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      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 "MCELF.h"
     15 #include "llvm/ADT/OwningPtr.h"
     16 #include "llvm/ADT/SmallPtrSet.h"
     17 #include "llvm/ADT/SmallString.h"
     18 #include "llvm/ADT/STLExtras.h"
     19 #include "llvm/ADT/StringMap.h"
     20 #include "llvm/MC/MCAsmBackend.h"
     21 #include "llvm/MC/MCAsmLayout.h"
     22 #include "llvm/MC/MCAssembler.h"
     23 #include "llvm/MC/MCContext.h"
     24 #include "llvm/MC/MCELFObjectWriter.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/Support/Debug.h"
     32 #include "llvm/Support/ErrorHandling.h"
     33 #include "llvm/Support/ELF.h"
     34 
     35 #include <vector>
     36 using namespace llvm;
     37 
     38 #undef  DEBUG_TYPE
     39 #define DEBUG_TYPE "reloc-info"
     40 
     41 namespace {
     42 class ELFObjectWriter : public MCObjectWriter {
     43   protected:
     44 
     45     static bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind);
     46     static bool RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant);
     47     static uint64_t SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout);
     48     static bool isInSymtab(const MCAssembler &Asm, const MCSymbolData &Data,
     49                            bool Used, bool Renamed);
     50     static bool isLocal(const MCSymbolData &Data, bool isSignature,
     51                         bool isUsedInReloc);
     52     static bool IsELFMetaDataSection(const MCSectionData &SD);
     53     static uint64_t DataSectionSize(const MCSectionData &SD);
     54     static uint64_t GetSectionFileSize(const MCAsmLayout &Layout,
     55                                        const MCSectionData &SD);
     56     static uint64_t GetSectionAddressSize(const MCAsmLayout &Layout,
     57                                           const MCSectionData &SD);
     58 
     59     void WriteDataSectionData(MCAssembler &Asm,
     60                               const MCAsmLayout &Layout,
     61                               const MCSectionELF &Section);
     62 
     63     /*static bool isFixupKindX86RIPRel(unsigned Kind) {
     64       return Kind == X86::reloc_riprel_4byte ||
     65         Kind == X86::reloc_riprel_4byte_movq_load;
     66     }*/
     67 
     68     /// ELFSymbolData - Helper struct for containing some precomputed
     69     /// information on symbols.
     70     struct ELFSymbolData {
     71       MCSymbolData *SymbolData;
     72       uint64_t StringIndex;
     73       uint32_t SectionIndex;
     74 
     75       // Support lexicographic sorting.
     76       bool operator<(const ELFSymbolData &RHS) const {
     77         if (MCELF::GetType(*SymbolData) == ELF::STT_FILE)
     78           return true;
     79         if (MCELF::GetType(*RHS.SymbolData) == ELF::STT_FILE)
     80           return false;
     81         return SymbolData->getSymbol().getName() <
     82                RHS.SymbolData->getSymbol().getName();
     83       }
     84     };
     85 
     86     /// The target specific ELF writer instance.
     87     llvm::OwningPtr<MCELFObjectTargetWriter> TargetObjectWriter;
     88 
     89     SmallPtrSet<const MCSymbol *, 16> UsedInReloc;
     90     SmallPtrSet<const MCSymbol *, 16> WeakrefUsedInReloc;
     91     DenseMap<const MCSymbol *, const MCSymbol *> Renames;
     92 
     93     llvm::DenseMap<const MCSectionData*,
     94                    std::vector<ELFRelocationEntry> > Relocations;
     95     DenseMap<const MCSection*, uint64_t> SectionStringTableIndex;
     96 
     97     /// @}
     98     /// @name Symbol Table Data
     99     /// @{
    100 
    101     SmallString<256> StringTable;
    102     std::vector<ELFSymbolData> LocalSymbolData;
    103     std::vector<ELFSymbolData> ExternalSymbolData;
    104     std::vector<ELFSymbolData> UndefinedSymbolData;
    105 
    106     /// @}
    107 
    108     bool NeedsGOT;
    109 
    110     bool NeedsSymtabShndx;
    111 
    112     // This holds the symbol table index of the last local symbol.
    113     unsigned LastLocalSymbolIndex;
    114     // This holds the .strtab section index.
    115     unsigned StringTableIndex;
    116     // This holds the .symtab section index.
    117     unsigned SymbolTableIndex;
    118 
    119     unsigned ShstrtabIndex;
    120 
    121 
    122     const MCSymbol *SymbolToReloc(const MCAssembler &Asm,
    123                                   const MCValue &Target,
    124                                   const MCFragment &F,
    125                                   const MCFixup &Fixup,
    126                                   bool IsPCRel) const;
    127 
    128     // TargetObjectWriter wrappers.
    129     const MCSymbol *ExplicitRelSym(const MCAssembler &Asm,
    130                                    const MCValue &Target,
    131                                    const MCFragment &F,
    132                                    const MCFixup &Fixup,
    133                                    bool IsPCRel) const {
    134       return TargetObjectWriter->ExplicitRelSym(Asm, Target, F, Fixup, IsPCRel);
    135     }
    136 
    137     bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
    138     bool hasRelocationAddend() const {
    139       return TargetObjectWriter->hasRelocationAddend();
    140     }
    141     unsigned getEFlags() const {
    142       return TargetObjectWriter->getEFlags();
    143     }
    144     unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup,
    145                           bool IsPCRel, bool IsRelocWithSymbol,
    146                           int64_t Addend) const {
    147       return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel,
    148                                               IsRelocWithSymbol, Addend);
    149     }
    150 
    151 
    152   public:
    153     ELFObjectWriter(MCELFObjectTargetWriter *MOTW,
    154                     raw_ostream &_OS, bool IsLittleEndian)
    155       : MCObjectWriter(_OS, IsLittleEndian),
    156         TargetObjectWriter(MOTW),
    157         NeedsGOT(false), NeedsSymtabShndx(false){
    158     }
    159 
    160     virtual ~ELFObjectWriter();
    161 
    162     void WriteWord(uint64_t W) {
    163       if (is64Bit())
    164         Write64(W);
    165       else
    166         Write32(W);
    167     }
    168 
    169     void StringLE16(char *buf, uint16_t Value) {
    170       buf[0] = char(Value >> 0);
    171       buf[1] = char(Value >> 8);
    172     }
    173 
    174     void StringLE32(char *buf, uint32_t Value) {
    175       StringLE16(buf, uint16_t(Value >> 0));
    176       StringLE16(buf + 2, uint16_t(Value >> 16));
    177     }
    178 
    179     void StringLE64(char *buf, uint64_t Value) {
    180       StringLE32(buf, uint32_t(Value >> 0));
    181       StringLE32(buf + 4, uint32_t(Value >> 32));
    182     }
    183 
    184     void StringBE16(char *buf ,uint16_t Value) {
    185       buf[0] = char(Value >> 8);
    186       buf[1] = char(Value >> 0);
    187     }
    188 
    189     void StringBE32(char *buf, uint32_t Value) {
    190       StringBE16(buf, uint16_t(Value >> 16));
    191       StringBE16(buf + 2, uint16_t(Value >> 0));
    192     }
    193 
    194     void StringBE64(char *buf, uint64_t Value) {
    195       StringBE32(buf, uint32_t(Value >> 32));
    196       StringBE32(buf + 4, uint32_t(Value >> 0));
    197     }
    198 
    199     void String8(MCDataFragment &F, uint8_t Value) {
    200       char buf[1];
    201       buf[0] = Value;
    202       F.getContents() += StringRef(buf, 1);
    203     }
    204 
    205     void String16(MCDataFragment &F, uint16_t Value) {
    206       char buf[2];
    207       if (isLittleEndian())
    208         StringLE16(buf, Value);
    209       else
    210         StringBE16(buf, Value);
    211       F.getContents() += StringRef(buf, 2);
    212     }
    213 
    214     void String32(MCDataFragment &F, uint32_t Value) {
    215       char buf[4];
    216       if (isLittleEndian())
    217         StringLE32(buf, Value);
    218       else
    219         StringBE32(buf, Value);
    220       F.getContents() += StringRef(buf, 4);
    221     }
    222 
    223     void String64(MCDataFragment &F, uint64_t Value) {
    224       char buf[8];
    225       if (isLittleEndian())
    226         StringLE64(buf, Value);
    227       else
    228         StringBE64(buf, Value);
    229       F.getContents() += StringRef(buf, 8);
    230     }
    231 
    232     void WriteHeader(uint64_t SectionDataSize,
    233                      unsigned NumberOfSections);
    234 
    235     void WriteSymbolEntry(MCDataFragment *SymtabF,
    236                           MCDataFragment *ShndxF,
    237                           uint64_t name, uint8_t info,
    238                           uint64_t value, uint64_t size,
    239                           uint8_t other, uint32_t shndx,
    240                           bool Reserved);
    241 
    242     void WriteSymbol(MCDataFragment *SymtabF,  MCDataFragment *ShndxF,
    243                      ELFSymbolData &MSD,
    244                      const MCAsmLayout &Layout);
    245 
    246     typedef DenseMap<const MCSectionELF*, uint32_t> SectionIndexMapTy;
    247     void WriteSymbolTable(MCDataFragment *SymtabF,
    248                           MCDataFragment *ShndxF,
    249                           const MCAssembler &Asm,
    250                           const MCAsmLayout &Layout,
    251                           const SectionIndexMapTy &SectionIndexMap);
    252 
    253     virtual void RecordRelocation(const MCAssembler &Asm,
    254                                   const MCAsmLayout &Layout,
    255                                   const MCFragment *Fragment,
    256                                   const MCFixup &Fixup,
    257                                   MCValue Target, uint64_t &FixedValue);
    258 
    259     uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm,
    260                                          const MCSymbol *S);
    261 
    262     // Map from a group section to the signature symbol
    263     typedef DenseMap<const MCSectionELF*, const MCSymbol*> GroupMapTy;
    264     // Map from a signature symbol to the group section
    265     typedef DenseMap<const MCSymbol*, const MCSectionELF*> RevGroupMapTy;
    266     // Map from a section to the section with the relocations
    267     typedef DenseMap<const MCSectionELF*, const MCSectionELF*> RelMapTy;
    268     // Map from a section to its offset
    269     typedef DenseMap<const MCSectionELF*, uint64_t> SectionOffsetMapTy;
    270 
    271     /// ComputeSymbolTable - Compute the symbol table data
    272     ///
    273     /// \param StringTable [out] - The string table data.
    274     /// \param StringIndexMap [out] - Map from symbol names to offsets in the
    275     /// string table.
    276     void ComputeSymbolTable(MCAssembler &Asm,
    277                             const SectionIndexMapTy &SectionIndexMap,
    278                             RevGroupMapTy RevGroupMap,
    279                             unsigned NumRegularSections);
    280 
    281     void ComputeIndexMap(MCAssembler &Asm,
    282                          SectionIndexMapTy &SectionIndexMap,
    283                          const RelMapTy &RelMap);
    284 
    285     void CreateRelocationSections(MCAssembler &Asm, MCAsmLayout &Layout,
    286                                   RelMapTy &RelMap);
    287 
    288     void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout,
    289                           const RelMapTy &RelMap);
    290 
    291     void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout,
    292                                 SectionIndexMapTy &SectionIndexMap,
    293                                 const RelMapTy &RelMap);
    294 
    295     // Create the sections that show up in the symbol table. Currently
    296     // those are the .note.GNU-stack section and the group sections.
    297     void CreateIndexedSections(MCAssembler &Asm, MCAsmLayout &Layout,
    298                                GroupMapTy &GroupMap,
    299                                RevGroupMapTy &RevGroupMap,
    300                                SectionIndexMapTy &SectionIndexMap,
    301                                const RelMapTy &RelMap);
    302 
    303     virtual void ExecutePostLayoutBinding(MCAssembler &Asm,
    304                                           const MCAsmLayout &Layout);
    305 
    306     void WriteSectionHeader(MCAssembler &Asm, const GroupMapTy &GroupMap,
    307                             const MCAsmLayout &Layout,
    308                             const SectionIndexMapTy &SectionIndexMap,
    309                             const SectionOffsetMapTy &SectionOffsetMap);
    310 
    311     void ComputeSectionOrder(MCAssembler &Asm,
    312                              std::vector<const MCSectionELF*> &Sections);
    313 
    314     void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
    315                           uint64_t Address, uint64_t Offset,
    316                           uint64_t Size, uint32_t Link, uint32_t Info,
    317                           uint64_t Alignment, uint64_t EntrySize);
    318 
    319     void WriteRelocationsFragment(const MCAssembler &Asm,
    320                                   MCDataFragment *F,
    321                                   const MCSectionData *SD);
    322 
    323     virtual bool
    324     IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
    325                                            const MCSymbolData &DataA,
    326                                            const MCFragment &FB,
    327                                            bool InSet,
    328                                            bool IsPCRel) const;
    329 
    330     virtual void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout);
    331     void WriteSection(MCAssembler &Asm,
    332                       const SectionIndexMapTy &SectionIndexMap,
    333                       uint32_t GroupSymbolIndex,
    334                       uint64_t Offset, uint64_t Size, uint64_t Alignment,
    335                       const MCSectionELF &Section);
    336   };
    337 }
    338 
    339 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
    340   const MCFixupKindInfo &FKI =
    341     Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
    342 
    343   return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
    344 }
    345 
    346 bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) {
    347   switch (Variant) {
    348   default:
    349     return false;
    350   case MCSymbolRefExpr::VK_GOT:
    351   case MCSymbolRefExpr::VK_PLT:
    352   case MCSymbolRefExpr::VK_GOTPCREL:
    353   case MCSymbolRefExpr::VK_GOTOFF:
    354   case MCSymbolRefExpr::VK_TPOFF:
    355   case MCSymbolRefExpr::VK_TLSGD:
    356   case MCSymbolRefExpr::VK_GOTTPOFF:
    357   case MCSymbolRefExpr::VK_INDNTPOFF:
    358   case MCSymbolRefExpr::VK_NTPOFF:
    359   case MCSymbolRefExpr::VK_GOTNTPOFF:
    360   case MCSymbolRefExpr::VK_TLSLDM:
    361   case MCSymbolRefExpr::VK_DTPOFF:
    362   case MCSymbolRefExpr::VK_TLSLD:
    363     return true;
    364   }
    365 }
    366 
    367 ELFObjectWriter::~ELFObjectWriter()
    368 {}
    369 
    370 // Emit the ELF header.
    371 void ELFObjectWriter::WriteHeader(uint64_t SectionDataSize,
    372                                   unsigned NumberOfSections) {
    373   // ELF Header
    374   // ----------
    375   //
    376   // Note
    377   // ----
    378   // emitWord method behaves differently for ELF32 and ELF64, writing
    379   // 4 bytes in the former and 8 in the latter.
    380 
    381   Write8(0x7f); // e_ident[EI_MAG0]
    382   Write8('E');  // e_ident[EI_MAG1]
    383   Write8('L');  // e_ident[EI_MAG2]
    384   Write8('F');  // e_ident[EI_MAG3]
    385 
    386   Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
    387 
    388   // e_ident[EI_DATA]
    389   Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
    390 
    391   Write8(ELF::EV_CURRENT);        // e_ident[EI_VERSION]
    392   // e_ident[EI_OSABI]
    393   Write8(TargetObjectWriter->getOSABI());
    394   Write8(0);                  // e_ident[EI_ABIVERSION]
    395 
    396   WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
    397 
    398   Write16(ELF::ET_REL);             // e_type
    399 
    400   Write16(TargetObjectWriter->getEMachine()); // e_machine = target
    401 
    402   Write32(ELF::EV_CURRENT);         // e_version
    403   WriteWord(0);                    // e_entry, no entry point in .o file
    404   WriteWord(0);                    // e_phoff, no program header for .o
    405   WriteWord(SectionDataSize + (is64Bit() ? sizeof(ELF::Elf64_Ehdr) :
    406             sizeof(ELF::Elf32_Ehdr)));  // e_shoff = sec hdr table off in bytes
    407 
    408   // e_flags = whatever the target wants
    409   Write32(getEFlags());
    410 
    411   // e_ehsize = ELF header size
    412   Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
    413 
    414   Write16(0);                  // e_phentsize = prog header entry size
    415   Write16(0);                  // e_phnum = # prog header entries = 0
    416 
    417   // e_shentsize = Section header entry size
    418   Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
    419 
    420   // e_shnum     = # of section header ents
    421   if (NumberOfSections >= ELF::SHN_LORESERVE)
    422     Write16(ELF::SHN_UNDEF);
    423   else
    424     Write16(NumberOfSections);
    425 
    426   // e_shstrndx  = Section # of '.shstrtab'
    427   if (ShstrtabIndex >= ELF::SHN_LORESERVE)
    428     Write16(ELF::SHN_XINDEX);
    429   else
    430     Write16(ShstrtabIndex);
    431 }
    432 
    433 void ELFObjectWriter::WriteSymbolEntry(MCDataFragment *SymtabF,
    434                                        MCDataFragment *ShndxF,
    435                                        uint64_t name,
    436                                        uint8_t info, uint64_t value,
    437                                        uint64_t size, uint8_t other,
    438                                        uint32_t shndx,
    439                                        bool Reserved) {
    440   if (ShndxF) {
    441     if (shndx >= ELF::SHN_LORESERVE && !Reserved)
    442       String32(*ShndxF, shndx);
    443     else
    444       String32(*ShndxF, 0);
    445   }
    446 
    447   uint16_t Index = (shndx >= ELF::SHN_LORESERVE && !Reserved) ?
    448     uint16_t(ELF::SHN_XINDEX) : shndx;
    449 
    450   if (is64Bit()) {
    451     String32(*SymtabF, name);  // st_name
    452     String8(*SymtabF, info);   // st_info
    453     String8(*SymtabF, other);  // st_other
    454     String16(*SymtabF, Index); // st_shndx
    455     String64(*SymtabF, value); // st_value
    456     String64(*SymtabF, size);  // st_size
    457   } else {
    458     String32(*SymtabF, name);  // st_name
    459     String32(*SymtabF, value); // st_value
    460     String32(*SymtabF, size);  // st_size
    461     String8(*SymtabF, info);   // st_info
    462     String8(*SymtabF, other);  // st_other
    463     String16(*SymtabF, Index); // st_shndx
    464   }
    465 }
    466 
    467 uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &Data,
    468                                       const MCAsmLayout &Layout) {
    469   if (Data.isCommon() && Data.isExternal())
    470     return Data.getCommonAlignment();
    471 
    472   const MCSymbol &Symbol = Data.getSymbol();
    473 
    474   if (Symbol.isAbsolute() && Symbol.isVariable()) {
    475     if (const MCExpr *Value = Symbol.getVariableValue()) {
    476       int64_t IntValue;
    477       if (Value->EvaluateAsAbsolute(IntValue, Layout))
    478         return (uint64_t)IntValue;
    479     }
    480   }
    481 
    482   if (!Symbol.isInSection())
    483     return 0;
    484 
    485 
    486   if (Data.getFragment()) {
    487     if (Data.getFlags() & ELF_Other_ThumbFunc)
    488       return Layout.getSymbolOffset(&Data)+1;
    489     else
    490       return Layout.getSymbolOffset(&Data);
    491   }
    492 
    493   return 0;
    494 }
    495 
    496 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
    497                                                const MCAsmLayout &Layout) {
    498   // The presence of symbol versions causes undefined symbols and
    499   // versions declared with @@@ to be renamed.
    500 
    501   for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
    502          ie = Asm.symbol_end(); it != ie; ++it) {
    503     const MCSymbol &Alias = it->getSymbol();
    504     const MCSymbol &Symbol = Alias.AliasedSymbol();
    505     MCSymbolData &SD = Asm.getSymbolData(Symbol);
    506 
    507     // Not an alias.
    508     if (&Symbol == &Alias)
    509       continue;
    510 
    511     StringRef AliasName = Alias.getName();
    512     size_t Pos = AliasName.find('@');
    513     if (Pos == StringRef::npos)
    514       continue;
    515 
    516     // Aliases defined with .symvar copy the binding from the symbol they alias.
    517     // This is the first place we are able to copy this information.
    518     it->setExternal(SD.isExternal());
    519     MCELF::SetBinding(*it, MCELF::GetBinding(SD));
    520 
    521     StringRef Rest = AliasName.substr(Pos);
    522     if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
    523       continue;
    524 
    525     // FIXME: produce a better error message.
    526     if (Symbol.isUndefined() && Rest.startswith("@@") &&
    527         !Rest.startswith("@@@"))
    528       report_fatal_error("A @@ version cannot be undefined");
    529 
    530     Renames.insert(std::make_pair(&Symbol, &Alias));
    531   }
    532 }
    533 
    534 void ELFObjectWriter::WriteSymbol(MCDataFragment *SymtabF,
    535                                   MCDataFragment *ShndxF,
    536                                   ELFSymbolData &MSD,
    537                                   const MCAsmLayout &Layout) {
    538   MCSymbolData &OrigData = *MSD.SymbolData;
    539   MCSymbolData &Data =
    540     Layout.getAssembler().getSymbolData(OrigData.getSymbol().AliasedSymbol());
    541 
    542   bool IsReserved = Data.isCommon() || Data.getSymbol().isAbsolute() ||
    543     Data.getSymbol().isVariable();
    544 
    545   uint8_t Binding = MCELF::GetBinding(OrigData);
    546   uint8_t Visibility = MCELF::GetVisibility(OrigData);
    547   uint8_t Type = MCELF::GetType(Data);
    548 
    549   uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
    550   uint8_t Other = Visibility;
    551 
    552   uint64_t Value = SymbolValue(Data, Layout);
    553   uint64_t Size = 0;
    554 
    555   assert(!(Data.isCommon() && !Data.isExternal()));
    556 
    557   const MCExpr *ESize = Data.getSize();
    558   if (ESize) {
    559     int64_t Res;
    560     if (!ESize->EvaluateAsAbsolute(Res, Layout))
    561       report_fatal_error("Size expression must be absolute.");
    562     Size = Res;
    563   }
    564 
    565   // Write out the symbol table entry
    566   WriteSymbolEntry(SymtabF, ShndxF, MSD.StringIndex, Info, Value,
    567                    Size, Other, MSD.SectionIndex, IsReserved);
    568 }
    569 
    570 void ELFObjectWriter::WriteSymbolTable(MCDataFragment *SymtabF,
    571                                        MCDataFragment *ShndxF,
    572                                        const MCAssembler &Asm,
    573                                        const MCAsmLayout &Layout,
    574                                     const SectionIndexMapTy &SectionIndexMap) {
    575   // The string table must be emitted first because we need the index
    576   // into the string table for all the symbol names.
    577   assert(StringTable.size() && "Missing string table");
    578 
    579   // FIXME: Make sure the start of the symbol table is aligned.
    580 
    581   // The first entry is the undefined symbol entry.
    582   WriteSymbolEntry(SymtabF, ShndxF, 0, 0, 0, 0, 0, 0, false);
    583 
    584   // Write the symbol table entries.
    585   LastLocalSymbolIndex = LocalSymbolData.size() + 1;
    586   for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
    587     ELFSymbolData &MSD = LocalSymbolData[i];
    588     WriteSymbol(SymtabF, ShndxF, MSD, Layout);
    589   }
    590 
    591   // Write out a symbol table entry for each regular section.
    592   for (MCAssembler::const_iterator i = Asm.begin(), e = Asm.end(); i != e;
    593        ++i) {
    594     const MCSectionELF &Section =
    595       static_cast<const MCSectionELF&>(i->getSection());
    596     if (Section.getType() == ELF::SHT_RELA ||
    597         Section.getType() == ELF::SHT_REL ||
    598         Section.getType() == ELF::SHT_STRTAB ||
    599         Section.getType() == ELF::SHT_SYMTAB ||
    600         Section.getType() == ELF::SHT_SYMTAB_SHNDX)
    601       continue;
    602     WriteSymbolEntry(SymtabF, ShndxF, 0, ELF::STT_SECTION, 0, 0,
    603                      ELF::STV_DEFAULT, SectionIndexMap.lookup(&Section),
    604                      false);
    605     LastLocalSymbolIndex++;
    606   }
    607 
    608   for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
    609     ELFSymbolData &MSD = ExternalSymbolData[i];
    610     MCSymbolData &Data = *MSD.SymbolData;
    611     assert(((Data.getFlags() & ELF_STB_Global) ||
    612             (Data.getFlags() & ELF_STB_Weak)) &&
    613            "External symbol requires STB_GLOBAL or STB_WEAK flag");
    614     WriteSymbol(SymtabF, ShndxF, MSD, Layout);
    615     if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
    616       LastLocalSymbolIndex++;
    617   }
    618 
    619   for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
    620     ELFSymbolData &MSD = UndefinedSymbolData[i];
    621     MCSymbolData &Data = *MSD.SymbolData;
    622     WriteSymbol(SymtabF, ShndxF, MSD, Layout);
    623     if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
    624       LastLocalSymbolIndex++;
    625   }
    626 }
    627 
    628 const MCSymbol *ELFObjectWriter::SymbolToReloc(const MCAssembler &Asm,
    629                                                const MCValue &Target,
    630                                                const MCFragment &F,
    631                                                const MCFixup &Fixup,
    632                                                bool IsPCRel) const {
    633   const MCSymbol &Symbol = Target.getSymA()->getSymbol();
    634   const MCSymbol &ASymbol = Symbol.AliasedSymbol();
    635   const MCSymbol *Renamed = Renames.lookup(&Symbol);
    636   const MCSymbolData &SD = Asm.getSymbolData(Symbol);
    637 
    638   if (ASymbol.isUndefined()) {
    639     if (Renamed)
    640       return Renamed;
    641     return &ASymbol;
    642   }
    643 
    644   if (SD.isExternal()) {
    645     if (Renamed)
    646       return Renamed;
    647     return &Symbol;
    648   }
    649 
    650   const MCSectionELF &Section =
    651     static_cast<const MCSectionELF&>(ASymbol.getSection());
    652   const SectionKind secKind = Section.getKind();
    653 
    654   if (secKind.isBSS())
    655     return ExplicitRelSym(Asm, Target, F, Fixup, IsPCRel);
    656 
    657   if (secKind.isThreadLocal()) {
    658     if (Renamed)
    659       return Renamed;
    660     return &Symbol;
    661   }
    662 
    663   MCSymbolRefExpr::VariantKind Kind = Target.getSymA()->getKind();
    664   const MCSectionELF &Sec2 =
    665     static_cast<const MCSectionELF&>(F.getParent()->getSection());
    666 
    667   if (&Sec2 != &Section &&
    668       (Kind == MCSymbolRefExpr::VK_PLT ||
    669        Kind == MCSymbolRefExpr::VK_GOTPCREL ||
    670        Kind == MCSymbolRefExpr::VK_GOTOFF)) {
    671     if (Renamed)
    672       return Renamed;
    673     return &Symbol;
    674   }
    675 
    676   if (Section.getFlags() & ELF::SHF_MERGE) {
    677     if (Target.getConstant() == 0)
    678       return ExplicitRelSym(Asm, Target, F, Fixup, IsPCRel);
    679     if (Renamed)
    680       return Renamed;
    681     return &Symbol;
    682   }
    683 
    684   return ExplicitRelSym(Asm, Target, F, Fixup, IsPCRel);
    685 
    686 }
    687 
    688 
    689 void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm,
    690                                        const MCAsmLayout &Layout,
    691                                        const MCFragment *Fragment,
    692                                        const MCFixup &Fixup,
    693                                        MCValue Target,
    694                                        uint64_t &FixedValue) {
    695   int64_t Addend = 0;
    696   int Index = 0;
    697   int64_t Value = Target.getConstant();
    698   const MCSymbol *RelocSymbol = NULL;
    699 
    700   bool IsPCRel = isFixupKindPCRel(Asm, Fixup.getKind());
    701   if (!Target.isAbsolute()) {
    702     const MCSymbol &Symbol = Target.getSymA()->getSymbol();
    703     const MCSymbol &ASymbol = Symbol.AliasedSymbol();
    704     RelocSymbol = SymbolToReloc(Asm, Target, *Fragment, Fixup, IsPCRel);
    705 
    706     if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
    707       const MCSymbol &SymbolB = RefB->getSymbol();
    708       MCSymbolData &SDB = Asm.getSymbolData(SymbolB);
    709       IsPCRel = true;
    710 
    711       // Offset of the symbol in the section
    712       int64_t a = Layout.getSymbolOffset(&SDB);
    713 
    714       // Offset of the relocation in the section
    715       int64_t b = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
    716       Value += b - a;
    717     }
    718 
    719     if (!RelocSymbol) {
    720       MCSymbolData &SD = Asm.getSymbolData(ASymbol);
    721       MCFragment *F = SD.getFragment();
    722 
    723       Index = F->getParent()->getOrdinal() + 1;
    724 
    725       // Offset of the symbol in the section
    726       Value += Layout.getSymbolOffset(&SD);
    727     } else {
    728       if (Asm.getSymbolData(Symbol).getFlags() & ELF_Other_Weakref)
    729         WeakrefUsedInReloc.insert(RelocSymbol);
    730       else
    731         UsedInReloc.insert(RelocSymbol);
    732       Index = -1;
    733     }
    734     Addend = Value;
    735     // Compensate for the addend on i386.
    736     if (is64Bit())
    737       Value = 0;
    738   }
    739 
    740   FixedValue = Value;
    741   unsigned Type = GetRelocType(Target, Fixup, IsPCRel,
    742                                (RelocSymbol != 0), Addend);
    743   MCSymbolRefExpr::VariantKind Modifier = Target.isAbsolute() ?
    744     MCSymbolRefExpr::VK_None : Target.getSymA()->getKind();
    745   if (RelocNeedsGOT(Modifier))
    746     NeedsGOT = true;
    747 
    748   uint64_t RelocOffset = Layout.getFragmentOffset(Fragment) +
    749     Fixup.getOffset();
    750 
    751   // FIXME: no tests cover this. Is adjustFixupOffset dead code?
    752   TargetObjectWriter->adjustFixupOffset(Fixup, RelocOffset);
    753 
    754   if (!hasRelocationAddend())
    755     Addend = 0;
    756 
    757   if (is64Bit())
    758     assert(isInt<64>(Addend));
    759   else
    760     assert(isInt<32>(Addend));
    761 
    762   ELFRelocationEntry ERE(RelocOffset, Index, Type, RelocSymbol, Addend, Fixup);
    763   Relocations[Fragment->getParent()].push_back(ERE);
    764 }
    765 
    766 
    767 uint64_t
    768 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
    769                                              const MCSymbol *S) {
    770   MCSymbolData &SD = Asm.getSymbolData(*S);
    771   return SD.getIndex();
    772 }
    773 
    774 bool ELFObjectWriter::isInSymtab(const MCAssembler &Asm,
    775                                  const MCSymbolData &Data,
    776                                  bool Used, bool Renamed) {
    777   if (Data.getFlags() & ELF_Other_Weakref)
    778     return false;
    779 
    780   if (Used)
    781     return true;
    782 
    783   if (Renamed)
    784     return false;
    785 
    786   const MCSymbol &Symbol = Data.getSymbol();
    787 
    788   if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
    789     return true;
    790 
    791   const MCSymbol &A = Symbol.AliasedSymbol();
    792   if (Symbol.isVariable() && !A.isVariable() && A.isUndefined())
    793     return false;
    794 
    795   bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
    796   if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
    797     return false;
    798 
    799   if (!Asm.isSymbolLinkerVisible(Symbol) && !Symbol.isUndefined())
    800     return false;
    801 
    802   if (Symbol.isTemporary())
    803     return false;
    804 
    805   return true;
    806 }
    807 
    808 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isSignature,
    809                               bool isUsedInReloc) {
    810   if (Data.isExternal())
    811     return false;
    812 
    813   const MCSymbol &Symbol = Data.getSymbol();
    814   const MCSymbol &RefSymbol = Symbol.AliasedSymbol();
    815 
    816   if (RefSymbol.isUndefined() && !RefSymbol.isVariable()) {
    817     if (isSignature && !isUsedInReloc)
    818       return true;
    819 
    820     return false;
    821   }
    822 
    823   return true;
    824 }
    825 
    826 void ELFObjectWriter::ComputeIndexMap(MCAssembler &Asm,
    827                                       SectionIndexMapTy &SectionIndexMap,
    828                                       const RelMapTy &RelMap) {
    829   unsigned Index = 1;
    830   for (MCAssembler::iterator it = Asm.begin(),
    831          ie = Asm.end(); it != ie; ++it) {
    832     const MCSectionELF &Section =
    833       static_cast<const MCSectionELF &>(it->getSection());
    834     if (Section.getType() != ELF::SHT_GROUP)
    835       continue;
    836     SectionIndexMap[&Section] = Index++;
    837   }
    838 
    839   for (MCAssembler::iterator it = Asm.begin(),
    840          ie = Asm.end(); it != ie; ++it) {
    841     const MCSectionELF &Section =
    842       static_cast<const MCSectionELF &>(it->getSection());
    843     if (Section.getType() == ELF::SHT_GROUP ||
    844         Section.getType() == ELF::SHT_REL ||
    845         Section.getType() == ELF::SHT_RELA)
    846       continue;
    847     SectionIndexMap[&Section] = Index++;
    848     const MCSectionELF *RelSection = RelMap.lookup(&Section);
    849     if (RelSection)
    850       SectionIndexMap[RelSection] = Index++;
    851   }
    852 }
    853 
    854 void ELFObjectWriter::ComputeSymbolTable(MCAssembler &Asm,
    855                                       const SectionIndexMapTy &SectionIndexMap,
    856                                          RevGroupMapTy RevGroupMap,
    857                                          unsigned NumRegularSections) {
    858   // FIXME: Is this the correct place to do this?
    859   // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?
    860   if (NeedsGOT) {
    861     llvm::StringRef Name = "_GLOBAL_OFFSET_TABLE_";
    862     MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
    863     MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
    864     Data.setExternal(true);
    865     MCELF::SetBinding(Data, ELF::STB_GLOBAL);
    866   }
    867 
    868   // Index 0 is always the empty string.
    869   StringMap<uint64_t> StringIndexMap;
    870   StringTable += '\x00';
    871 
    872   // FIXME: We could optimize suffixes in strtab in the same way we
    873   // optimize them in shstrtab.
    874 
    875   // Add the data for the symbols.
    876   for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
    877          ie = Asm.symbol_end(); it != ie; ++it) {
    878     const MCSymbol &Symbol = it->getSymbol();
    879 
    880     bool Used = UsedInReloc.count(&Symbol);
    881     bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
    882     bool isSignature = RevGroupMap.count(&Symbol);
    883 
    884     if (!isInSymtab(Asm, *it,
    885                     Used || WeakrefUsed || isSignature,
    886                     Renames.count(&Symbol)))
    887       continue;
    888 
    889     ELFSymbolData MSD;
    890     MSD.SymbolData = it;
    891     const MCSymbol &RefSymbol = Symbol.AliasedSymbol();
    892 
    893     // Undefined symbols are global, but this is the first place we
    894     // are able to set it.
    895     bool Local = isLocal(*it, isSignature, Used);
    896     if (!Local && MCELF::GetBinding(*it) == ELF::STB_LOCAL) {
    897       MCSymbolData &SD = Asm.getSymbolData(RefSymbol);
    898       MCELF::SetBinding(*it, ELF::STB_GLOBAL);
    899       MCELF::SetBinding(SD, ELF::STB_GLOBAL);
    900     }
    901 
    902     if (RefSymbol.isUndefined() && !Used && WeakrefUsed)
    903       MCELF::SetBinding(*it, ELF::STB_WEAK);
    904 
    905     if (it->isCommon()) {
    906       assert(!Local);
    907       MSD.SectionIndex = ELF::SHN_COMMON;
    908     } else if (Symbol.isAbsolute() || RefSymbol.isVariable()) {
    909       MSD.SectionIndex = ELF::SHN_ABS;
    910     } else if (RefSymbol.isUndefined()) {
    911       if (isSignature && !Used)
    912         MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap[&Symbol]);
    913       else
    914         MSD.SectionIndex = ELF::SHN_UNDEF;
    915     } else {
    916       const MCSectionELF &Section =
    917         static_cast<const MCSectionELF&>(RefSymbol.getSection());
    918       MSD.SectionIndex = SectionIndexMap.lookup(&Section);
    919       if (MSD.SectionIndex >= ELF::SHN_LORESERVE)
    920         NeedsSymtabShndx = true;
    921       assert(MSD.SectionIndex && "Invalid section index!");
    922     }
    923 
    924     // The @@@ in symbol version is replaced with @ in undefined symbols and
    925     // @@ in defined ones.
    926     StringRef Name = Symbol.getName();
    927     SmallString<32> Buf;
    928 
    929     size_t Pos = Name.find("@@@");
    930     if (Pos != StringRef::npos) {
    931       Buf += Name.substr(0, Pos);
    932       unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
    933       Buf += Name.substr(Pos + Skip);
    934       Name = Buf;
    935     }
    936 
    937     uint64_t &Entry = StringIndexMap[Name];
    938     if (!Entry) {
    939       Entry = StringTable.size();
    940       StringTable += Name;
    941       StringTable += '\x00';
    942     }
    943     MSD.StringIndex = Entry;
    944     if (MSD.SectionIndex == ELF::SHN_UNDEF)
    945       UndefinedSymbolData.push_back(MSD);
    946     else if (Local)
    947       LocalSymbolData.push_back(MSD);
    948     else
    949       ExternalSymbolData.push_back(MSD);
    950   }
    951 
    952   // Symbols are required to be in lexicographic order.
    953   array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
    954   array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
    955   array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
    956 
    957   // Set the symbol indices. Local symbols must come before all other
    958   // symbols with non-local bindings.
    959   unsigned Index = 1;
    960   for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
    961     LocalSymbolData[i].SymbolData->setIndex(Index++);
    962 
    963   Index += NumRegularSections;
    964 
    965   for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
    966     ExternalSymbolData[i].SymbolData->setIndex(Index++);
    967   for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
    968     UndefinedSymbolData[i].SymbolData->setIndex(Index++);
    969 
    970   if (NumRegularSections > ELF::SHN_LORESERVE)
    971     NeedsSymtabShndx = true;
    972 }
    973 
    974 void ELFObjectWriter::CreateRelocationSections(MCAssembler &Asm,
    975                                                MCAsmLayout &Layout,
    976                                                RelMapTy &RelMap) {
    977   for (MCAssembler::const_iterator it = Asm.begin(),
    978          ie = Asm.end(); it != ie; ++it) {
    979     const MCSectionData &SD = *it;
    980     if (Relocations[&SD].empty())
    981       continue;
    982 
    983     MCContext &Ctx = Asm.getContext();
    984     const MCSectionELF &Section =
    985       static_cast<const MCSectionELF&>(SD.getSection());
    986 
    987     const StringRef SectionName = Section.getSectionName();
    988     std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel";
    989     RelaSectionName += SectionName;
    990 
    991     unsigned EntrySize;
    992     if (hasRelocationAddend())
    993       EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
    994     else
    995       EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
    996 
    997     const MCSectionELF *RelaSection =
    998       Ctx.getELFSection(RelaSectionName, hasRelocationAddend() ?
    999                         ELF::SHT_RELA : ELF::SHT_REL, 0,
   1000                         SectionKind::getReadOnly(),
   1001                         EntrySize, "");
   1002     RelMap[&Section] = RelaSection;
   1003     Asm.getOrCreateSectionData(*RelaSection);
   1004   }
   1005 }
   1006 
   1007 void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout,
   1008                                        const RelMapTy &RelMap) {
   1009   for (MCAssembler::const_iterator it = Asm.begin(),
   1010          ie = Asm.end(); it != ie; ++it) {
   1011     const MCSectionData &SD = *it;
   1012     const MCSectionELF &Section =
   1013       static_cast<const MCSectionELF&>(SD.getSection());
   1014 
   1015     const MCSectionELF *RelaSection = RelMap.lookup(&Section);
   1016     if (!RelaSection)
   1017       continue;
   1018     MCSectionData &RelaSD = Asm.getOrCreateSectionData(*RelaSection);
   1019     RelaSD.setAlignment(is64Bit() ? 8 : 4);
   1020 
   1021     MCDataFragment *F = new MCDataFragment(&RelaSD);
   1022     WriteRelocationsFragment(Asm, F, &*it);
   1023   }
   1024 }
   1025 
   1026 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
   1027                                        uint64_t Flags, uint64_t Address,
   1028                                        uint64_t Offset, uint64_t Size,
   1029                                        uint32_t Link, uint32_t Info,
   1030                                        uint64_t Alignment,
   1031                                        uint64_t EntrySize) {
   1032   Write32(Name);        // sh_name: index into string table
   1033   Write32(Type);        // sh_type
   1034   WriteWord(Flags);     // sh_flags
   1035   WriteWord(Address);   // sh_addr
   1036   WriteWord(Offset);    // sh_offset
   1037   WriteWord(Size);      // sh_size
   1038   Write32(Link);        // sh_link
   1039   Write32(Info);        // sh_info
   1040   WriteWord(Alignment); // sh_addralign
   1041   WriteWord(EntrySize); // sh_entsize
   1042 }
   1043 
   1044 void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm,
   1045                                                MCDataFragment *F,
   1046                                                const MCSectionData *SD) {
   1047   std::vector<ELFRelocationEntry> &Relocs = Relocations[SD];
   1048 
   1049   // Sort the relocation entries. Most targets just sort by r_offset, but some
   1050   // (e.g., MIPS) have additional constraints.
   1051   TargetObjectWriter->sortRelocs(Asm, Relocs);
   1052 
   1053   for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
   1054     ELFRelocationEntry entry = Relocs[e - i - 1];
   1055 
   1056     if (!entry.Index)
   1057       ;
   1058     else if (entry.Index < 0)
   1059       entry.Index = getSymbolIndexInSymbolTable(Asm, entry.Symbol);
   1060     else
   1061       entry.Index += LocalSymbolData.size();
   1062     if (is64Bit()) {
   1063       String64(*F, entry.r_offset);
   1064 
   1065       struct ELF::Elf64_Rela ERE64;
   1066       ERE64.setSymbolAndType(entry.Index, entry.Type);
   1067       String64(*F, ERE64.r_info);
   1068 
   1069       if (hasRelocationAddend())
   1070         String64(*F, entry.r_addend);
   1071     } else {
   1072       String32(*F, entry.r_offset);
   1073 
   1074       struct ELF::Elf32_Rela ERE32;
   1075       ERE32.setSymbolAndType(entry.Index, entry.Type);
   1076       String32(*F, ERE32.r_info);
   1077 
   1078       if (hasRelocationAddend())
   1079         String32(*F, entry.r_addend);
   1080     }
   1081   }
   1082 }
   1083 
   1084 static int compareBySuffix(const void *a, const void *b) {
   1085   const MCSectionELF *secA = *static_cast<const MCSectionELF* const *>(a);
   1086   const MCSectionELF *secB = *static_cast<const MCSectionELF* const *>(b);
   1087   const StringRef &NameA = secA->getSectionName();
   1088   const StringRef &NameB = secB->getSectionName();
   1089   const unsigned sizeA = NameA.size();
   1090   const unsigned sizeB = NameB.size();
   1091   const unsigned len = std::min(sizeA, sizeB);
   1092   for (unsigned int i = 0; i < len; ++i) {
   1093     char ca = NameA[sizeA - i - 1];
   1094     char cb = NameB[sizeB - i - 1];
   1095     if (ca != cb)
   1096       return cb - ca;
   1097   }
   1098 
   1099   return sizeB - sizeA;
   1100 }
   1101 
   1102 void ELFObjectWriter::CreateMetadataSections(MCAssembler &Asm,
   1103                                              MCAsmLayout &Layout,
   1104                                              SectionIndexMapTy &SectionIndexMap,
   1105                                              const RelMapTy &RelMap) {
   1106   MCContext &Ctx = Asm.getContext();
   1107   MCDataFragment *F;
   1108 
   1109   unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
   1110 
   1111   // We construct .shstrtab, .symtab and .strtab in this order to match gnu as.
   1112   const MCSectionELF *ShstrtabSection =
   1113     Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0,
   1114                       SectionKind::getReadOnly());
   1115   MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection);
   1116   ShstrtabSD.setAlignment(1);
   1117 
   1118   const MCSectionELF *SymtabSection =
   1119     Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
   1120                       SectionKind::getReadOnly(),
   1121                       EntrySize, "");
   1122   MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
   1123   SymtabSD.setAlignment(is64Bit() ? 8 : 4);
   1124 
   1125   MCSectionData *SymtabShndxSD = NULL;
   1126 
   1127   if (NeedsSymtabShndx) {
   1128     const MCSectionELF *SymtabShndxSection =
   1129       Ctx.getELFSection(".symtab_shndx", ELF::SHT_SYMTAB_SHNDX, 0,
   1130                         SectionKind::getReadOnly(), 4, "");
   1131     SymtabShndxSD = &Asm.getOrCreateSectionData(*SymtabShndxSection);
   1132     SymtabShndxSD->setAlignment(4);
   1133   }
   1134 
   1135   const MCSectionELF *StrtabSection;
   1136   StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0,
   1137                                     SectionKind::getReadOnly());
   1138   MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection);
   1139   StrtabSD.setAlignment(1);
   1140 
   1141   ComputeIndexMap(Asm, SectionIndexMap, RelMap);
   1142 
   1143   ShstrtabIndex = SectionIndexMap.lookup(ShstrtabSection);
   1144   SymbolTableIndex = SectionIndexMap.lookup(SymtabSection);
   1145   StringTableIndex = SectionIndexMap.lookup(StrtabSection);
   1146 
   1147   // Symbol table
   1148   F = new MCDataFragment(&SymtabSD);
   1149   MCDataFragment *ShndxF = NULL;
   1150   if (NeedsSymtabShndx) {
   1151     ShndxF = new MCDataFragment(SymtabShndxSD);
   1152   }
   1153   WriteSymbolTable(F, ShndxF, Asm, Layout, SectionIndexMap);
   1154 
   1155   F = new MCDataFragment(&StrtabSD);
   1156   F->getContents().append(StringTable.begin(), StringTable.end());
   1157 
   1158   F = new MCDataFragment(&ShstrtabSD);
   1159 
   1160   std::vector<const MCSectionELF*> Sections;
   1161   for (MCAssembler::const_iterator it = Asm.begin(),
   1162          ie = Asm.end(); it != ie; ++it) {
   1163     const MCSectionELF &Section =
   1164       static_cast<const MCSectionELF&>(it->getSection());
   1165     Sections.push_back(&Section);
   1166   }
   1167   array_pod_sort(Sections.begin(), Sections.end(), compareBySuffix);
   1168 
   1169   // Section header string table.
   1170   //
   1171   // The first entry of a string table holds a null character so skip
   1172   // section 0.
   1173   uint64_t Index = 1;
   1174   F->getContents() += '\x00';
   1175 
   1176   for (unsigned int I = 0, E = Sections.size(); I != E; ++I) {
   1177     const MCSectionELF &Section = *Sections[I];
   1178 
   1179     StringRef Name = Section.getSectionName();
   1180     if (I != 0) {
   1181       StringRef PreviousName = Sections[I - 1]->getSectionName();
   1182       if (PreviousName.endswith(Name)) {
   1183         SectionStringTableIndex[&Section] = Index - Name.size() - 1;
   1184         continue;
   1185       }
   1186     }
   1187     // Remember the index into the string table so we can write it
   1188     // into the sh_name field of the section header table.
   1189     SectionStringTableIndex[&Section] = Index;
   1190 
   1191     Index += Name.size() + 1;
   1192     F->getContents() += Name;
   1193     F->getContents() += '\x00';
   1194   }
   1195 }
   1196 
   1197 void ELFObjectWriter::CreateIndexedSections(MCAssembler &Asm,
   1198                                             MCAsmLayout &Layout,
   1199                                             GroupMapTy &GroupMap,
   1200                                             RevGroupMapTy &RevGroupMap,
   1201                                             SectionIndexMapTy &SectionIndexMap,
   1202                                             const RelMapTy &RelMap) {
   1203   // Create the .note.GNU-stack section if needed.
   1204   MCContext &Ctx = Asm.getContext();
   1205   if (Asm.getNoExecStack()) {
   1206     const MCSectionELF *GnuStackSection =
   1207       Ctx.getELFSection(".note.GNU-stack", ELF::SHT_PROGBITS, 0,
   1208                         SectionKind::getReadOnly());
   1209     Asm.getOrCreateSectionData(*GnuStackSection);
   1210   }
   1211 
   1212   // Build the groups
   1213   for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
   1214        it != ie; ++it) {
   1215     const MCSectionELF &Section =
   1216       static_cast<const MCSectionELF&>(it->getSection());
   1217     if (!(Section.getFlags() & ELF::SHF_GROUP))
   1218       continue;
   1219 
   1220     const MCSymbol *SignatureSymbol = Section.getGroup();
   1221     Asm.getOrCreateSymbolData(*SignatureSymbol);
   1222     const MCSectionELF *&Group = RevGroupMap[SignatureSymbol];
   1223     if (!Group) {
   1224       Group = Ctx.CreateELFGroupSection();
   1225       MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
   1226       Data.setAlignment(4);
   1227       MCDataFragment *F = new MCDataFragment(&Data);
   1228       String32(*F, ELF::GRP_COMDAT);
   1229     }
   1230     GroupMap[Group] = SignatureSymbol;
   1231   }
   1232 
   1233   ComputeIndexMap(Asm, SectionIndexMap, RelMap);
   1234 
   1235   // Add sections to the groups
   1236   for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end();
   1237        it != ie; ++it) {
   1238     const MCSectionELF &Section =
   1239       static_cast<const MCSectionELF&>(it->getSection());
   1240     if (!(Section.getFlags() & ELF::SHF_GROUP))
   1241       continue;
   1242     const MCSectionELF *Group = RevGroupMap[Section.getGroup()];
   1243     MCSectionData &Data = Asm.getOrCreateSectionData(*Group);
   1244     // FIXME: we could use the previous fragment
   1245     MCDataFragment *F = new MCDataFragment(&Data);
   1246     unsigned Index = SectionIndexMap.lookup(&Section);
   1247     String32(*F, Index);
   1248   }
   1249 }
   1250 
   1251 void ELFObjectWriter::WriteSection(MCAssembler &Asm,
   1252                                    const SectionIndexMapTy &SectionIndexMap,
   1253                                    uint32_t GroupSymbolIndex,
   1254                                    uint64_t Offset, uint64_t Size,
   1255                                    uint64_t Alignment,
   1256                                    const MCSectionELF &Section) {
   1257   uint64_t sh_link = 0;
   1258   uint64_t sh_info = 0;
   1259 
   1260   switch(Section.getType()) {
   1261   case ELF::SHT_DYNAMIC:
   1262     sh_link = SectionStringTableIndex[&Section];
   1263     sh_info = 0;
   1264     break;
   1265 
   1266   case ELF::SHT_REL:
   1267   case ELF::SHT_RELA: {
   1268     const MCSectionELF *SymtabSection;
   1269     const MCSectionELF *InfoSection;
   1270     SymtabSection = Asm.getContext().getELFSection(".symtab", ELF::SHT_SYMTAB,
   1271                                                    0,
   1272                                                    SectionKind::getReadOnly());
   1273     sh_link = SectionIndexMap.lookup(SymtabSection);
   1274     assert(sh_link && ".symtab not found");
   1275 
   1276     // Remove ".rel" and ".rela" prefixes.
   1277     unsigned SecNameLen = (Section.getType() == ELF::SHT_REL) ? 4 : 5;
   1278     StringRef SectionName = Section.getSectionName().substr(SecNameLen);
   1279 
   1280     InfoSection = Asm.getContext().getELFSection(SectionName,
   1281                                                  ELF::SHT_PROGBITS, 0,
   1282                                                  SectionKind::getReadOnly());
   1283     sh_info = SectionIndexMap.lookup(InfoSection);
   1284     break;
   1285   }
   1286 
   1287   case ELF::SHT_SYMTAB:
   1288   case ELF::SHT_DYNSYM:
   1289     sh_link = StringTableIndex;
   1290     sh_info = LastLocalSymbolIndex;
   1291     break;
   1292 
   1293   case ELF::SHT_SYMTAB_SHNDX:
   1294     sh_link = SymbolTableIndex;
   1295     break;
   1296 
   1297   case ELF::SHT_PROGBITS:
   1298   case ELF::SHT_STRTAB:
   1299   case ELF::SHT_NOBITS:
   1300   case ELF::SHT_NOTE:
   1301   case ELF::SHT_NULL:
   1302   case ELF::SHT_ARM_ATTRIBUTES:
   1303   case ELF::SHT_INIT_ARRAY:
   1304   case ELF::SHT_FINI_ARRAY:
   1305   case ELF::SHT_PREINIT_ARRAY:
   1306   case ELF::SHT_X86_64_UNWIND:
   1307     // Nothing to do.
   1308     break;
   1309 
   1310   case ELF::SHT_GROUP:
   1311     sh_link = SymbolTableIndex;
   1312     sh_info = GroupSymbolIndex;
   1313     break;
   1314 
   1315   default:
   1316     assert(0 && "FIXME: sh_type value not supported!");
   1317     break;
   1318   }
   1319 
   1320   WriteSecHdrEntry(SectionStringTableIndex[&Section], Section.getType(),
   1321                    Section.getFlags(), 0, Offset, Size, sh_link, sh_info,
   1322                    Alignment, Section.getEntrySize());
   1323 }
   1324 
   1325 bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) {
   1326   return SD.getOrdinal() == ~UINT32_C(0) &&
   1327     !SD.getSection().isVirtualSection();
   1328 }
   1329 
   1330 uint64_t ELFObjectWriter::DataSectionSize(const MCSectionData &SD) {
   1331   uint64_t Ret = 0;
   1332   for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
   1333        ++i) {
   1334     const MCFragment &F = *i;
   1335     assert(F.getKind() == MCFragment::FT_Data);
   1336     Ret += cast<MCDataFragment>(F).getContents().size();
   1337   }
   1338   return Ret;
   1339 }
   1340 
   1341 uint64_t ELFObjectWriter::GetSectionFileSize(const MCAsmLayout &Layout,
   1342                                              const MCSectionData &SD) {
   1343   if (IsELFMetaDataSection(SD))
   1344     return DataSectionSize(SD);
   1345   return Layout.getSectionFileSize(&SD);
   1346 }
   1347 
   1348 uint64_t ELFObjectWriter::GetSectionAddressSize(const MCAsmLayout &Layout,
   1349                                                 const MCSectionData &SD) {
   1350   if (IsELFMetaDataSection(SD))
   1351     return DataSectionSize(SD);
   1352   return Layout.getSectionAddressSize(&SD);
   1353 }
   1354 
   1355 void ELFObjectWriter::WriteDataSectionData(MCAssembler &Asm,
   1356                                            const MCAsmLayout &Layout,
   1357                                            const MCSectionELF &Section) {
   1358   const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
   1359 
   1360   uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
   1361   WriteZeros(Padding);
   1362 
   1363   if (IsELFMetaDataSection(SD)) {
   1364     for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e;
   1365          ++i) {
   1366       const MCFragment &F = *i;
   1367       assert(F.getKind() == MCFragment::FT_Data);
   1368       WriteBytes(cast<MCDataFragment>(F).getContents().str());
   1369     }
   1370   } else {
   1371     Asm.writeSectionData(&SD, Layout);
   1372   }
   1373 }
   1374 
   1375 void ELFObjectWriter::WriteSectionHeader(MCAssembler &Asm,
   1376                                          const GroupMapTy &GroupMap,
   1377                                          const MCAsmLayout &Layout,
   1378                                       const SectionIndexMapTy &SectionIndexMap,
   1379                                    const SectionOffsetMapTy &SectionOffsetMap) {
   1380   const unsigned NumSections = Asm.size() + 1;
   1381 
   1382   std::vector<const MCSectionELF*> Sections;
   1383   Sections.resize(NumSections - 1);
   1384 
   1385   for (SectionIndexMapTy::const_iterator i=
   1386          SectionIndexMap.begin(), e = SectionIndexMap.end(); i != e; ++i) {
   1387     const std::pair<const MCSectionELF*, uint32_t> &p = *i;
   1388     Sections[p.second - 1] = p.first;
   1389   }
   1390 
   1391   // Null section first.
   1392   uint64_t FirstSectionSize =
   1393     NumSections >= ELF::SHN_LORESERVE ? NumSections : 0;
   1394   uint32_t FirstSectionLink =
   1395     ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0;
   1396   WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0);
   1397 
   1398   for (unsigned i = 0; i < NumSections - 1; ++i) {
   1399     const MCSectionELF &Section = *Sections[i];
   1400     const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
   1401     uint32_t GroupSymbolIndex;
   1402     if (Section.getType() != ELF::SHT_GROUP)
   1403       GroupSymbolIndex = 0;
   1404     else
   1405       GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm,
   1406                                                      GroupMap.lookup(&Section));
   1407 
   1408     uint64_t Size = GetSectionAddressSize(Layout, SD);
   1409 
   1410     WriteSection(Asm, SectionIndexMap, GroupSymbolIndex,
   1411                  SectionOffsetMap.lookup(&Section), Size,
   1412                  SD.getAlignment(), Section);
   1413   }
   1414 }
   1415 
   1416 void ELFObjectWriter::ComputeSectionOrder(MCAssembler &Asm,
   1417                                   std::vector<const MCSectionELF*> &Sections) {
   1418   for (MCAssembler::iterator it = Asm.begin(),
   1419          ie = Asm.end(); it != ie; ++it) {
   1420     const MCSectionELF &Section =
   1421       static_cast<const MCSectionELF &>(it->getSection());
   1422     if (Section.getType() == ELF::SHT_GROUP)
   1423       Sections.push_back(&Section);
   1424   }
   1425 
   1426   for (MCAssembler::iterator it = Asm.begin(),
   1427          ie = Asm.end(); it != ie; ++it) {
   1428     const MCSectionELF &Section =
   1429       static_cast<const MCSectionELF &>(it->getSection());
   1430     if (Section.getType() != ELF::SHT_GROUP &&
   1431         Section.getType() != ELF::SHT_REL &&
   1432         Section.getType() != ELF::SHT_RELA)
   1433       Sections.push_back(&Section);
   1434   }
   1435 
   1436   for (MCAssembler::iterator it = Asm.begin(),
   1437          ie = Asm.end(); it != ie; ++it) {
   1438     const MCSectionELF &Section =
   1439       static_cast<const MCSectionELF &>(it->getSection());
   1440     if (Section.getType() == ELF::SHT_REL ||
   1441         Section.getType() == ELF::SHT_RELA)
   1442       Sections.push_back(&Section);
   1443   }
   1444 }
   1445 
   1446 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
   1447                                   const MCAsmLayout &Layout) {
   1448   GroupMapTy GroupMap;
   1449   RevGroupMapTy RevGroupMap;
   1450   SectionIndexMapTy SectionIndexMap;
   1451 
   1452   unsigned NumUserSections = Asm.size();
   1453 
   1454   DenseMap<const MCSectionELF*, const MCSectionELF*> RelMap;
   1455   CreateRelocationSections(Asm, const_cast<MCAsmLayout&>(Layout), RelMap);
   1456 
   1457   const unsigned NumUserAndRelocSections = Asm.size();
   1458   CreateIndexedSections(Asm, const_cast<MCAsmLayout&>(Layout), GroupMap,
   1459                         RevGroupMap, SectionIndexMap, RelMap);
   1460   const unsigned AllSections = Asm.size();
   1461   const unsigned NumIndexedSections = AllSections - NumUserAndRelocSections;
   1462 
   1463   unsigned NumRegularSections = NumUserSections + NumIndexedSections;
   1464 
   1465   // Compute symbol table information.
   1466   ComputeSymbolTable(Asm, SectionIndexMap, RevGroupMap, NumRegularSections);
   1467 
   1468 
   1469   WriteRelocations(Asm, const_cast<MCAsmLayout&>(Layout), RelMap);
   1470 
   1471   CreateMetadataSections(const_cast<MCAssembler&>(Asm),
   1472                          const_cast<MCAsmLayout&>(Layout),
   1473                          SectionIndexMap,
   1474                          RelMap);
   1475 
   1476   uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
   1477   uint64_t HeaderSize = is64Bit() ? sizeof(ELF::Elf64_Ehdr) :
   1478                                     sizeof(ELF::Elf32_Ehdr);
   1479   uint64_t FileOff = HeaderSize;
   1480 
   1481   std::vector<const MCSectionELF*> Sections;
   1482   ComputeSectionOrder(Asm, Sections);
   1483   unsigned NumSections = Sections.size();
   1484   SectionOffsetMapTy SectionOffsetMap;
   1485   for (unsigned i = 0; i < NumRegularSections + 1; ++i) {
   1486     const MCSectionELF &Section = *Sections[i];
   1487     const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
   1488 
   1489     FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
   1490 
   1491     // Remember the offset into the file for this section.
   1492     SectionOffsetMap[&Section] = FileOff;
   1493 
   1494     // Get the size of the section in the output file (including padding).
   1495     FileOff += GetSectionFileSize(Layout, SD);
   1496   }
   1497 
   1498   FileOff = RoundUpToAlignment(FileOff, NaturalAlignment);
   1499 
   1500   const unsigned SectionHeaderOffset = FileOff - HeaderSize;
   1501 
   1502   uint64_t SectionHeaderEntrySize = is64Bit() ?
   1503     sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr);
   1504   FileOff += (NumSections + 1) * SectionHeaderEntrySize;
   1505 
   1506   for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) {
   1507     const MCSectionELF &Section = *Sections[i];
   1508     const MCSectionData &SD = Asm.getOrCreateSectionData(Section);
   1509 
   1510     FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
   1511 
   1512     // Remember the offset into the file for this section.
   1513     SectionOffsetMap[&Section] = FileOff;
   1514 
   1515     // Get the size of the section in the output file (including padding).
   1516     FileOff += GetSectionFileSize(Layout, SD);
   1517   }
   1518 
   1519   // Write out the ELF header ...
   1520   WriteHeader(SectionHeaderOffset, NumSections + 1);
   1521 
   1522   // ... then the regular sections ...
   1523   // + because of .shstrtab
   1524   for (unsigned i = 0; i < NumRegularSections + 1; ++i)
   1525     WriteDataSectionData(Asm, Layout, *Sections[i]);
   1526 
   1527   uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
   1528   WriteZeros(Padding);
   1529 
   1530   // ... then the section header table ...
   1531   WriteSectionHeader(Asm, GroupMap, Layout, SectionIndexMap,
   1532                      SectionOffsetMap);
   1533 
   1534   // ... and then the remaining sections ...
   1535   for (unsigned i = NumRegularSections + 1; i < NumSections; ++i)
   1536     WriteDataSectionData(Asm, Layout, *Sections[i]);
   1537 }
   1538 
   1539 bool
   1540 ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
   1541                                                       const MCSymbolData &DataA,
   1542                                                       const MCFragment &FB,
   1543                                                       bool InSet,
   1544                                                       bool IsPCRel) const {
   1545   if (DataA.getFlags() & ELF_STB_Weak)
   1546     return false;
   1547   return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
   1548                                                  Asm, DataA, FB,InSet, IsPCRel);
   1549 }
   1550 
   1551 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
   1552                                             raw_ostream &OS,
   1553                                             bool IsLittleEndian) {
   1554   return new ELFObjectWriter(MOTW, OS, IsLittleEndian);
   1555 }
   1556