lib/MC/MCMachOStreamer.cpp

   1 //===- lib/MC/MCMachOStreamer.cpp - Mach-O 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 #include "llvm/MC/MCStreamer.h"
  11
  12 #include "llvm/MC/MCAssembler.h"
  13 #include "llvm/MC/MCContext.h"
  14 #include "llvm/MC/MCCodeEmitter.h"
  15 #include "llvm/MC/MCExpr.h"
  16 #include "llvm/MC/MCInst.h"
  17 #include "llvm/MC/MCObjectStreamer.h"
  18 #include "llvm/MC/MCSection.h"
  19 #include "llvm/MC/MCSymbol.h"
  20 #include "llvm/MC/MCMachOSymbolFlags.h"
  21 #include "llvm/MC/MCSectionMachO.h"
  22 #include "llvm/MC/MCDwarf.h"
  23 #include "llvm/Support/ErrorHandling.h"
  24 #include "llvm/Support/raw_ostream.h"
  25 #include "llvm/Target/TargetAsmBackend.h"
  26
  27 using namespace llvm;
  28
  29 namespace {
  30
  31 class MCMachOStreamer : public MCObjectStreamer {
  32 private:
  33   void EmitInstToFragment(const MCInst &Inst);
  34   void EmitInstToData(const MCInst &Inst);
  35   // FIXME: These will likely moved to a better place.
  36   void MakeLineEntryForSection(const MCSection *Section);
  37   const MCExpr * MakeStartMinusEndExpr(MCSymbol *Start, MCSymbol *End,
  38                                                         int IntVal);
  39   void EmitDwarfFileTable(void);
  40
  41 public:
  42   MCMachOStreamer(MCContext &Context, TargetAsmBackend &TAB,
  43                   raw_ostream &OS, MCCodeEmitter *Emitter)
  44     : MCObjectStreamer(Context, TAB, OS, Emitter, true) {}
  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 EmitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute);
  54   virtual void EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue);
  55   virtual void EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
  56                                 unsigned ByteAlignment);
  57   virtual void BeginCOFFSymbolDef(const MCSymbol *Symbol) {
  58     assert(0 && "macho doesn't support this directive");
  59   }
  60   virtual void EmitCOFFSymbolStorageClass(int StorageClass) {
  61     assert(0 && "macho doesn't support this directive");
  62   }
  63   virtual void EmitCOFFSymbolType(int Type) {
  64     assert(0 && "macho doesn't support this directive");
  65   }
  66   virtual void EndCOFFSymbolDef() {
  67     assert(0 && "macho doesn't support this directive");
  68   }
  69   virtual void EmitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
  70     assert(0 && "macho doesn't support this directive");
  71   }
  72   virtual void EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size) {
  73     assert(0 && "macho doesn't support this directive");
  74   }
  75   virtual void EmitZerofill(const MCSection *Section, MCSymbol *Symbol = 0,
  76                             unsigned Size = 0, unsigned ByteAlignment = 0);
  77   virtual void EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol,
  78                               uint64_t Size, unsigned ByteAlignment = 0);
  79   virtual void EmitBytes(StringRef Data, unsigned AddrSpace);
  80   virtual void EmitValue(const MCExpr *Value, unsigned Size,unsigned AddrSpace);
  81   virtual void EmitGPRel32Value(const MCExpr *Value) {
  82     assert(0 && "macho doesn't support this directive");
  83   }
  84   virtual void EmitValueToAlignment(unsigned ByteAlignment, int64_t Value = 0,
  85                                     unsigned ValueSize = 1,
  86                                     unsigned MaxBytesToEmit = 0);
  87   virtual void EmitCodeAlignment(unsigned ByteAlignment,
  88                                  unsigned MaxBytesToEmit = 0);
  89   virtual void EmitValueToOffset(const MCExpr *Offset,
  90                                  unsigned char Value = 0);
  91
  92   virtual void EmitFileDirective(StringRef Filename) {
  93     // FIXME: Just ignore the .file; it isn't important enough to fail the
  94     // entire assembly.
  95
  96     //report_fatal_error("unsupported directive: '.file'");
  97   }
  98   virtual void EmitDwarfFileDirective(unsigned FileNo, StringRef Filename) {
  99     // FIXME: Just ignore the .file; it isn't important enough to fail the
 100     // entire assembly.
 101
 102     //report_fatal_error("unsupported directive: '.file'");
 103   }
 104
 105   virtual void EmitInstruction(const MCInst &Inst);
 106
 107   virtual void Finish();
 108
 109   /// @}
 110 };
 111
 112 } // end anonymous namespace.
 113
 114 void MCMachOStreamer::InitSections() {
 115   SwitchSection(getContext().getMachOSection("__TEXT", "__text",
 116                                     MCSectionMachO::S_ATTR_PURE_INSTRUCTIONS,
 117                                     0, SectionKind::getText()));
 118
 119 }
 120
 121 void MCMachOStreamer::EmitLabel(MCSymbol *Symbol) {
 122   // TODO: This is almost exactly the same as WinCOFFStreamer. Consider merging
 123   // into MCObjectStreamer.
 124   assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
 125   assert(!Symbol->isVariable() && "Cannot emit a variable symbol!");
 126   assert(CurSection && "Cannot emit before setting section!");
 127
 128   Symbol->setSection(*CurSection);
 129
 130   MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
 131
 132   // We have to create a new fragment if this is an atom defining symbol,
 133   // fragments cannot span atoms.
 134   if (getAssembler().isSymbolLinkerVisible(SD.getSymbol()))
 135     new MCDataFragment(getCurrentSectionData());
 136
 137   // FIXME: This is wasteful, we don't necessarily need to create a data
 138   // fragment. Instead, we should mark the symbol as pointing into the data
 139   // fragment if it exists, otherwise we should just queue the label and set its
 140   // fragment pointer when we emit the next fragment.
 141   MCDataFragment *F = getOrCreateDataFragment();
 142   assert(!SD.getFragment() && "Unexpected fragment on symbol data!");
 143   SD.setFragment(F);
 144   SD.setOffset(F->getContents().size());
 145
 146   // This causes the reference type flag to be cleared. Darwin 'as' was "trying"
 147   // to clear the weak reference and weak definition bits too, but the
 148   // implementation was buggy. For now we just try to match 'as', for
 149   // diffability.
 150   //
 151   // FIXME: Cleanup this code, these bits should be emitted based on semantic
 152   // properties, not on the order of definition, etc.
 153   SD.setFlags(SD.getFlags() & ~SF_ReferenceTypeMask);
 154 }
 155
 156 void MCMachOStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
 157   switch (Flag) {
 158   case MCAF_SubsectionsViaSymbols:
 159     getAssembler().setSubsectionsViaSymbols(true);
 160     return;
 161   default:
 162     llvm_unreachable("invalid assembler flag!");
 163   }
 164 }
 165
 166 void MCMachOStreamer::EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) {
 167   // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
 168   // MCObjectStreamer.
 169   // FIXME: Lift context changes into super class.
 170   getAssembler().getOrCreateSymbolData(*Symbol);
 171   Symbol->setVariableValue(AddValueSymbols(Value));
 172 }
 173
 174 void MCMachOStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
 175                                           MCSymbolAttr Attribute) {
 176   // Indirect symbols are handled differently, to match how 'as' handles
 177   // them. This makes writing matching .o files easier.
 178   if (Attribute == MCSA_IndirectSymbol) {
 179     // Note that we intentionally cannot use the symbol data here; this is
 180     // important for matching the string table that 'as' generates.
 181     IndirectSymbolData ISD;
 182     ISD.Symbol = Symbol;
 183     ISD.SectionData = getCurrentSectionData();
 184     getAssembler().getIndirectSymbols().push_back(ISD);
 185     return;
 186   }
 187
 188   // Adding a symbol attribute always introduces the symbol, note that an
 189   // important side effect of calling getOrCreateSymbolData here is to register
 190   // the symbol with the assembler.
 191   MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
 192
 193   // The implementation of symbol attributes is designed to match 'as', but it
 194   // leaves much to desired. It doesn't really make sense to arbitrarily add and
 195   // remove flags, but 'as' allows this (in particular, see .desc).
 196   //
 197   // In the future it might be worth trying to make these operations more well
 198   // defined.
 199   switch (Attribute) {
 200   case MCSA_Invalid:
 201   case MCSA_ELF_TypeFunction:
 202   case MCSA_ELF_TypeIndFunction:
 203   case MCSA_ELF_TypeObject:
 204   case MCSA_ELF_TypeTLS:
 205   case MCSA_ELF_TypeCommon:
 206   case MCSA_ELF_TypeNoType:
 207   case MCSA_IndirectSymbol:
 208   case MCSA_Hidden:
 209   case MCSA_Internal:
 210   case MCSA_Protected:
 211   case MCSA_Weak:
 212   case MCSA_Local:
 213     assert(0 && "Invalid symbol attribute for Mach-O!");
 214     break;
 215
 216   case MCSA_Global:
 217     SD.setExternal(true);
 218     // This effectively clears the undefined lazy bit, in Darwin 'as', although
 219     // it isn't very consistent because it implements this as part of symbol
 220     // lookup.
 221     //
 222     // FIXME: Cleanup this code, these bits should be emitted based on semantic
 223     // properties, not on the order of definition, etc.
 224     SD.setFlags(SD.getFlags() & ~SF_ReferenceTypeUndefinedLazy);
 225     break;
 226
 227   case MCSA_LazyReference:
 228     // FIXME: This requires -dynamic.
 229     SD.setFlags(SD.getFlags() | SF_NoDeadStrip);
 230     if (Symbol->isUndefined())
 231       SD.setFlags(SD.getFlags() | SF_ReferenceTypeUndefinedLazy);
 232     break;
 233
 234     // Since .reference sets the no dead strip bit, it is equivalent to
 235     // .no_dead_strip in practice.
 236   case MCSA_Reference:
 237   case MCSA_NoDeadStrip:
 238     SD.setFlags(SD.getFlags() | SF_NoDeadStrip);
 239     break;
 240
 241   case MCSA_PrivateExtern:
 242     SD.setExternal(true);
 243     SD.setPrivateExtern(true);
 244     break;
 245
 246   case MCSA_WeakReference:
 247     // FIXME: This requires -dynamic.
 248     if (Symbol->isUndefined())
 249       SD.setFlags(SD.getFlags() | SF_WeakReference);
 250     break;
 251
 252   case MCSA_WeakDefinition:
 253     // FIXME: 'as' enforces that this is defined and global. The manual claims
 254     // it has to be in a coalesced section, but this isn't enforced.
 255     SD.setFlags(SD.getFlags() | SF_WeakDefinition);
 256     break;
 257
 258   case MCSA_WeakDefAutoPrivate:
 259     SD.setFlags(SD.getFlags() | SF_WeakDefinition | SF_WeakReference);
 260     break;
 261   }
 262 }
 263
 264 void MCMachOStreamer::EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
 265   // Encode the 'desc' value into the lowest implementation defined bits.
 266   assert(DescValue == (DescValue & SF_DescFlagsMask) &&
 267          "Invalid .desc value!");
 268   getAssembler().getOrCreateSymbolData(*Symbol).setFlags(
 269     DescValue & SF_DescFlagsMask);
 270 }
 271
 272 void MCMachOStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
 273                                        unsigned ByteAlignment) {
 274   // FIXME: Darwin 'as' does appear to allow redef of a .comm by itself.
 275   assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
 276
 277   MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
 278   SD.setExternal(true);
 279   SD.setCommon(Size, ByteAlignment);
 280 }
 281
 282 void MCMachOStreamer::EmitZerofill(const MCSection *Section, MCSymbol *Symbol,
 283                                    unsigned Size, unsigned ByteAlignment) {
 284   MCSectionData &SectData = getAssembler().getOrCreateSectionData(*Section);
 285
 286   // The symbol may not be present, which only creates the section.
 287   if (!Symbol)
 288     return;
 289
 290   // FIXME: Assert that this section has the zerofill type.
 291
 292   assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
 293
 294   MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
 295
 296   // Emit an align fragment if necessary.
 297   if (ByteAlignment != 1)
 298     new MCAlignFragment(ByteAlignment, 0, 0, ByteAlignment, &SectData);
 299
 300   MCFragment *F = new MCFillFragment(0, 0, Size, &SectData);
 301   SD.setFragment(F);
 302
 303   Symbol->setSection(*Section);
 304
 305   // Update the maximum alignment on the zero fill section if necessary.
 306   if (ByteAlignment > SectData.getAlignment())
 307     SectData.setAlignment(ByteAlignment);
 308 }
 309
 310 // This should always be called with the thread local bss section.  Like the
 311 // .zerofill directive this doesn't actually switch sections on us.
 312 void MCMachOStreamer::EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol,
 313                                      uint64_t Size, unsigned ByteAlignment) {
 314   EmitZerofill(Section, Symbol, Size, ByteAlignment);
 315   return;
 316 }
 317
 318 void MCMachOStreamer::EmitBytes(StringRef Data, unsigned AddrSpace) {
 319   // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
 320   // MCObjectStreamer.
 321   getOrCreateDataFragment()->getContents().append(Data.begin(), Data.end());
 322 }
 323
 324 void MCMachOStreamer::EmitValue(const MCExpr *Value, unsigned Size,
 325                                 unsigned AddrSpace) {
 326   // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
 327   // MCObjectStreamer.
 328   MCDataFragment *DF = getOrCreateDataFragment();
 329
 330   // Avoid fixups when possible.
 331   int64_t AbsValue;
 332   if (AddValueSymbols(Value)->EvaluateAsAbsolute(AbsValue)) {
 333     // FIXME: Endianness assumption.
 334     for (unsigned i = 0; i != Size; ++i)
 335       DF->getContents().push_back(uint8_t(AbsValue >> (i * 8)));
 336   } else {
 337     DF->addFixup(MCFixup::Create(DF->getContents().size(),
 338                                  AddValueSymbols(Value),
 339                                  MCFixup::getKindForSize(Size)));
 340     DF->getContents().resize(DF->getContents().size() + Size, 0);
 341   }
 342 }
 343
 344 void MCMachOStreamer::EmitValueToAlignment(unsigned ByteAlignment,
 345                                            int64_t Value, unsigned ValueSize,
 346                                            unsigned MaxBytesToEmit) {
 347   // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
 348   // MCObjectStreamer.
 349   if (MaxBytesToEmit == 0)
 350     MaxBytesToEmit = ByteAlignment;
 351   new MCAlignFragment(ByteAlignment, Value, ValueSize, MaxBytesToEmit,
 352                       getCurrentSectionData());
 353
 354   // Update the maximum alignment on the current section if necessary.
 355   if (ByteAlignment > getCurrentSectionData()->getAlignment())
 356     getCurrentSectionData()->setAlignment(ByteAlignment);
 357 }
 358
 359 void MCMachOStreamer::EmitCodeAlignment(unsigned ByteAlignment,
 360                                         unsigned MaxBytesToEmit) {
 361   // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
 362   // MCObjectStreamer.
 363   if (MaxBytesToEmit == 0)
 364     MaxBytesToEmit = ByteAlignment;
 365   MCAlignFragment *F = new MCAlignFragment(ByteAlignment, 0, 1, MaxBytesToEmit,
 366                                            getCurrentSectionData());
 367   F->setEmitNops(true);
 368
 369   // Update the maximum alignment on the current section if necessary.
 370   if (ByteAlignment > getCurrentSectionData()->getAlignment())
 371     getCurrentSectionData()->setAlignment(ByteAlignment);
 372 }
 373
 374 void MCMachOStreamer::EmitValueToOffset(const MCExpr *Offset,
 375                                         unsigned char Value) {
 376   new MCOrgFragment(*Offset, Value, getCurrentSectionData());
 377 }
 378
 379 void MCMachOStreamer::EmitInstToFragment(const MCInst &Inst) {
 380   MCInstFragment *IF = new MCInstFragment(Inst, getCurrentSectionData());
 381
 382   // Add the fixups and data.
 383   //
 384   // FIXME: Revisit this design decision when relaxation is done, we may be
 385   // able to get away with not storing any extra data in the MCInst.
 386   SmallVector<MCFixup, 4> Fixups;
 387   SmallString<256> Code;
 388   raw_svector_ostream VecOS(Code);
 389   getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
 390   VecOS.flush();
 391
 392   IF->getCode() = Code;
 393   IF->getFixups() = Fixups;
 394 }
 395
 396 void MCMachOStreamer::EmitInstToData(const MCInst &Inst) {
 397   MCDataFragment *DF = getOrCreateDataFragment();
 398
 399   SmallVector<MCFixup, 4> Fixups;
 400   SmallString<256> Code;
 401   raw_svector_ostream VecOS(Code);
 402   getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
 403   VecOS.flush();
 404
 405   // Add the fixups and data.
 406   for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
 407     Fixups[i].setOffset(Fixups[i].getOffset() + DF->getContents().size());
 408     DF->addFixup(Fixups[i]);
 409   }
 410   DF->getContents().append(Code.begin(), Code.end());
 411 }
 412
 413 void MCMachOStreamer::EmitInstruction(const MCInst &Inst) {
 414   // Scan for values.
 415   for (unsigned i = Inst.getNumOperands(); i--; )
 416     if (Inst.getOperand(i).isExpr())
 417       AddValueSymbols(Inst.getOperand(i).getExpr());
 418
 419   getCurrentSectionData()->setHasInstructions(true);
 420
 421   // Now that a machine instruction has been assembled into this section, make
 422   // a line entry for any .loc directive that has been seen.
 423   MakeLineEntryForSection(getCurrentSection());
 424
 425   // If this instruction doesn't need relaxation, just emit it as data.
 426   if (!getAssembler().getBackend().MayNeedRelaxation(Inst)) {
 427     EmitInstToData(Inst);
 428     return;
 429   }
 430
 431   // Otherwise, if we are relaxing everything, relax the instruction as much as
 432   // possible and emit it as data.
 433   if (getAssembler().getRelaxAll()) {
 434     MCInst Relaxed;
 435     getAssembler().getBackend().RelaxInstruction(Inst, Relaxed);
 436     while (getAssembler().getBackend().MayNeedRelaxation(Relaxed))
 437       getAssembler().getBackend().RelaxInstruction(Relaxed, Relaxed);
 438     EmitInstToData(Relaxed);
 439     return;
 440   }
 441
 442   // Otherwise emit to a separate fragment.
 443   EmitInstToFragment(Inst);
 444 }
 445
 446 //
 447 // This is called when an instruction is assembled into the specified section
 448 // and if there is information from the last .loc directive that has yet to have
 449 // a line entry made for it is made.
 450 //
 451 void MCMachOStreamer::MakeLineEntryForSection(const MCSection *Section) {
 452   if (!getContext().getDwarfLocSeen())
 453     return;
 454
 455   // Create a symbol at in the current section for use in the line entry.
 456   MCSymbol *LineSym = getContext().CreateTempSymbol();
 457   // Set the value of the symbol to use for the MCLineEntry.
 458   EmitLabel(LineSym);
 459
 460   // Get the current .loc info saved in the context.
 461   const MCDwarfLoc &DwarfLoc = getContext().getCurrentDwarfLoc();
 462
 463   // Create a (local) line entry with the symbol and the current .loc info.
 464   MCLineEntry LineEntry(LineSym, DwarfLoc);
 465
 466   // clear DwarfLocSeen saying the current .loc info is now used.
 467   getContext().clearDwarfLocSeen();
 468
 469   // Get the MCLineSection for this section, if one does not exist for this
 470   // section create it.
 471   DenseMap<const MCSection *, MCLineSection *> &MCLineSections =
 472     getContext().getMCLineSections();
 473   MCLineSection *LineSection = MCLineSections[Section];
 474   if (!LineSection) {
 475     // Create a new MCLineSection.  This will be deleted after the dwarf line
 476     // table is created using it by iterating through the MCLineSections
 477     // DenseMap.
 478     LineSection = new MCLineSection;
 479     // Save a pointer to the new LineSection into the MCLineSections DenseMap.
 480     MCLineSections[Section] = LineSection;
 481   }
 482
 483   // Add the line entry to this section's entries.
 484   LineSection->addLineEntry(LineEntry);
 485 }
 486
 487 //
 488 // This helper routine returns an expression of End - Start + IntVal for use
 489 // by EmitDwarfFileTable() below.
 490 //
 491 const MCExpr * MCMachOStreamer::MakeStartMinusEndExpr(MCSymbol *Start,
 492                                                       MCSymbol *End,
 493                                                       int IntVal) {
 494   MCSymbolRefExpr::VariantKind Variant = MCSymbolRefExpr::VK_None;
 495   const MCExpr *Res =
 496     MCSymbolRefExpr::Create(End, Variant, getContext());
 497   const MCExpr *RHS =
 498     MCSymbolRefExpr::Create(Start, Variant, getContext());
 499   const MCExpr *Res1 =
 500     MCBinaryExpr::Create(MCBinaryExpr::Sub, Res, RHS,getContext());
 501   const MCExpr *Res2 =
 502     MCConstantExpr::Create(IntVal, getContext());
 503   const MCExpr *Res3 =
 504     MCBinaryExpr::Create(MCBinaryExpr::Sub, Res1, Res2, getContext());
 505   return Res3;
 506 }
 507
 508 //
 509 // This emits the Dwarf file (and eventually the line) table.
 510 //
 511 void MCMachOStreamer::EmitDwarfFileTable(void) {
 512   // For now make sure we don't put out the Dwarf file table if no .file
 513   // directives were seen.
 514   const std::vector<MCDwarfFile *> &MCDwarfFiles =
 515     getContext().getMCDwarfFiles();
 516   if (MCDwarfFiles.size() == 0)
 517     return;
 518
 519   // This is the Mach-O section, for ELF it is the .debug_line section.
 520   SwitchSection(getContext().getMachOSection("__DWARF", "__debug_line",
 521                                          MCSectionMachO::S_ATTR_DEBUG,
 522                                          0, SectionKind::getDataRelLocal()));
 523
 524   // Create a symbol at the beginning of this section.
 525   MCSymbol *LineStartSym = getContext().CreateTempSymbol();
 526   // Set the value of the symbol, as we are at the start of the section.
 527   EmitLabel(LineStartSym);
 528
 529   // Create a symbol for the end of the section (to be set when we get there).
 530   MCSymbol *LineEndSym = getContext().CreateTempSymbol();
 531
 532   // The first 4 bytes is the total length of the information for this
 533   // compilation unit (not including these 4 bytes for the length).
 534   EmitValue(MakeStartMinusEndExpr(LineStartSym, LineEndSym, 4), 4, 0);
 535
 536   // Next 2 bytes is the Version, which is Dwarf 2.
 537   EmitIntValue(2, 2);
 538
 539   // Create a symbol for the end of the prologue (to be set when we get there).
 540   MCSymbol *ProEndSym = getContext().CreateTempSymbol(); // Lprologue_end
 541
 542   // Length of the prologue, is the next 4 bytes.  Which is the start of the
 543   // section to the end of the prologue.  Not including the 4 bytes for the
 544   // total length, the 2 bytes for the version, and these 4 bytes for the
 545   // length of the prologue.
 546   EmitValue(MakeStartMinusEndExpr(LineStartSym, ProEndSym, (4 + 2 + 4)), 4, 0);
 547
 548   // Parameters of the state machine, are next.
 549   //  Define the architecture-dependent minimum instruction length (in
 550   //  bytes).  This value should be rather too small than too big.  */
 551   //  DWARF2_LINE_MIN_INSN_LENGTH
 552   EmitIntValue(1, 1);
 553   //  Flag that indicates the initial value of the is_stmt_start flag.
 554   //  DWARF2_LINE_DEFAULT_IS_STMT
 555   EmitIntValue(1, 1);
 556   //  Minimum line offset in a special line info. opcode.  This value
 557   //  was chosen to give a reasonable range of values.  */
 558   //  DWARF2_LINE_BASE
 559   EmitIntValue(uint64_t(-5), 1);
 560   //  Range of line offsets in a special line info. opcode.
 561   //  DWARF2_LINE_RANGE
 562   EmitIntValue(14, 1);
 563   //  First special line opcode - leave room for the standard opcodes.
 564   //  DWARF2_LINE_OPCODE_BASE
 565   EmitIntValue(13, 1);
 566
 567   // Standard opcode lengths
 568   EmitIntValue(0, 1); // length of DW_LNS_copy
 569   EmitIntValue(1, 1); // length of DW_LNS_advance_pc
 570   EmitIntValue(1, 1); // length of DW_LNS_advance_line
 571   EmitIntValue(1, 1); // length of DW_LNS_set_file
 572   EmitIntValue(1, 1); // length of DW_LNS_set_column
 573   EmitIntValue(0, 1); // length of DW_LNS_negate_stmt
 574   EmitIntValue(0, 1); // length of DW_LNS_set_basic_block
 575   EmitIntValue(0, 1); // length of DW_LNS_const_add_pc
 576   EmitIntValue(1, 1); // length of DW_LNS_fixed_advance_pc
 577   EmitIntValue(0, 1); // length of DW_LNS_set_prologue_end
 578   EmitIntValue(0, 1); // length of DW_LNS_set_epilogue_begin
 579   EmitIntValue(1, 1); // DW_LNS_set_isa
 580
 581   // Put out the directory and file tables.
 582
 583   // First the directory table.
 584   const std::vector<StringRef> &MCDwarfDirs =
 585     getContext().getMCDwarfDirs();
 586   for (unsigned i = 0; i < MCDwarfDirs.size(); i++) {
 587     EmitBytes(MCDwarfDirs[i], 0); // the DirectoryName
 588     EmitBytes(StringRef("\0", 1), 0); // the null termination of the string
 589   }
 590   EmitIntValue(0, 1); // Terminate the directory list
 591
 592   // Second the file table.
 593   for (unsigned i = 1; i < MCDwarfFiles.size(); i++) {
 594     EmitBytes(MCDwarfFiles[i]->getName(), 0); // FileName
 595     EmitBytes(StringRef("\0", 1), 0); // the null termination of the string
 596     // FIXME the Directory number should be a .uleb128 not a .byte
 597     EmitIntValue(MCDwarfFiles[i]->getDirIndex(), 1);
 598     EmitIntValue(0, 1); // last modification timestamp (always 0)
 599     EmitIntValue(0, 1); // filesize (always 0)
 600   }
 601   EmitIntValue(0, 1); // Terminate the file list
 602
 603   // This is the end of the prologue, so set the value of the symbol at the
 604   // end of the prologue (that was used in a previous expression).
 605   EmitLabel(ProEndSym);
 606
 607   // TODO: This is the point where the line tables would be emitted.
 608
 609   // Delete the MCLineSections that were created in
 610   // MCMachOStreamer::MakeLineEntryForSection() and used to emit the line
 611   // tables.
 612   DenseMap<const MCSection *, MCLineSection *> &MCLineSections =
 613     getContext().getMCLineSections();
 614   for (DenseMap<const MCSection *, MCLineSection *>::iterator it =
 615         MCLineSections.begin(), ie = MCLineSections.end(); it != ie; ++it) {
 616     delete it->second;
 617   }
 618
 619   // If there are no line tables emited then we emit:
 620   // The following DW_LNE_set_address sequence to set the address to zero
 621   //   TODO test for 32-bit or 64-bit output
 622   //     This is the sequence for 32-bit code
 623   EmitIntValue(0, 1);
 624   EmitIntValue(5, 1);
 625   EmitIntValue(2, 1);
 626   EmitIntValue(0, 1);
 627   EmitIntValue(0, 1);
 628   EmitIntValue(0, 1);
 629   EmitIntValue(0, 1);
 630
 631   // Lastly emit the DW_LNE_end_sequence which consists of 3 bytes '00 01 01'
 632   // (00 is the code for extended opcodes, followed by a ULEB128 length of the
 633   // extended opcode (01), and the DW_LNE_end_sequence (01).
 634   EmitIntValue(0, 1); // DW_LNS_extended_op
 635   EmitIntValue(1, 1); // ULEB128 length of the extended opcode
 636   EmitIntValue(1, 1); // DW_LNE_end_sequence
 637
 638   // This is the end of the section, so set the value of the symbol at the end
 639   // of this section (that was used in a previous expression).
 640   EmitLabel(LineEndSym);
 641 }
 642
 643 void MCMachOStreamer::Finish() {
 644   // Dump out the dwarf file and directory tables (soon to include line table)
 645   EmitDwarfFileTable();
 646
 647   // We have to set the fragment atom associations so we can relax properly for
 648   // Mach-O.
 649
 650   // First, scan the symbol table to build a lookup table from fragments to
 651   // defining symbols.
 652   DenseMap<const MCFragment*, MCSymbolData*> DefiningSymbolMap;
 653   for (MCAssembler::symbol_iterator it = getAssembler().symbol_begin(),
 654          ie = getAssembler().symbol_end(); it != ie; ++it) {
 655     if (getAssembler().isSymbolLinkerVisible(it->getSymbol()) &&
 656         it->getFragment()) {
 657       // An atom defining symbol should never be internal to a fragment.
 658       assert(it->getOffset() == 0 && "Invalid offset in atom defining symbol!");
 659       DefiningSymbolMap[it->getFragment()] = it;
 660     }
 661   }
 662
 663   // Set the fragment atom associations by tracking the last seen atom defining
 664   // symbol.
 665   for (MCAssembler::iterator it = getAssembler().begin(),
 666          ie = getAssembler().end(); it != ie; ++it) {
 667     MCSymbolData *CurrentAtom = 0;
 668     for (MCSectionData::iterator it2 = it->begin(),
 669            ie2 = it->end(); it2 != ie2; ++it2) {
 670       if (MCSymbolData *SD = DefiningSymbolMap.lookup(it2))
 671         CurrentAtom = SD;
 672       it2->setAtom(CurrentAtom);
 673     }
 674   }
 675
 676   this->MCObjectStreamer::Finish();
 677 }
 678
 679 MCStreamer *llvm::createMachOStreamer(MCContext &Context, TargetAsmBackend &TAB,
 680                                       raw_ostream &OS, MCCodeEmitter *CE,
 681                                       bool RelaxAll) {
 682   MCMachOStreamer *S = new MCMachOStreamer(Context, TAB, OS, CE);
 683   if (RelaxAll)
 684     S->getAssembler().setRelaxAll(true);
 685   return S;
 686 }