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.getSectionName();
 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 && "Creating regular section after DWARF");
 159
 160   // Output a linker-local symbol so we don't need section-relative local
 161   // relocations. The linker hates us when we do that.
 162   if (LabelSections && !HasSectionLabel[Section] &&
 163       !Section->getBeginSymbol()) {
 164     MCSymbol *Label = getContext().createLinkerPrivateTempSymbol();
 165     Section->setBeginSymbol(Label);
 166     HasSectionLabel[Section] = true;
 167   }
 168 }
 169
 170 void MCMachOStreamer::EmitEHSymAttributes(const MCSymbol *Symbol,
 171                                           MCSymbol *EHSymbol) {
 172   getAssembler().registerSymbol(*Symbol);
 173   if (Symbol->isExternal())
 174     EmitSymbolAttribute(EHSymbol, MCSA_Global);
 175   if (cast<MCSymbolMachO>(Symbol)->isWeakDefinition())
 176     EmitSymbolAttribute(EHSymbol, MCSA_WeakDefinition);
 177   if (Symbol->isPrivateExtern())
 178     EmitSymbolAttribute(EHSymbol, MCSA_PrivateExtern);
 179 }
 180
 181 void MCMachOStreamer::EmitLabel(MCSymbol *Symbol, SMLoc Loc) {
 182   // We have to create a new fragment if this is an atom defining symbol,
 183   // fragments cannot span atoms.
 184   if (getAssembler().isSymbolLinkerVisible(*Symbol))
 185     insert(new MCDataFragment());
 186
 187   MCObjectStreamer::EmitLabel(Symbol, Loc);
 188
 189   // This causes the reference type flag to be cleared. Darwin 'as' was "trying"
 190   // to clear the weak reference and weak definition bits too, but the
 191   // implementation was buggy. For now we just try to match 'as', for
 192   // diffability.
 193   //
 194   // FIXME: Cleanup this code, these bits should be emitted based on semantic
 195   // properties, not on the order of definition, etc.
 196   cast<MCSymbolMachO>(Symbol)->clearReferenceType();
 197 }
 198
 199 void MCMachOStreamer::EmitAssignment(MCSymbol *Symbol, const MCExpr *Value) {
 200   MCValue Res;
 201
 202   if (Value->evaluateAsRelocatable(Res, nullptr, nullptr)) {
 203     if (const MCSymbolRefExpr *SymAExpr = Res.getSymA()) {
 204       const MCSymbol &SymA = SymAExpr->getSymbol();
 205       if (!Res.getSymB() && (SymA.getName() == "" || Res.getConstant() != 0))
 206         cast<MCSymbolMachO>(Symbol)->setAltEntry();
 207     }
 208   }
 209   MCObjectStreamer::EmitAssignment(Symbol, Value);
 210 }
 211
 212 void MCMachOStreamer::EmitDataRegion(DataRegionData::KindTy Kind) {
 213   // Create a temporary label to mark the start of the data region.
 214   MCSymbol *Start = getContext().createTempSymbol();
 215   EmitLabel(Start);
 216   // Record the region for the object writer to use.
 217   DataRegionData Data = { Kind, Start, nullptr };
 218   std::vector<DataRegionData> &Regions = getAssembler().getDataRegions();
 219   Regions.push_back(Data);
 220 }
 221
 222 void MCMachOStreamer::EmitDataRegionEnd() {
 223   std::vector<DataRegionData> &Regions = getAssembler().getDataRegions();
 224   assert(!Regions.empty() && "Mismatched .end_data_region!");
 225   DataRegionData &Data = Regions.back();
 226   assert(!Data.End && "Mismatched .end_data_region!");
 227   // Create a temporary label to mark the end of the data region.
 228   Data.End = getContext().createTempSymbol();
 229   EmitLabel(Data.End);
 230 }
 231
 232 void MCMachOStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
 233   // Let the target do whatever target specific stuff it needs to do.
 234   getAssembler().getBackend().handleAssemblerFlag(Flag);
 235   // Do any generic stuff we need to do.
 236   switch (Flag) {
 237   case MCAF_SyntaxUnified: return; // no-op here.
 238   case MCAF_Code16: return; // Change parsing mode; no-op here.
 239   case MCAF_Code32: return; // Change parsing mode; no-op here.
 240   case MCAF_Code64: return; // Change parsing mode; no-op here.
 241   case MCAF_SubsectionsViaSymbols:
 242     getAssembler().setSubsectionsViaSymbols(true);
 243     return;
 244   }
 245 }
 246
 247 void MCMachOStreamer::EmitLinkerOptions(ArrayRef<std::string> Options) {
 248   getAssembler().getLinkerOptions().push_back(Options);
 249 }
 250
 251 void MCMachOStreamer::EmitDataRegion(MCDataRegionType Kind) {
 252   switch (Kind) {
 253   case MCDR_DataRegion:
 254     EmitDataRegion(DataRegionData::Data);
 255     return;
 256   case MCDR_DataRegionJT8:
 257     EmitDataRegion(DataRegionData::JumpTable8);
 258     return;
 259   case MCDR_DataRegionJT16:
 260     EmitDataRegion(DataRegionData::JumpTable16);
 261     return;
 262   case MCDR_DataRegionJT32:
 263     EmitDataRegion(DataRegionData::JumpTable32);
 264     return;
 265   case MCDR_DataRegionEnd:
 266     EmitDataRegionEnd();
 267     return;
 268   }
 269 }
 270
 271 void MCMachOStreamer::EmitVersionMin(MCVersionMinType Kind, unsigned Major,
 272                                      unsigned Minor, unsigned Update,
 273                                      VersionTuple SDKVersion) {
 274   getAssembler().setVersionMin(Kind, Major, Minor, Update, SDKVersion);
 275 }
 276
 277 void MCMachOStreamer::EmitBuildVersion(unsigned Platform, unsigned Major,
 278                                        unsigned Minor, unsigned Update,
 279                                        VersionTuple SDKVersion) {
 280   getAssembler().setBuildVersion((MachO::PlatformType)Platform, Major, Minor,
 281                                  Update, SDKVersion);
 282 }
 283
 284 void MCMachOStreamer::EmitThumbFunc(MCSymbol *Symbol) {
 285   // Remember that the function is a thumb function. Fixup and relocation
 286   // values will need adjusted.
 287   getAssembler().setIsThumbFunc(Symbol);
 288   cast<MCSymbolMachO>(Symbol)->setThumbFunc();
 289 }
 290
 291 bool MCMachOStreamer::EmitSymbolAttribute(MCSymbol *Sym,
 292                                           MCSymbolAttr Attribute) {
 293   MCSymbolMachO *Symbol = cast<MCSymbolMachO>(Sym);
 294
 295   // Indirect symbols are handled differently, to match how 'as' handles
 296   // them. This makes writing matching .o files easier.
 297   if (Attribute == MCSA_IndirectSymbol) {
 298     // Note that we intentionally cannot use the symbol data here; this is
 299     // important for matching the string table that 'as' generates.
 300     IndirectSymbolData ISD;
 301     ISD.Symbol = Symbol;
 302     ISD.Section = getCurrentSectionOnly();
 303     getAssembler().getIndirectSymbols().push_back(ISD);
 304     return true;
 305   }
 306
 307   // Adding a symbol attribute always introduces the symbol, note that an
 308   // important side effect of calling registerSymbol here is to register
 309   // the symbol with the assembler.
 310   getAssembler().registerSymbol(*Symbol);
 311
 312   // The implementation of symbol attributes is designed to match 'as', but it
 313   // leaves much to desired. It doesn't really make sense to arbitrarily add and
 314   // remove flags, but 'as' allows this (in particular, see .desc).
 315   //
 316   // In the future it might be worth trying to make these operations more well
 317   // defined.
 318   switch (Attribute) {
 319   case MCSA_Invalid:
 320   case MCSA_ELF_TypeFunction:
 321   case MCSA_ELF_TypeIndFunction:
 322   case MCSA_ELF_TypeObject:
 323   case MCSA_ELF_TypeTLS:
 324   case MCSA_ELF_TypeCommon:
 325   case MCSA_ELF_TypeNoType:
 326   case MCSA_ELF_TypeGnuUniqueObject:
 327   case MCSA_Hidden:
 328   case MCSA_IndirectSymbol:
 329   case MCSA_Internal:
 330   case MCSA_Protected:
 331   case MCSA_Weak:
 332   case MCSA_Local:
 333   case MCSA_LGlobal:
 334     return false;
 335
 336   case MCSA_Global:
 337     Symbol->setExternal(true);
 338     // This effectively clears the undefined lazy bit, in Darwin 'as', although
 339     // it isn't very consistent because it implements this as part of symbol
 340     // lookup.
 341     //
 342     // FIXME: Cleanup this code, these bits should be emitted based on semantic
 343     // properties, not on the order of definition, etc.
 344     Symbol->setReferenceTypeUndefinedLazy(false);
 345     break;
 346
 347   case MCSA_LazyReference:
 348     // FIXME: This requires -dynamic.
 349     Symbol->setNoDeadStrip();
 350     if (Symbol->isUndefined())
 351       Symbol->setReferenceTypeUndefinedLazy(true);
 352     break;
 353
 354     // Since .reference sets the no dead strip bit, it is equivalent to
 355     // .no_dead_strip in practice.
 356   case MCSA_Reference:
 357   case MCSA_NoDeadStrip:
 358     Symbol->setNoDeadStrip();
 359     break;
 360
 361   case MCSA_SymbolResolver:
 362     Symbol->setSymbolResolver();
 363     break;
 364
 365   case MCSA_AltEntry:
 366     Symbol->setAltEntry();
 367     break;
 368
 369   case MCSA_PrivateExtern:
 370     Symbol->setExternal(true);
 371     Symbol->setPrivateExtern(true);
 372     break;
 373
 374   case MCSA_WeakReference:
 375     // FIXME: This requires -dynamic.
 376     if (Symbol->isUndefined())
 377       Symbol->setWeakReference();
 378     break;
 379
 380   case MCSA_WeakDefinition:
 381     // FIXME: 'as' enforces that this is defined and global. The manual claims
 382     // it has to be in a coalesced section, but this isn't enforced.
 383     Symbol->setWeakDefinition();
 384     break;
 385
 386   case MCSA_WeakDefAutoPrivate:
 387     Symbol->setWeakDefinition();
 388     Symbol->setWeakReference();
 389     break;
 390
 391   case MCSA_Cold:
 392     Symbol->setCold();
 393     break;
 394   }
 395
 396   return true;
 397 }
 398
 399 void MCMachOStreamer::EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
 400   // Encode the 'desc' value into the lowest implementation defined bits.
 401   getAssembler().registerSymbol(*Symbol);
 402   cast<MCSymbolMachO>(Symbol)->setDesc(DescValue);
 403 }
 404
 405 void MCMachOStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
 406                                        unsigned ByteAlignment) {
 407   // FIXME: Darwin 'as' does appear to allow redef of a .comm by itself.
 408   assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
 409
 410   getAssembler().registerSymbol(*Symbol);
 411   Symbol->setExternal(true);
 412   Symbol->setCommon(Size, ByteAlignment);
 413 }
 414
 415 void MCMachOStreamer::EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
 416                                             unsigned ByteAlignment) {
 417   // '.lcomm' is equivalent to '.zerofill'.
 418   return EmitZerofill(getContext().getObjectFileInfo()->getDataBSSSection(),
 419                       Symbol, Size, ByteAlignment);
 420 }
 421
 422 void MCMachOStreamer::EmitZerofill(MCSection *Section, MCSymbol *Symbol,
 423                                    uint64_t Size, unsigned ByteAlignment,
 424                                    SMLoc Loc) {
 425   // On darwin all virtual sections have zerofill type. Disallow the usage of
 426   // .zerofill in non-virtual functions. If something similar is needed, use
 427   // .space or .zero.
 428   if (!Section->isVirtualSection()) {
 429     getContext().reportError(
 430         Loc, "The usage of .zerofill is restricted to sections of "
 431              "ZEROFILL type. Use .zero or .space instead.");
 432     return; // Early returning here shouldn't harm. EmitZeros should work on any
 433             // section.
 434   }
 435
 436   PushSection();
 437   SwitchSection(Section);
 438
 439   // The symbol may not be present, which only creates the section.
 440   if (Symbol) {
 441     EmitValueToAlignment(ByteAlignment, 0, 1, 0);
 442     EmitLabel(Symbol);
 443     EmitZeros(Size);
 444   }
 445   PopSection();
 446 }
 447
 448 // This should always be called with the thread local bss section.  Like the
 449 // .zerofill directive this doesn't actually switch sections on us.
 450 void MCMachOStreamer::EmitTBSSSymbol(MCSection *Section, MCSymbol *Symbol,
 451                                      uint64_t Size, unsigned ByteAlignment) {
 452   EmitZerofill(Section, Symbol, Size, ByteAlignment);
 453 }
 454
 455 void MCMachOStreamer::EmitInstToData(const MCInst &Inst,
 456                                      const MCSubtargetInfo &STI) {
 457   MCDataFragment *DF = getOrCreateDataFragment();
 458
 459   SmallVector<MCFixup, 4> Fixups;
 460   SmallString<256> Code;
 461   raw_svector_ostream VecOS(Code);
 462   getAssembler().getEmitter().encodeInstruction(Inst, VecOS, Fixups, STI);
 463
 464   // Add the fixups and data.
 465   for (MCFixup &Fixup : Fixups) {
 466     Fixup.setOffset(Fixup.getOffset() + DF->getContents().size());
 467     DF->getFixups().push_back(Fixup);
 468   }
 469   DF->setHasInstructions(STI);
 470   DF->getContents().append(Code.begin(), Code.end());
 471 }
 472
 473 void MCMachOStreamer::FinishImpl() {
 474   EmitFrames(&getAssembler().getBackend());
 475
 476   // We have to set the fragment atom associations so we can relax properly for
 477   // Mach-O.
 478
 479   // First, scan the symbol table to build a lookup table from fragments to
 480   // defining symbols.
 481   DenseMap<const MCFragment *, const MCSymbol *> DefiningSymbolMap;
 482   for (const MCSymbol &Symbol : getAssembler().symbols()) {
 483     if (getAssembler().isSymbolLinkerVisible(Symbol) && Symbol.isInSection() &&
 484         !Symbol.isVariable()) {
 485       // An atom defining symbol should never be internal to a fragment.
 486       assert(Symbol.getOffset() == 0 &&
 487              "Invalid offset in atom defining symbol!");
 488       DefiningSymbolMap[Symbol.getFragment()] = &Symbol;
 489     }
 490   }
 491
 492   // Set the fragment atom associations by tracking the last seen atom defining
 493   // symbol.
 494   for (MCSection &Sec : getAssembler()) {
 495     const MCSymbol *CurrentAtom = nullptr;
 496     for (MCFragment &Frag : Sec) {
 497       if (const MCSymbol *Symbol = DefiningSymbolMap.lookup(&Frag))
 498         CurrentAtom = Symbol;
 499       Frag.setAtom(CurrentAtom);
 500     }
 501   }
 502
 503   this->MCObjectStreamer::FinishImpl();
 504 }
 505
 506 MCStreamer *llvm::createMachOStreamer(MCContext &Context,
 507                                       std::unique_ptr<MCAsmBackend> &&MAB,
 508                                       std::unique_ptr<MCObjectWriter> &&OW,
 509                                       std::unique_ptr<MCCodeEmitter> &&CE,
 510                                       bool RelaxAll, bool DWARFMustBeAtTheEnd,
 511                                       bool LabelSections) {
 512   MCMachOStreamer *S =
 513       new MCMachOStreamer(Context, std::move(MAB), std::move(OW), std::move(CE),
 514                           DWARFMustBeAtTheEnd, LabelSections);
 515   const Triple &Target = Context.getObjectFileInfo()->getTargetTriple();
 516   S->EmitVersionForTarget(Target, Context.getObjectFileInfo()->getSDKVersion());
 517   if (RelaxAll)
 518     S->getAssembler().setRelaxAll(true);
 519   return S;
 520 }