lib/MC/ELFObjectWriter.cpp

   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/ELFObjectWriter.h"
  15 #include "llvm/ADT/SmallPtrSet.h"
  16 #include "llvm/ADT/STLExtras.h"
  17 #include "llvm/ADT/StringMap.h"
  18 #include "llvm/ADT/Twine.h"
  19 #include "llvm/MC/MCAssembler.h"
  20 #include "llvm/MC/MCAsmLayout.h"
  21 #include "llvm/MC/MCContext.h"
  22 #include "llvm/MC/MCELFSymbolFlags.h"
  23 #include "llvm/MC/MCExpr.h"
  24 #include "llvm/MC/MCObjectWriter.h"
  25 #include "llvm/MC/MCSectionELF.h"
  26 #include "llvm/MC/MCSymbol.h"
  27 #include "llvm/MC/MCValue.h"
  28 #include "llvm/Support/Debug.h"
  29 #include "llvm/Support/ErrorHandling.h"
  30 #include "llvm/Support/ELF.h"
  31 #include "llvm/Target/TargetAsmBackend.h"
  32
  33 #include "../Target/X86/X86FixupKinds.h"
  34
  35 #include <vector>
  36 using namespace llvm;
  37
  38 static unsigned GetType(const MCSymbolData &SD) {
  39   uint32_t Type = (SD.getFlags() & (0xf << ELF_STT_Shift)) >> ELF_STT_Shift;
  40   assert(Type == ELF::STT_NOTYPE || Type == ELF::STT_OBJECT ||
  41          Type == ELF::STT_FUNC || Type == ELF::STT_SECTION ||
  42          Type == ELF::STT_FILE || Type == ELF::STT_COMMON ||
  43          Type == ELF::STT_TLS);
  44   return Type;
  45 }
  46
  47 static unsigned GetBinding(const MCSymbolData &SD) {
  48   uint32_t Binding = (SD.getFlags() & (0xf << ELF_STB_Shift)) >> ELF_STB_Shift;
  49   assert(Binding == ELF::STB_LOCAL || Binding == ELF::STB_GLOBAL ||
  50          Binding == ELF::STB_WEAK);
  51   return Binding;
  52 }
  53
  54 static void SetBinding(MCSymbolData &SD, unsigned Binding) {
  55   assert(Binding == ELF::STB_LOCAL || Binding == ELF::STB_GLOBAL ||
  56          Binding == ELF::STB_WEAK);
  57   uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STB_Shift);
  58   SD.setFlags(OtherFlags | (Binding << ELF_STB_Shift));
  59 }
  60
  61 static unsigned GetVisibility(MCSymbolData &SD) {
  62   unsigned Visibility =
  63     (SD.getFlags() & (0xf << ELF_STV_Shift)) >> ELF_STV_Shift;
  64   assert(Visibility == ELF::STV_DEFAULT || Visibility == ELF::STV_INTERNAL ||
  65          Visibility == ELF::STV_HIDDEN || Visibility == ELF::STV_PROTECTED);
  66   return Visibility;
  67 }
  68
  69 static bool isFixupKindX86PCRel(unsigned Kind) {
  70   switch (Kind) {
  71   default:
  72     return false;
  73   case X86::reloc_pcrel_1byte:
  74   case X86::reloc_pcrel_4byte:
  75   case X86::reloc_riprel_4byte:
  76   case X86::reloc_riprel_4byte_movq_load:
  77     return true;
  78   }
  79 }
  80
  81 static bool RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) {
  82   switch (Variant) {
  83   default:
  84     return false;
  85   case MCSymbolRefExpr::VK_GOT:
  86   case MCSymbolRefExpr::VK_PLT:
  87   case MCSymbolRefExpr::VK_GOTPCREL:
  88   case MCSymbolRefExpr::VK_TPOFF:
  89   case MCSymbolRefExpr::VK_TLSGD:
  90   case MCSymbolRefExpr::VK_GOTTPOFF:
  91   case MCSymbolRefExpr::VK_INDNTPOFF:
  92   case MCSymbolRefExpr::VK_NTPOFF:
  93   case MCSymbolRefExpr::VK_GOTNTPOFF:
  94   case MCSymbolRefExpr::VK_TLSLDM:
  95   case MCSymbolRefExpr::VK_DTPOFF:
  96   case MCSymbolRefExpr::VK_TLSLD:
  97     return true;
  98   }
  99 }
 100
 101 namespace {
 102
 103   class ELFObjectWriterImpl {
 104     /*static bool isFixupKindX86RIPRel(unsigned Kind) {
 105       return Kind == X86::reloc_riprel_4byte ||
 106         Kind == X86::reloc_riprel_4byte_movq_load;
 107     }*/
 108
 109
 110     /// ELFSymbolData - Helper struct for containing some precomputed information
 111     /// on symbols.
 112     struct ELFSymbolData {
 113       MCSymbolData *SymbolData;
 114       uint64_t StringIndex;
 115       uint32_t SectionIndex;
 116
 117       // Support lexicographic sorting.
 118       bool operator<(const ELFSymbolData &RHS) const {
 119         if (GetType(*SymbolData) == ELF::STT_FILE)
 120           return true;
 121         if (GetType(*RHS.SymbolData) == ELF::STT_FILE)
 122           return false;
 123         return SymbolData->getSymbol().getName() <
 124                RHS.SymbolData->getSymbol().getName();
 125       }
 126     };
 127
 128     /// @name Relocation Data
 129     /// @{
 130
 131     struct ELFRelocationEntry {
 132       // Make these big enough for both 32-bit and 64-bit
 133       uint64_t r_offset;
 134       int Index;
 135       unsigned Type;
 136       const MCSymbol *Symbol;
 137       uint64_t r_addend;
 138
 139       // Support lexicographic sorting.
 140       bool operator<(const ELFRelocationEntry &RE) const {
 141         return RE.r_offset < r_offset;
 142       }
 143     };
 144
 145     SmallPtrSet<const MCSymbol *, 16> UsedInReloc;
 146     SmallPtrSet<const MCSymbol *, 16> WeakrefUsedInReloc;
 147     DenseMap<const MCSymbol *, const MCSymbol *> Renames;
 148
 149     llvm::DenseMap<const MCSectionData*,
 150                    std::vector<ELFRelocationEntry> > Relocations;
 151     DenseMap<const MCSection*, uint64_t> SectionStringTableIndex;
 152
 153     /// @}
 154     /// @name Symbol Table Data
 155     /// @{
 156
 157     SmallString<256> StringTable;
 158     std::vector<ELFSymbolData> LocalSymbolData;
 159     std::vector<ELFSymbolData> ExternalSymbolData;
 160     std::vector<ELFSymbolData> UndefinedSymbolData;
 161
 162     /// @}
 163
 164     int NumRegularSections;
 165
 166     bool NeedsGOT;
 167
 168     bool NeedsSymtabShndx;
 169
 170     ELFObjectWriter *Writer;
 171
 172     raw_ostream &OS;
 173
 174     unsigned Is64Bit : 1;
 175
 176     bool HasRelocationAddend;
 177
 178     Triple::OSType OSType;
 179
 180     uint16_t EMachine;
 181
 182     // This holds the symbol table index of the last local symbol.
 183     unsigned LastLocalSymbolIndex;
 184     // This holds the .strtab section index.
 185     unsigned StringTableIndex;
 186     // This holds the .symtab section index.
 187     unsigned SymbolTableIndex;
 188
 189     unsigned ShstrtabIndex;
 190
 191   public:
 192     ELFObjectWriterImpl(ELFObjectWriter *_Writer, bool _Is64Bit,
 193                         uint16_t _EMachine, bool _HasRelAddend,
 194                         Triple::OSType _OSType)
 195       : NeedsGOT(false), NeedsSymtabShndx(false), Writer(_Writer),
 196         OS(Writer->getStream()),
 197         Is64Bit(_Is64Bit), HasRelocationAddend(_HasRelAddend),
 198         OSType(_OSType), EMachine(_EMachine) {
 199     }
 200
 201     void Write8(uint8_t Value) { Writer->Write8(Value); }
 202     void Write16(uint16_t Value) { Writer->Write16(Value); }
 203     void Write32(uint32_t Value) { Writer->Write32(Value); }
 204     //void Write64(uint64_t Value) { Writer->Write64(Value); }
 205     void WriteZeros(unsigned N) { Writer->WriteZeros(N); }
 206     //void WriteBytes(StringRef Str, unsigned ZeroFillSize = 0) {
 207     //  Writer->WriteBytes(Str, ZeroFillSize);
 208     //}
 209
 210     void WriteWord(uint64_t W) {
 211       if (Is64Bit)
 212         Writer->Write64(W);
 213       else
 214         Writer->Write32(W);
 215     }
 216
 217     void String8(char *buf, uint8_t Value) {
 218       buf[0] = Value;
 219     }
 220
 221     void StringLE16(char *buf, uint16_t Value) {
 222       buf[0] = char(Value >> 0);
 223       buf[1] = char(Value >> 8);
 224     }
 225
 226     void StringLE32(char *buf, uint32_t Value) {
 227       StringLE16(buf, uint16_t(Value >> 0));
 228       StringLE16(buf + 2, uint16_t(Value >> 16));
 229     }
 230
 231     void StringLE64(char *buf, uint64_t Value) {
 232       StringLE32(buf, uint32_t(Value >> 0));
 233       StringLE32(buf + 4, uint32_t(Value >> 32));
 234     }
 235
 236     void StringBE16(char *buf ,uint16_t Value) {
 237       buf[0] = char(Value >> 8);
 238       buf[1] = char(Value >> 0);
 239     }
 240
 241     void StringBE32(char *buf, uint32_t Value) {
 242       StringBE16(buf, uint16_t(Value >> 16));
 243       StringBE16(buf + 2, uint16_t(Value >> 0));
 244     }
 245
 246     void StringBE64(char *buf, uint64_t Value) {
 247       StringBE32(buf, uint32_t(Value >> 32));
 248       StringBE32(buf + 4, uint32_t(Value >> 0));
 249     }
 250
 251     void String16(char *buf, uint16_t Value) {
 252       if (Writer->isLittleEndian())
 253         StringLE16(buf, Value);
 254       else
 255         StringBE16(buf, Value);
 256     }
 257
 258     void String32(char *buf, uint32_t Value) {
 259       if (Writer->isLittleEndian())
 260         StringLE32(buf, Value);
 261       else
 262         StringBE32(buf, Value);
 263     }
 264
 265     void String64(char *buf, uint64_t Value) {
 266       if (Writer->isLittleEndian())
 267         StringLE64(buf, Value);
 268       else
 269         StringBE64(buf, Value);
 270     }
 271
 272     void WriteHeader(uint64_t SectionDataSize, unsigned NumberOfSections);
 273
 274     void WriteSymbolEntry(MCDataFragment *SymtabF, MCDataFragment *ShndxF,
 275                           uint64_t name, uint8_t info,
 276                           uint64_t value, uint64_t size,
 277                           uint8_t other, uint32_t shndx,
 278                           bool Reserved);
 279
 280     void WriteSymbol(MCDataFragment *SymtabF,  MCDataFragment *ShndxF,
 281                      ELFSymbolData &MSD,
 282                      const MCAsmLayout &Layout);
 283
 284     void WriteSymbolTable(MCDataFragment *SymtabF, MCDataFragment *ShndxF,
 285                           const MCAssembler &Asm,
 286                           const MCAsmLayout &Layout,
 287                           unsigned NumRegularSections);
 288
 289     void RecordRelocation(const MCAssembler &Asm, const MCAsmLayout &Layout,
 290                           const MCFragment *Fragment, const MCFixup &Fixup,
 291                           MCValue Target, uint64_t &FixedValue);
 292
 293     uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm,
 294                                          const MCSymbol *S);
 295
 296     /// ComputeSymbolTable - Compute the symbol table data
 297     ///
 298     /// \param StringTable [out] - The string table data.
 299     /// \param StringIndexMap [out] - Map from symbol names to offsets in the
 300     /// string table.
 301     void ComputeSymbolTable(MCAssembler &Asm);
 302
 303     void WriteRelocation(MCAssembler &Asm, MCAsmLayout &Layout,
 304                          const MCSectionData &SD);
 305
 306     void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout) {
 307       for (MCAssembler::const_iterator it = Asm.begin(),
 308              ie = Asm.end(); it != ie; ++it) {
 309         WriteRelocation(Asm, Layout, *it);
 310       }
 311     }
 312
 313     void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout);
 314
 315     void ExecutePostLayoutBinding(MCAssembler &Asm);
 316
 317     void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
 318                           uint64_t Address, uint64_t Offset,
 319                           uint64_t Size, uint32_t Link, uint32_t Info,
 320                           uint64_t Alignment, uint64_t EntrySize);
 321
 322     void WriteRelocationsFragment(const MCAssembler &Asm, MCDataFragment *F,
 323                                   const MCSectionData *SD);
 324
 325     bool IsFixupFullyResolved(const MCAssembler &Asm,
 326                               const MCValue Target,
 327                               bool IsPCRel,
 328                               const MCFragment *DF) const;
 329
 330     void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout);
 331   };
 332
 333 }
 334
 335 // Emit the ELF header.
 336 void ELFObjectWriterImpl::WriteHeader(uint64_t SectionDataSize,
 337                                       unsigned NumberOfSections) {
 338   // ELF Header
 339   // ----------
 340   //
 341   // Note
 342   // ----
 343   // emitWord method behaves differently for ELF32 and ELF64, writing
 344   // 4 bytes in the former and 8 in the latter.
 345
 346   Write8(0x7f); // e_ident[EI_MAG0]
 347   Write8('E');  // e_ident[EI_MAG1]
 348   Write8('L');  // e_ident[EI_MAG2]
 349   Write8('F');  // e_ident[EI_MAG3]
 350
 351   Write8(Is64Bit ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
 352
 353   // e_ident[EI_DATA]
 354   Write8(Writer->isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
 355
 356   Write8(ELF::EV_CURRENT);        // e_ident[EI_VERSION]
 357   // e_ident[EI_OSABI]
 358   switch (OSType) {
 359     case Triple::FreeBSD:  Write8(ELF::ELFOSABI_FREEBSD); break;
 360     case Triple::Linux:    Write8(ELF::ELFOSABI_LINUX); break;
 361     default:               Write8(ELF::ELFOSABI_NONE); break;
 362   }
 363   Write8(0);                  // e_ident[EI_ABIVERSION]
 364
 365   WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
 366
 367   Write16(ELF::ET_REL);             // e_type
 368
 369   Write16(EMachine); // e_machine = target
 370
 371   Write32(ELF::EV_CURRENT);         // e_version
 372   WriteWord(0);                    // e_entry, no entry point in .o file
 373   WriteWord(0);                    // e_phoff, no program header for .o
 374   WriteWord(SectionDataSize + (Is64Bit ? sizeof(ELF::Elf64_Ehdr) :
 375             sizeof(ELF::Elf32_Ehdr)));  // e_shoff = sec hdr table off in bytes
 376
 377   // FIXME: Make this configurable.
 378   Write32(0);   // e_flags = whatever the target wants
 379
 380   // e_ehsize = ELF header size
 381   Write16(Is64Bit ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
 382
 383   Write16(0);                  // e_phentsize = prog header entry size
 384   Write16(0);                  // e_phnum = # prog header entries = 0
 385
 386   // e_shentsize = Section header entry size
 387   Write16(Is64Bit ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
 388
 389   // e_shnum     = # of section header ents
 390   if (NumberOfSections >= ELF::SHN_LORESERVE)
 391     Write16(0);
 392   else
 393     Write16(NumberOfSections);
 394
 395   // e_shstrndx  = Section # of '.shstrtab'
 396   if (NumberOfSections >= ELF::SHN_LORESERVE)
 397     Write16(ELF::SHN_XINDEX);
 398   else
 399     Write16(ShstrtabIndex);
 400 }
 401
 402 void ELFObjectWriterImpl::WriteSymbolEntry(MCDataFragment *SymtabF,
 403                                            MCDataFragment *ShndxF,
 404                                            uint64_t name,
 405                                            uint8_t info, uint64_t value,
 406                                            uint64_t size, uint8_t other,
 407                                            uint32_t shndx,
 408                                            bool Reserved) {
 409   if (ShndxF) {
 410     char buf[4];
 411     if (shndx >= ELF::SHN_LORESERVE && !Reserved)
 412       String32(buf, shndx);
 413     else
 414       String32(buf, 0);
 415     ShndxF->getContents() += StringRef(buf, 4);
 416   }
 417
 418   if (Is64Bit) {
 419     char buf[8];
 420
 421     String32(buf, name);
 422     SymtabF->getContents() += StringRef(buf, 4); // st_name
 423
 424     String8(buf, info);
 425     SymtabF->getContents() += StringRef(buf, 1);  // st_info
 426
 427     String8(buf, other);
 428     SymtabF->getContents() += StringRef(buf, 1); // st_other
 429
 430     if (shndx >= ELF::SHN_LORESERVE && !Reserved)
 431       String16(buf, ELF::SHN_XINDEX);
 432     else
 433       String16(buf, shndx);
 434
 435     SymtabF->getContents() += StringRef(buf, 2); // st_shndx
 436
 437     String64(buf, value);
 438     SymtabF->getContents() += StringRef(buf, 8); // st_value
 439
 440     String64(buf, size);
 441     SymtabF->getContents() += StringRef(buf, 8);  // st_size
 442   } else {
 443     char buf[4];
 444
 445     String32(buf, name);
 446     SymtabF->getContents() += StringRef(buf, 4);  // st_name
 447
 448     String32(buf, value);
 449     SymtabF->getContents() += StringRef(buf, 4); // st_value
 450
 451     String32(buf, size);
 452     SymtabF->getContents() += StringRef(buf, 4);  // st_size
 453
 454     String8(buf, info);
 455     SymtabF->getContents() += StringRef(buf, 1);  // st_info
 456
 457     String8(buf, other);
 458     SymtabF->getContents() += StringRef(buf, 1); // st_other
 459
 460     if (shndx >= ELF::SHN_LORESERVE && !Reserved)
 461       String16(buf, ELF::SHN_XINDEX);
 462     else
 463       String16(buf, shndx);
 464
 465     SymtabF->getContents() += StringRef(buf, 2); // st_shndx
 466   }
 467 }
 468
 469 static uint64_t SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout) {
 470   if (Data.isCommon() && Data.isExternal())
 471     return Data.getCommonAlignment();
 472
 473   const MCSymbol &Symbol = Data.getSymbol();
 474   if (!Symbol.isInSection())
 475     return 0;
 476
 477   if (MCFragment *FF = Data.getFragment())
 478     return Layout.getSymbolAddress(&Data) -
 479       Layout.getSectionAddress(FF->getParent());
 480
 481   return 0;
 482 }
 483
 484 static const MCSymbol &AliasedSymbol(const MCSymbol &Symbol) {
 485   const MCSymbol *S = &Symbol;
 486   while (S->isVariable()) {
 487     const MCExpr *Value = S->getVariableValue();
 488     if (Value->getKind() != MCExpr::SymbolRef)
 489       return *S;
 490     const MCSymbolRefExpr *Ref = static_cast<const MCSymbolRefExpr*>(Value);
 491     S = &Ref->getSymbol();
 492   }
 493   return *S;
 494 }
 495
 496 void ELFObjectWriterImpl::ExecutePostLayoutBinding(MCAssembler &Asm) {
 497   // The presence of symbol versions causes undefined symbols and
 498   // versions declared with @@@ to be renamed.
 499
 500   for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
 501          ie = Asm.symbol_end(); it != ie; ++it) {
 502     const MCSymbol &Alias = it->getSymbol();
 503     const MCSymbol &Symbol = AliasedSymbol(Alias);
 504     MCSymbolData &SD = Asm.getSymbolData(Symbol);
 505
 506     // Undefined symbols are global, but this is the first place we
 507     // are able to set it.
 508     if (Symbol.isUndefined() && !Symbol.isVariable()) {
 509       if (GetBinding(SD) == ELF::STB_LOCAL) {
 510         SetBinding(SD, ELF::STB_GLOBAL);
 511         SetBinding(*it, ELF::STB_GLOBAL);
 512       }
 513     }
 514
 515     // Not an alias.
 516     if (&Symbol == &Alias)
 517       continue;
 518
 519     StringRef AliasName = Alias.getName();
 520     size_t Pos = AliasName.find('@');
 521     if (Pos == StringRef::npos)
 522       continue;
 523
 524     // Aliases defined with .symvar copy the binding from the symbol they alias.
 525     // This is the first place we are able to copy this information.
 526     it->setExternal(SD.isExternal());
 527     SetBinding(*it, GetBinding(SD));
 528
 529     StringRef Rest = AliasName.substr(Pos);
 530     if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
 531       continue;
 532
 533     // FIXME: produce a better error message.
 534     if (Symbol.isUndefined() && Rest.startswith("@@") &&
 535         !Rest.startswith("@@@"))
 536       report_fatal_error("A @@ version cannot be undefined");
 537
 538     Renames.insert(std::make_pair(&Symbol, &Alias));
 539   }
 540 }
 541
 542 void ELFObjectWriterImpl::WriteSymbol(MCDataFragment *SymtabF,
 543                                       MCDataFragment *ShndxF,
 544                                       ELFSymbolData &MSD,
 545                                       const MCAsmLayout &Layout) {
 546   MCSymbolData &OrigData = *MSD.SymbolData;
 547   MCSymbolData &Data =
 548     Layout.getAssembler().getSymbolData(AliasedSymbol(OrigData.getSymbol()));
 549
 550   bool IsReserved = Data.isCommon() || Data.getSymbol().isAbsolute() ||
 551     Data.getSymbol().isVariable();
 552
 553   uint8_t Binding = GetBinding(OrigData);
 554   uint8_t Visibility = GetVisibility(OrigData);
 555   uint8_t Type = GetType(Data);
 556
 557   uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
 558   uint8_t Other = Visibility;
 559
 560   uint64_t Value = SymbolValue(Data, Layout);
 561   uint64_t Size = 0;
 562   const MCExpr *ESize;
 563
 564   assert(!(Data.isCommon() && !Data.isExternal()));
 565
 566   ESize = Data.getSize();
 567   if (Data.getSize()) {
 568     MCValue Res;
 569     if (ESize->getKind() == MCExpr::Binary) {
 570       const MCBinaryExpr *BE = static_cast<const MCBinaryExpr *>(ESize);
 571
 572       if (BE->EvaluateAsRelocatable(Res, &Layout)) {
 573         assert(!Res.getSymA() || !Res.getSymA()->getSymbol().isDefined());
 574         assert(!Res.getSymB() || !Res.getSymB()->getSymbol().isDefined());
 575         Size = Res.getConstant();
 576       }
 577     } else if (ESize->getKind() == MCExpr::Constant) {
 578       Size = static_cast<const MCConstantExpr *>(ESize)->getValue();
 579     } else {
 580       assert(0 && "Unsupported size expression");
 581     }
 582   }
 583
 584   // Write out the symbol table entry
 585   WriteSymbolEntry(SymtabF, ShndxF, MSD.StringIndex, Info, Value,
 586                    Size, Other, MSD.SectionIndex, IsReserved);
 587 }
 588
 589 void ELFObjectWriterImpl::WriteSymbolTable(MCDataFragment *SymtabF,
 590                                            MCDataFragment *ShndxF,
 591                                            const MCAssembler &Asm,
 592                                            const MCAsmLayout &Layout,
 593                                            unsigned NumRegularSections) {
 594   // The string table must be emitted first because we need the index
 595   // into the string table for all the symbol names.
 596   assert(StringTable.size() && "Missing string table");
 597
 598   // FIXME: Make sure the start of the symbol table is aligned.
 599
 600   // The first entry is the undefined symbol entry.
 601   WriteSymbolEntry(SymtabF, ShndxF, 0, 0, 0, 0, 0, 0, false);
 602
 603   // Write the symbol table entries.
 604   LastLocalSymbolIndex = LocalSymbolData.size() + 1;
 605   for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
 606     ELFSymbolData &MSD = LocalSymbolData[i];
 607     WriteSymbol(SymtabF, ShndxF, MSD, Layout);
 608   }
 609
 610   // Write out a symbol table entry for each regular section.
 611   unsigned Index = 1;
 612   for (MCAssembler::const_iterator it = Asm.begin();
 613        Index <= NumRegularSections; ++it, ++Index) {
 614     const MCSectionELF &Section =
 615       static_cast<const MCSectionELF&>(it->getSection());
 616     // Leave out relocations so we don't have indexes within
 617     // the relocations messed up
 618     if (Section.getType() == ELF::SHT_RELA || Section.getType() == ELF::SHT_REL)
 619       continue;
 620     WriteSymbolEntry(SymtabF, ShndxF, 0, ELF::STT_SECTION, 0, 0,
 621                      ELF::STV_DEFAULT, Index, false);
 622     LastLocalSymbolIndex++;
 623   }
 624
 625   for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
 626     ELFSymbolData &MSD = ExternalSymbolData[i];
 627     MCSymbolData &Data = *MSD.SymbolData;
 628     assert(((Data.getFlags() & ELF_STB_Global) ||
 629             (Data.getFlags() & ELF_STB_Weak)) &&
 630            "External symbol requires STB_GLOBAL or STB_WEAK flag");
 631     WriteSymbol(SymtabF, ShndxF, MSD, Layout);
 632     if (GetBinding(Data) == ELF::STB_LOCAL)
 633       LastLocalSymbolIndex++;
 634   }
 635
 636   for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
 637     ELFSymbolData &MSD = UndefinedSymbolData[i];
 638     MCSymbolData &Data = *MSD.SymbolData;
 639     WriteSymbol(SymtabF, ShndxF, MSD, Layout);
 640     if (GetBinding(Data) == ELF::STB_LOCAL)
 641       LastLocalSymbolIndex++;
 642   }
 643 }
 644
 645 static bool ShouldRelocOnSymbol(const MCSymbolData &SD,
 646                                 const MCValue &Target,
 647                                 const MCFragment &F) {
 648   const MCSymbol &Symbol = SD.getSymbol();
 649   if (Symbol.isUndefined())
 650     return true;
 651
 652   const MCSectionELF &Section =
 653     static_cast<const MCSectionELF&>(Symbol.getSection());
 654
 655   if (SD.isExternal())
 656     return true;
 657
 658   MCSymbolRefExpr::VariantKind Kind = Target.getSymA()->getKind();
 659   const MCSectionELF &Sec2 =
 660     static_cast<const MCSectionELF&>(F.getParent()->getSection());
 661
 662   if (Section.getKind().isBSS())
 663     return false;
 664
 665   if (&Sec2 != &Section &&
 666       (Kind == MCSymbolRefExpr::VK_PLT ||
 667        Kind == MCSymbolRefExpr::VK_GOTPCREL ||
 668        Kind == MCSymbolRefExpr::VK_GOTOFF))
 669     return true;
 670
 671   if (Section.getFlags() & MCSectionELF::SHF_MERGE)
 672     return Target.getConstant() != 0;
 673
 674   return false;
 675 }
 676
 677 // FIXME: this is currently X86/X86_64 only
 678 void ELFObjectWriterImpl::RecordRelocation(const MCAssembler &Asm,
 679                                            const MCAsmLayout &Layout,
 680                                            const MCFragment *Fragment,
 681                                            const MCFixup &Fixup,
 682                                            MCValue Target,
 683                                            uint64_t &FixedValue) {
 684   int64_t Addend = 0;
 685   int Index = 0;
 686   int64_t Value = Target.getConstant();
 687   const MCSymbol *Symbol = 0;
 688   const MCSymbol *Renamed = 0;
 689
 690   bool IsPCRel = isFixupKindX86PCRel(Fixup.getKind());
 691   if (!Target.isAbsolute()) {
 692     Symbol = &AliasedSymbol(Target.getSymA()->getSymbol());
 693     Renamed = Renames.lookup(Symbol);
 694     if (!Renamed)
 695       Renamed = &Target.getSymA()->getSymbol();
 696     MCSymbolData &SD = Asm.getSymbolData(*Symbol);
 697     MCFragment *F = SD.getFragment();
 698
 699     if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
 700       const MCSymbol &SymbolB = RefB->getSymbol();
 701       MCSymbolData &SDB = Asm.getSymbolData(SymbolB);
 702       IsPCRel = true;
 703       MCSectionData *Sec = Fragment->getParent();
 704
 705       // Offset of the symbol in the section
 706       int64_t a = Layout.getSymbolAddress(&SDB) - Layout.getSectionAddress(Sec);
 707
 708       // Ofeset of the relocation in the section
 709       int64_t b = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
 710       Value += b - a;
 711     }
 712
 713     // Check that this case has already been fully resolved before we get
 714     // here.
 715     if (Symbol->isDefined() && !SD.isExternal() &&
 716         IsPCRel &&
 717         &Fragment->getParent()->getSection() == &Symbol->getSection()) {
 718       llvm_unreachable("We don't need a relocation in this case.");
 719       return;
 720     }
 721
 722     bool RelocOnSymbol = ShouldRelocOnSymbol(SD, Target, *Fragment);
 723     if (!RelocOnSymbol) {
 724       Index = F->getParent()->getOrdinal();
 725
 726       MCSectionData *FSD = F->getParent();
 727       // Offset of the symbol in the section
 728       Value += Layout.getSymbolAddress(&SD) - Layout.getSectionAddress(FSD);
 729     } else {
 730       UsedInReloc.insert(Renamed);
 731       MCSymbolData &RenamedSD = Asm.getSymbolData(*Renamed);
 732       if (RenamedSD.getFlags() & ELF_Other_Weakref) {
 733         WeakrefUsedInReloc.insert(Symbol);
 734       }
 735       Index = -1;
 736     }
 737     Addend = Value;
 738     // Compensate for the addend on i386.
 739     if (Is64Bit)
 740       Value = 0;
 741   }
 742
 743   FixedValue = Value;
 744
 745   // determine the type of the relocation
 746
 747   MCSymbolRefExpr::VariantKind Modifier = Target.getSymA()->getKind();
 748   unsigned Type;
 749   if (Is64Bit) {
 750     if (IsPCRel) {
 751       switch (Modifier) {
 752       default:
 753         llvm_unreachable("Unimplemented");
 754       case MCSymbolRefExpr::VK_None:
 755         Type = ELF::R_X86_64_PC32;
 756         break;
 757       case MCSymbolRefExpr::VK_PLT:
 758         Type = ELF::R_X86_64_PLT32;
 759         break;
 760       case MCSymbolRefExpr::VK_GOTPCREL:
 761         Type = ELF::R_X86_64_GOTPCREL;
 762         break;
 763       case MCSymbolRefExpr::VK_GOTTPOFF:
 764         Type = ELF::R_X86_64_GOTTPOFF;
 765         break;
 766       case MCSymbolRefExpr::VK_TLSGD:
 767         Type = ELF::R_X86_64_TLSGD;
 768         break;
 769       case MCSymbolRefExpr::VK_TLSLD:
 770         Type = ELF::R_X86_64_TLSLD;
 771         break;
 772       }
 773     } else {
 774       switch ((unsigned)Fixup.getKind()) {
 775       default: llvm_unreachable("invalid fixup kind!");
 776       case FK_Data_8: Type = ELF::R_X86_64_64; break;
 777       case X86::reloc_signed_4byte:
 778       case X86::reloc_pcrel_4byte:
 779         assert(isInt<32>(Target.getConstant()));
 780         switch (Modifier) {
 781         default:
 782           llvm_unreachable("Unimplemented");
 783         case MCSymbolRefExpr::VK_None:
 784           Type = ELF::R_X86_64_32S;
 785           break;
 786         case MCSymbolRefExpr::VK_GOT:
 787           Type = ELF::R_X86_64_GOT32;
 788           break;
 789         case MCSymbolRefExpr::VK_GOTPCREL:
 790           Type = ELF::R_X86_64_GOTPCREL;
 791           break;
 792         case MCSymbolRefExpr::VK_TPOFF:
 793           Type = ELF::R_X86_64_TPOFF32;
 794           break;
 795         case MCSymbolRefExpr::VK_DTPOFF:
 796           Type = ELF::R_X86_64_DTPOFF32;
 797           break;
 798         }
 799         break;
 800       case FK_Data_4:
 801         Type = ELF::R_X86_64_32;
 802         break;
 803       case FK_Data_2: Type = ELF::R_X86_64_16; break;
 804       case X86::reloc_pcrel_1byte:
 805       case FK_Data_1: Type = ELF::R_X86_64_8; break;
 806       }
 807     }
 808   } else {
 809     if (IsPCRel) {
 810       switch (Modifier) {
 811       default:
 812         llvm_unreachable("Unimplemented");
 813       case MCSymbolRefExpr::VK_None:
 814         Type = ELF::R_386_PC32;
 815         break;
 816       case MCSymbolRefExpr::VK_PLT:
 817         Type = ELF::R_386_PLT32;
 818         break;
 819       }
 820     } else {
 821       switch ((unsigned)Fixup.getKind()) {
 822       default: llvm_unreachable("invalid fixup kind!");
 823
 824       case X86::reloc_global_offset_table:
 825         Type = ELF::R_386_GOTPC;
 826         break;
 827
 828       // FIXME: Should we avoid selecting reloc_signed_4byte in 32 bit mode
 829       // instead?
 830       case X86::reloc_signed_4byte:
 831       case X86::reloc_pcrel_4byte:
 832       case FK_Data_4:
 833         switch (Modifier) {
 834         default:
 835           llvm_unreachable("Unimplemented");
 836         case MCSymbolRefExpr::VK_None:
 837           Type = ELF::R_386_32;
 838           break;
 839         case MCSymbolRefExpr::VK_GOT:
 840           Type = ELF::R_386_GOT32;
 841           break;
 842         case MCSymbolRefExpr::VK_GOTOFF:
 843           Type = ELF::R_386_GOTOFF;
 844           break;
 845         case MCSymbolRefExpr::VK_TLSGD:
 846           Type = ELF::R_386_TLS_GD;
 847           break;
 848         case MCSymbolRefExpr::VK_TPOFF:
 849           Type = ELF::R_386_TLS_LE_32;
 850           break;
 851         case MCSymbolRefExpr::VK_INDNTPOFF:
 852           Type = ELF::R_386_TLS_IE;
 853           break;
 854         case MCSymbolRefExpr::VK_NTPOFF:
 855           Type = ELF::R_386_TLS_LE;
 856           break;
 857         case MCSymbolRefExpr::VK_GOTNTPOFF:
 858           Type = ELF::R_386_TLS_GOTIE;
 859           break;
 860         case MCSymbolRefExpr::VK_TLSLDM:
 861           Type = ELF::R_386_TLS_LDM;
 862           break;
 863         case MCSymbolRefExpr::VK_DTPOFF:
 864           Type = ELF::R_386_TLS_LDO_32;
 865           break;
 866         }
 867         break;
 868       case FK_Data_2: Type = ELF::R_386_16; break;
 869       case X86::reloc_pcrel_1byte:
 870       case FK_Data_1: Type = ELF::R_386_8; break;
 871       }
 872     }
 873   }
 874
 875   if (RelocNeedsGOT(Modifier))
 876     NeedsGOT = true;
 877
 878   ELFRelocationEntry ERE;
 879
 880   ERE.Index = Index;
 881   ERE.Type = Type;
 882   ERE.Symbol = Renamed;
 883
 884   ERE.r_offset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
 885
 886   if (HasRelocationAddend)
 887     ERE.r_addend = Addend;
 888   else
 889     ERE.r_addend = 0; // Silence compiler warning.
 890
 891   Relocations[Fragment->getParent()].push_back(ERE);
 892 }
 893
 894 uint64_t
 895 ELFObjectWriterImpl::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
 896                                                  const MCSymbol *S) {
 897   MCSymbolData &SD = Asm.getSymbolData(*S);
 898
 899   // Local symbol.
 900   if (!SD.isExternal() && !S->isUndefined())
 901     return SD.getIndex() + /* empty symbol */ 1;
 902
 903   // External or undefined symbol.
 904   return SD.getIndex() + NumRegularSections + /* empty symbol */ 1;
 905 }
 906
 907 static bool isInSymtab(const MCAssembler &Asm, const MCSymbolData &Data,
 908                        bool Used, bool Renamed) {
 909   if (Data.getFlags() & ELF_Other_Weakref)
 910     return false;
 911
 912   if (Used)
 913     return true;
 914
 915   if (Renamed)
 916     return false;
 917
 918   const MCSymbol &Symbol = Data.getSymbol();
 919
 920   if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
 921     return true;
 922
 923   const MCSymbol &A = AliasedSymbol(Symbol);
 924   if (!A.isVariable() && A.isUndefined() && !Data.isCommon())
 925     return false;
 926
 927   if (!Asm.isSymbolLinkerVisible(Symbol) && !Symbol.isUndefined())
 928     return false;
 929
 930   if (Symbol.isTemporary())
 931     return false;
 932
 933   return true;
 934 }
 935
 936 static bool isLocal(const MCSymbolData &Data) {
 937   if (Data.isExternal())
 938     return false;
 939
 940   const MCSymbol &Symbol = Data.getSymbol();
 941   if (Symbol.isUndefined() && !Symbol.isVariable())
 942     return false;
 943
 944   return true;
 945 }
 946
 947 void ELFObjectWriterImpl::ComputeSymbolTable(MCAssembler &Asm) {
 948   // FIXME: Is this the correct place to do this?
 949   if (NeedsGOT) {
 950     llvm::StringRef Name = "_GLOBAL_OFFSET_TABLE_";
 951     MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
 952     MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
 953     Data.setExternal(true);
 954     SetBinding(Data, ELF::STB_GLOBAL);
 955   }
 956
 957   // Build section lookup table.
 958   NumRegularSections = Asm.size();
 959   DenseMap<const MCSection*, uint32_t> SectionIndexMap;
 960   unsigned Index = 1;
 961   for (MCAssembler::iterator it = Asm.begin(),
 962          ie = Asm.end(); it != ie; ++it, ++Index)
 963     SectionIndexMap[&it->getSection()] = Index;
 964
 965   // Index 0 is always the empty string.
 966   StringMap<uint64_t> StringIndexMap;
 967   StringTable += '\x00';
 968
 969   // Add the data for the symbols.
 970   for (MCAssembler::symbol_iterator it = Asm.symbol_begin(),
 971          ie = Asm.symbol_end(); it != ie; ++it) {
 972     const MCSymbol &Symbol = it->getSymbol();
 973
 974     bool Used = UsedInReloc.count(&Symbol);
 975     bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
 976     if (!isInSymtab(Asm, *it, Used || WeakrefUsed,
 977                     Renames.count(&Symbol)))
 978       continue;
 979
 980     ELFSymbolData MSD;
 981     MSD.SymbolData = it;
 982     bool Local = isLocal(*it);
 983     const MCSymbol &RefSymbol = AliasedSymbol(Symbol);
 984
 985     if (RefSymbol.isUndefined() && !Used && WeakrefUsed)
 986       SetBinding(*it, ELF::STB_WEAK);
 987
 988     if (it->isCommon()) {
 989       assert(!Local);
 990       MSD.SectionIndex = ELF::SHN_COMMON;
 991     } else if (Symbol.isAbsolute() || RefSymbol.isVariable()) {
 992       MSD.SectionIndex = ELF::SHN_ABS;
 993     } else if (RefSymbol.isUndefined()) {
 994       MSD.SectionIndex = ELF::SHN_UNDEF;
 995     } else {
 996       MSD.SectionIndex = SectionIndexMap.lookup(&RefSymbol.getSection());
 997       if (MSD.SectionIndex >= ELF::SHN_LORESERVE)
 998         NeedsSymtabShndx = true;
 999       assert(MSD.SectionIndex && "Invalid section index!");
1000     }
1001
1002     // The @@@ in symbol version is replaced with @ in undefined symbols and
1003     // @@ in defined ones.
1004     StringRef Name = Symbol.getName();
1005     size_t Pos = Name.find("@@@");
1006     std::string FinalName;
1007     if (Pos != StringRef::npos) {
1008       StringRef Prefix = Name.substr(0, Pos);
1009       unsigned n = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
1010       StringRef Suffix = Name.substr(Pos + n);
1011       FinalName = Prefix.str() + Suffix.str();
1012     } else {
1013       FinalName = Name.str();
1014     }
1015
1016     uint64_t &Entry = StringIndexMap[FinalName];
1017     if (!Entry) {
1018       Entry = StringTable.size();
1019       StringTable += FinalName;
1020       StringTable += '\x00';
1021     }
1022     MSD.StringIndex = Entry;
1023     if (MSD.SectionIndex == ELF::SHN_UNDEF)
1024       UndefinedSymbolData.push_back(MSD);
1025     else if (Local)
1026       LocalSymbolData.push_back(MSD);
1027     else
1028       ExternalSymbolData.push_back(MSD);
1029   }
1030
1031   // Symbols are required to be in lexicographic order.
1032   array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
1033   array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
1034   array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
1035
1036   // Set the symbol indices. Local symbols must come before all other
1037   // symbols with non-local bindings.
1038   Index = 0;
1039   for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
1040     LocalSymbolData[i].SymbolData->setIndex(Index++);
1041   for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
1042     ExternalSymbolData[i].SymbolData->setIndex(Index++);
1043   for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
1044     UndefinedSymbolData[i].SymbolData->setIndex(Index++);
1045 }
1046
1047 void ELFObjectWriterImpl::WriteRelocation(MCAssembler &Asm, MCAsmLayout &Layout,
1048                                           const MCSectionData &SD) {
1049   if (!Relocations[&SD].empty()) {
1050     MCContext &Ctx = Asm.getContext();
1051     const MCSection *RelaSection;
1052     const MCSectionELF &Section =
1053       static_cast<const MCSectionELF&>(SD.getSection());
1054
1055     const StringRef SectionName = Section.getSectionName();
1056     std::string RelaSectionName = HasRelocationAddend ? ".rela" : ".rel";
1057     RelaSectionName += SectionName;
1058
1059     unsigned EntrySize;
1060     if (HasRelocationAddend)
1061       EntrySize = Is64Bit ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
1062     else
1063       EntrySize = Is64Bit ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
1064
1065     RelaSection = Ctx.getELFSection(RelaSectionName, HasRelocationAddend ?
1066                                     ELF::SHT_RELA : ELF::SHT_REL, 0,
1067                                     SectionKind::getReadOnly(),
1068                                     false, EntrySize);
1069
1070     MCSectionData &RelaSD = Asm.getOrCreateSectionData(*RelaSection);
1071     RelaSD.setAlignment(Is64Bit ? 8 : 4);
1072
1073     MCDataFragment *F = new MCDataFragment(&RelaSD);
1074
1075     WriteRelocationsFragment(Asm, F, &SD);
1076
1077     Asm.AddSectionToTheEnd(*Writer, RelaSD, Layout);
1078   }
1079 }
1080
1081 void ELFObjectWriterImpl::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
1082                                            uint64_t Flags, uint64_t Address,
1083                                            uint64_t Offset, uint64_t Size,
1084                                            uint32_t Link, uint32_t Info,
1085                                            uint64_t Alignment,
1086                                            uint64_t EntrySize) {
1087   Write32(Name);        // sh_name: index into string table
1088   Write32(Type);        // sh_type
1089   WriteWord(Flags);     // sh_flags
1090   WriteWord(Address);   // sh_addr
1091   WriteWord(Offset);    // sh_offset
1092   WriteWord(Size);      // sh_size
1093   Write32(Link);        // sh_link
1094   Write32(Info);        // sh_info
1095   WriteWord(Alignment); // sh_addralign
1096   WriteWord(EntrySize); // sh_entsize
1097 }
1098
1099 void ELFObjectWriterImpl::WriteRelocationsFragment(const MCAssembler &Asm,
1100                                                    MCDataFragment *F,
1101                                                    const MCSectionData *SD) {
1102   std::vector<ELFRelocationEntry> &Relocs = Relocations[SD];
1103   // sort by the r_offset just like gnu as does
1104   array_pod_sort(Relocs.begin(), Relocs.end());
1105
1106   for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
1107     ELFRelocationEntry entry = Relocs[e - i - 1];
1108
1109     if (entry.Index < 0)
1110       entry.Index = getSymbolIndexInSymbolTable(Asm, entry.Symbol);
1111     else
1112       entry.Index += LocalSymbolData.size() + 1;
1113     if (Is64Bit) {
1114       char buf[8];
1115
1116       String64(buf, entry.r_offset);
1117       F->getContents() += StringRef(buf, 8);
1118
1119       struct ELF::Elf64_Rela ERE64;
1120       ERE64.setSymbolAndType(entry.Index, entry.Type);
1121       String64(buf, ERE64.r_info);
1122       F->getContents() += StringRef(buf, 8);
1123
1124       if (HasRelocationAddend) {
1125         String64(buf, entry.r_addend);
1126         F->getContents() += StringRef(buf, 8);
1127       }
1128     } else {
1129       char buf[4];
1130
1131       String32(buf, entry.r_offset);
1132       F->getContents() += StringRef(buf, 4);
1133
1134       struct ELF::Elf32_Rela ERE32;
1135       ERE32.setSymbolAndType(entry.Index, entry.Type);
1136       String32(buf, ERE32.r_info);
1137       F->getContents() += StringRef(buf, 4);
1138
1139       if (HasRelocationAddend) {
1140         String32(buf, entry.r_addend);
1141         F->getContents() += StringRef(buf, 4);
1142       }
1143     }
1144   }
1145 }
1146
1147 void ELFObjectWriterImpl::CreateMetadataSections(MCAssembler &Asm,
1148                                                  MCAsmLayout &Layout) {
1149   MCContext &Ctx = Asm.getContext();
1150   MCDataFragment *F;
1151
1152   unsigned EntrySize = Is64Bit ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
1153
1154   unsigned NumRegularSections = Asm.size();
1155
1156   // We construct .shstrtab, .symtab and .strtab in this order to match gnu as.
1157   const MCSection *ShstrtabSection =
1158     Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0,
1159                       SectionKind::getReadOnly(), false);
1160   MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection);
1161   ShstrtabSD.setAlignment(1);
1162   ShstrtabIndex = Asm.size();
1163
1164   const MCSection *SymtabSection =
1165     Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
1166                       SectionKind::getReadOnly(),
1167                       false, EntrySize);
1168   MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
1169   SymtabSD.setAlignment(Is64Bit ? 8 : 4);
1170   SymbolTableIndex = Asm.size();
1171
1172   MCSectionData *SymtabShndxSD = NULL;
1173
1174   if (NeedsSymtabShndx) {
1175     const MCSection *SymtabShndxSection =
1176       Ctx.getELFSection(".symtab_shndx", ELF::SHT_SYMTAB_SHNDX, 0,
1177                         SectionKind::getReadOnly(), false, 4);
1178     SymtabShndxSD = &Asm.getOrCreateSectionData(*SymtabShndxSection);
1179     SymtabShndxSD->setAlignment(4);
1180   }
1181
1182   const MCSection *StrtabSection;
1183   StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0,
1184                                     SectionKind::getReadOnly(), false);
1185   MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection);
1186   StrtabSD.setAlignment(1);
1187   StringTableIndex = Asm.size();
1188
1189   WriteRelocations(Asm, Layout);
1190
1191   // Symbol table
1192   F = new MCDataFragment(&SymtabSD);
1193   MCDataFragment *ShndxF = NULL;
1194   if (NeedsSymtabShndx) {
1195     ShndxF = new MCDataFragment(SymtabShndxSD);
1196     Asm.AddSectionToTheEnd(*Writer, *SymtabShndxSD, Layout);
1197   }
1198   WriteSymbolTable(F, ShndxF, Asm, Layout, NumRegularSections);
1199   Asm.AddSectionToTheEnd(*Writer, SymtabSD, Layout);
1200
1201   F = new MCDataFragment(&StrtabSD);
1202   F->getContents().append(StringTable.begin(), StringTable.end());
1203   Asm.AddSectionToTheEnd(*Writer, StrtabSD, Layout);
1204
1205   F = new MCDataFragment(&ShstrtabSD);
1206
1207   // Section header string table.
1208   //
1209   // The first entry of a string table holds a null character so skip
1210   // section 0.
1211   uint64_t Index = 1;
1212   F->getContents() += '\x00';
1213
1214   for (MCAssembler::const_iterator it = Asm.begin(),
1215          ie = Asm.end(); it != ie; ++it) {
1216     const MCSectionELF &Section =
1217       static_cast<const MCSectionELF&>(it->getSection());
1218     // FIXME: We could merge suffixes like in .text and .rela.text.
1219
1220     // Remember the index into the string table so we can write it
1221     // into the sh_name field of the section header table.
1222     SectionStringTableIndex[&it->getSection()] = Index;
1223
1224     Index += Section.getSectionName().size() + 1;
1225     F->getContents() += Section.getSectionName();
1226     F->getContents() += '\x00';
1227   }
1228
1229   Asm.AddSectionToTheEnd(*Writer, ShstrtabSD, Layout);
1230 }
1231
1232 bool ELFObjectWriterImpl::IsFixupFullyResolved(const MCAssembler &Asm,
1233                                                const MCValue Target,
1234                                                bool IsPCRel,
1235                                                const MCFragment *DF) const {
1236   // If this is a PCrel relocation, find the section this fixup value is
1237   // relative to.
1238   const MCSection *BaseSection = 0;
1239   if (IsPCRel) {
1240     BaseSection = &DF->getParent()->getSection();
1241     assert(BaseSection);
1242   }
1243
1244   const MCSection *SectionA = 0;
1245   const MCSymbol *SymbolA = 0;
1246   if (const MCSymbolRefExpr *A = Target.getSymA()) {
1247     SymbolA = &A->getSymbol();
1248     SectionA = &SymbolA->getSection();
1249   }
1250
1251   const MCSection *SectionB = 0;
1252   if (const MCSymbolRefExpr *B = Target.getSymB()) {
1253     SectionB = &B->getSymbol().getSection();
1254   }
1255
1256   if (!BaseSection)
1257     return SectionA == SectionB;
1258
1259   const MCSymbolData &DataA = Asm.getSymbolData(*SymbolA);
1260   if (DataA.isExternal())
1261     return false;
1262
1263   return !SectionB && BaseSection == SectionA;
1264 }
1265
1266 void ELFObjectWriterImpl::WriteObject(MCAssembler &Asm,
1267                                       const MCAsmLayout &Layout) {
1268   // Compute symbol table information.
1269   ComputeSymbolTable(Asm);
1270
1271   CreateMetadataSections(const_cast<MCAssembler&>(Asm),
1272                          const_cast<MCAsmLayout&>(Layout));
1273
1274   // Add 1 for the null section.
1275   unsigned NumSections = Asm.size() + 1;
1276   uint64_t NaturalAlignment = Is64Bit ? 8 : 4;
1277   uint64_t HeaderSize = Is64Bit ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr);
1278   uint64_t FileOff = HeaderSize;
1279
1280   for (MCAssembler::const_iterator it = Asm.begin(),
1281          ie = Asm.end(); it != ie; ++it) {
1282     const MCSectionData &SD = *it;
1283
1284     FileOff = RoundUpToAlignment(FileOff, SD.getAlignment());
1285
1286     // Get the size of the section in the output file (including padding).
1287     uint64_t Size = Layout.getSectionFileSize(&SD);
1288
1289     FileOff += Size;
1290   }
1291
1292   FileOff = RoundUpToAlignment(FileOff, NaturalAlignment);
1293
1294   // Write out the ELF header ...
1295   WriteHeader(FileOff - HeaderSize, NumSections);
1296
1297   FileOff = HeaderSize;
1298
1299   // ... then all of the sections ...
1300   DenseMap<const MCSection*, uint64_t> SectionOffsetMap;
1301
1302   DenseMap<const MCSection*, uint32_t> SectionIndexMap;
1303
1304   unsigned Index = 1;
1305   for (MCAssembler::const_iterator it = Asm.begin(),
1306          ie = Asm.end(); it != ie; ++it) {
1307     const MCSectionData &SD = *it;
1308
1309     uint64_t Padding = OffsetToAlignment(FileOff, SD.getAlignment());
1310     WriteZeros(Padding);
1311     FileOff += Padding;
1312
1313     // Remember the offset into the file for this section.
1314     SectionOffsetMap[&it->getSection()] = FileOff;
1315     SectionIndexMap[&it->getSection()] = Index++;
1316
1317     FileOff += Layout.getSectionFileSize(&SD);
1318
1319     Asm.WriteSectionData(it, Layout, Writer);
1320   }
1321
1322   uint64_t Padding = OffsetToAlignment(FileOff, NaturalAlignment);
1323   WriteZeros(Padding);
1324   FileOff += Padding;
1325
1326   // ... and then the section header table.
1327   // Should we align the section header table?
1328   //
1329   // Null section first.
1330   uint64_t FirstSectionSize =
1331     NumSections >= ELF::SHN_LORESERVE ? NumSections : 0;
1332   uint32_t FirstSectionLink =
1333     ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0;
1334   WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0);
1335
1336   for (MCAssembler::const_iterator it = Asm.begin(),
1337          ie = Asm.end(); it != ie; ++it) {
1338     const MCSectionData &SD = *it;
1339     const MCSectionELF &Section =
1340       static_cast<const MCSectionELF&>(SD.getSection());
1341
1342     uint64_t sh_link = 0;
1343     uint64_t sh_info = 0;
1344
1345     switch(Section.getType()) {
1346     case ELF::SHT_DYNAMIC:
1347       sh_link = SectionStringTableIndex[&it->getSection()];
1348       sh_info = 0;
1349       break;
1350
1351     case ELF::SHT_REL:
1352     case ELF::SHT_RELA: {
1353       const MCSection *SymtabSection;
1354       const MCSection *InfoSection;
1355
1356       SymtabSection = Asm.getContext().getELFSection(".symtab", ELF::SHT_SYMTAB, 0,
1357                                                      SectionKind::getReadOnly(),
1358                                                      false);
1359       sh_link = SectionIndexMap[SymtabSection];
1360
1361       // Remove ".rel" and ".rela" prefixes.
1362       unsigned SecNameLen = (Section.getType() == ELF::SHT_REL) ? 4 : 5;
1363       StringRef SectionName = Section.getSectionName().substr(SecNameLen);
1364
1365       InfoSection = Asm.getContext().getELFSection(SectionName,
1366                                                    ELF::SHT_PROGBITS, 0,
1367                                                    SectionKind::getReadOnly(),
1368                                                    false);
1369       sh_info = SectionIndexMap[InfoSection];
1370       break;
1371     }
1372
1373     case ELF::SHT_SYMTAB:
1374     case ELF::SHT_DYNSYM:
1375       sh_link = StringTableIndex;
1376       sh_info = LastLocalSymbolIndex;
1377       break;
1378
1379     case ELF::SHT_SYMTAB_SHNDX:
1380       sh_link = SymbolTableIndex;
1381       break;
1382
1383     case ELF::SHT_PROGBITS:
1384     case ELF::SHT_STRTAB:
1385     case ELF::SHT_NOBITS:
1386     case ELF::SHT_NULL:
1387     case ELF::SHT_ARM_ATTRIBUTES:
1388       // Nothing to do.
1389       break;
1390
1391     default:
1392       assert(0 && "FIXME: sh_type value not supported!");
1393       break;
1394     }
1395
1396     WriteSecHdrEntry(SectionStringTableIndex[&it->getSection()],
1397                      Section.getType(), Section.getFlags(),
1398                      0,
1399                      SectionOffsetMap.lookup(&SD.getSection()),
1400                      Layout.getSectionSize(&SD), sh_link,
1401                      sh_info, SD.getAlignment(),
1402                      Section.getEntrySize());
1403   }
1404 }
1405
1406 ELFObjectWriter::ELFObjectWriter(raw_ostream &OS,
1407                                  bool Is64Bit,
1408                                  Triple::OSType OSType,
1409                                  uint16_t EMachine,
1410                                  bool IsLittleEndian,
1411                                  bool HasRelocationAddend)
1412   : MCObjectWriter(OS, IsLittleEndian)
1413 {
1414   Impl = new ELFObjectWriterImpl(this, Is64Bit, EMachine,
1415                                  HasRelocationAddend, OSType);
1416 }
1417
1418 ELFObjectWriter::~ELFObjectWriter() {
1419   delete (ELFObjectWriterImpl*) Impl;
1420 }
1421
1422 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm) {
1423   ((ELFObjectWriterImpl*) Impl)->ExecutePostLayoutBinding(Asm);
1424 }
1425
1426 void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm,
1427                                        const MCAsmLayout &Layout,
1428                                        const MCFragment *Fragment,
1429                                        const MCFixup &Fixup, MCValue Target,
1430                                        uint64_t &FixedValue) {
1431   ((ELFObjectWriterImpl*) Impl)->RecordRelocation(Asm, Layout, Fragment, Fixup,
1432                                                   Target, FixedValue);
1433 }
1434
1435 bool ELFObjectWriter::IsFixupFullyResolved(const MCAssembler &Asm,
1436                                            const MCValue Target,
1437                                            bool IsPCRel,
1438                                            const MCFragment *DF) const {
1439   return ((ELFObjectWriterImpl*) Impl)->IsFixupFullyResolved(Asm, Target,
1440                                                              IsPCRel, DF);
1441 }
1442
1443 void ELFObjectWriter::WriteObject(MCAssembler &Asm,
1444                                   const MCAsmLayout &Layout) {
1445   ((ELFObjectWriterImpl*) Impl)->WriteObject(Asm, Layout);
1446 }