lib/MC/MCELFStreamer.cpp

   1 //===- lib/MC/MCELFStreamer.cpp - ELF Object Output ------------===//
   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 assembles .s files and emits ELF .o object files.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "llvm/MC/MCStreamer.h"
  15
  16 #include "llvm/ADT/SmallPtrSet.h"
  17 #include "llvm/MC/MCAssembler.h"
  18 #include "llvm/MC/MCContext.h"
  19 #include "llvm/MC/MCCodeEmitter.h"
  20 #include "llvm/MC/MCELFSymbolFlags.h"
  21 #include "llvm/MC/MCExpr.h"
  22 #include "llvm/MC/MCInst.h"
  23 #include "llvm/MC/MCObjectStreamer.h"
  24 #include "llvm/MC/MCSection.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/ELF.h"
  30 #include "llvm/Support/ErrorHandling.h"
  31 #include "llvm/Support/raw_ostream.h"
  32 #include "llvm/Target/TargetAsmBackend.h"
  33
  34 using namespace llvm;
  35
  36 namespace {
  37
  38 class MCELFStreamer : public MCObjectStreamer {
  39 public:
  40   MCELFStreamer(MCContext &Context, TargetAsmBackend &TAB,
  41                   raw_ostream &OS, MCCodeEmitter *Emitter)
  42     : MCObjectStreamer(Context, TAB, OS, Emitter, false) {}
  43
  44   ~MCELFStreamer() {}
  45
  46   /// @name MCStreamer Interface
  47   /// @{
  48
  49   virtual void InitSections();
  50   virtual void EmitLabel(MCSymbol *Symbol);
  51   virtual void EmitAssemblerFlag(MCAssemblerFlag Flag);
  52   virtual void EmitAssignment(MCSymbol *Symbol, const MCExpr *Value);
  53   virtual void EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol);
  54   virtual void EmitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute);
  55   virtual void EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
  56     assert(0 && "ELF doesn't support this directive");
  57   }
  58   virtual void EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
  59                                 unsigned ByteAlignment);
  60   virtual void BeginCOFFSymbolDef(const MCSymbol *Symbol) {
  61     assert(0 && "ELF doesn't support this directive");
  62   }
  63
  64   virtual void EmitCOFFSymbolStorageClass(int StorageClass) {
  65     assert(0 && "ELF doesn't support this directive");
  66   }
  67
  68   virtual void EmitCOFFSymbolType(int Type) {
  69     assert(0 && "ELF doesn't support this directive");
  70   }
  71
  72   virtual void EndCOFFSymbolDef() {
  73     assert(0 && "ELF doesn't support this directive");
  74   }
  75
  76   virtual void EmitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
  77      MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
  78      SD.setSize(Value);
  79   }
  80
  81   virtual void EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size) {
  82     assert(0 && "ELF doesn't support this directive");
  83   }
  84   virtual void EmitZerofill(const MCSection *Section, MCSymbol *Symbol = 0,
  85                             unsigned Size = 0, unsigned ByteAlignment = 0) {
  86     assert(0 && "ELF doesn't support this directive");
  87   }
  88   virtual void EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol,
  89                               uint64_t Size, unsigned ByteAlignment = 0) {
  90     assert(0 && "ELF doesn't support this directive");
  91   }
  92   virtual void EmitBytes(StringRef Data, unsigned AddrSpace);
  93   virtual void EmitValue(const MCExpr *Value, unsigned Size,unsigned AddrSpace);
  94   virtual void EmitGPRel32Value(const MCExpr *Value) {
  95     assert(0 && "ELF doesn't support this directive");
  96   }
  97   virtual void EmitValueToAlignment(unsigned ByteAlignment, int64_t Value = 0,
  98                                     unsigned ValueSize = 1,
  99                                     unsigned MaxBytesToEmit = 0);
 100   virtual void EmitCodeAlignment(unsigned ByteAlignment,
 101                                  unsigned MaxBytesToEmit = 0);
 102   virtual void EmitValueToOffset(const MCExpr *Offset,
 103                                  unsigned char Value = 0);
 104
 105   virtual void EmitFileDirective(StringRef Filename);
 106   virtual void EmitDwarfFileDirective(unsigned FileNo, StringRef Filename) {
 107     DEBUG(dbgs() << "FIXME: MCELFStreamer:EmitDwarfFileDirective not implemented\n");
 108   }
 109
 110   virtual void Finish();
 111
 112 private:
 113   virtual void EmitInstToFragment(const MCInst &Inst);
 114   virtual void EmitInstToData(const MCInst &Inst);
 115
 116   struct LocalCommon {
 117     MCSymbolData *SD;
 118     uint64_t Size;
 119     unsigned ByteAlignment;
 120   };
 121   std::vector<LocalCommon> LocalCommons;
 122
 123   SmallPtrSet<MCSymbol *, 16> BindingExplicitlySet;
 124   /// @}
 125   void SetSection(StringRef Section, unsigned Type, unsigned Flags,
 126                   SectionKind Kind) {
 127     SwitchSection(getContext().getELFSection(Section, Type, Flags, Kind));
 128   }
 129
 130   void SetSectionData() {
 131     SetSection(".data", MCSectionELF::SHT_PROGBITS,
 132                MCSectionELF::SHF_WRITE |MCSectionELF::SHF_ALLOC,
 133                SectionKind::getDataRel());
 134     EmitCodeAlignment(4, 0);
 135   }
 136   void SetSectionText() {
 137     SetSection(".text", MCSectionELF::SHT_PROGBITS,
 138                MCSectionELF::SHF_EXECINSTR |
 139                MCSectionELF::SHF_ALLOC, SectionKind::getText());
 140     EmitCodeAlignment(4, 0);
 141   }
 142   void SetSectionBss() {
 143     SetSection(".bss", MCSectionELF::SHT_NOBITS,
 144                MCSectionELF::SHF_WRITE |
 145                MCSectionELF::SHF_ALLOC, SectionKind::getBSS());
 146     EmitCodeAlignment(4, 0);
 147   }
 148 };
 149
 150 } // end anonymous namespace.
 151
 152 void MCELFStreamer::InitSections() {
 153   // This emulates the same behavior of GNU as. This makes it easier
 154   // to compare the output as the major sections are in the same order.
 155   SetSectionText();
 156   SetSectionData();
 157   SetSectionBss();
 158   SetSectionText();
 159 }
 160
 161 void MCELFStreamer::EmitLabel(MCSymbol *Symbol) {
 162   assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
 163
 164   Symbol->setSection(*CurSection);
 165
 166   MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
 167
 168   // FIXME: This is wasteful, we don't necessarily need to create a data
 169   // fragment. Instead, we should mark the symbol as pointing into the data
 170   // fragment if it exists, otherwise we should just queue the label and set its
 171   // fragment pointer when we emit the next fragment.
 172   MCDataFragment *F = getOrCreateDataFragment();
 173
 174   assert(!SD.getFragment() && "Unexpected fragment on symbol data!");
 175   SD.setFragment(F);
 176   SD.setOffset(F->getContents().size());
 177 }
 178
 179 void MCELFStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
 180   switch (Flag) {
 181   case MCAF_SyntaxUnified:  return; // no-op here?
 182   case MCAF_SubsectionsViaSymbols:
 183     getAssembler().setSubsectionsViaSymbols(true);
 184     return;
 185   }
 186
 187   assert(0 && "invalid assembler flag!");
 188 }
 189
 190 void MCELFStreamer::EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) {
 191   // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
 192   // MCObjectStreamer.
 193   // FIXME: Lift context changes into super class.
 194   getAssembler().getOrCreateSymbolData(*Symbol);
 195   Symbol->setVariableValue(AddValueSymbols(Value));
 196 }
 197
 198 // This is a hack. To be able to implement weakrefs the writer has to be able
 199 // to distinguish
 200 //    .weakref foo, bar
 201 //    .long foo
 202 // from
 203 //   .weakref foo, bar
 204 //   .long bar
 205 // since the first case should produce a weak undefined reference and the second
 206 // one a strong one.
 207 // If we created foo as a regular alias pointing to bar (foo = bar), then
 208 // MCExpr::EvaluateAsRelocatable would recurse on foo and the writer would
 209 // never see it used in a relocation.
 210 // What we do is create a MCTargetExpr that when evaluated produces a symbol
 211 // ref to a temporary symbol. This temporary symbol in turn is a variable
 212 // that equals the original symbol (tmp = bar). With this hack the writer
 213 // gets a relocation with tmp and can correctly implement weak references.
 214
 215 class WeakRefExpr : public MCTargetExpr {
 216 private:
 217   const MCSymbolRefExpr *Alias;
 218
 219   explicit WeakRefExpr(const MCSymbolRefExpr *Alias_)
 220     : MCTargetExpr(), Alias(Alias_) {}
 221
 222 public:
 223   virtual void PrintImpl(raw_ostream &OS) const {
 224     llvm_unreachable("Unimplemented");
 225   }
 226
 227   virtual bool EvaluateAsRelocatableImpl(MCValue &Res,
 228                                          const MCAsmLayout *Layout) const {
 229     Res = MCValue::get(Alias, 0, 0);
 230     return true;
 231   }
 232
 233   static const WeakRefExpr *Create(const MCSymbol *Alias, MCContext &Ctx) {
 234     const MCSymbolRefExpr *A = MCSymbolRefExpr::Create(Alias, Ctx);
 235     return new (Ctx) WeakRefExpr(A);
 236   }
 237 };
 238
 239 void MCELFStreamer::EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) {
 240   getAssembler().getOrCreateSymbolData(*Symbol);
 241   MCSymbolData &AliasSD = getAssembler().getOrCreateSymbolData(*Alias);
 242   AliasSD.setFlags(AliasSD.getFlags() | ELF_Other_Weakref);
 243
 244   // Create the alias that actually points to Symbol
 245   const MCSymbolRefExpr *SymRef = MCSymbolRefExpr::Create(Symbol, getContext());
 246   MCSymbol *RealAlias = getContext().CreateTempSymbol();
 247   RealAlias->setVariableValue(SymRef);
 248
 249   MCSymbolData &RealAliasSD = getAssembler().getOrCreateSymbolData(*RealAlias);
 250   RealAliasSD.setFlags(RealAliasSD.getFlags() | ELF_Other_Weakref);
 251
 252   const MCExpr *Value = WeakRefExpr::Create(RealAlias, getContext());
 253   Alias->setVariableValue(Value);
 254 }
 255
 256 static void SetBinding(MCSymbolData &SD, unsigned Binding) {
 257   assert(Binding == ELF::STB_LOCAL || Binding == ELF::STB_GLOBAL ||
 258          Binding == ELF::STB_WEAK);
 259   uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STB_Shift);
 260   SD.setFlags(OtherFlags | (Binding << ELF_STB_Shift));
 261 }
 262
 263 static unsigned GetBinding(const MCSymbolData &SD) {
 264   uint32_t Binding = (SD.getFlags() & (0xf << ELF_STB_Shift)) >> ELF_STB_Shift;
 265   assert(Binding == ELF::STB_LOCAL || Binding == ELF::STB_GLOBAL ||
 266          Binding == ELF::STB_WEAK);
 267   return Binding;
 268 }
 269
 270 static void SetType(MCSymbolData &SD, unsigned Type) {
 271   assert(Type == ELF::STT_NOTYPE || Type == ELF::STT_OBJECT ||
 272          Type == ELF::STT_FUNC || Type == ELF::STT_SECTION ||
 273          Type == ELF::STT_FILE || Type == ELF::STT_COMMON ||
 274          Type == ELF::STT_TLS);
 275
 276   uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STT_Shift);
 277   SD.setFlags(OtherFlags | (Type << ELF_STT_Shift));
 278 }
 279
 280 static void SetVisibility(MCSymbolData &SD, unsigned Visibility) {
 281   assert(Visibility == ELF::STV_DEFAULT || Visibility == ELF::STV_INTERNAL ||
 282          Visibility == ELF::STV_HIDDEN || Visibility == ELF::STV_PROTECTED);
 283
 284   uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STV_Shift);
 285   SD.setFlags(OtherFlags | (Visibility << ELF_STV_Shift));
 286 }
 287
 288 void MCELFStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
 289                                           MCSymbolAttr Attribute) {
 290   // Indirect symbols are handled differently, to match how 'as' handles
 291   // them. This makes writing matching .o files easier.
 292   if (Attribute == MCSA_IndirectSymbol) {
 293     // Note that we intentionally cannot use the symbol data here; this is
 294     // important for matching the string table that 'as' generates.
 295     IndirectSymbolData ISD;
 296     ISD.Symbol = Symbol;
 297     ISD.SectionData = getCurrentSectionData();
 298     getAssembler().getIndirectSymbols().push_back(ISD);
 299     return;
 300   }
 301
 302   // Adding a symbol attribute always introduces the symbol, note that an
 303   // important side effect of calling getOrCreateSymbolData here is to register
 304   // the symbol with the assembler.
 305   MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
 306
 307   // The implementation of symbol attributes is designed to match 'as', but it
 308   // leaves much to desired. It doesn't really make sense to arbitrarily add and
 309   // remove flags, but 'as' allows this (in particular, see .desc).
 310   //
 311   // In the future it might be worth trying to make these operations more well
 312   // defined.
 313   switch (Attribute) {
 314   case MCSA_LazyReference:
 315   case MCSA_Reference:
 316   case MCSA_NoDeadStrip:
 317   case MCSA_PrivateExtern:
 318   case MCSA_WeakDefinition:
 319   case MCSA_WeakDefAutoPrivate:
 320   case MCSA_Invalid:
 321   case MCSA_ELF_TypeIndFunction:
 322   case MCSA_IndirectSymbol:
 323     assert(0 && "Invalid symbol attribute for ELF!");
 324     break;
 325
 326   case MCSA_Global:
 327     SetBinding(SD, ELF::STB_GLOBAL);
 328     SD.setExternal(true);
 329     BindingExplicitlySet.insert(Symbol);
 330     break;
 331
 332   case MCSA_WeakReference:
 333   case MCSA_Weak:
 334     SetBinding(SD, ELF::STB_WEAK);
 335     SD.setExternal(true);
 336     BindingExplicitlySet.insert(Symbol);
 337     break;
 338
 339   case MCSA_Local:
 340     SetBinding(SD, ELF::STB_LOCAL);
 341     SD.setExternal(false);
 342     BindingExplicitlySet.insert(Symbol);
 343     break;
 344
 345   case MCSA_ELF_TypeFunction:
 346     SetType(SD, ELF::STT_FUNC);
 347     break;
 348
 349   case MCSA_ELF_TypeObject:
 350     SetType(SD, ELF::STT_OBJECT);
 351     break;
 352
 353   case MCSA_ELF_TypeTLS:
 354     SetType(SD, ELF::STT_TLS);
 355     break;
 356
 357   case MCSA_ELF_TypeCommon:
 358     SetType(SD, ELF::STT_COMMON);
 359     break;
 360
 361   case MCSA_ELF_TypeNoType:
 362     SetType(SD, ELF::STT_NOTYPE);
 363     break;
 364
 365   case MCSA_Protected:
 366     SetVisibility(SD, ELF::STV_PROTECTED);
 367     break;
 368
 369   case MCSA_Hidden:
 370     SetVisibility(SD, ELF::STV_HIDDEN);
 371     break;
 372
 373   case MCSA_Internal:
 374     SetVisibility(SD, ELF::STV_INTERNAL);
 375     break;
 376   }
 377 }
 378
 379 void MCELFStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
 380                                        unsigned ByteAlignment) {
 381   MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
 382
 383   if (!BindingExplicitlySet.count(Symbol)) {
 384     SetBinding(SD, ELF::STB_GLOBAL);
 385     SD.setExternal(true);
 386   }
 387
 388   if (GetBinding(SD) == ELF_STB_Local) {
 389     const MCSection *Section = getAssembler().getContext().getELFSection(".bss",
 390                                                                     MCSectionELF::SHT_NOBITS,
 391                                                                     MCSectionELF::SHF_WRITE |
 392                                                                     MCSectionELF::SHF_ALLOC,
 393                                                                     SectionKind::getBSS());
 394     Symbol->setSection(*Section);
 395
 396     struct LocalCommon L = {&SD, Size, ByteAlignment};
 397     LocalCommons.push_back(L);
 398   } else {
 399     SD.setCommon(Size, ByteAlignment);
 400   }
 401
 402   SD.setSize(MCConstantExpr::Create(Size, getContext()));
 403 }
 404
 405 void MCELFStreamer::EmitBytes(StringRef Data, unsigned AddrSpace) {
 406   // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
 407   // MCObjectStreamer.
 408   getOrCreateDataFragment()->getContents().append(Data.begin(), Data.end());
 409 }
 410
 411 void MCELFStreamer::EmitValue(const MCExpr *Value, unsigned Size,
 412                                 unsigned AddrSpace) {
 413   // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
 414   // MCObjectStreamer.
 415   MCDataFragment *DF = getOrCreateDataFragment();
 416
 417   // Avoid fixups when possible.
 418   int64_t AbsValue;
 419   if (AddValueSymbols(Value)->EvaluateAsAbsolute(AbsValue)) {
 420     // FIXME: Endianness assumption.
 421     for (unsigned i = 0; i != Size; ++i)
 422       DF->getContents().push_back(uint8_t(AbsValue >> (i * 8)));
 423   } else {
 424     DF->addFixup(MCFixup::Create(DF->getContents().size(), AddValueSymbols(Value),
 425                                  MCFixup::getKindForSize(Size)));
 426     DF->getContents().resize(DF->getContents().size() + Size, 0);
 427   }
 428 }
 429
 430 void MCELFStreamer::EmitValueToAlignment(unsigned ByteAlignment,
 431                                            int64_t Value, unsigned ValueSize,
 432                                            unsigned MaxBytesToEmit) {
 433   // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
 434   // MCObjectStreamer.
 435   if (MaxBytesToEmit == 0)
 436     MaxBytesToEmit = ByteAlignment;
 437   new MCAlignFragment(ByteAlignment, Value, ValueSize, MaxBytesToEmit,
 438                       getCurrentSectionData());
 439
 440   // Update the maximum alignment on the current section if necessary.
 441   if (ByteAlignment > getCurrentSectionData()->getAlignment())
 442     getCurrentSectionData()->setAlignment(ByteAlignment);
 443 }
 444
 445 void MCELFStreamer::EmitCodeAlignment(unsigned ByteAlignment,
 446                                         unsigned MaxBytesToEmit) {
 447   // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
 448   // MCObjectStreamer.
 449   if (MaxBytesToEmit == 0)
 450     MaxBytesToEmit = ByteAlignment;
 451   MCAlignFragment *F = new MCAlignFragment(ByteAlignment, 0, 1, MaxBytesToEmit,
 452                                            getCurrentSectionData());
 453   F->setEmitNops(true);
 454
 455   // Update the maximum alignment on the current section if necessary.
 456   if (ByteAlignment > getCurrentSectionData()->getAlignment())
 457     getCurrentSectionData()->setAlignment(ByteAlignment);
 458 }
 459
 460 void MCELFStreamer::EmitValueToOffset(const MCExpr *Offset,
 461                                         unsigned char Value) {
 462   // TODO: This is exactly the same as MCMachOStreamer. Consider merging into
 463   // MCObjectStreamer.
 464   new MCOrgFragment(*Offset, Value, getCurrentSectionData());
 465 }
 466
 467 // Add a symbol for the file name of this module. This is the second
 468 // entry in the module's symbol table (the first being the null symbol).
 469 void MCELFStreamer::EmitFileDirective(StringRef Filename) {
 470   MCSymbol *Symbol = getAssembler().getContext().GetOrCreateSymbol(Filename);
 471   Symbol->setSection(*CurSection);
 472   Symbol->setAbsolute();
 473
 474   MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
 475
 476   SD.setFlags(ELF_STT_File | ELF_STB_Local | ELF_STV_Default);
 477 }
 478
 479 void MCELFStreamer::EmitInstToFragment(const MCInst &Inst) {
 480   MCInstFragment *IF = new MCInstFragment(Inst, getCurrentSectionData());
 481
 482   // Add the fixups and data.
 483   //
 484   // FIXME: Revisit this design decision when relaxation is done, we may be
 485   // able to get away with not storing any extra data in the MCInst.
 486   SmallVector<MCFixup, 4> Fixups;
 487   SmallString<256> Code;
 488   raw_svector_ostream VecOS(Code);
 489   getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
 490   VecOS.flush();
 491
 492   IF->getCode() = Code;
 493   IF->getFixups() = Fixups;
 494 }
 495
 496 void MCELFStreamer::EmitInstToData(const MCInst &Inst) {
 497   MCDataFragment *DF = getOrCreateDataFragment();
 498
 499   SmallVector<MCFixup, 4> Fixups;
 500   SmallString<256> Code;
 501   raw_svector_ostream VecOS(Code);
 502   getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
 503   VecOS.flush();
 504
 505   // Add the fixups and data.
 506   for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
 507     Fixups[i].setOffset(Fixups[i].getOffset() + DF->getContents().size());
 508     DF->addFixup(Fixups[i]);
 509   }
 510   DF->getContents().append(Code.begin(), Code.end());
 511 }
 512
 513 void MCELFStreamer::Finish() {
 514   // FIXME: duplicated code with the MachO streamer.
 515   // Dump out the dwarf file & directory tables and line tables.
 516   if (getContext().hasDwarfFiles()) {
 517     const MCSection *DwarfLineSection =
 518       getContext().getELFSection(".debug_line", 0, 0,
 519                                  SectionKind::getDataRelLocal());
 520     MCDwarfFileTable::Emit(this, DwarfLineSection);
 521   }
 522
 523   for (std::vector<LocalCommon>::const_iterator i = LocalCommons.begin(),
 524                                                 e = LocalCommons.end();
 525        i != e; ++i) {
 526     MCSymbolData *SD = i->SD;
 527     uint64_t Size = i->Size;
 528     unsigned ByteAlignment = i->ByteAlignment;
 529     const MCSymbol &Symbol = SD->getSymbol();
 530     const MCSection &Section = Symbol.getSection();
 531
 532     MCSectionData &SectData = getAssembler().getOrCreateSectionData(Section);
 533     new MCAlignFragment(ByteAlignment, 0, 1, ByteAlignment, &SectData);
 534
 535     MCFragment *F = new MCFillFragment(0, 0, Size, &SectData);
 536     SD->setFragment(F);
 537
 538     // Update the maximum alignment of the section if necessary.
 539     if (ByteAlignment > SectData.getAlignment())
 540       SectData.setAlignment(ByteAlignment);
 541   }
 542
 543   this->MCObjectStreamer::Finish();
 544 }
 545
 546 MCStreamer *llvm::createELFStreamer(MCContext &Context, TargetAsmBackend &TAB,
 547                                       raw_ostream &OS, MCCodeEmitter *CE,
 548                                       bool RelaxAll) {
 549   MCELFStreamer *S = new MCELFStreamer(Context, TAB, OS, CE);
 550   if (RelaxAll)
 551     S->getAssembler().setRelaxAll(true);
 552   return S;
 553 }