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