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/Dwarf.h"
  24 #include "llvm/Support/ErrorHandling.h"
  25 #include "llvm/Support/raw_ostream.h"
  26 #include "llvm/Target/TargetAsmBackend.h"
  27
  28 using namespace llvm;
  29
  30 namespace {
  31
  32 class MCMachOStreamer : public MCObjectStreamer {
  33 private:
  34   virtual void EmitInstToFragment(const MCInst &Inst);
  35   virtual void EmitInstToData(const MCInst &Inst);
  36
  37 public:
  38   MCMachOStreamer(MCContext &Context, TargetAsmBackend &TAB,
  39                   raw_ostream &OS, MCCodeEmitter *Emitter)
  40     : MCObjectStreamer(Context, TAB, OS, Emitter, true) {}
  41
  42   /// @name MCStreamer Interface
  43   /// @{
  44
  45   virtual void InitSections();
  46   virtual void EmitLabel(MCSymbol *Symbol);
  47   virtual void EmitAssemblerFlag(MCAssemblerFlag Flag);
  48   virtual void EmitAssignment(MCSymbol *Symbol, const MCExpr *Value);
  49   virtual void EmitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute);
  50   virtual void EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue);
  51   virtual void EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
  52                                 unsigned ByteAlignment);
  53   virtual void BeginCOFFSymbolDef(const MCSymbol *Symbol) {
  54     assert(0 && "macho doesn't support this directive");
  55   }
  56   virtual void EmitCOFFSymbolStorageClass(int StorageClass) {
  57     assert(0 && "macho doesn't support this directive");
  58   }
  59   virtual void EmitCOFFSymbolType(int Type) {
  60     assert(0 && "macho doesn't support this directive");
  61   }
  62   virtual void EndCOFFSymbolDef() {
  63     assert(0 && "macho doesn't support this directive");
  64   }
  65   virtual void EmitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
  66     assert(0 && "macho doesn't support this directive");
  67   }
  68   virtual void EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size) {
  69     assert(0 && "macho doesn't support this directive");
  70   }
  71   virtual void EmitZerofill(const MCSection *Section, MCSymbol *Symbol = 0,
  72                             unsigned Size = 0, unsigned ByteAlignment = 0);
  73   virtual void EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol,
  74                               uint64_t Size, unsigned ByteAlignment = 0);
  75   virtual void EmitBytes(StringRef Data, unsigned AddrSpace);
  76   virtual void EmitValue(const MCExpr *Value, unsigned Size,unsigned AddrSpace);
  77   virtual void EmitGPRel32Value(const MCExpr *Value) {
  78     assert(0 && "macho doesn't support this directive");
  79   }
  80   virtual void EmitValueToAlignment(unsigned ByteAlignment, int64_t Value = 0,
  81                                     unsigned ValueSize = 1,
  82                                     unsigned MaxBytesToEmit = 0);
  83   virtual void EmitCodeAlignment(unsigned ByteAlignment,
  84                                  unsigned MaxBytesToEmit = 0);
  85   virtual void EmitValueToOffset(const MCExpr *Offset,
  86                                  unsigned char Value = 0);
  87
  88   virtual void EmitFileDirective(StringRef Filename) {
  89     // FIXME: Just ignore the .file; it isn't important enough to fail the
  90     // entire assembly.
  91
  92     //report_fatal_error("unsupported directive: '.file'");
  93   }
  94   virtual void EmitDwarfFileDirective(unsigned FileNo, StringRef Filename) {
  95     // FIXME: Just ignore the .file; it isn't important enough to fail the
  96     // entire assembly.
  97
  98     //report_fatal_error("unsupported directive: '.file'");
  99   }
 100
 101   virtual void Finish();
 102
 103   /// @}
 104 };
 105
 106 } // end anonymous namespace.
 107
 108 void MCMachOStreamer::InitSections() {
 109   SwitchSection(getContext().getMachOSection("__TEXT", "__text",
 110                                     MCSectionMachO::S_ATTR_PURE_INSTRUCTIONS,
 111                                     0, SectionKind::getText()));
 112
 113 }
 114
 115 void MCMachOStreamer::EmitLabel(MCSymbol *Symbol) {
 116   // TODO: This is almost exactly the same as WinCOFFStreamer. Consider merging
 117   // into MCObjectStreamer.
 118   assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
 119   assert(!Symbol->isVariable() && "Cannot emit a variable symbol!");
 120   assert(CurSection && "Cannot emit before setting section!");
 121
 122   Symbol->setSection(*CurSection);
 123
 124   MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
 125
 126   // We have to create a new fragment if this is an atom defining symbol,
 127   // fragments cannot span atoms.
 128   if (getAssembler().isSymbolLinkerVisible(SD.getSymbol()))
 129     new MCDataFragment(getCurrentSectionData());
 130
 131   // FIXME: This is wasteful, we don't necessarily need to create a data
 132   // fragment. Instead, we should mark the symbol as pointing into the data
 133   // fragment if it exists, otherwise we should just queue the label and set its
 134   // fragment pointer when we emit the next fragment.
 135   MCDataFragment *F = getOrCreateDataFragment();
 136   assert(!SD.getFragment() && "Unexpected fragment on symbol data!");
 137   SD.setFragment(F);
 138   SD.setOffset(F->getContents().size());
 139
 140   // This causes the reference type flag to be cleared. Darwin 'as' was "trying"
 141   // to clear the weak reference and weak definition bits too, but the
 142   // implementation was buggy. For now we just try to match 'as', for
 143   // diffability.
 144   //
 145   // FIXME: Cleanup this code, these bits should be emitted based on semantic
 146   // properties, not on the order of definition, etc.
 147   SD.setFlags(SD.getFlags() & ~SF_ReferenceTypeMask);
 148 }
 149
 150 void MCMachOStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
 151   switch (Flag) {
 152   case MCAF_SubsectionsViaSymbols:
 153     getAssembler().setSubsectionsViaSymbols(true);
 154     return;
 155   default:
 156     llvm_unreachable("invalid assembler flag!");
 157   }
 158 }
 159
 160 void MCMachOStreamer::EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) {
 161   // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
 162   // MCObjectStreamer.
 163   // FIXME: Lift context changes into super class.
 164   getAssembler().getOrCreateSymbolData(*Symbol);
 165   Symbol->setVariableValue(AddValueSymbols(Value));
 166 }
 167
 168 void MCMachOStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
 169                                           MCSymbolAttr Attribute) {
 170   // Indirect symbols are handled differently, to match how 'as' handles
 171   // them. This makes writing matching .o files easier.
 172   if (Attribute == MCSA_IndirectSymbol) {
 173     // Note that we intentionally cannot use the symbol data here; this is
 174     // important for matching the string table that 'as' generates.
 175     IndirectSymbolData ISD;
 176     ISD.Symbol = Symbol;
 177     ISD.SectionData = getCurrentSectionData();
 178     getAssembler().getIndirectSymbols().push_back(ISD);
 179     return;
 180   }
 181
 182   // Adding a symbol attribute always introduces the symbol, note that an
 183   // important side effect of calling getOrCreateSymbolData here is to register
 184   // the symbol with the assembler.
 185   MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
 186
 187   // The implementation of symbol attributes is designed to match 'as', but it
 188   // leaves much to desired. It doesn't really make sense to arbitrarily add and
 189   // remove flags, but 'as' allows this (in particular, see .desc).
 190   //
 191   // In the future it might be worth trying to make these operations more well
 192   // defined.
 193   switch (Attribute) {
 194   case MCSA_Invalid:
 195   case MCSA_ELF_TypeFunction:
 196   case MCSA_ELF_TypeIndFunction:
 197   case MCSA_ELF_TypeObject:
 198   case MCSA_ELF_TypeTLS:
 199   case MCSA_ELF_TypeCommon:
 200   case MCSA_ELF_TypeNoType:
 201   case MCSA_IndirectSymbol:
 202   case MCSA_Hidden:
 203   case MCSA_Internal:
 204   case MCSA_Protected:
 205   case MCSA_Weak:
 206   case MCSA_Local:
 207     assert(0 && "Invalid symbol attribute for Mach-O!");
 208     break;
 209
 210   case MCSA_Global:
 211     SD.setExternal(true);
 212     // This effectively clears the undefined lazy bit, in Darwin 'as', although
 213     // it isn't very consistent because it implements this as part of symbol
 214     // lookup.
 215     //
 216     // FIXME: Cleanup this code, these bits should be emitted based on semantic
 217     // properties, not on the order of definition, etc.
 218     SD.setFlags(SD.getFlags() & ~SF_ReferenceTypeUndefinedLazy);
 219     break;
 220
 221   case MCSA_LazyReference:
 222     // FIXME: This requires -dynamic.
 223     SD.setFlags(SD.getFlags() | SF_NoDeadStrip);
 224     if (Symbol->isUndefined())
 225       SD.setFlags(SD.getFlags() | SF_ReferenceTypeUndefinedLazy);
 226     break;
 227
 228     // Since .reference sets the no dead strip bit, it is equivalent to
 229     // .no_dead_strip in practice.
 230   case MCSA_Reference:
 231   case MCSA_NoDeadStrip:
 232     SD.setFlags(SD.getFlags() | SF_NoDeadStrip);
 233     break;
 234
 235   case MCSA_PrivateExtern:
 236     SD.setExternal(true);
 237     SD.setPrivateExtern(true);
 238     break;
 239
 240   case MCSA_WeakReference:
 241     // FIXME: This requires -dynamic.
 242     if (Symbol->isUndefined())
 243       SD.setFlags(SD.getFlags() | SF_WeakReference);
 244     break;
 245
 246   case MCSA_WeakDefinition:
 247     // FIXME: 'as' enforces that this is defined and global. The manual claims
 248     // it has to be in a coalesced section, but this isn't enforced.
 249     SD.setFlags(SD.getFlags() | SF_WeakDefinition);
 250     break;
 251
 252   case MCSA_WeakDefAutoPrivate:
 253     SD.setFlags(SD.getFlags() | SF_WeakDefinition | SF_WeakReference);
 254     break;
 255   }
 256 }
 257
 258 void MCMachOStreamer::EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
 259   // Encode the 'desc' value into the lowest implementation defined bits.
 260   assert(DescValue == (DescValue & SF_DescFlagsMask) &&
 261          "Invalid .desc value!");
 262   getAssembler().getOrCreateSymbolData(*Symbol).setFlags(
 263     DescValue & SF_DescFlagsMask);
 264 }
 265
 266 void MCMachOStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
 267                                        unsigned ByteAlignment) {
 268   // FIXME: Darwin 'as' does appear to allow redef of a .comm by itself.
 269   assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
 270
 271   MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
 272   SD.setExternal(true);
 273   SD.setCommon(Size, ByteAlignment);
 274 }
 275
 276 void MCMachOStreamer::EmitZerofill(const MCSection *Section, MCSymbol *Symbol,
 277                                    unsigned Size, unsigned ByteAlignment) {
 278   MCSectionData &SectData = getAssembler().getOrCreateSectionData(*Section);
 279
 280   // The symbol may not be present, which only creates the section.
 281   if (!Symbol)
 282     return;
 283
 284   // FIXME: Assert that this section has the zerofill type.
 285
 286   assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
 287
 288   MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
 289
 290   // Emit an align fragment if necessary.
 291   if (ByteAlignment != 1)
 292     new MCAlignFragment(ByteAlignment, 0, 0, ByteAlignment, &SectData);
 293
 294   MCFragment *F = new MCFillFragment(0, 0, Size, &SectData);
 295   SD.setFragment(F);
 296
 297   Symbol->setSection(*Section);
 298
 299   // Update the maximum alignment on the zero fill section if necessary.
 300   if (ByteAlignment > SectData.getAlignment())
 301     SectData.setAlignment(ByteAlignment);
 302 }
 303
 304 // This should always be called with the thread local bss section.  Like the
 305 // .zerofill directive this doesn't actually switch sections on us.
 306 void MCMachOStreamer::EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol,
 307                                      uint64_t Size, unsigned ByteAlignment) {
 308   EmitZerofill(Section, Symbol, Size, ByteAlignment);
 309   return;
 310 }
 311
 312 void MCMachOStreamer::EmitBytes(StringRef Data, unsigned AddrSpace) {
 313   // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
 314   // MCObjectStreamer.
 315   getOrCreateDataFragment()->getContents().append(Data.begin(), Data.end());
 316 }
 317
 318 void MCMachOStreamer::EmitValue(const MCExpr *Value, unsigned Size,
 319                                 unsigned AddrSpace) {
 320   // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
 321   // MCObjectStreamer.
 322   MCDataFragment *DF = getOrCreateDataFragment();
 323
 324   // Avoid fixups when possible.
 325   int64_t AbsValue;
 326   if (AddValueSymbols(Value)->EvaluateAsAbsolute(AbsValue)) {
 327     // FIXME: Endianness assumption.
 328     for (unsigned i = 0; i != Size; ++i)
 329       DF->getContents().push_back(uint8_t(AbsValue >> (i * 8)));
 330   } else {
 331     DF->addFixup(MCFixup::Create(DF->getContents().size(),
 332                                  AddValueSymbols(Value),
 333                                  MCFixup::getKindForSize(Size)));
 334     DF->getContents().resize(DF->getContents().size() + Size, 0);
 335   }
 336 }
 337
 338 void MCMachOStreamer::EmitValueToAlignment(unsigned ByteAlignment,
 339                                            int64_t Value, unsigned ValueSize,
 340                                            unsigned MaxBytesToEmit) {
 341   // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
 342   // MCObjectStreamer.
 343   if (MaxBytesToEmit == 0)
 344     MaxBytesToEmit = ByteAlignment;
 345   new MCAlignFragment(ByteAlignment, Value, ValueSize, MaxBytesToEmit,
 346                       getCurrentSectionData());
 347
 348   // Update the maximum alignment on the current section if necessary.
 349   if (ByteAlignment > getCurrentSectionData()->getAlignment())
 350     getCurrentSectionData()->setAlignment(ByteAlignment);
 351 }
 352
 353 void MCMachOStreamer::EmitCodeAlignment(unsigned ByteAlignment,
 354                                         unsigned MaxBytesToEmit) {
 355   // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
 356   // MCObjectStreamer.
 357   if (MaxBytesToEmit == 0)
 358     MaxBytesToEmit = ByteAlignment;
 359   MCAlignFragment *F = new MCAlignFragment(ByteAlignment, 0, 1, MaxBytesToEmit,
 360                                            getCurrentSectionData());
 361   F->setEmitNops(true);
 362
 363   // Update the maximum alignment on the current section if necessary.
 364   if (ByteAlignment > getCurrentSectionData()->getAlignment())
 365     getCurrentSectionData()->setAlignment(ByteAlignment);
 366 }
 367
 368 void MCMachOStreamer::EmitValueToOffset(const MCExpr *Offset,
 369                                         unsigned char Value) {
 370   new MCOrgFragment(*Offset, Value, getCurrentSectionData());
 371 }
 372
 373 void MCMachOStreamer::EmitInstToFragment(const MCInst &Inst) {
 374   MCInstFragment *IF = new MCInstFragment(Inst, getCurrentSectionData());
 375
 376   // Add the fixups and data.
 377   //
 378   // FIXME: Revisit this design decision when relaxation is done, we may be
 379   // able to get away with not storing any extra data in the MCInst.
 380   SmallVector<MCFixup, 4> Fixups;
 381   SmallString<256> Code;
 382   raw_svector_ostream VecOS(Code);
 383   getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
 384   VecOS.flush();
 385
 386   IF->getCode() = Code;
 387   IF->getFixups() = Fixups;
 388 }
 389
 390 void MCMachOStreamer::EmitInstToData(const MCInst &Inst) {
 391   MCDataFragment *DF = getOrCreateDataFragment();
 392
 393   SmallVector<MCFixup, 4> Fixups;
 394   SmallString<256> Code;
 395   raw_svector_ostream VecOS(Code);
 396   getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
 397   VecOS.flush();
 398
 399   // Add the fixups and data.
 400   for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
 401     Fixups[i].setOffset(Fixups[i].getOffset() + DF->getContents().size());
 402     DF->addFixup(Fixups[i]);
 403   }
 404   DF->getContents().append(Code.begin(), Code.end());
 405 }
 406
 407 void MCMachOStreamer::Finish() {
 408   // Dump out the dwarf file & directory tables and line tables.
 409   if (getContext().hasDwarfFiles()) {
 410     const MCSection *DwarfLineSection = getContext().getMachOSection("__DWARF",
 411                                          "__debug_line",
 412                                          MCSectionMachO::S_ATTR_DEBUG,
 413                                          0, SectionKind::getDataRelLocal());
 414     MCDwarfFileTable::Emit(this, DwarfLineSection);
 415   }
 416
 417   // We have to set the fragment atom associations so we can relax properly for
 418   // Mach-O.
 419
 420   // First, scan the symbol table to build a lookup table from fragments to
 421   // defining symbols.
 422   DenseMap<const MCFragment*, MCSymbolData*> DefiningSymbolMap;
 423   for (MCAssembler::symbol_iterator it = getAssembler().symbol_begin(),
 424          ie = getAssembler().symbol_end(); it != ie; ++it) {
 425     if (getAssembler().isSymbolLinkerVisible(it->getSymbol()) &&
 426         it->getFragment()) {
 427       // An atom defining symbol should never be internal to a fragment.
 428       assert(it->getOffset() == 0 && "Invalid offset in atom defining symbol!");
 429       DefiningSymbolMap[it->getFragment()] = it;
 430     }
 431   }
 432
 433   // Set the fragment atom associations by tracking the last seen atom defining
 434   // symbol.
 435   for (MCAssembler::iterator it = getAssembler().begin(),
 436          ie = getAssembler().end(); it != ie; ++it) {
 437     MCSymbolData *CurrentAtom = 0;
 438     for (MCSectionData::iterator it2 = it->begin(),
 439            ie2 = it->end(); it2 != ie2; ++it2) {
 440       if (MCSymbolData *SD = DefiningSymbolMap.lookup(it2))
 441         CurrentAtom = SD;
 442       it2->setAtom(CurrentAtom);
 443     }
 444   }
 445
 446   this->MCObjectStreamer::Finish();
 447 }
 448
 449 MCStreamer *llvm::createMachOStreamer(MCContext &Context, TargetAsmBackend &TAB,
 450                                       raw_ostream &OS, MCCodeEmitter *CE,
 451                                       bool RelaxAll) {
 452   MCMachOStreamer *S = new MCMachOStreamer(Context, TAB, OS, CE);
 453   if (RelaxAll)
 454     S->getAssembler().setRelaxAll(true);
 455   return S;
 456 }