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/MCSection.h"
  18 #include "llvm/MC/MCSymbol.h"
  19 #include "llvm/MC/MCValue.h"
  20 #include "llvm/Support/ErrorHandling.h"
  21 #include "llvm/Support/raw_ostream.h"
  22 using namespace llvm;
  23
  24 namespace {
  25
  26 class MCMachOStreamer : public MCStreamer {
  27   /// SymbolFlags - We store the value for the 'desc' symbol field in the lowest
  28   /// 16 bits of the implementation defined flags.
  29   enum SymbolFlags { // See <mach-o/nlist.h>.
  30     SF_DescFlagsMask                        = 0xFFFF,
  31
  32     // Reference type flags.
  33     SF_ReferenceTypeMask                    = 0x0007,
  34     SF_ReferenceTypeUndefinedNonLazy        = 0x0000,
  35     SF_ReferenceTypeUndefinedLazy           = 0x0001,
  36     SF_ReferenceTypeDefined                 = 0x0002,
  37     SF_ReferenceTypePrivateDefined          = 0x0003,
  38     SF_ReferenceTypePrivateUndefinedNonLazy = 0x0004,
  39     SF_ReferenceTypePrivateUndefinedLazy    = 0x0005,
  40
  41     // Other 'desc' flags.
  42     SF_NoDeadStrip                          = 0x0020,
  43     SF_WeakReference                        = 0x0040,
  44     SF_WeakDefinition                       = 0x0080
  45   };
  46
  47 private:
  48   MCAssembler Assembler;
  49
  50   MCCodeEmitter *Emitter;
  51
  52   MCSectionData *CurSectionData;
  53
  54   DenseMap<const MCSection*, MCSectionData*> SectionMap;
  55
  56   DenseMap<const MCSymbol*, MCSymbolData*> SymbolMap;
  57
  58 private:
  59   MCFragment *getCurrentFragment() const {
  60     assert(CurSectionData && "No current section!");
  61
  62     if (!CurSectionData->empty())
  63       return &CurSectionData->getFragmentList().back();
  64
  65     return 0;
  66   }
  67
  68   MCSectionData &getSectionData(const MCSection &Section) {
  69     MCSectionData *&Entry = SectionMap[&Section];
  70
  71     if (!Entry)
  72       Entry = new MCSectionData(Section, &Assembler);
  73
  74     return *Entry;
  75   }
  76
  77   MCSymbolData &getSymbolData(const MCSymbol &Symbol) {
  78     MCSymbolData *&Entry = SymbolMap[&Symbol];
  79
  80     if (!Entry)
  81       Entry = new MCSymbolData(Symbol, 0, 0, &Assembler);
  82
  83     return *Entry;
  84   }
  85
  86 public:
  87   MCMachOStreamer(MCContext &Context, raw_ostream &_OS, MCCodeEmitter *_Emitter)
  88     : MCStreamer(Context), Assembler(Context, _OS), Emitter(_Emitter),
  89       CurSectionData(0) {}
  90   ~MCMachOStreamer() {}
  91
  92   const MCExpr *AddValueSymbols(const MCExpr *Value) {
  93     switch (Value->getKind()) {
  94     case MCExpr::Constant:
  95       break;
  96
  97     case MCExpr::Binary: {
  98       const MCBinaryExpr *BE = cast<MCBinaryExpr>(Value);
  99       AddValueSymbols(BE->getLHS());
 100       AddValueSymbols(BE->getRHS());
 101       break;
 102     }
 103
 104     case MCExpr::SymbolRef:
 105       getSymbolData(cast<MCSymbolRefExpr>(Value)->getSymbol());
 106       break;
 107
 108     case MCExpr::Unary:
 109       AddValueSymbols(cast<MCUnaryExpr>(Value)->getSubExpr());
 110       break;
 111     }
 112
 113     return Value;
 114   }
 115
 116   /// @name MCStreamer Interface
 117   /// @{
 118
 119   virtual void SwitchSection(const MCSection *Section);
 120
 121   virtual void EmitLabel(MCSymbol *Symbol);
 122
 123   virtual void EmitAssemblerFlag(AssemblerFlag Flag);
 124
 125   virtual void EmitAssignment(MCSymbol *Symbol, const MCExpr *Value);
 126
 127   virtual void EmitSymbolAttribute(MCSymbol *Symbol, SymbolAttr Attribute);
 128
 129   virtual void EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue);
 130
 131   virtual void EmitCommonSymbol(MCSymbol *Symbol, unsigned Size,
 132                                 unsigned ByteAlignment);
 133
 134   virtual void EmitZerofill(const MCSection *Section, MCSymbol *Symbol = 0,
 135                             unsigned Size = 0, unsigned ByteAlignment = 0);
 136
 137   virtual void EmitBytes(const StringRef &Data);
 138
 139   virtual void EmitValue(const MCExpr *Value, unsigned Size);
 140
 141   virtual void EmitValueToAlignment(unsigned ByteAlignment, int64_t Value = 0,
 142                                     unsigned ValueSize = 1,
 143                                     unsigned MaxBytesToEmit = 0);
 144
 145   virtual void EmitValueToOffset(const MCExpr *Offset,
 146                                  unsigned char Value = 0);
 147
 148   virtual void EmitInstruction(const MCInst &Inst);
 149
 150   virtual void Finish();
 151
 152   /// @}
 153 };
 154
 155 } // end anonymous namespace.
 156
 157 void MCMachOStreamer::SwitchSection(const MCSection *Section) {
 158   assert(Section && "Cannot switch to a null section!");
 159
 160   // If already in this section, then this is a noop.
 161   if (Section == CurSection) return;
 162
 163   CurSection = Section;
 164   CurSectionData = &getSectionData(*Section);
 165 }
 166
 167 void MCMachOStreamer::EmitLabel(MCSymbol *Symbol) {
 168   assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
 169
 170   // FIXME: We should also use offsets into Fill fragments.
 171   MCDataFragment *F = dyn_cast_or_null<MCDataFragment>(getCurrentFragment());
 172   if (!F)
 173     F = new MCDataFragment(CurSectionData);
 174
 175   MCSymbolData &SD = getSymbolData(*Symbol);
 176   assert(!SD.getFragment() && "Unexpected fragment on symbol data!");
 177   SD.setFragment(F);
 178   SD.setOffset(F->getContents().size());
 179
 180   // This causes the reference type and weak reference flags to be cleared.
 181   SD.setFlags(SD.getFlags() & ~(SF_WeakReference | SF_ReferenceTypeMask));
 182
 183   Symbol->setSection(*CurSection);
 184 }
 185
 186 void MCMachOStreamer::EmitAssemblerFlag(AssemblerFlag Flag) {
 187   switch (Flag) {
 188   case SubsectionsViaSymbols:
 189     Assembler.setSubsectionsViaSymbols(true);
 190     return;
 191   }
 192
 193   assert(0 && "invalid assembler flag!");
 194 }
 195
 196 void MCMachOStreamer::EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) {
 197   // Only absolute symbols can be redefined.
 198   assert((Symbol->isUndefined() || Symbol->isAbsolute()) &&
 199          "Cannot define a symbol twice!");
 200
 201   llvm_unreachable("FIXME: Not yet implemented!");
 202 }
 203
 204 void MCMachOStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
 205                                           SymbolAttr Attribute) {
 206   // Indirect symbols are handled differently, to match how 'as' handles
 207   // them. This makes writing matching .o files easier.
 208   if (Attribute == MCStreamer::IndirectSymbol) {
 209     // Note that we intentionally cannot use the symbol data here; this is
 210     // important for matching the string table that 'as' generates.
 211     IndirectSymbolData ISD;
 212     ISD.Symbol = Symbol;
 213     ISD.SectionData = CurSectionData;
 214     Assembler.getIndirectSymbols().push_back(ISD);
 215     return;
 216   }
 217
 218   // Adding a symbol attribute always introduces the symbol, note that an
 219   // important side effect of calling getSymbolData here is to register the
 220   // symbol with the assembler.
 221   MCSymbolData &SD = getSymbolData(*Symbol);
 222
 223   // The implementation of symbol attributes is designed to match 'as', but it
 224   // leaves much to desired. It doesn't really make sense to arbitrarily add and
 225   // remove flags, but 'as' allows this (in particular, see .desc).
 226   //
 227   // In the future it might be worth trying to make these operations more well
 228   // defined.
 229   switch (Attribute) {
 230   case MCStreamer::IndirectSymbol:
 231   case MCStreamer::Hidden:
 232   case MCStreamer::Internal:
 233   case MCStreamer::Protected:
 234   case MCStreamer::Weak:
 235     assert(0 && "Invalid symbol attribute for Mach-O!");
 236     break;
 237
 238   case MCStreamer::Global:
 239     SD.setExternal(true);
 240     break;
 241
 242   case MCStreamer::LazyReference:
 243     // FIXME: This requires -dynamic.
 244     SD.setFlags(SD.getFlags() | SF_NoDeadStrip);
 245     if (Symbol->isUndefined())
 246       SD.setFlags(SD.getFlags() | SF_ReferenceTypeUndefinedLazy);
 247     break;
 248
 249     // Since .reference sets the no dead strip bit, it is equivalent to
 250     // .no_dead_strip in practice.
 251   case MCStreamer::Reference:
 252   case MCStreamer::NoDeadStrip:
 253     SD.setFlags(SD.getFlags() | SF_NoDeadStrip);
 254     break;
 255
 256   case MCStreamer::PrivateExtern:
 257     SD.setExternal(true);
 258     SD.setPrivateExtern(true);
 259     break;
 260
 261   case MCStreamer::WeakReference:
 262     // FIXME: This requires -dynamic.
 263     if (Symbol->isUndefined())
 264       SD.setFlags(SD.getFlags() | SF_WeakReference);
 265     break;
 266
 267   case MCStreamer::WeakDefinition:
 268     // FIXME: 'as' enforces that this is defined and global. The manual claims
 269     // it has to be in a coalesced section, but this isn't enforced.
 270     SD.setFlags(SD.getFlags() | SF_WeakDefinition);
 271     break;
 272   }
 273 }
 274
 275 void MCMachOStreamer::EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
 276   // Encode the 'desc' value into the lowest implementation defined bits.
 277   assert(DescValue == (DescValue & SF_DescFlagsMask) &&
 278          "Invalid .desc value!");
 279   getSymbolData(*Symbol).setFlags(DescValue & SF_DescFlagsMask);
 280 }
 281
 282 void MCMachOStreamer::EmitCommonSymbol(MCSymbol *Symbol, unsigned Size,
 283                                        unsigned ByteAlignment) {
 284   // FIXME: Darwin 'as' does appear to allow redef of a .comm by itself.
 285   assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
 286
 287   MCSymbolData &SD = getSymbolData(*Symbol);
 288   SD.setExternal(true);
 289   SD.setCommon(Size, ByteAlignment);
 290 }
 291
 292 void MCMachOStreamer::EmitZerofill(const MCSection *Section, MCSymbol *Symbol,
 293                                    unsigned Size, unsigned ByteAlignment) {
 294   MCSectionData &SectData = getSectionData(*Section);
 295
 296   // The symbol may not be present, which only creates the section.
 297   if (!Symbol)
 298     return;
 299
 300   // FIXME: Assert that this section has the zerofill type.
 301
 302   assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
 303
 304   MCSymbolData &SD = getSymbolData(*Symbol);
 305
 306   MCFragment *F = new MCZeroFillFragment(Size, ByteAlignment, &SectData);
 307   SD.setFragment(F);
 308
 309   Symbol->setSection(*Section);
 310
 311   // Update the maximum alignment on the zero fill section if necessary.
 312   if (ByteAlignment > SectData.getAlignment())
 313     SectData.setAlignment(ByteAlignment);
 314 }
 315
 316 void MCMachOStreamer::EmitBytes(const StringRef &Data) {
 317   MCDataFragment *DF = dyn_cast_or_null<MCDataFragment>(getCurrentFragment());
 318   if (!DF)
 319     DF = new MCDataFragment(CurSectionData);
 320   DF->getContents().append(Data.begin(), Data.end());
 321 }
 322
 323 void MCMachOStreamer::EmitValue(const MCExpr *Value, unsigned Size) {
 324   MCValue RelocValue;
 325
 326   if (!AddValueSymbols(Value)->EvaluateAsRelocatable(getContext(), RelocValue))
 327     return llvm_report_error("expected relocatable expression");
 328
 329   new MCFillFragment(RelocValue, Size, 1, CurSectionData);
 330 }
 331
 332 void MCMachOStreamer::EmitValueToAlignment(unsigned ByteAlignment,
 333                                            int64_t Value, unsigned ValueSize,
 334                                            unsigned MaxBytesToEmit) {
 335   if (MaxBytesToEmit == 0)
 336     MaxBytesToEmit = ByteAlignment;
 337   new MCAlignFragment(ByteAlignment, Value, ValueSize, MaxBytesToEmit,
 338                       CurSectionData);
 339
 340   // Update the maximum alignment on the current section if necessary.
 341   if (ByteAlignment > CurSectionData->getAlignment())
 342     CurSectionData->setAlignment(ByteAlignment);
 343 }
 344
 345 void MCMachOStreamer::EmitValueToOffset(const MCExpr *Offset,
 346                                         unsigned char Value) {
 347   MCValue RelocOffset;
 348
 349   if (!AddValueSymbols(Offset)->EvaluateAsRelocatable(getContext(),
 350                                                       RelocOffset))
 351     return llvm_report_error("expected relocatable expression");
 352
 353   new MCOrgFragment(RelocOffset, Value, CurSectionData);
 354 }
 355
 356 void MCMachOStreamer::EmitInstruction(const MCInst &Inst) {
 357   // Scan for values.
 358   for (unsigned i = 0; i != Inst.getNumOperands(); ++i)
 359     if (Inst.getOperand(i).isExpr())
 360       AddValueSymbols(Inst.getOperand(i).getExpr());
 361
 362   if (!Emitter)
 363     llvm_unreachable("no code emitter available!");
 364
 365   // FIXME: Relocations!
 366   SmallString<256> Code;
 367   raw_svector_ostream VecOS(Code);
 368   Emitter->EncodeInstruction(Inst, VecOS);
 369   EmitBytes(VecOS.str());
 370 }
 371
 372 void MCMachOStreamer::Finish() {
 373   Assembler.Finish();
 374 }
 375
 376 MCStreamer *llvm::createMachOStreamer(MCContext &Context, raw_ostream &OS,
 377                                       MCCodeEmitter *CE) {
 378   return new MCMachOStreamer(Context, OS, CE);
 379 }