.getContext();
1462  if (Asm.getNoExecStack()) {
1463    const MCSectionELF *GnuStackSection =
1464      Ctx.getELFSection(".note.GNU-stack", ELF::SHT_PROGBITS, 0,
1465                        SectionKind::getReadOnly());
1466    Asm.getOrCreateSectionData(*GnuStackSection);
1467  }
1468
1469  // Build the groups
1470  for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
1471       it != ie; ++it) {
1472    const MCSectionELF &Section =
1473      static_cast<const MCSectionELF&>(it->getSection());
1474    if (!(Section.getFlags() & ELF::SHF_GROUP))
1475      continue;
1476
1477    const MCSymbol *SignatureSymbol = Section.getGroup();
1478    Asm.getOrCreateSymbolData(*SignatureSymbol);
1479    const MCSectionELF *&Group = RevGroupMap[SignatureSymbol];
1480    if (!Group) {
1481      Group = Ctx.CreateELFGroupSection();
1482      MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1483      Data.setAlignment(4);
1484      MCDataFragment *F = new MCDataFragment(&Data);
1485      write(*F, uint32_t(ELF::GRP_COMDAT));
1486    }
1487    GroupMap[Group] = SignatureSymbol;
1488  }
1489
1490  ComputeIndexMap(Asm, SectionIndexMap, RelMap);
1491
1492  // Add sections to the groups
1493  for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
1494       it != ie; ++it) {
1495    const MCSectionELF &Section =
1496      static_cast<const MCSectionELF&>(it->getSection());
1497    if (!(Section.getFlags() & ELF::SHF_GROUP))
1498      continue;
1499    const MCSectionELF *Group = RevGroupMap[Section.getGroup()];
1500    MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
1501    // FIXME: we could use the previous fragment
1502    MCDataFragment *F = new MCDataFragment(&Data);
1503    uint32_t Index = SectionIndexMap.lookup(&Section);
1504    write(*F, Index);
1505  }
1506}
1507
1508void ELFObjectWriter::WriteSection(MCAssembler &Asm,
1509                                   const SectionIndexMapTy &SectionIndexMap,
1510                                   uint32_t GroupSymbolIndex,
1511                                   uint64_t Offset, uint64_t Size,
1512                                   uint64_t Alignment,
1513                                   const MCSectionELF &Section) {
1514  uint64_t sh_link = 0;
1515  uint64_t sh_info = 0;
1516
1517  switch(Section.getType()) {
1518  case ELF::SHT_DYNAMIC:
1519    sh_link = ShStrTabBuilder.getOffset(Section.getSectionName());
1520    sh_info = 0;
1521    break;
1522
1523  case ELF::SHT_REL:
1524  case ELF::SHT_RELA: {
1525    const MCSectionELF *SymtabSection;
1526    const MCSectionELF *InfoSection;
1527    SymtabSection = Asm.getContext().getELFSection(".symtab", ELF::SHT_SYMTAB,
1528                                                   0,
1529                                                   SectionKind::getReadOnly());
1530    sh_link = SectionIndexMap.lookup(SymtabSection);
1531    assert(sh_link && ".symtab not found");
1532
1533    // Remove ".rel" and ".rela" prefixes.
1534    unsigned SecNameLen = (Section.getType() == ELF::SHT_REL) ? 4 : 5;
1535    StringRef SectionName = Section.getSectionName().substr(SecNameLen);
1536    StringRef GroupName =
1537        Section.getGroup() ? Section.getGroup()->getName() : "";
1538
1539    InfoSection = Asm.getContext().getELFSection(SectionName, ELF::SHT_PROGBITS,
1540                                                 0, SectionKind::getReadOnly(),
1541                                                 0, GroupName);
1542    sh_info = SectionIndexMap.lookup(InfoSection);
1543    break;
1544  }
1545
1546  case ELF::SHT_SYMTAB:
1547  case ELF::SHT_DYNSYM:
1548    sh_link = StringTableIndex;
1549    sh_info = LastLocalSymbolIndex;
1550    break;
1551
1552  case ELF::SHT_SYMTAB_SHNDX:
1553    sh_link = SymbolTableIndex;
1554    break;
1555
1556  case ELF::SHT_PROGBITS:
1557  case ELF::SHT_STRTAB:
1558  case ELF::SHT_NOBITS:
1559  case ELF::SHT_NOTE:
1560  case ELF::SHT_NULL:
1561  case ELF::SHT_ARM_ATTRIBUTES:
1562  case ELF::SHT_INIT_ARRAY:
1563  case ELF::SHT_FINI_ARRAY:
1564  case ELF::SHT_PREINIT_ARRAY:
1565  case ELF::SHT_X86_64_UNWIND:
1566  case ELF::SHT_MIPS_REGINFO:
1567  case ELF::SHT_MIPS_OPTIONS:
1568    // Nothing to do.
1569    break;
1570
1571  case ELF::SHT_GROUP:
1572    sh_link = SymbolTableIndex;
1573    sh_info = GroupSymbolIndex;
1574    break;
1575
1576  default:
1577    assert(0 && "FIXME: sh_type value not supported!");
1578    break;
1579  }
1580
1581  if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
1582      Section.getType() == ELF::SHT_ARM_EXIDX) {
1583    StringRef SecName(Section.getSectionName());
1584    if (SecName == ".ARM.exidx") {
1585      sh_link = SectionIndexMap.lookup(
1586        Asm.getContext().getELFSection(".text",
1587                                       ELF::SHT_PROGBITS,
1588                                       ELF::SHF_EXECINSTR | ELF::SHF_ALLOC,
1589                                       SectionKind::getText()));
1590    } else if (SecName.startswith(".ARM.exidx")) {
1591      StringRef GroupName =
1592          Section.getGroup() ? Section.getGroup()->getName() : "";
1593      sh_link = SectionIndexMap.lookup(Asm.getContext().getELFSection(
1594          SecName.substr(sizeof(".ARM.exidx") - 1), ELF::SHT_PROGBITS,
1595          ELF::SHF_EXECINSTR | ELF::SHF_ALLOC, SectionKind::getText(), 0,
1596          GroupName));
1597    }
1598  }
1599
1600  WriteSecHdrEntry(ShStrTabBuilder.getOffset(Section.getSectionName()),
1601                   Section.getType(),
1602                   Section.getFlags(), 0, Offset, Size, sh_link, sh_info,
1603                   Alignment, Section.getEntrySize());
1604}
1605
1606bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) {
1607  return SD.getOrdinal() == ~UINT32_C(0) &&
1608    !SD.getSection().isVirtualSection();
1609}
1610
1611uint64_t ELFObjectWriter::DataSectionSize(const MCSectionData &SD) {
1612  uint64_t Ret = 0;
1613  for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1614       ++i) {
1615    const MCFragment &F = *i;
1616    assert(F.getKind() == MCFragment::FT_Data);
1617    Ret += cast<MCDataFragment>(F).getContents().size();
1618  }
1619  return Ret;
1620}
1621
1622uint64_t ELFObjectWriter::GetSectionFileSize(const MCAsmLayout &Layout,
1623                                             const MCSectionData &SD) {
1624  if (IsELFMetaDataSection(SD))
1625    return DataSectionSize(SD);
1626  return Layout.getSectionFileSize(&SD);
1627}
1628
1629uint64_t ELFObjectWriter::GetSectionAddressSize(const MCAsmLayout &Layout,
1630                                                const MCSectionData &SD) {
1631  if (IsELFMetaDataSection(SD))
1632    return DataSectionSize(SD);
1633  return Layout.getSectionAddressSize(&SD);
1634}
1635
1636void ELFObjectWriter::WriteDataSectionData(MCAssembler &Asm,
1637                                           const MCAsmLayout &Layout,
1638                                           const MCSectionELF &Section) {
1639  const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1640
1641  uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
1642  WriteZeros(Padding);
1643
1644  if (IsELFMetaDataSection(SD)) {
1645    for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
1646         ++i) {
1647      const MCFragment &F = *i;
1648      assert(F.getKind() == MCFragment::FT_Data);
1649      WriteBytes(cast<MCDataFragment>(F).getContents());
1650    }
1651  } else {
1652    Asm.writeSectionData(&SD, Layout);
1653  }
1654}
1655
1656void ELFObjectWriter::WriteSectionHeader(MCAssembler &Asm,
1657                                         const GroupMapTy &GroupMap,
1658                                         const MCAsmLayout &Layout,
1659                                      const SectionIndexMapTy &SectionIndexMap,
1660                                   const SectionOffsetMapTy &SectionOffsetMap) {
1661  const unsigned NumSections = Asm.size() + 1;
1662
1663  std::vector<const MCSectionELF*> Sections;
1664  Sections.resize(NumSections - 1);
1665
1666  for (SectionIndexMapTy::const_iterator i=
1667         SectionIndexMap.begin(), e = SectionIndexMap.end(); i != e; ++i) {
1668    const std::pair<const MCSectionELF*, uint32_t> &p = *i;
1669    Sections[p.second - 1] = p.first;
1670  }
1671
1672  // Null section first.
1673  uint64_t FirstSectionSize =
1674    NumSections >= ELF::SHN_LORESERVE ? NumSections : 0;
1675  uint32_t FirstSectionLink =
1676    ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0;
1677  WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0);
1678
1679  for (unsigned i = 0; i < NumSections - 1; ++i) {
1680    const MCSectionELF &Section = *Sections[i];
1681    const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1682    uint32_t GroupSymbolIndex;
1683    if (Section.getType() != ELF::SHT_GROUP)
1684      GroupSymbolIndex = 0;
1685    else
1686      GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm,
1687                                                     GroupMap.lookup(&Section));
1688
1689    uint64_t Size = GetSectionAddressSize(Layout, SD);
1690
1691    WriteSection(Asm, SectionIndexMap, GroupSymbolIndex,
1692                 SectionOffsetMap.lookup(&Section), Size,
1693                 SD.getAlignment(), Section);
1694  }
1695}
1696
1697void ELFObjectWriter::ComputeSectionOrder(MCAssembler &Asm,
1698                                  std::vector<const MCSectionELF*> &Sections) {
1699  for (MCAssembler::iterator it = Asm.begin(),
1700         ie = Asm.end(); it != ie; ++it) {
1701    const MCSectionELF &Section =
1702      static_cast<const MCSectionELF &>(it->getSection());
1703    if (Section.getType() == ELF::SHT_GROUP)
1704      Sections.push_back(&Section);
1705  }
1706
1707  for (MCAssembler::iterator it = Asm.begin(),
1708         ie = Asm.end(); it != ie; ++it) {
1709    const MCSectionELF &Section =
1710      static_cast<const MCSectionELF &>(it->getSection());
1711    if (Section.getType() != ELF::SHT_GROUP &&
1712        Section.getType() != ELF::SHT_REL &&
1713        Section.getType() != ELF::SHT_RELA)
1714      Sections.push_back(&Section);
1715  }
1716
1717  for (MCAssembler::iterator it = Asm.begin(),
1718         ie = Asm.end(); it != ie; ++it) {
1719    const MCSectionELF &Section =
1720      static_cast<const MCSectionELF &>(it->getSection());
1721    if (Section.getType() == ELF::SHT_REL ||
1722        Section.getType() == ELF::SHT_RELA)
1723      Sections.push_back(&Section);
1724  }
1725}
1726
1727void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1728                                  const MCAsmLayout &Layout) {
1729  GroupMapTy GroupMap;
1730  RevGroupMapTy RevGroupMap;
1731  SectionIndexMapTy SectionIndexMap;
1732
1733  unsigned NumUserSections = Asm.size();
1734
1735  CompressDebugSections(Asm, const_cast<MCAsmLayout &>(Layout));
1736
1737  DenseMap<const MCSectionELF*, const MCSectionELF*> RelMap;
1738  CreateRelocationSections(Asm, const_cast<MCAsmLayout&>(Layout), RelMap);
1739
1740  const unsigned NumUserAndRelocSections = Asm.size();
1741  CreateIndexedSections(Asm, const_cast<MCAsmLayout&>(Layout), GroupMap,
1742                        RevGroupMap, SectionIndexMap, RelMap);
1743  const unsigned AllSections = Asm.size();
1744  const unsigned NumIndexedSections = AllSections - NumUserAndRelocSections;
1745
1746  unsigned NumRegularSections = NumUserSections + NumIndexedSections;
1747
1748  // Compute symbol table information.
1749  computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap,
1750                     NumRegularSections);
1751
1752  WriteRelocations(Asm, const_cast<MCAsmLayout&>(Layout), RelMap);
1753
1754  CreateMetadataSections(const_cast<MCAssembler&>(Asm),
1755                         const_cast<MCAsmLayout&>(Layout),
1756                         SectionIndexMap,
1757                         RelMap);
1758
1759  uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
1760  uint64_t HeaderSize = is64Bit() ? sizeof(ELF::Elf64_Ehdr) :
1761                                    sizeof(ELF::Elf32_Ehdr);
1762  uint64_t FileOff = HeaderSize;
1763
1764  std::vector<const MCSectionELF*> Sections;
1765  ComputeSectionOrder(Asm, Sections);
1766  unsigned NumSections = Sections.size();
1767  SectionOffsetMapTy SectionOffsetMap;
1768  for (unsigned i = 0; i < NumRegularSections + 1; ++i) {
1769    const MCSectionELF &Section = *Sections[i];
1770    const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1771
1772    FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
1773
1774    // Remember the offset into the file for this section.
1775    SectionOffsetMap[&Section] = FileOff;
1776
1777    // Get the size of the section in the output file (including padding).
1778    FileOff += GetSectionFileSize(Layout, SD);
1779  }
1780
1781  FileOff = RoundUpToAlignment(FileOff, NaturalAlignment);
1782
1783  const unsigned SectionHeaderOffset = FileOff - HeaderSize;
1784
1785  uint64_t SectionHeaderEntrySize = is64Bit() ?
1786    sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr);
1787  FileOff += (NumSections + 1) * SectionHeaderEntrySize;
1788
1789  for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) {
1790    const MCSectionELF &Section = *Sections[i];
1791    const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
1792
1793    FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
1794
1795    // Remember the offset into the file for this section.
1796    SectionOffsetMap[&Section] = FileOff;
1797
1798    // Get the size of the section in the output file (including padding).
1799    FileOff += GetSectionFileSize(Layout, SD);
1800  }
1801
1802  // Write out the ELF header ...
1803  WriteHeader(Asm, SectionHeaderOffset, NumSections + 1);
1804
1805  // ... then the regular sections ...
1806  // + because of .shstrtab
1807  for (unsigned i = 0; i < NumRegularSections + 1; ++i)
1808    WriteDataSectionData(Asm, Layout, *Sections[i]);
1809
1810  uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
1811  WriteZeros(Padding);
1812
1813  // ... then the section header table ...
1814  WriteSectionHeader(Asm, GroupMap, Layout, SectionIndexMap,
1815                     SectionOffsetMap);
1816
1817  // ... and then the remaining sections ...
1818  for (unsigned i = NumRegularSections + 1; i < NumSections; ++i)
1819    WriteDataSectionData(Asm, Layout, *Sections[i]);
1820}
1821
1822bool
1823ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
1824                                                      const MCSymbolData &DataA,
1825                                                      const MCFragment &FB,
1826                                                      bool InSet,
1827                                                      bool IsPCRel) const {
1828  if (DataA.getFlags() & ELF_STB_Weak || MCELF::GetType(DataA) == ELF::STT_GNU_IFUNC)
1829    return false;
1830  return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
1831                                                 Asm, DataA, FB,InSet, IsPCRel);
1832}
1833
1834MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
1835                                            raw_ostream &OS,
1836                                            bool IsLittleEndian) {
1837  return new ELFObjectWriter(MOTW, OS, IsLittleEndian);
1838}
1839