lib/MC/MCELFStreamer.cpp

   1 //===- lib/MC/MCELFStreamer.cpp - ELF 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 // This file assembles .s files and emits ELF .o object files.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "llvm/MC/MCStreamer.h"
  15
  16 #include "llvm/ADT/SmallPtrSet.h"
  17 #include "llvm/MC/MCAssembler.h"
  18 #include "llvm/MC/MCContext.h"
  19 #include "llvm/MC/MCCodeEmitter.h"
  20 #include "llvm/MC/MCELFSymbolFlags.h"
  21 #include "llvm/MC/MCExpr.h"
  22 #include "llvm/MC/MCInst.h"
  23 #include "llvm/MC/MCObjectStreamer.h"
  24 #include "llvm/MC/MCSection.h"
  25 #include "llvm/MC/MCSectionELF.h"
  26 #include "llvm/MC/MCSymbol.h"
  27 #include "llvm/MC/MCValue.h"
  28 #include "llvm/Support/Debug.h"
  29 #include "llvm/Support/ELF.h"
  30 #include "llvm/Support/ErrorHandling.h"
  31 #include "llvm/Support/raw_ostream.h"
  32 #include "llvm/Target/TargetAsmBackend.h"
  33
  34 using namespace llvm;
  35
  36 namespace {
  37
  38 static void SetBinding(MCSymbolData &SD, unsigned Binding) {
  39   assert(Binding == ELF::STB_LOCAL || Binding == ELF::STB_GLOBAL ||
  40          Binding == ELF::STB_WEAK);
  41   uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STB_Shift);
  42   SD.setFlags(OtherFlags | (Binding << ELF_STB_Shift));
  43 }
  44
  45 static unsigned GetBinding(const MCSymbolData &SD) {
  46   uint32_t Binding = (SD.getFlags() & (0xf << ELF_STB_Shift)) >> ELF_STB_Shift;
  47   assert(Binding == ELF::STB_LOCAL || Binding == ELF::STB_GLOBAL ||
  48          Binding == ELF::STB_WEAK);
  49   return Binding;
  50 }
  51
  52 static void SetType(MCSymbolData &SD, unsigned Type) {
  53   assert(Type == ELF::STT_NOTYPE || Type == ELF::STT_OBJECT ||
  54          Type == ELF::STT_FUNC || Type == ELF::STT_SECTION ||
  55          Type == ELF::STT_FILE || Type == ELF::STT_COMMON ||
  56          Type == ELF::STT_TLS);
  57
  58   uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STT_Shift);
  59   SD.setFlags(OtherFlags | (Type << ELF_STT_Shift));
  60 }
  61
  62 static void SetVisibility(MCSymbolData &SD, unsigned Visibility) {
  63   assert(Visibility == ELF::STV_DEFAULT || Visibility == ELF::STV_INTERNAL ||
  64          Visibility == ELF::STV_HIDDEN || Visibility == ELF::STV_PROTECTED);
  65
  66   uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STV_Shift);
  67   SD.setFlags(OtherFlags | (Visibility << ELF_STV_Shift));
  68 }
  69
  70 class MCELFStreamer : public MCObjectStreamer {
  71 public:
  72   MCELFStreamer(MCContext &Context, TargetAsmBackend &TAB,
  73                   raw_ostream &OS, MCCodeEmitter *Emitter)
  74     : MCObjectStreamer(Context, TAB, OS, Emitter, false) {}
  75
  76   ~MCELFStreamer() {}
  77
  78   /// @name MCStreamer Interface
  79   /// @{
  80
  81   virtual void InitSections();
  82   virtual void EmitLabel(MCSymbol *Symbol);
  83   virtual void EmitAssemblerFlag(MCAssemblerFlag Flag);
  84   virtual void EmitThumbFunc(MCSymbol *Func);
  85   virtual void EmitAssignment(MCSymbol *Symbol, const MCExpr *Value);
  86   virtual void EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol);
  87   virtual void SwitchSection(const MCSection *Section);
  88   virtual void EmitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute);
  89   virtual void EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
  90     assert(0 && "ELF doesn't support this directive");
  91   }
  92   virtual void EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
  93                                 unsigned ByteAlignment);
  94   virtual void BeginCOFFSymbolDef(const MCSymbol *Symbol) {
  95     assert(0 && "ELF doesn't support this directive");
  96   }
  97
  98   virtual void EmitCOFFSymbolStorageClass(int StorageClass) {
  99     assert(0 && "ELF doesn't support this directive");
 100   }
 101
 102   virtual void EmitCOFFSymbolType(int Type) {
 103     assert(0 && "ELF doesn't support this directive");
 104   }
 105
 106   virtual void EndCOFFSymbolDef() {
 107     assert(0 && "ELF doesn't support this directive");
 108   }
 109
 110   virtual void EmitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
 111      MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
 112      SD.setSize(Value);
 113   }
 114
 115   virtual void EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size) {
 116     assert(0 && "ELF doesn't support this directive");
 117   }
 118   virtual void EmitZerofill(const MCSection *Section, MCSymbol *Symbol = 0,
 119                             unsigned Size = 0, unsigned ByteAlignment = 0) {
 120     assert(0 && "ELF doesn't support this directive");
 121   }
 122   virtual void EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol,
 123                               uint64_t Size, unsigned ByteAlignment = 0) {
 124     assert(0 && "ELF doesn't support this directive");
 125   }
 126   virtual void EmitBytes(StringRef Data, unsigned AddrSpace);
 127   virtual void EmitValueToAlignment(unsigned ByteAlignment, int64_t Value = 0,
 128                                     unsigned ValueSize = 1,
 129                                     unsigned MaxBytesToEmit = 0);
 130   virtual void EmitCodeAlignment(unsigned ByteAlignment,
 131                                  unsigned MaxBytesToEmit = 0);
 132   virtual void EmitValueToOffset(const MCExpr *Offset,
 133                                  unsigned char Value = 0);
 134
 135   virtual void EmitFileDirective(StringRef Filename);
 136
 137   virtual void Finish();
 138
 139 private:
 140   virtual void EmitInstToFragment(const MCInst &Inst);
 141   virtual void EmitInstToData(const MCInst &Inst);
 142
 143   void fixSymbolsInTLSFixups(const MCExpr *expr);
 144
 145   struct LocalCommon {
 146     MCSymbolData *SD;
 147     uint64_t Size;
 148     unsigned ByteAlignment;
 149   };
 150   std::vector<LocalCommon> LocalCommons;
 151
 152   SmallPtrSet<MCSymbol *, 16> BindingExplicitlySet;
 153   /// @}
 154   void SetSection(StringRef Section, unsigned Type, unsigned Flags,
 155                   SectionKind Kind) {
 156     SwitchSection(getContext().getELFSection(Section, Type, Flags, Kind));
 157   }
 158
 159   void SetSectionData() {
 160     SetSection(".data", MCSectionELF::SHT_PROGBITS,
 161                MCSectionELF::SHF_WRITE |MCSectionELF::SHF_ALLOC,
 162                SectionKind::getDataRel());
 163     EmitCodeAlignment(4, 0);
 164   }
 165   void SetSectionText() {
 166     SetSection(".text", MCSectionELF::SHT_PROGBITS,
 167                MCSectionELF::SHF_EXECINSTR |
 168                MCSectionELF::SHF_ALLOC, SectionKind::getText());
 169     EmitCodeAlignment(4, 0);
 170   }
 171   void SetSectionBss() {
 172     SetSection(".bss", MCSectionELF::SHT_NOBITS,
 173                MCSectionELF::SHF_WRITE |
 174                MCSectionELF::SHF_ALLOC, SectionKind::getBSS());
 175     EmitCodeAlignment(4, 0);
 176   }
 177 };
 178
 179 } // end anonymous namespace.
 180
 181 void MCELFStreamer::InitSections() {
 182   // This emulates the same behavior of GNU as. This makes it easier
 183   // to compare the output as the major sections are in the same order.
 184   SetSectionText();
 185   SetSectionData();
 186   SetSectionBss();
 187   SetSectionText();
 188 }
 189
 190 void MCELFStreamer::EmitLabel(MCSymbol *Symbol) {
 191   assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
 192
 193   MCObjectStreamer::EmitLabel(Symbol);
 194
 195   const MCSectionELF &Section =
 196     static_cast<const MCSectionELF&>(Symbol->getSection());
 197   MCSymbolData &SD = getAssembler().getSymbolData(*Symbol);
 198   if (Section.getFlags() & MCSectionELF::SHF_TLS)
 199     SetType(SD, ELF::STT_TLS);
 200 }
 201
 202 void MCELFStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
 203   switch (Flag) {
 204   case MCAF_SyntaxUnified: return; // no-op here.
 205   case MCAF_Code16: return; // no-op here.
 206   case MCAF_Code32: return; // no-op here.
 207   case MCAF_SubsectionsViaSymbols:
 208     getAssembler().setSubsectionsViaSymbols(true);
 209     return;
 210   }
 211
 212   assert(0 && "invalid assembler flag!");
 213 }
 214
 215 void MCELFStreamer::EmitThumbFunc(MCSymbol *Func) {
 216   // FIXME: Anything needed here to flag the function as thumb?
 217 }
 218
 219 void MCELFStreamer::EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) {
 220   // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
 221   // MCObjectStreamer.
 222   // FIXME: Lift context changes into super class.
 223   getAssembler().getOrCreateSymbolData(*Symbol);
 224   Symbol->setVariableValue(AddValueSymbols(Value));
 225 }
 226
 227 void MCELFStreamer::SwitchSection(const MCSection *Section) {
 228   const MCSymbol *Grp = static_cast<const MCSectionELF *>(Section)->getGroup();
 229   if (Grp)
 230     getAssembler().getOrCreateSymbolData(*Grp);
 231   this->MCObjectStreamer::SwitchSection(Section);
 232 }
 233
 234 void MCELFStreamer::EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) {
 235   getAssembler().getOrCreateSymbolData(*Symbol);
 236   MCSymbolData &AliasSD = getAssembler().getOrCreateSymbolData(*Alias);
 237   AliasSD.setFlags(AliasSD.getFlags() | ELF_Other_Weakref);
 238   const MCExpr *Value = MCSymbolRefExpr::Create(Symbol, getContext());
 239   Alias->setVariableValue(Value);
 240 }
 241
 242 void MCELFStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
 243                                           MCSymbolAttr Attribute) {
 244   // Indirect symbols are handled differently, to match how 'as' handles
 245   // them. This makes writing matching .o files easier.
 246   if (Attribute == MCSA_IndirectSymbol) {
 247     // Note that we intentionally cannot use the symbol data here; this is
 248     // important for matching the string table that 'as' generates.
 249     IndirectSymbolData ISD;
 250     ISD.Symbol = Symbol;
 251     ISD.SectionData = getCurrentSectionData();
 252     getAssembler().getIndirectSymbols().push_back(ISD);
 253     return;
 254   }
 255
 256   // Adding a symbol attribute always introduces the symbol, note that an
 257   // important side effect of calling getOrCreateSymbolData here is to register
 258   // the symbol with the assembler.
 259   MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
 260
 261   // The implementation of symbol attributes is designed to match 'as', but it
 262   // leaves much to desired. It doesn't really make sense to arbitrarily add and
 263   // remove flags, but 'as' allows this (in particular, see .desc).
 264   //
 265   // In the future it might be worth trying to make these operations more well
 266   // defined.
 267   switch (Attribute) {
 268   case MCSA_LazyReference:
 269   case MCSA_Reference:
 270   case MCSA_NoDeadStrip:
 271   case MCSA_SymbolResolver:
 272   case MCSA_PrivateExtern:
 273   case MCSA_WeakDefinition:
 274   case MCSA_WeakDefAutoPrivate:
 275   case MCSA_Invalid:
 276   case MCSA_ELF_TypeIndFunction:
 277   case MCSA_IndirectSymbol:
 278     assert(0 && "Invalid symbol attribute for ELF!");
 279     break;
 280
 281   case MCSA_ELF_TypeGnuUniqueObject:
 282     // Ignore for now.
 283     break;
 284
 285   case MCSA_Global:
 286     SetBinding(SD, ELF::STB_GLOBAL);
 287     SD.setExternal(true);
 288     BindingExplicitlySet.insert(Symbol);
 289     break;
 290
 291   case MCSA_WeakReference:
 292   case MCSA_Weak:
 293     SetBinding(SD, ELF::STB_WEAK);
 294     SD.setExternal(true);
 295     BindingExplicitlySet.insert(Symbol);
 296     break;
 297
 298   case MCSA_Local:
 299     SetBinding(SD, ELF::STB_LOCAL);
 300     SD.setExternal(false);
 301     BindingExplicitlySet.insert(Symbol);
 302     break;
 303
 304   case MCSA_ELF_TypeFunction:
 305     SetType(SD, ELF::STT_FUNC);
 306     break;
 307
 308   case MCSA_ELF_TypeObject:
 309     SetType(SD, ELF::STT_OBJECT);
 310     break;
 311
 312   case MCSA_ELF_TypeTLS:
 313     SetType(SD, ELF::STT_TLS);
 314     break;
 315
 316   case MCSA_ELF_TypeCommon:
 317     SetType(SD, ELF::STT_COMMON);
 318     break;
 319
 320   case MCSA_ELF_TypeNoType:
 321     SetType(SD, ELF::STT_NOTYPE);
 322     break;
 323
 324   case MCSA_Protected:
 325     SetVisibility(SD, ELF::STV_PROTECTED);
 326     break;
 327
 328   case MCSA_Hidden:
 329     SetVisibility(SD, ELF::STV_HIDDEN);
 330     break;
 331
 332   case MCSA_Internal:
 333     SetVisibility(SD, ELF::STV_INTERNAL);
 334     break;
 335   }
 336 }
 337
 338 void MCELFStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
 339                                        unsigned ByteAlignment) {
 340   MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
 341
 342   if (!BindingExplicitlySet.count(Symbol)) {
 343     SetBinding(SD, ELF::STB_GLOBAL);
 344     SD.setExternal(true);
 345   }
 346
 347   SetType(SD, ELF::STT_OBJECT);
 348
 349   if (GetBinding(SD) == ELF_STB_Local) {
 350     const MCSection *Section = getAssembler().getContext().getELFSection(".bss",
 351                                                                     MCSectionELF::SHT_NOBITS,
 352                                                                     MCSectionELF::SHF_WRITE |
 353                                                                     MCSectionELF::SHF_ALLOC,
 354                                                                     SectionKind::getBSS());
 355     Symbol->setSection(*Section);
 356
 357     struct LocalCommon L = {&SD, Size, ByteAlignment};
 358     LocalCommons.push_back(L);
 359   } else {
 360     SD.setCommon(Size, ByteAlignment);
 361   }
 362
 363   SD.setSize(MCConstantExpr::Create(Size, getContext()));
 364 }
 365
 366 void MCELFStreamer::EmitBytes(StringRef Data, unsigned AddrSpace) {
 367   // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
 368   // MCObjectStreamer.
 369   getOrCreateDataFragment()->getContents().append(Data.begin(), Data.end());
 370 }
 371
 372 void MCELFStreamer::EmitValueToAlignment(unsigned ByteAlignment,
 373                                            int64_t Value, unsigned ValueSize,
 374                                            unsigned MaxBytesToEmit) {
 375   // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
 376   // MCObjectStreamer.
 377   if (MaxBytesToEmit == 0)
 378     MaxBytesToEmit = ByteAlignment;
 379   new MCAlignFragment(ByteAlignment, Value, ValueSize, MaxBytesToEmit,
 380                       getCurrentSectionData());
 381
 382   // Update the maximum alignment on the current section if necessary.
 383   if (ByteAlignment > getCurrentSectionData()->getAlignment())
 384     getCurrentSectionData()->setAlignment(ByteAlignment);
 385 }
 386
 387 void MCELFStreamer::EmitCodeAlignment(unsigned ByteAlignment,
 388                                         unsigned MaxBytesToEmit) {
 389   // TODO: This is exactly the same as WinCOFFStreamer. Consider merging into
 390   // MCObjectStreamer.
 391   if (MaxBytesToEmit == 0)
 392     MaxBytesToEmit = ByteAlignment;
 393   MCAlignFragment *F = new MCAlignFragment(ByteAlignment, 0, 1, MaxBytesToEmit,
 394                                            getCurrentSectionData());
 395   F->setEmitNops(true);
 396
 397   // Update the maximum alignment on the current section if necessary.
 398   if (ByteAlignment > getCurrentSectionData()->getAlignment())
 399     getCurrentSectionData()->setAlignment(ByteAlignment);
 400 }
 401
 402 void MCELFStreamer::EmitValueToOffset(const MCExpr *Offset,
 403                                         unsigned char Value) {
 404   // TODO: This is exactly the same as MCMachOStreamer. Consider merging into
 405   // MCObjectStreamer.
 406   new MCOrgFragment(*Offset, Value, getCurrentSectionData());
 407 }
 408
 409 // Add a symbol for the file name of this module. This is the second
 410 // entry in the module's symbol table (the first being the null symbol).
 411 void MCELFStreamer::EmitFileDirective(StringRef Filename) {
 412   MCSymbol *Symbol = getAssembler().getContext().GetOrCreateSymbol(Filename);
 413   Symbol->setSection(*CurSection);
 414   Symbol->setAbsolute();
 415
 416   MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
 417
 418   SD.setFlags(ELF_STT_File | ELF_STB_Local | ELF_STV_Default);
 419 }
 420
 421 void  MCELFStreamer::fixSymbolsInTLSFixups(const MCExpr *expr) {
 422   switch (expr->getKind()) {
 423   case MCExpr::Target: llvm_unreachable("Can't handle target exprs yet!");
 424   case MCExpr::Constant:
 425     break;
 426
 427   case MCExpr::Binary: {
 428     const MCBinaryExpr *be = cast<MCBinaryExpr>(expr);
 429     fixSymbolsInTLSFixups(be->getLHS());
 430     fixSymbolsInTLSFixups(be->getRHS());
 431     break;
 432   }
 433
 434   case MCExpr::SymbolRef: {
 435     const MCSymbolRefExpr &symRef = *cast<MCSymbolRefExpr>(expr);
 436     switch (symRef.getKind()) {
 437     default:
 438       return;
 439     case MCSymbolRefExpr::VK_NTPOFF:
 440     case MCSymbolRefExpr::VK_GOTNTPOFF:
 441     case MCSymbolRefExpr::VK_TLSGD:
 442     case MCSymbolRefExpr::VK_TLSLDM:
 443     case MCSymbolRefExpr::VK_TPOFF:
 444     case MCSymbolRefExpr::VK_DTPOFF:
 445     case MCSymbolRefExpr::VK_GOTTPOFF:
 446     case MCSymbolRefExpr::VK_TLSLD:
 447     case MCSymbolRefExpr::VK_ARM_TLSGD:
 448       break;
 449     }
 450     MCSymbolData &SD = getAssembler().getOrCreateSymbolData(symRef.getSymbol());
 451     SetType(SD, ELF::STT_TLS);
 452     break;
 453   }
 454
 455   case MCExpr::Unary:
 456     fixSymbolsInTLSFixups(cast<MCUnaryExpr>(expr)->getSubExpr());
 457     break;
 458   }
 459 }
 460
 461 void MCELFStreamer::EmitInstToFragment(const MCInst &Inst) {
 462   this->MCObjectStreamer::EmitInstToFragment(Inst);
 463   MCInstFragment &F = *cast<MCInstFragment>(getCurrentFragment());
 464
 465   for (unsigned i = 0, e = F.getFixups().size(); i != e; ++i)
 466     fixSymbolsInTLSFixups(F.getFixups()[i].getValue());
 467 }
 468
 469 void MCELFStreamer::EmitInstToData(const MCInst &Inst) {
 470   MCDataFragment *DF = getOrCreateDataFragment();
 471
 472   SmallVector<MCFixup, 4> Fixups;
 473   SmallString<256> Code;
 474   raw_svector_ostream VecOS(Code);
 475   getAssembler().getEmitter().EncodeInstruction(Inst, VecOS, Fixups);
 476   VecOS.flush();
 477
 478   for (unsigned i = 0, e = Fixups.size(); i != e; ++i)
 479     fixSymbolsInTLSFixups(Fixups[i].getValue());
 480
 481   // Add the fixups and data.
 482   for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
 483     Fixups[i].setOffset(Fixups[i].getOffset() + DF->getContents().size());
 484     DF->addFixup(Fixups[i]);
 485   }
 486   DF->getContents().append(Code.begin(), Code.end());
 487 }
 488
 489 void MCELFStreamer::Finish() {
 490   // FIXME: duplicated code with the MachO streamer.
 491   // Dump out the dwarf file & directory tables and line tables.
 492   if (getContext().hasDwarfFiles()) {
 493     const MCSection *DwarfLineSection =
 494       getContext().getELFSection(".debug_line", 0, 0,
 495                                  SectionKind::getDataRelLocal());
 496     MCSectionData &DLS =
 497       getAssembler().getOrCreateSectionData(*DwarfLineSection);
 498     int PointerSize = getAssembler().getBackend().getPointerSize();
 499     MCDwarfFileTable::Emit(this, DwarfLineSection, &DLS, PointerSize);
 500   }
 501
 502   for (std::vector<LocalCommon>::const_iterator i = LocalCommons.begin(),
 503                                                 e = LocalCommons.end();
 504        i != e; ++i) {
 505     MCSymbolData *SD = i->SD;
 506     uint64_t Size = i->Size;
 507     unsigned ByteAlignment = i->ByteAlignment;
 508     const MCSymbol &Symbol = SD->getSymbol();
 509     const MCSection &Section = Symbol.getSection();
 510
 511     MCSectionData &SectData = getAssembler().getOrCreateSectionData(Section);
 512     new MCAlignFragment(ByteAlignment, 0, 1, ByteAlignment, &SectData);
 513
 514     MCFragment *F = new MCFillFragment(0, 0, Size, &SectData);
 515     SD->setFragment(F);
 516
 517     // Update the maximum alignment of the section if necessary.
 518     if (ByteAlignment > SectData.getAlignment())
 519       SectData.setAlignment(ByteAlignment);
 520   }
 521
 522   this->MCObjectStreamer::Finish();
 523 }
 524
 525 MCStreamer *llvm::createELFStreamer(MCContext &Context, TargetAsmBackend &TAB,
 526                                       raw_ostream &OS, MCCodeEmitter *CE,
 527                                       bool RelaxAll) {
 528   MCELFStreamer *S = new MCELFStreamer(Context, TAB, OS, CE);
 529   if (RelaxAll)
 530     S->getAssembler().setRelaxAll(true);
 531   return S;
 532 }