llvm/lib/MC/MCMachOStreamer.cpp

   1 //===- MCMachOStreamer.cpp - MachO Streamer -------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include "llvm/ADT/DenseMap.h"
  10 #include "llvm/ADT/SmallString.h"
  11 #include "llvm/ADT/SmallVector.h"
  12 #include "llvm/ADT/StringRef.h"
  13 #include "llvm/ADT/Triple.h"
  14 #include "llvm/MC/MCAsmBackend.h"
  15 #include "llvm/MC/MCAssembler.h"
  16 #include "llvm/MC/MCCodeEmitter.h"
  17 #include "llvm/MC/MCContext.h"
  18 #include "llvm/MC/MCDirectives.h"
  19 #include "llvm/MC/MCExpr.h"
  20 #include "llvm/MC/MCFixup.h"
  21 #include "llvm/MC/MCFragment.h"
  22 #include "llvm/MC/MCInst.h"
  23 #include "llvm/MC/MCLinkerOptimizationHint.h"
  24 #include "llvm/MC/MCObjectFileInfo.h"
  25 #include "llvm/MC/MCObjectStreamer.h"
  26 #include "llvm/MC/MCObjectWriter.h"
  27 #include "llvm/MC/MCSection.h"
  28 #include "llvm/MC/MCSectionMachO.h"
  29 #include "llvm/MC/MCStreamer.h"
  30 #include "llvm/MC/MCSymbol.h"
  31 #include "llvm/MC/MCSymbolMachO.h"
  32 #include "llvm/MC/MCValue.h"
  33 #include "llvm/Support/Casting.h"
  34 #include "llvm/Support/ErrorHandling.h"
  35 #include "llvm/Support/TargetRegistry.h"
  36 #include "llvm/Support/raw_ostream.h"
  37 #include <cassert>
  38 #include <vector>
  39
  40 using namespace llvm;
  41
  42 namespace {
  43
  44 class MCMachOStreamer : public MCObjectStreamer {
  45 private:
  46   /// LabelSections - true if each section change should emit a linker local
  47   /// label for use in relocations for assembler local references. Obviates the
  48   /// need for local relocations. False by default.
  49   bool LabelSections;
  50
  51   bool DWARFMustBeAtTheEnd;
  52   bool CreatedADWARFSection;
  53
  54   /// HasSectionLabel - map of which sections have already had a non-local
  55   /// label emitted to them. Used so we don't emit extraneous linker local
  56   /// labels in the middle of the section.
  57   DenseMap<const MCSection*, bool> HasSectionLabel;
  58
  59   void emitInstToData(const MCInst &Inst, const MCSubtargetInfo &STI) override;
  60
  61   void emitDataRegion(DataRegionData::KindTy Kind);
  62   void emitDataRegionEnd();
  63
  64 public:
  65   MCMachOStreamer(MCContext &Context, std::unique_ptr<MCAsmBackend> MAB,
  66                   std::unique_ptr<MCObjectWriter> OW,
  67                   std::unique_ptr<MCCodeEmitter> Emitter,
  68                   bool DWARFMustBeAtTheEnd, bool label)
  69       : MCObjectStreamer(Context, std::move(MAB), std::move(OW),
  70                          std::move(Emitter)),
  71         LabelSections(label), DWARFMustBeAtTheEnd(DWARFMustBeAtTheEnd),
  72         CreatedADWARFSection(false) {}
  73
  74   /// state management
  75   void reset() override {
  76     CreatedADWARFSection = false;
  77     HasSectionLabel.clear();
  78     MCObjectStreamer::reset();
  79   }
  80
  81   /// @name MCStreamer Interface
  82   /// @{
  83
  84   void changeSection(MCSection *Sect, const MCExpr *Subsect) override;
  85   void emitLabel(MCSymbol *Symbol, SMLoc Loc = SMLoc()) override;
  86   void emitAssignment(MCSymbol *Symbol, const MCExpr *Value) override;
  87   void emitEHSymAttributes(const MCSymbol *Symbol, MCSymbol *EHSymbol) override;
  88   void emitAssemblerFlag(MCAssemblerFlag Flag) override;
  89   void emitLinkerOptions(ArrayRef<std::string> Options) override;
  90   void emitDataRegion(MCDataRegionType Kind) override;
  91   void emitVersionMin(MCVersionMinType Kind, unsigned Major, unsigned Minor,
  92                       unsigned Update, VersionTuple SDKVersion) override;
  93   void emitBuildVersion(unsigned Platform, unsigned Major, unsigned Minor,
  94                         unsigned Update, VersionTuple SDKVersion) override;
  95   void emitThumbFunc(MCSymbol *Func) override;
  96   bool emitSymbolAttribute(MCSymbol *Symbol, MCSymbolAttr Attribute) override;
  97   void emitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) override;
  98   void emitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
  99                         unsigned ByteAlignment) override;
 100
 101   void emitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
 102                              unsigned ByteAlignment) override;
 103   void emitZerofill(MCSection *Section, MCSymbol *Symbol = nullptr,
 104                     uint64_t Size = 0, unsigned ByteAlignment = 0,
 105                     SMLoc Loc = SMLoc()) override;
 106   void emitTBSSSymbol(MCSection *Section, MCSymbol *Symbol, uint64_t Size,
 107                       unsigned ByteAlignment = 0) override;
 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 static bool canGoAfterDWARF(const MCSectionMachO &MSec) {
 123   // These sections are created by the assembler itself after the end of
 124   // the .s file.
 125   StringRef SegName = MSec.getSegmentName();
 126   StringRef SecName = MSec.getName();
 127
 128   if (SegName == "__LD" && SecName == "__compact_unwind")
 129     return true;
 130
 131   if (SegName == "__IMPORT") {
 132     if (SecName == "__jump_table")
 133       return true;
 134
 135     if (SecName == "__pointers")
 136       return true;
 137   }
 138
 139   if (SegName == "__TEXT" && SecName == "__eh_frame")
 140     return true;
 141
 142   if (SegName == "__DATA" && (SecName == "__nl_symbol_ptr" ||
 143                               SecName == "__thread_ptr"))
 144     return true;
 145
 146   return false;
 147 }
 148
 149 void MCMachOStreamer::changeSection(MCSection *Section,
 150                                     const MCExpr *Subsection) {
 151   // Change the section normally.
 152   bool Created = changeSectionImpl(Section, Subsection);
 153   const MCSectionMachO &MSec = *cast<MCSectionMachO>(Section);
 154   StringRef SegName = MSec.getSegmentName();
 155   if (SegName == "__DWARF")
 156     CreatedADWARFSection = true;
 157   else if (Created && DWARFMustBeAtTheEnd && !canGoAfterDWARF(MSec))
 158     assert((!CreatedADWARFSection ||
 159             Section == getContext().getObjectFileInfo()->getStackMapSection())
 160            && "Creating regular section after DWARF");
 161
 162   // Output a linker-local symbol so we don't need section-relative local
 163   // relocations. The linker hates us when we do that.
 164   if (LabelSections && !HasSectionLabel[Section] &&
 165       !Section->getBeginSymbol()) {
 166     MCSymbol *Label = getContext().createLinkerPrivateTempSymbol();
 167     Section->setBeginSymbol(Label);
 168     HasSectionLabel[Section] = true;
 169   }
 170 }
 171
 172 void MCMachOStreamer::emitEHSymAttributes(const MCSymbol *Symbol,
 173                                           MCSymbol *EHSymbol) {
 174   getAssembler().registerSymbol(*Symbol);
 175   if (Symbol->isExternal())
 176     emitSymbolAttribute(EHSymbol, MCSA_Global);
 177   if (cast<MCSymbolMachO>(Symbol)->isWeakDefinition())
 178     emitSymbolAttribute(EHSymbol, MCSA_WeakDefinition);
 179   if (Symbol->isPrivateExtern())
 180     emitSymbolAttribute(EHSymbol, MCSA_PrivateExtern);
 181 }
 182
 183 void MCMachOStreamer::emitLabel(MCSymbol *Symbol, SMLoc Loc) {
 184   // We have to create a new fragment if this is an atom defining symbol,
 185   // fragments cannot span atoms.
 186   if (getAssembler().isSymbolLinkerVisible(*Symbol))
 187     insert(new MCDataFragment());
 188
 189   MCObjectStreamer::emitLabel(Symbol, Loc);
 190
 191   // This causes the reference type flag to be cleared. Darwin 'as' was "trying"
 192   // to clear the weak reference and weak definition bits too, but the
 193   // implementation was buggy. For now we just try to match 'as', for
 194   // diffability.
 195   //
 196   // FIXME: Cleanup this code, these bits should be emitted based on semantic
 197   // properties, not on the order of definition, etc.
 198   cast<MCSymbolMachO>(Symbol)->clearReferenceType();
 199 }
 200
 201 void MCMachOStreamer::emitAssignment(MCSymbol *Symbol, const MCExpr *Value) {
 202   MCValue Res;
 203
 204   if (Value->evaluateAsRelocatable(Res, nullptr, nullptr)) {
 205     if (const MCSymbolRefExpr *SymAExpr = Res.getSymA()) {
 206       const MCSymbol &SymA = SymAExpr->getSymbol();
 207       if (!Res.getSymB() && (SymA.getName() == "" || Res.getConstant() != 0))
 208         cast<MCSymbolMachO>(Symbol)->setAltEntry();
 209     }
 210   }
 211   MCObjectStreamer::emitAssignment(Symbol, Value);
 212 }
 213
 214 void MCMachOStreamer::emitDataRegion(DataRegionData::KindTy Kind) {
 215   // Create a temporary label to mark the start of the data region.
 216   MCSymbol *Start = getContext().createTempSymbol();
 217   emitLabel(Start);
 218   // Record the region for the object writer to use.
 219   DataRegionData Data = { Kind, Start, nullptr };
 220   std::vector<DataRegionData> &Regions = getAssembler().getDataRegions();
 221   Regions.push_back(Data);
 222 }
 223
 224 void MCMachOStreamer::emitDataRegionEnd() {
 225   std::vector<DataRegionData> &Regions = getAssembler().getDataRegions();
 226   assert(!Regions.empty() && "Mismatched .end_data_region!");
 227   DataRegionData &Data = Regions.back();
 228   assert(!Data.End && "Mismatched .end_data_region!");
 229   // Create a temporary label to mark the end of the data region.
 230   Data.End = getContext().createTempSymbol();
 231   emitLabel(Data.End);
 232 }
 233
 234 void MCMachOStreamer::emitAssemblerFlag(MCAssemblerFlag Flag) {
 235   // Let the target do whatever target specific stuff it needs to do.
 236   getAssembler().getBackend().handleAssemblerFlag(Flag);
 237   // Do any generic stuff we need to do.
 238   switch (Flag) {
 239   case MCAF_SyntaxUnified: return; // no-op here.
 240   case MCAF_Code16: return; // Change parsing mode; no-op here.
 241   case MCAF_Code32: return; // Change parsing mode; no-op here.
 242   case MCAF_Code64: return; // Change parsing mode; no-op here.
 243   case MCAF_SubsectionsViaSymbols:
 244     getAssembler().setSubsectionsViaSymbols(true);
 245     return;
 246   }
 247 }
 248
 249 void MCMachOStreamer::emitLinkerOptions(ArrayRef<std::string> Options) {
 250   getAssembler().getLinkerOptions().push_back(Options);
 251 }
 252
 253 void MCMachOStreamer::emitDataRegion(MCDataRegionType Kind) {
 254   switch (Kind) {
 255   case MCDR_DataRegion:
 256     emitDataRegion(DataRegionData::Data);
 257     return;
 258   case MCDR_DataRegionJT8:
 259     emitDataRegion(DataRegionData::JumpTable8);
 260     return;
 261   case MCDR_DataRegionJT16:
 262     emitDataRegion(DataRegionData::JumpTable16);
 263     return;
 264   case MCDR_DataRegionJT32:
 265     emitDataRegion(DataRegionData::JumpTable32);
 266     return;
 267   case MCDR_DataRegionEnd:
 268     emitDataRegionEnd();
 269     return;
 270   }
 271 }
 272
 273 void MCMachOStreamer::emitVersionMin(MCVersionMinType Kind, unsigned Major,
 274                                      unsigned Minor, unsigned Update,
 275                                      VersionTuple SDKVersion) {
 276   getAssembler().setVersionMin(Kind, Major, Minor, Update, SDKVersion);
 277 }
 278
 279 void MCMachOStreamer::emitBuildVersion(unsigned Platform, unsigned Major,
 280                                        unsigned Minor, unsigned Update,
 281                                        VersionTuple SDKVersion) {
 282   getAssembler().setBuildVersion((MachO::PlatformType)Platform, Major, Minor,
 283                                  Update, SDKVersion);
 284 }
 285
 286 void MCMachOStreamer::emitThumbFunc(MCSymbol *Symbol) {
 287   // Remember that the function is a thumb function. Fixup and relocation
 288   // values will need adjusted.
 289   getAssembler().setIsThumbFunc(Symbol);
 290   cast<MCSymbolMachO>(Symbol)->setThumbFunc();
 291 }
 292
 293 bool MCMachOStreamer::emitSymbolAttribute(MCSymbol *Sym,
 294                                           MCSymbolAttr Attribute) {
 295   MCSymbolMachO *Symbol = cast<MCSymbolMachO>(Sym);
 296
 297   // Indirect symbols are handled differently, to match how 'as' handles
 298   // them. This makes writing matching .o files easier.
 299   if (Attribute == MCSA_IndirectSymbol) {
 300     // Note that we intentionally cannot use the symbol data here; this is
 301     // important for matching the string table that 'as' generates.
 302     IndirectSymbolData ISD;
 303     ISD.Symbol = Symbol;
 304     ISD.Section = getCurrentSectionOnly();
 305     getAssembler().getIndirectSymbols().push_back(ISD);
 306     return true;
 307   }
 308
 309   // Adding a symbol attribute always introduces the symbol, note that an
 310   // important side effect of calling registerSymbol here is to register
 311   // the symbol with the assembler.
 312   getAssembler().registerSymbol(*Symbol);
 313
 314   // The implementation of symbol attributes is designed to match 'as', but it
 315   // leaves much to desired. It doesn't really make sense to arbitrarily add and
 316   // remove flags, but 'as' allows this (in particular, see .desc).
 317   //
 318   // In the future it might be worth trying to make these operations more well
 319   // defined.
 320   switch (Attribute) {
 321   case MCSA_Invalid:
 322   case MCSA_ELF_TypeFunction:
 323   case MCSA_ELF_TypeIndFunction:
 324   case MCSA_ELF_TypeObject:
 325   case MCSA_ELF_TypeTLS:
 326   case MCSA_ELF_TypeCommon:
 327   case MCSA_ELF_TypeNoType:
 328   case MCSA_ELF_TypeGnuUniqueObject:
 329   case MCSA_Extern:
 330   case MCSA_Hidden:
 331   case MCSA_IndirectSymbol:
 332   case MCSA_Internal:
 333   case MCSA_Protected:
 334   case MCSA_Weak:
 335   case MCSA_Local:
 336   case MCSA_LGlobal:
 337     return false;
 338
 339   case MCSA_Global:
 340     Symbol->setExternal(true);
 341     // This effectively clears the undefined lazy bit, in Darwin 'as', although
 342     // it isn't very consistent because it implements this as part of symbol
 343     // lookup.
 344     //
 345     // FIXME: Cleanup this code, these bits should be emitted based on semantic
 346     // properties, not on the order of definition, etc.
 347     Symbol->setReferenceTypeUndefinedLazy(false);
 348     break;
 349
 350   case MCSA_LazyReference:
 351     // FIXME: This requires -dynamic.
 352     Symbol->setNoDeadStrip();
 353     if (Symbol->isUndefined())
 354       Symbol->setReferenceTypeUndefinedLazy(true);
 355     break;
 356
 357     // Since .reference sets the no dead strip bit, it is equivalent to
 358     // .no_dead_strip in practice.
 359   case MCSA_Reference:
 360   case MCSA_NoDeadStrip:
 361     Symbol->setNoDeadStrip();
 362     break;
 363
 364   case MCSA_SymbolResolver:
 365     Symbol->setSymbolResolver();
 366     break;
 367
 368   case MCSA_AltEntry:
 369     Symbol->setAltEntry();
 370     break;
 371
 372   case MCSA_PrivateExtern:
 373     Symbol->setExternal(true);
 374     Symbol->setPrivateExtern(true);
 375     break;
 376
 377   case MCSA_WeakReference:
 378     // FIXME: This requires -dynamic.
 379     if (Symbol->isUndefined())
 380       Symbol->setWeakReference();
 381     break;
 382
 383   case MCSA_WeakDefinition:
 384     // FIXME: 'as' enforces that this is defined and global. The manual claims
 385     // it has to be in a coalesced section, but this isn't enforced.
 386     Symbol->setWeakDefinition();
 387     break;
 388
 389   case MCSA_WeakDefAutoPrivate:
 390     Symbol->setWeakDefinition();
 391     Symbol->setWeakReference();
 392     break;
 393
 394   case MCSA_Cold:
 395     Symbol->setCold();
 396     break;
 397   }
 398
 399   return true;
 400 }
 401
 402 void MCMachOStreamer::emitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
 403   // Encode the 'desc' value into the lowest implementation defined bits.
 404   getAssembler().registerSymbol(*Symbol);
 405   cast<MCSymbolMachO>(Symbol)->setDesc(DescValue);
 406 }
 407
 408 void MCMachOStreamer::emitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
 409                                        unsigned ByteAlignment) {
 410   // FIXME: Darwin 'as' does appear to allow redef of a .comm by itself.
 411   assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
 412
 413   getAssembler().registerSymbol(*Symbol);
 414   Symbol->setExternal(true);
 415   Symbol->setCommon(Size, ByteAlignment);
 416 }
 417
 418 void MCMachOStreamer::emitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
 419                                             unsigned ByteAlignment) {
 420   // '.lcomm' is equivalent to '.zerofill'.
 421   return emitZerofill(getContext().getObjectFileInfo()->getDataBSSSection(),
 422                       Symbol, Size, ByteAlignment);
 423 }
 424
 425 void MCMachOStreamer::emitZerofill(MCSection *Section, MCSymbol *Symbol,
 426                                    uint64_t Size, unsigned ByteAlignment,
 427                                    SMLoc Loc) {
 428   // On darwin all virtual sections have zerofill type. Disallow the usage of
 429   // .zerofill in non-virtual functions. If something similar is needed, use
 430   // .space or .zero.
 431   if (!Section->isVirtualSection()) {
 432     getContext().reportError(
 433         Loc, "The usage of .zerofill is restricted to sections of "
 434              "ZEROFILL type. Use .zero or .space instead.");
 435     return; // Early returning here shouldn't harm. EmitZeros should work on any
 436             // section.
 437   }
 438
 439   PushSection();
 440   SwitchSection(Section);
 441
 442   // The symbol may not be present, which only creates the section.
 443   if (Symbol) {
 444     emitValueToAlignment(ByteAlignment, 0, 1, 0);
 445     emitLabel(Symbol);
 446     emitZeros(Size);
 447   }
 448   PopSection();
 449 }
 450
 451 // This should always be called with the thread local bss section.  Like the
 452 // .zerofill directive this doesn't actually switch sections on us.
 453 void MCMachOStreamer::emitTBSSSymbol(MCSection *Section, MCSymbol *Symbol,
 454                                      uint64_t Size, unsigned ByteAlignment) {
 455   emitZerofill(Section, Symbol, Size, ByteAlignment);
 456 }
 457
 458 void MCMachOStreamer::emitInstToData(const MCInst &Inst,
 459                                      const MCSubtargetInfo &STI) {
 460   MCDataFragment *DF = getOrCreateDataFragment();
 461
 462   SmallVector<MCFixup, 4> Fixups;
 463   SmallString<256> Code;
 464   raw_svector_ostream VecOS(Code);
 465   getAssembler().getEmitter().encodeInstruction(Inst, VecOS, Fixups, STI);
 466
 467   // Add the fixups and data.
 468   for (MCFixup &Fixup : Fixups) {
 469     Fixup.setOffset(Fixup.getOffset() + DF->getContents().size());
 470     DF->getFixups().push_back(Fixup);
 471   }
 472   DF->setHasInstructions(STI);
 473   DF->getContents().append(Code.begin(), Code.end());
 474 }
 475
 476 void MCMachOStreamer::finishImpl() {
 477   emitFrames(&getAssembler().getBackend());
 478
 479   // We have to set the fragment atom associations so we can relax properly for
 480   // Mach-O.
 481
 482   // First, scan the symbol table to build a lookup table from fragments to
 483   // defining symbols.
 484   DenseMap<const MCFragment *, const MCSymbol *> DefiningSymbolMap;
 485   for (const MCSymbol &Symbol : getAssembler().symbols()) {
 486     if (getAssembler().isSymbolLinkerVisible(Symbol) && Symbol.isInSection() &&
 487         !Symbol.isVariable()) {
 488       // An atom defining symbol should never be internal to a fragment.
 489       assert(Symbol.getOffset() == 0 &&
 490              "Invalid offset in atom defining symbol!");
 491       DefiningSymbolMap[Symbol.getFragment()] = &Symbol;
 492     }
 493   }
 494
 495   // Set the fragment atom associations by tracking the last seen atom defining
 496   // symbol.
 497   for (MCSection &Sec : getAssembler()) {
 498     const MCSymbol *CurrentAtom = nullptr;
 499     for (MCFragment &Frag : Sec) {
 500       if (const MCSymbol *Symbol = DefiningSymbolMap.lookup(&Frag))
 501         CurrentAtom = Symbol;
 502       Frag.setAtom(CurrentAtom);
 503     }
 504   }
 505
 506   this->MCObjectStreamer::finishImpl();
 507 }
 508
 509 MCStreamer *llvm::createMachOStreamer(MCContext &Context,
 510                                       std::unique_ptr<MCAsmBackend> &&MAB,
 511                                       std::unique_ptr<MCObjectWriter> &&OW,
 512                                       std::unique_ptr<MCCodeEmitter> &&CE,
 513                                       bool RelaxAll, bool DWARFMustBeAtTheEnd,
 514                                       bool LabelSections) {
 515   MCMachOStreamer *S =
 516       new MCMachOStreamer(Context, std::move(MAB), std::move(OW), std::move(CE),
 517                           DWARFMustBeAtTheEnd, LabelSections);
 518   const Triple &Target = Context.getTargetTriple();
 519   S->emitVersionForTarget(Target, Context.getObjectFileInfo()->getSDKVersion());
 520   if (RelaxAll)
 521     S->getAssembler().setRelaxAll(true);
 522   return S;
 523 }