src/llvm/lib/MC/MCMachOStreamer.cpp

   1 //===-- MCMachOStreamer.cpp - MachO Streamer ------------------------------===//
   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 #include "llvm/ADT/DenseMap.h"
  12 #include "llvm/ADT/SmallVector.h"
  13 #include "llvm/MC/MCAsmBackend.h"
  14 #include "llvm/MC/MCAssembler.h"
  15 #include "llvm/MC/MCCodeEmitter.h"
  16 #include "llvm/MC/MCContext.h"
  17 #include "llvm/MC/MCDwarf.h"
  18 #include "llvm/MC/MCExpr.h"
  19 #include "llvm/MC/MCInst.h"
  20 #include "llvm/MC/MCLinkerOptimizationHint.h"
  21 #include "llvm/MC/MCMachOSymbolFlags.h"
  22 #include "llvm/MC/MCObjectFileInfo.h"
  23 #include "llvm/MC/MCObjectStreamer.h"
  24 #include "llvm/MC/MCSection.h"
  25 #include "llvm/MC/MCSectionMachO.h"
  26 #include "llvm/MC/MCSymbol.h"
  27 #include "llvm/Support/Dwarf.h"
  28 #include "llvm/Support/ErrorHandling.h"
  29 #include "llvm/Support/raw_ostream.h"
  30
  31 using namespace llvm;
  32
  33 namespace {
  34
  35 class MCMachOStreamer : public MCObjectStreamer {
  36 private:
  37   /// LabelSections - true if each section change should emit a linker local
  38   /// label for use in relocations for assembler local references. Obviates the
  39   /// need for local relocations. False by default.
  40   bool LabelSections;
  41
  42   /// HasSectionLabel - map of which sections have already had a non-local
  43   /// label emitted to them. Used so we don't emit extraneous linker local
  44   /// labels in the middle of the section.
  45   DenseMap<const MCSection*, bool> HasSectionLabel;
  46
  47   void EmitInstToData(const MCInst &Inst, const MCSubtargetInfo &STI) override;
  48
  49   void EmitDataRegion(DataRegionData::KindTy Kind);
  50   void EmitDataRegionEnd();
  51
  52 public:
  53   MCMachOStreamer(MCContext &Context, MCAsmBackend &MAB, raw_ostream &OS,
  54                   MCCodeEmitter *Emitter, bool label)
  55       : MCObjectStreamer(Context, MAB, OS, Emitter),
  56         LabelSections(label) {}
  57
  58   /// state management
  59   void reset() override {
  60     HasSectionLabel.clear();
  61     MCObjectStreamer::reset();
  62   }
  63
  64   /// @name MCStreamer Interface
  65   /// @{
  66
  67   void ChangeSection(const MCSection *Sect, const MCExpr *Subsect) override;
  68   void EmitLabel(MCSymbol *Symbol) override;
  69   void EmitEHSymAttributes(const MCSymbol *Symbol, MCSymbol *EHSymbol) override;
  70   void EmitAssemblerFlag(MCAssemblerFlag Flag) override;
  71   void EmitLinkerOptions(ArrayRef<std::string> Options) override;
  72   void EmitDataRegion(MCDataRegionType Kind) override;
  73   void EmitVersionMin(MCVersionMinType Kind, unsigned Major,
  74                       unsigned Minor, unsigned Update) override;
  75   void EmitThumbFunc(MCSymbol *Func) override;
  76   bool EmitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute) override;
  77   void EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) override;
  78   void EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
  79                         unsigned ByteAlignment) override;
  80   void BeginCOFFSymbolDef(const MCSymbol *Symbol) override {
  81     llvm_unreachable("macho doesn't support this directive");
  82   }
  83   void EmitCOFFSymbolStorageClass(int StorageClass) override {
  84     llvm_unreachable("macho doesn't support this directive");
  85   }
  86   void EmitCOFFSymbolType(int Type) override {
  87     llvm_unreachable("macho doesn't support this directive");
  88   }
  89   void EndCOFFSymbolDef() override {
  90     llvm_unreachable("macho doesn't support this directive");
  91   }
  92   void EmitELFSize(MCSymbol *Symbol, const MCExpr *Value) override {
  93     llvm_unreachable("macho doesn't support this directive");
  94   }
  95   void EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
  96                              unsigned ByteAlignment) override;
  97   void EmitZerofill(const MCSection *Section, MCSymbol *Symbol = nullptr,
  98                     uint64_t Size = 0, unsigned ByteAlignment = 0) override;
  99   void EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol, uint64_t Size,
 100                       unsigned ByteAlignment = 0) override;
 101
 102   void EmitFileDirective(StringRef Filename) override {
 103     // FIXME: Just ignore the .file; it isn't important enough to fail the
 104     // entire assembly.
 105
 106     // report_fatal_error("unsupported directive: '.file'");
 107   }
 108
 109   void EmitIdent(StringRef IdentString) override {
 110     llvm_unreachable("macho doesn't support this directive");
 111   }
 112
 113   void EmitLOHDirective(MCLOHType Kind, const MCLOHArgs &Args) override {
 114     getAssembler().getLOHContainer().addDirective(Kind, Args);
 115   }
 116
 117   void FinishImpl() override;
 118 };
 119
 120 } // end anonymous namespace.
 121
 122 void MCMachOStreamer::ChangeSection(const MCSection *Section,
 123                                     const MCExpr *Subsection) {
 124   // Change the section normally.
 125   MCObjectStreamer::ChangeSection(Section, Subsection);
 126   // Output a linker-local symbol so we don't need section-relative local
 127   // relocations. The linker hates us when we do that.
 128   if (LabelSections && !HasSectionLabel[Section]) {
 129     MCSymbol *Label = getContext().CreateLinkerPrivateTempSymbol();
 130     EmitLabel(Label);
 131     HasSectionLabel[Section] = true;
 132   }
 133 }
 134
 135 void MCMachOStreamer::EmitEHSymAttributes(const MCSymbol *Symbol,
 136                                           MCSymbol *EHSymbol) {
 137   MCSymbolData &SD =
 138     getAssembler().getOrCreateSymbolData(*Symbol);
 139   if (SD.isExternal())
 140     EmitSymbolAttribute(EHSymbol, MCSA_Global);
 141   if (SD.getFlags() & SF_WeakDefinition)
 142     EmitSymbolAttribute(EHSymbol, MCSA_WeakDefinition);
 143   if (SD.isPrivateExtern())
 144     EmitSymbolAttribute(EHSymbol, MCSA_PrivateExtern);
 145 }
 146
 147 void MCMachOStreamer::EmitLabel(MCSymbol *Symbol) {
 148   assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
 149
 150   // isSymbolLinkerVisible uses the section.
 151   AssignSection(Symbol, getCurrentSection().first);
 152   // We have to create a new fragment if this is an atom defining symbol,
 153   // fragments cannot span atoms.
 154   if (getAssembler().isSymbolLinkerVisible(*Symbol))
 155     insert(new MCDataFragment());
 156
 157   MCObjectStreamer::EmitLabel(Symbol);
 158
 159   MCSymbolData &SD = getAssembler().getSymbolData(*Symbol);
 160   // This causes the reference type flag to be cleared. Darwin 'as' was "trying"
 161   // to clear the weak reference and weak definition bits too, but the
 162   // implementation was buggy. For now we just try to match 'as', for
 163   // diffability.
 164   //
 165   // FIXME: Cleanup this code, these bits should be emitted based on semantic
 166   // properties, not on the order of definition, etc.
 167   SD.setFlags(SD.getFlags() & ~SF_ReferenceTypeMask);
 168 }
 169
 170 void MCMachOStreamer::EmitDataRegion(DataRegionData::KindTy Kind) {
 171   if (!getAssembler().getBackend().hasDataInCodeSupport())
 172     return;
 173   // Create a temporary label to mark the start of the data region.
 174   MCSymbol *Start = getContext().CreateTempSymbol();
 175   EmitLabel(Start);
 176   // Record the region for the object writer to use.
 177   DataRegionData Data = { Kind, Start, nullptr };
 178   std::vector<DataRegionData> &Regions = getAssembler().getDataRegions();
 179   Regions.push_back(Data);
 180 }
 181
 182 void MCMachOStreamer::EmitDataRegionEnd() {
 183   if (!getAssembler().getBackend().hasDataInCodeSupport())
 184     return;
 185   std::vector<DataRegionData> &Regions = getAssembler().getDataRegions();
 186   assert(Regions.size() && "Mismatched .end_data_region!");
 187   DataRegionData &Data = Regions.back();
 188   assert(!Data.End && "Mismatched .end_data_region!");
 189   // Create a temporary label to mark the end of the data region.
 190   Data.End = getContext().CreateTempSymbol();
 191   EmitLabel(Data.End);
 192 }
 193
 194 void MCMachOStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
 195   // Let the target do whatever target specific stuff it needs to do.
 196   getAssembler().getBackend().handleAssemblerFlag(Flag);
 197   // Do any generic stuff we need to do.
 198   switch (Flag) {
 199   case MCAF_SyntaxUnified: return; // no-op here.
 200   case MCAF_Code16: return; // Change parsing mode; no-op here.
 201   case MCAF_Code32: return; // Change parsing mode; no-op here.
 202   case MCAF_Code64: return; // Change parsing mode; no-op here.
 203   case MCAF_SubsectionsViaSymbols:
 204     getAssembler().setSubsectionsViaSymbols(true);
 205     return;
 206   }
 207 }
 208
 209 void MCMachOStreamer::EmitLinkerOptions(ArrayRef<std::string> Options) {
 210   getAssembler().getLinkerOptions().push_back(Options);
 211 }
 212
 213 void MCMachOStreamer::EmitDataRegion(MCDataRegionType Kind) {
 214   switch (Kind) {
 215   case MCDR_DataRegion:
 216     EmitDataRegion(DataRegionData::Data);
 217     return;
 218   case MCDR_DataRegionJT8:
 219     EmitDataRegion(DataRegionData::JumpTable8);
 220     return;
 221   case MCDR_DataRegionJT16:
 222     EmitDataRegion(DataRegionData::JumpTable16);
 223     return;
 224   case MCDR_DataRegionJT32:
 225     EmitDataRegion(DataRegionData::JumpTable32);
 226     return;
 227   case MCDR_DataRegionEnd:
 228     EmitDataRegionEnd();
 229     return;
 230   }
 231 }
 232
 233 void MCMachOStreamer::EmitVersionMin(MCVersionMinType Kind, unsigned Major,
 234                                      unsigned Minor, unsigned Update) {
 235   getAssembler().setVersionMinInfo(Kind, Major, Minor, Update);
 236 }
 237
 238 void MCMachOStreamer::EmitThumbFunc(MCSymbol *Symbol) {
 239   // Remember that the function is a thumb function. Fixup and relocation
 240   // values will need adjusted.
 241   getAssembler().setIsThumbFunc(Symbol);
 242 }
 243
 244 bool MCMachOStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
 245                                           MCSymbolAttr Attribute) {
 246   // Indirect symbols are handled differently, to match how 'as' handles
 247   // them. This makes writing matching .o files easier.
 248   if (Attribute == MCSA_IndirectSymbol) {
 249     // Note that we intentionally cannot use the symbol data here; this is
 250     // important for matching the string table that 'as' generates.
 251     IndirectSymbolData ISD;
 252     ISD.Symbol = Symbol;
 253     ISD.SectionData = getCurrentSectionData();
 254     getAssembler().getIndirectSymbols().push_back(ISD);
 255     return true;
 256   }
 257
 258   // Adding a symbol attribute always introduces the symbol, note that an
 259   // important side effect of calling getOrCreateSymbolData here is to register
 260   // the symbol with the assembler.
 261   MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
 262
 263   // The implementation of symbol attributes is designed to match 'as', but it
 264   // leaves much to desired. It doesn't really make sense to arbitrarily add and
 265   // remove flags, but 'as' allows this (in particular, see .desc).
 266   //
 267   // In the future it might be worth trying to make these operations more well
 268   // defined.
 269   switch (Attribute) {
 270   case MCSA_Invalid:
 271   case MCSA_ELF_TypeFunction:
 272   case MCSA_ELF_TypeIndFunction:
 273   case MCSA_ELF_TypeObject:
 274   case MCSA_ELF_TypeTLS:
 275   case MCSA_ELF_TypeCommon:
 276   case MCSA_ELF_TypeNoType:
 277   case MCSA_ELF_TypeGnuUniqueObject:
 278   case MCSA_Hidden:
 279   case MCSA_IndirectSymbol:
 280   case MCSA_Internal:
 281   case MCSA_Protected:
 282   case MCSA_Weak:
 283   case MCSA_Local:
 284     return false;
 285
 286   case MCSA_Global:
 287     SD.setExternal(true);
 288     // This effectively clears the undefined lazy bit, in Darwin 'as', although
 289     // it isn't very consistent because it implements this as part of symbol
 290     // lookup.
 291     //
 292     // FIXME: Cleanup this code, these bits should be emitted based on semantic
 293     // properties, not on the order of definition, etc.
 294     SD.setFlags(SD.getFlags() & ~SF_ReferenceTypeUndefinedLazy);
 295     break;
 296
 297   case MCSA_LazyReference:
 298     // FIXME: This requires -dynamic.
 299     SD.setFlags(SD.getFlags() | SF_NoDeadStrip);
 300     if (Symbol->isUndefined())
 301       SD.setFlags(SD.getFlags() | SF_ReferenceTypeUndefinedLazy);
 302     break;
 303
 304     // Since .reference sets the no dead strip bit, it is equivalent to
 305     // .no_dead_strip in practice.
 306   case MCSA_Reference:
 307   case MCSA_NoDeadStrip:
 308     SD.setFlags(SD.getFlags() | SF_NoDeadStrip);
 309     break;
 310
 311   case MCSA_SymbolResolver:
 312     SD.setFlags(SD.getFlags() | SF_SymbolResolver);
 313     break;
 314
 315   case MCSA_PrivateExtern:
 316     SD.setExternal(true);
 317     SD.setPrivateExtern(true);
 318     break;
 319
 320   case MCSA_WeakReference:
 321     // FIXME: This requires -dynamic.
 322     if (Symbol->isUndefined())
 323       SD.setFlags(SD.getFlags() | SF_WeakReference);
 324     break;
 325
 326   case MCSA_WeakDefinition:
 327     // FIXME: 'as' enforces that this is defined and global. The manual claims
 328     // it has to be in a coalesced section, but this isn't enforced.
 329     SD.setFlags(SD.getFlags() | SF_WeakDefinition);
 330     break;
 331
 332   case MCSA_WeakDefAutoPrivate:
 333     SD.setFlags(SD.getFlags() | SF_WeakDefinition | SF_WeakReference);
 334     break;
 335   }
 336
 337   return true;
 338 }
 339
 340 void MCMachOStreamer::EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
 341   // Encode the 'desc' value into the lowest implementation defined bits.
 342   assert(DescValue == (DescValue & SF_DescFlagsMask) &&
 343          "Invalid .desc value!");
 344   getAssembler().getOrCreateSymbolData(*Symbol).setFlags(
 345     DescValue & SF_DescFlagsMask);
 346 }
 347
 348 void MCMachOStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
 349                                        unsigned ByteAlignment) {
 350   // FIXME: Darwin 'as' does appear to allow redef of a .comm by itself.
 351   assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
 352
 353   AssignSection(Symbol, nullptr);
 354
 355   MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
 356   SD.setExternal(true);
 357   SD.setCommon(Size, ByteAlignment);
 358 }
 359
 360 void MCMachOStreamer::EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
 361                                             unsigned ByteAlignment) {
 362   // '.lcomm' is equivalent to '.zerofill'.
 363   return EmitZerofill(getContext().getObjectFileInfo()->getDataBSSSection(),
 364                       Symbol, Size, ByteAlignment);
 365 }
 366
 367 void MCMachOStreamer::EmitZerofill(const MCSection *Section, MCSymbol *Symbol,
 368                                    uint64_t Size, unsigned ByteAlignment) {
 369   MCSectionData &SectData = getAssembler().getOrCreateSectionData(*Section);
 370
 371   // The symbol may not be present, which only creates the section.
 372   if (!Symbol)
 373     return;
 374
 375   // On darwin all virtual sections have zerofill type.
 376   assert(Section->isVirtualSection() && "Section does not have zerofill type!");
 377
 378   assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
 379
 380   MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
 381
 382   // Emit an align fragment if necessary.
 383   if (ByteAlignment != 1)
 384     new MCAlignFragment(ByteAlignment, 0, 0, ByteAlignment, &SectData);
 385
 386   MCFragment *F = new MCFillFragment(0, 0, Size, &SectData);
 387   SD.setFragment(F);
 388
 389   AssignSection(Symbol, Section);
 390
 391   // Update the maximum alignment on the zero fill section if necessary.
 392   if (ByteAlignment > SectData.getAlignment())
 393     SectData.setAlignment(ByteAlignment);
 394 }
 395
 396 // This should always be called with the thread local bss section.  Like the
 397 // .zerofill directive this doesn't actually switch sections on us.
 398 void MCMachOStreamer::EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol,
 399                                      uint64_t Size, unsigned ByteAlignment) {
 400   EmitZerofill(Section, Symbol, Size, ByteAlignment);
 401   return;
 402 }
 403
 404 void MCMachOStreamer::EmitInstToData(const MCInst &Inst,
 405                                      const MCSubtargetInfo &STI) {
 406   MCDataFragment *DF = getOrCreateDataFragment();
 407
 408   SmallVector<MCFixup, 4> Fixups;
 409   SmallString<256> Code;
 410   raw_svector_ostream VecOS(Code);
 411   getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, Fixups, STI);
 412   VecOS.flush();
 413
 414   // Add the fixups and data.
 415   for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
 416     Fixups[i].setOffset(Fixups[i].getOffset() + DF->getContents().size());
 417     DF->getFixups().push_back(Fixups[i]);
 418   }
 419   DF->getContents().append(Code.begin(), Code.end());
 420 }
 421
 422 void MCMachOStreamer::FinishImpl() {
 423   EmitFrames(&getAssembler().getBackend());
 424
 425   // We have to set the fragment atom associations so we can relax properly for
 426   // Mach-O.
 427
 428   // First, scan the symbol table to build a lookup table from fragments to
 429   // defining symbols.
 430   DenseMap<const MCFragment*, MCSymbolData*> DefiningSymbolMap;
 431   for (MCSymbolData &SD : getAssembler().symbols()) {
 432     if (getAssembler().isSymbolLinkerVisible(SD.getSymbol()) &&
 433         SD.getFragment()) {
 434       // An atom defining symbol should never be internal to a fragment.
 435       assert(SD.getOffset() == 0 && "Invalid offset in atom defining symbol!");
 436       DefiningSymbolMap[SD.getFragment()] = &SD;
 437     }
 438   }
 439
 440   // Set the fragment atom associations by tracking the last seen atom defining
 441   // symbol.
 442   for (MCAssembler::iterator it = getAssembler().begin(),
 443          ie = getAssembler().end(); it != ie; ++it) {
 444     MCSymbolData *CurrentAtom = nullptr;
 445     for (MCSectionData::iterator it2 = it->begin(),
 446            ie2 = it->end(); it2 != ie2; ++it2) {
 447       if (MCSymbolData *SD = DefiningSymbolMap.lookup(it2))
 448         CurrentAtom = SD;
 449       it2->setAtom(CurrentAtom);
 450     }
 451   }
 452
 453   this->MCObjectStreamer::FinishImpl();
 454 }
 455
 456 MCStreamer *llvm::createMachOStreamer(MCContext &Context, MCAsmBackend &MAB,
 457                                       raw_ostream &OS, MCCodeEmitter *CE,
 458                                       bool RelaxAll,
 459                                       bool LabelSections) {
 460   MCMachOStreamer *S = new MCMachOStreamer(Context, MAB, OS, CE, LabelSections);
 461   if (RelaxAll)
 462     S->getAssembler().setRelaxAll(true);
 463   return S;
 464 }