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      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/MCELFStreamer.h"
     15 #include "llvm/ADT/SmallString.h"
     16 #include "llvm/ADT/SmallVector.h"
     17 #include "llvm/BinaryFormat/ELF.h"
     18 #include "llvm/MC/MCAsmBackend.h"
     19 #include "llvm/MC/MCAsmInfo.h"
     20 #include "llvm/MC/MCAssembler.h"
     21 #include "llvm/MC/MCCodeEmitter.h"
     22 #include "llvm/MC/MCContext.h"
     23 #include "llvm/MC/MCExpr.h"
     24 #include "llvm/MC/MCFixup.h"
     25 #include "llvm/MC/MCFragment.h"
     26 #include "llvm/MC/MCObjectFileInfo.h"
     27 #include "llvm/MC/MCObjectWriter.h"
     28 #include "llvm/MC/MCSection.h"
     29 #include "llvm/MC/MCSectionELF.h"
     30 #include "llvm/MC/MCStreamer.h"
     31 #include "llvm/MC/MCSymbol.h"
     32 #include "llvm/MC/MCSymbolELF.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 <cstdint>
     39 
     40 using namespace llvm;
     41 
     42 MCELFStreamer::MCELFStreamer(MCContext &Context,
     43                              std::unique_ptr<MCAsmBackend> TAB,
     44                              std::unique_ptr<MCObjectWriter> OW,
     45                              std::unique_ptr<MCCodeEmitter> Emitter)
     46     : MCObjectStreamer(Context, std::move(TAB), std::move(OW),
     47                        std::move(Emitter)) {}
     48 
     49 bool MCELFStreamer::isBundleLocked() const {
     50   return getCurrentSectionOnly()->isBundleLocked();
     51 }
     52 
     53 void MCELFStreamer::mergeFragment(MCDataFragment *DF,
     54                                   MCDataFragment *EF) {
     55   MCAssembler &Assembler = getAssembler();
     56 
     57   if (Assembler.isBundlingEnabled() && Assembler.getRelaxAll()) {
     58     uint64_t FSize = EF->getContents().size();
     59 
     60     if (FSize > Assembler.getBundleAlignSize())
     61       report_fatal_error("Fragment can't be larger than a bundle size");
     62 
     63     uint64_t RequiredBundlePadding = computeBundlePadding(
     64         Assembler, EF, DF->getContents().size(), FSize);
     65 
     66     if (RequiredBundlePadding > UINT8_MAX)
     67       report_fatal_error("Padding cannot exceed 255 bytes");
     68 
     69     if (RequiredBundlePadding > 0) {
     70       SmallString<256> Code;
     71       raw_svector_ostream VecOS(Code);
     72       EF->setBundlePadding(static_cast<uint8_t>(RequiredBundlePadding));
     73       Assembler.writeFragmentPadding(VecOS, *EF, FSize);
     74 
     75       DF->getContents().append(Code.begin(), Code.end());
     76     }
     77   }
     78 
     79   flushPendingLabels(DF, DF->getContents().size());
     80 
     81   for (unsigned i = 0, e = EF->getFixups().size(); i != e; ++i) {
     82     EF->getFixups()[i].setOffset(EF->getFixups()[i].getOffset() +
     83                                  DF->getContents().size());
     84     DF->getFixups().push_back(EF->getFixups()[i]);
     85   }
     86   if (DF->getSubtargetInfo() == nullptr && EF->getSubtargetInfo())
     87     DF->setHasInstructions(*EF->getSubtargetInfo());
     88   DF->getContents().append(EF->getContents().begin(), EF->getContents().end());
     89 }
     90 
     91 void MCELFStreamer::InitSections(bool NoExecStack) {
     92   MCContext &Ctx = getContext();
     93   SwitchSection(Ctx.getObjectFileInfo()->getTextSection());
     94   EmitCodeAlignment(4);
     95 
     96   if (NoExecStack)
     97     SwitchSection(Ctx.getAsmInfo()->getNonexecutableStackSection(Ctx));
     98 }
     99 
    100 void MCELFStreamer::EmitLabel(MCSymbol *S, SMLoc Loc) {
    101   auto *Symbol = cast<MCSymbolELF>(S);
    102   MCObjectStreamer::EmitLabel(Symbol, Loc);
    103 
    104   const MCSectionELF &Section =
    105       static_cast<const MCSectionELF &>(*getCurrentSectionOnly());
    106   if (Section.getFlags() & ELF::SHF_TLS)
    107     Symbol->setType(ELF::STT_TLS);
    108 }
    109 
    110 void MCELFStreamer::EmitLabel(MCSymbol *S, SMLoc Loc, MCFragment *F) {
    111   auto *Symbol = cast<MCSymbolELF>(S);
    112   MCObjectStreamer::EmitLabel(Symbol, Loc, F);
    113 
    114   const MCSectionELF &Section =
    115       static_cast<const MCSectionELF &>(*getCurrentSectionOnly());
    116   if (Section.getFlags() & ELF::SHF_TLS)
    117     Symbol->setType(ELF::STT_TLS);
    118 }
    119 
    120 void MCELFStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
    121   // Let the target do whatever target specific stuff it needs to do.
    122   getAssembler().getBackend().handleAssemblerFlag(Flag);
    123   // Do any generic stuff we need to do.
    124   switch (Flag) {
    125   case MCAF_SyntaxUnified: return; // no-op here.
    126   case MCAF_Code16: return; // Change parsing mode; no-op here.
    127   case MCAF_Code32: return; // Change parsing mode; no-op here.
    128   case MCAF_Code64: return; // Change parsing mode; no-op here.
    129   case MCAF_SubsectionsViaSymbols:
    130     getAssembler().setSubsectionsViaSymbols(true);
    131     return;
    132   }
    133 
    134   llvm_unreachable("invalid assembler flag!");
    135 }
    136 
    137 // If bundle alignment is used and there are any instructions in the section, it
    138 // needs to be aligned to at least the bundle size.
    139 static void setSectionAlignmentForBundling(const MCAssembler &Assembler,
    140                                            MCSection *Section) {
    141   if (Section && Assembler.isBundlingEnabled() && Section->hasInstructions() &&
    142       Section->getAlignment() < Assembler.getBundleAlignSize())
    143     Section->setAlignment(Assembler.getBundleAlignSize());
    144 }
    145 
    146 void MCELFStreamer::ChangeSection(MCSection *Section,
    147                                   const MCExpr *Subsection) {
    148   MCSection *CurSection = getCurrentSectionOnly();
    149   if (CurSection && isBundleLocked())
    150     report_fatal_error("Unterminated .bundle_lock when changing a section");
    151 
    152   MCAssembler &Asm = getAssembler();
    153   // Ensure the previous section gets aligned if necessary.
    154   setSectionAlignmentForBundling(Asm, CurSection);
    155   auto *SectionELF = static_cast<const MCSectionELF *>(Section);
    156   const MCSymbol *Grp = SectionELF->getGroup();
    157   if (Grp)
    158     Asm.registerSymbol(*Grp);
    159 
    160   changeSectionImpl(Section, Subsection);
    161   Asm.registerSymbol(*Section->getBeginSymbol());
    162 }
    163 
    164 void MCELFStreamer::EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) {
    165   getAssembler().registerSymbol(*Symbol);
    166   const MCExpr *Value = MCSymbolRefExpr::create(
    167       Symbol, MCSymbolRefExpr::VK_WEAKREF, getContext());
    168   Alias->setVariableValue(Value);
    169 }
    170 
    171 // When GNU as encounters more than one .type declaration for an object it seems
    172 // to use a mechanism similar to the one below to decide which type is actually
    173 // used in the object file.  The greater of T1 and T2 is selected based on the
    174 // following ordering:
    175 //  STT_NOTYPE < STT_OBJECT < STT_FUNC < STT_GNU_IFUNC < STT_TLS < anything else
    176 // If neither T1 < T2 nor T2 < T1 according to this ordering, use T2 (the user
    177 // provided type).
    178 static unsigned CombineSymbolTypes(unsigned T1, unsigned T2) {
    179   for (unsigned Type : {ELF::STT_NOTYPE, ELF::STT_OBJECT, ELF::STT_FUNC,
    180                         ELF::STT_GNU_IFUNC, ELF::STT_TLS}) {
    181     if (T1 == Type)
    182       return T2;
    183     if (T2 == Type)
    184       return T1;
    185   }
    186 
    187   return T2;
    188 }
    189 
    190 bool MCELFStreamer::EmitSymbolAttribute(MCSymbol *S, MCSymbolAttr Attribute) {
    191   auto *Symbol = cast<MCSymbolELF>(S);
    192 
    193   // Adding a symbol attribute always introduces the symbol, note that an
    194   // important side effect of calling registerSymbol here is to register
    195   // the symbol with the assembler.
    196   getAssembler().registerSymbol(*Symbol);
    197 
    198   // The implementation of symbol attributes is designed to match 'as', but it
    199   // leaves much to desired. It doesn't really make sense to arbitrarily add and
    200   // remove flags, but 'as' allows this (in particular, see .desc).
    201   //
    202   // In the future it might be worth trying to make these operations more well
    203   // defined.
    204   switch (Attribute) {
    205   case MCSA_LazyReference:
    206   case MCSA_Reference:
    207   case MCSA_SymbolResolver:
    208   case MCSA_PrivateExtern:
    209   case MCSA_WeakDefinition:
    210   case MCSA_WeakDefAutoPrivate:
    211   case MCSA_Invalid:
    212   case MCSA_IndirectSymbol:
    213     return false;
    214 
    215   case MCSA_NoDeadStrip:
    216     // Ignore for now.
    217     break;
    218 
    219   case MCSA_ELF_TypeGnuUniqueObject:
    220     Symbol->setType(CombineSymbolTypes(Symbol->getType(), ELF::STT_OBJECT));
    221     Symbol->setBinding(ELF::STB_GNU_UNIQUE);
    222     Symbol->setExternal(true);
    223     break;
    224 
    225   case MCSA_Global:
    226     Symbol->setBinding(ELF::STB_GLOBAL);
    227     Symbol->setExternal(true);
    228     break;
    229 
    230   case MCSA_WeakReference:
    231   case MCSA_Weak:
    232     Symbol->setBinding(ELF::STB_WEAK);
    233     Symbol->setExternal(true);
    234     break;
    235 
    236   case MCSA_Local:
    237     Symbol->setBinding(ELF::STB_LOCAL);
    238     Symbol->setExternal(false);
    239     break;
    240 
    241   case MCSA_ELF_TypeFunction:
    242     Symbol->setType(CombineSymbolTypes(Symbol->getType(), ELF::STT_FUNC));
    243     break;
    244 
    245   case MCSA_ELF_TypeIndFunction:
    246     Symbol->setType(CombineSymbolTypes(Symbol->getType(), ELF::STT_GNU_IFUNC));
    247     break;
    248 
    249   case MCSA_ELF_TypeObject:
    250     Symbol->setType(CombineSymbolTypes(Symbol->getType(), ELF::STT_OBJECT));
    251     break;
    252 
    253   case MCSA_ELF_TypeTLS:
    254     Symbol->setType(CombineSymbolTypes(Symbol->getType(), ELF::STT_TLS));
    255     break;
    256 
    257   case MCSA_ELF_TypeCommon:
    258     // TODO: Emit these as a common symbol.
    259     Symbol->setType(CombineSymbolTypes(Symbol->getType(), ELF::STT_OBJECT));
    260     break;
    261 
    262   case MCSA_ELF_TypeNoType:
    263     Symbol->setType(CombineSymbolTypes(Symbol->getType(), ELF::STT_NOTYPE));
    264     break;
    265 
    266   case MCSA_Protected:
    267     Symbol->setVisibility(ELF::STV_PROTECTED);
    268     break;
    269 
    270   case MCSA_Hidden:
    271     Symbol->setVisibility(ELF::STV_HIDDEN);
    272     break;
    273 
    274   case MCSA_Internal:
    275     Symbol->setVisibility(ELF::STV_INTERNAL);
    276     break;
    277 
    278   case MCSA_AltEntry:
    279     llvm_unreachable("ELF doesn't support the .alt_entry attribute");
    280   }
    281 
    282   return true;
    283 }
    284 
    285 void MCELFStreamer::EmitCommonSymbol(MCSymbol *S, uint64_t Size,
    286                                      unsigned ByteAlignment) {
    287   auto *Symbol = cast<MCSymbolELF>(S);
    288   getAssembler().registerSymbol(*Symbol);
    289 
    290   if (!Symbol->isBindingSet()) {
    291     Symbol->setBinding(ELF::STB_GLOBAL);
    292     Symbol->setExternal(true);
    293   }
    294 
    295   Symbol->setType(ELF::STT_OBJECT);
    296 
    297   if (Symbol->getBinding() == ELF::STB_LOCAL) {
    298     MCSection &Section = *getAssembler().getContext().getELFSection(
    299         ".bss", ELF::SHT_NOBITS, ELF::SHF_WRITE | ELF::SHF_ALLOC);
    300     MCSectionSubPair P = getCurrentSection();
    301     SwitchSection(&Section);
    302 
    303     EmitValueToAlignment(ByteAlignment, 0, 1, 0);
    304     EmitLabel(Symbol);
    305     EmitZeros(Size);
    306 
    307     // Update the maximum alignment of the section if necessary.
    308     if (ByteAlignment > Section.getAlignment())
    309       Section.setAlignment(ByteAlignment);
    310 
    311     SwitchSection(P.first, P.second);
    312   } else {
    313     if(Symbol->declareCommon(Size, ByteAlignment))
    314       report_fatal_error("Symbol: " + Symbol->getName() +
    315                          " redeclared as different type");
    316   }
    317 
    318   cast<MCSymbolELF>(Symbol)
    319       ->setSize(MCConstantExpr::create(Size, getContext()));
    320 }
    321 
    322 void MCELFStreamer::emitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
    323   cast<MCSymbolELF>(Symbol)->setSize(Value);
    324 }
    325 
    326 void MCELFStreamer::emitELFSymverDirective(StringRef AliasName,
    327                                            const MCSymbol *Aliasee) {
    328   getAssembler().Symvers.push_back({AliasName, Aliasee});
    329 }
    330 
    331 void MCELFStreamer::EmitLocalCommonSymbol(MCSymbol *S, uint64_t Size,
    332                                           unsigned ByteAlignment) {
    333   auto *Symbol = cast<MCSymbolELF>(S);
    334   // FIXME: Should this be caught and done earlier?
    335   getAssembler().registerSymbol(*Symbol);
    336   Symbol->setBinding(ELF::STB_LOCAL);
    337   Symbol->setExternal(false);
    338   EmitCommonSymbol(Symbol, Size, ByteAlignment);
    339 }
    340 
    341 void MCELFStreamer::EmitValueImpl(const MCExpr *Value, unsigned Size,
    342                                   SMLoc Loc) {
    343   if (isBundleLocked())
    344     report_fatal_error("Emitting values inside a locked bundle is forbidden");
    345   fixSymbolsInTLSFixups(Value);
    346   MCObjectStreamer::EmitValueImpl(Value, Size, Loc);
    347 }
    348 
    349 void MCELFStreamer::EmitValueToAlignment(unsigned ByteAlignment,
    350                                          int64_t Value,
    351                                          unsigned ValueSize,
    352                                          unsigned MaxBytesToEmit) {
    353   if (isBundleLocked())
    354     report_fatal_error("Emitting values inside a locked bundle is forbidden");
    355   MCObjectStreamer::EmitValueToAlignment(ByteAlignment, Value,
    356                                          ValueSize, MaxBytesToEmit);
    357 }
    358 
    359 void MCELFStreamer::emitCGProfileEntry(const MCSymbolRefExpr *From,
    360                                        const MCSymbolRefExpr *To,
    361                                        uint64_t Count) {
    362   getAssembler().CGProfile.push_back({From, To, Count});
    363 }
    364 
    365 void MCELFStreamer::EmitIdent(StringRef IdentString) {
    366   MCSection *Comment = getAssembler().getContext().getELFSection(
    367       ".comment", ELF::SHT_PROGBITS, ELF::SHF_MERGE | ELF::SHF_STRINGS, 1, "");
    368   PushSection();
    369   SwitchSection(Comment);
    370   if (!SeenIdent) {
    371     EmitIntValue(0, 1);
    372     SeenIdent = true;
    373   }
    374   EmitBytes(IdentString);
    375   EmitIntValue(0, 1);
    376   PopSection();
    377 }
    378 
    379 void MCELFStreamer::fixSymbolsInTLSFixups(const MCExpr *expr) {
    380   switch (expr->getKind()) {
    381   case MCExpr::Target:
    382     cast<MCTargetExpr>(expr)->fixELFSymbolsInTLSFixups(getAssembler());
    383     break;
    384   case MCExpr::Constant:
    385     break;
    386 
    387   case MCExpr::Binary: {
    388     const MCBinaryExpr *be = cast<MCBinaryExpr>(expr);
    389     fixSymbolsInTLSFixups(be->getLHS());
    390     fixSymbolsInTLSFixups(be->getRHS());
    391     break;
    392   }
    393 
    394   case MCExpr::SymbolRef: {
    395     const MCSymbolRefExpr &symRef = *cast<MCSymbolRefExpr>(expr);
    396     switch (symRef.getKind()) {
    397     default:
    398       return;
    399     case MCSymbolRefExpr::VK_GOTTPOFF:
    400     case MCSymbolRefExpr::VK_INDNTPOFF:
    401     case MCSymbolRefExpr::VK_NTPOFF:
    402     case MCSymbolRefExpr::VK_GOTNTPOFF:
    403     case MCSymbolRefExpr::VK_TLSGD:
    404     case MCSymbolRefExpr::VK_TLSLD:
    405     case MCSymbolRefExpr::VK_TLSLDM:
    406     case MCSymbolRefExpr::VK_TPOFF:
    407     case MCSymbolRefExpr::VK_TPREL:
    408     case MCSymbolRefExpr::VK_DTPOFF:
    409     case MCSymbolRefExpr::VK_DTPREL:
    410     case MCSymbolRefExpr::VK_PPC_DTPMOD:
    411     case MCSymbolRefExpr::VK_PPC_TPREL_LO:
    412     case MCSymbolRefExpr::VK_PPC_TPREL_HI:
    413     case MCSymbolRefExpr::VK_PPC_TPREL_HA:
    414     case MCSymbolRefExpr::VK_PPC_TPREL_HIGH:
    415     case MCSymbolRefExpr::VK_PPC_TPREL_HIGHA:
    416     case MCSymbolRefExpr::VK_PPC_TPREL_HIGHER:
    417     case MCSymbolRefExpr::VK_PPC_TPREL_HIGHERA:
    418     case MCSymbolRefExpr::VK_PPC_TPREL_HIGHEST:
    419     case MCSymbolRefExpr::VK_PPC_TPREL_HIGHESTA:
    420     case MCSymbolRefExpr::VK_PPC_DTPREL_LO:
    421     case MCSymbolRefExpr::VK_PPC_DTPREL_HI:
    422     case MCSymbolRefExpr::VK_PPC_DTPREL_HA:
    423     case MCSymbolRefExpr::VK_PPC_DTPREL_HIGH:
    424     case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHA:
    425     case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHER:
    426     case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHERA:
    427     case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHEST:
    428     case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHESTA:
    429     case MCSymbolRefExpr::VK_PPC_GOT_TPREL:
    430     case MCSymbolRefExpr::VK_PPC_GOT_TPREL_LO:
    431     case MCSymbolRefExpr::VK_PPC_GOT_TPREL_HI:
    432     case MCSymbolRefExpr::VK_PPC_GOT_TPREL_HA:
    433     case MCSymbolRefExpr::VK_PPC_GOT_DTPREL:
    434     case MCSymbolRefExpr::VK_PPC_GOT_DTPREL_LO:
    435     case MCSymbolRefExpr::VK_PPC_GOT_DTPREL_HI:
    436     case MCSymbolRefExpr::VK_PPC_GOT_DTPREL_HA:
    437     case MCSymbolRefExpr::VK_PPC_TLS:
    438     case MCSymbolRefExpr::VK_PPC_GOT_TLSGD:
    439     case MCSymbolRefExpr::VK_PPC_GOT_TLSGD_LO:
    440     case MCSymbolRefExpr::VK_PPC_GOT_TLSGD_HI:
    441     case MCSymbolRefExpr::VK_PPC_GOT_TLSGD_HA:
    442     case MCSymbolRefExpr::VK_PPC_TLSGD:
    443     case MCSymbolRefExpr::VK_PPC_GOT_TLSLD:
    444     case MCSymbolRefExpr::VK_PPC_GOT_TLSLD_LO:
    445     case MCSymbolRefExpr::VK_PPC_GOT_TLSLD_HI:
    446     case MCSymbolRefExpr::VK_PPC_GOT_TLSLD_HA:
    447     case MCSymbolRefExpr::VK_PPC_TLSLD:
    448       break;
    449     }
    450     getAssembler().registerSymbol(symRef.getSymbol());
    451     cast<MCSymbolELF>(symRef.getSymbol()).setType(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::finalizeCGProfileEntry(const MCSymbolRefExpr *&SRE) {
    462   const MCSymbol *S = &SRE->getSymbol();
    463   if (S->isTemporary()) {
    464     if (!S->isInSection()) {
    465       getContext().reportError(
    466           SRE->getLoc(), Twine("Reference to undefined temporary symbol ") +
    467                              "`" + S->getName() + "`");
    468       return;
    469     }
    470     S = S->getSection().getBeginSymbol();
    471     S->setUsedInReloc();
    472     SRE =
    473         MCSymbolRefExpr::create(S, SRE->getKind(), getContext(), SRE->getLoc());
    474     return;
    475   }
    476   // Not a temporary, referece it as a weak undefined.
    477   bool Created;
    478   getAssembler().registerSymbol(*S, &Created);
    479   if (Created) {
    480     cast<MCSymbolELF>(S)->setBinding(ELF::STB_WEAK);
    481     cast<MCSymbolELF>(S)->setExternal(true);
    482   }
    483 }
    484 
    485 void MCELFStreamer::finalizeCGProfile() {
    486   for (MCAssembler::CGProfileEntry &E : getAssembler().CGProfile) {
    487     finalizeCGProfileEntry(E.From);
    488     finalizeCGProfileEntry(E.To);
    489   }
    490 }
    491 
    492 void MCELFStreamer::EmitInstToFragment(const MCInst &Inst,
    493                                        const MCSubtargetInfo &STI) {
    494   this->MCObjectStreamer::EmitInstToFragment(Inst, STI);
    495   MCRelaxableFragment &F = *cast<MCRelaxableFragment>(getCurrentFragment());
    496 
    497   for (unsigned i = 0, e = F.getFixups().size(); i != e; ++i)
    498     fixSymbolsInTLSFixups(F.getFixups()[i].getValue());
    499 }
    500 
    501 // A fragment can only have one Subtarget, and when bundling is enabled we
    502 // sometimes need to use the same fragment. We give an error if there
    503 // are conflicting Subtargets.
    504 static void CheckBundleSubtargets(const MCSubtargetInfo *OldSTI,
    505                                   const MCSubtargetInfo *NewSTI) {
    506   if (OldSTI && NewSTI && OldSTI != NewSTI)
    507     report_fatal_error("A Bundle can only have one Subtarget.");
    508 }
    509 
    510 void MCELFStreamer::EmitInstToData(const MCInst &Inst,
    511                                    const MCSubtargetInfo &STI) {
    512   MCAssembler &Assembler = getAssembler();
    513   SmallVector<MCFixup, 4> Fixups;
    514   SmallString<256> Code;
    515   raw_svector_ostream VecOS(Code);
    516   Assembler.getEmitter().encodeInstruction(Inst, VecOS, Fixups, STI);
    517 
    518   for (unsigned i = 0, e = Fixups.size(); i != e; ++i)
    519     fixSymbolsInTLSFixups(Fixups[i].getValue());
    520 
    521   // There are several possibilities here:
    522   //
    523   // If bundling is disabled, append the encoded instruction to the current data
    524   // fragment (or create a new such fragment if the current fragment is not a
    525   // data fragment, or the Subtarget has changed).
    526   //
    527   // If bundling is enabled:
    528   // - If we're not in a bundle-locked group, emit the instruction into a
    529   //   fragment of its own. If there are no fixups registered for the
    530   //   instruction, emit a MCCompactEncodedInstFragment. Otherwise, emit a
    531   //   MCDataFragment.
    532   // - If we're in a bundle-locked group, append the instruction to the current
    533   //   data fragment because we want all the instructions in a group to get into
    534   //   the same fragment. Be careful not to do that for the first instruction in
    535   //   the group, though.
    536   MCDataFragment *DF;
    537 
    538   if (Assembler.isBundlingEnabled()) {
    539     MCSection &Sec = *getCurrentSectionOnly();
    540     if (Assembler.getRelaxAll() && isBundleLocked()) {
    541       // If the -mc-relax-all flag is used and we are bundle-locked, we re-use
    542       // the current bundle group.
    543       DF = BundleGroups.back();
    544       CheckBundleSubtargets(DF->getSubtargetInfo(), &STI);
    545     }
    546     else if (Assembler.getRelaxAll() && !isBundleLocked())
    547       // When not in a bundle-locked group and the -mc-relax-all flag is used,
    548       // we create a new temporary fragment which will be later merged into
    549       // the current fragment.
    550       DF = new MCDataFragment();
    551     else if (isBundleLocked() && !Sec.isBundleGroupBeforeFirstInst()) {
    552       // If we are bundle-locked, we re-use the current fragment.
    553       // The bundle-locking directive ensures this is a new data fragment.
    554       DF = cast<MCDataFragment>(getCurrentFragment());
    555       CheckBundleSubtargets(DF->getSubtargetInfo(), &STI);
    556     }
    557     else if (!isBundleLocked() && Fixups.size() == 0) {
    558       // Optimize memory usage by emitting the instruction to a
    559       // MCCompactEncodedInstFragment when not in a bundle-locked group and
    560       // there are no fixups registered.
    561       MCCompactEncodedInstFragment *CEIF = new MCCompactEncodedInstFragment();
    562       insert(CEIF);
    563       CEIF->getContents().append(Code.begin(), Code.end());
    564       CEIF->setHasInstructions(STI);
    565       return;
    566     } else {
    567       DF = new MCDataFragment();
    568       insert(DF);
    569     }
    570     if (Sec.getBundleLockState() == MCSection::BundleLockedAlignToEnd) {
    571       // If this fragment is for a group marked "align_to_end", set a flag
    572       // in the fragment. This can happen after the fragment has already been
    573       // created if there are nested bundle_align groups and an inner one
    574       // is the one marked align_to_end.
    575       DF->setAlignToBundleEnd(true);
    576     }
    577 
    578     // We're now emitting an instruction in a bundle group, so this flag has
    579     // to be turned off.
    580     Sec.setBundleGroupBeforeFirstInst(false);
    581   } else {
    582     DF = getOrCreateDataFragment(&STI);
    583   }
    584 
    585   // Add the fixups and data.
    586   for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
    587     Fixups[i].setOffset(Fixups[i].getOffset() + DF->getContents().size());
    588     DF->getFixups().push_back(Fixups[i]);
    589   }
    590   DF->setHasInstructions(STI);
    591   DF->getContents().append(Code.begin(), Code.end());
    592 
    593   if (Assembler.isBundlingEnabled() && Assembler.getRelaxAll()) {
    594     if (!isBundleLocked()) {
    595       mergeFragment(getOrCreateDataFragment(&STI), DF);
    596       delete DF;
    597     }
    598   }
    599 }
    600 
    601 void MCELFStreamer::EmitBundleAlignMode(unsigned AlignPow2) {
    602   assert(AlignPow2 <= 30 && "Invalid bundle alignment");
    603   MCAssembler &Assembler = getAssembler();
    604   if (AlignPow2 > 0 && (Assembler.getBundleAlignSize() == 0 ||
    605                         Assembler.getBundleAlignSize() == 1U << AlignPow2))
    606     Assembler.setBundleAlignSize(1U << AlignPow2);
    607   else
    608     report_fatal_error(".bundle_align_mode cannot be changed once set");
    609 }
    610 
    611 void MCELFStreamer::EmitBundleLock(bool AlignToEnd) {
    612   MCSection &Sec = *getCurrentSectionOnly();
    613 
    614   // Sanity checks
    615   //
    616   if (!getAssembler().isBundlingEnabled())
    617     report_fatal_error(".bundle_lock forbidden when bundling is disabled");
    618 
    619   if (!isBundleLocked())
    620     Sec.setBundleGroupBeforeFirstInst(true);
    621 
    622   if (getAssembler().getRelaxAll() && !isBundleLocked()) {
    623     // TODO: drop the lock state and set directly in the fragment
    624     MCDataFragment *DF = new MCDataFragment();
    625     BundleGroups.push_back(DF);
    626   }
    627 
    628   Sec.setBundleLockState(AlignToEnd ? MCSection::BundleLockedAlignToEnd
    629                                     : MCSection::BundleLocked);
    630 }
    631 
    632 void MCELFStreamer::EmitBundleUnlock() {
    633   MCSection &Sec = *getCurrentSectionOnly();
    634 
    635   // Sanity checks
    636   if (!getAssembler().isBundlingEnabled())
    637     report_fatal_error(".bundle_unlock forbidden when bundling is disabled");
    638   else if (!isBundleLocked())
    639     report_fatal_error(".bundle_unlock without matching lock");
    640   else if (Sec.isBundleGroupBeforeFirstInst())
    641     report_fatal_error("Empty bundle-locked group is forbidden");
    642 
    643   // When the -mc-relax-all flag is used, we emit instructions to fragments
    644   // stored on a stack. When the bundle unlock is emitted, we pop a fragment
    645   // from the stack a merge it to the one below.
    646   if (getAssembler().getRelaxAll()) {
    647     assert(!BundleGroups.empty() && "There are no bundle groups");
    648     MCDataFragment *DF = BundleGroups.back();
    649 
    650     // FIXME: Use BundleGroups to track the lock state instead.
    651     Sec.setBundleLockState(MCSection::NotBundleLocked);
    652 
    653     // FIXME: Use more separate fragments for nested groups.
    654     if (!isBundleLocked()) {
    655       mergeFragment(getOrCreateDataFragment(DF->getSubtargetInfo()), DF);
    656       BundleGroups.pop_back();
    657       delete DF;
    658     }
    659 
    660     if (Sec.getBundleLockState() != MCSection::BundleLockedAlignToEnd)
    661       getOrCreateDataFragment()->setAlignToBundleEnd(false);
    662   } else
    663     Sec.setBundleLockState(MCSection::NotBundleLocked);
    664 }
    665 
    666 void MCELFStreamer::FinishImpl() {
    667   // Ensure the last section gets aligned if necessary.
    668   MCSection *CurSection = getCurrentSectionOnly();
    669   setSectionAlignmentForBundling(getAssembler(), CurSection);
    670 
    671   finalizeCGProfile();
    672   EmitFrames(nullptr);
    673 
    674   this->MCObjectStreamer::FinishImpl();
    675 }
    676 
    677 void MCELFStreamer::EmitThumbFunc(MCSymbol *Func) {
    678   llvm_unreachable("Generic ELF doesn't support this directive");
    679 }
    680 
    681 void MCELFStreamer::EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
    682   llvm_unreachable("ELF doesn't support this directive");
    683 }
    684 
    685 void MCELFStreamer::EmitZerofill(MCSection *Section, MCSymbol *Symbol,
    686                                  uint64_t Size, unsigned ByteAlignment,
    687                                  SMLoc Loc) {
    688   llvm_unreachable("ELF doesn't support this directive");
    689 }
    690 
    691 void MCELFStreamer::EmitTBSSSymbol(MCSection *Section, MCSymbol *Symbol,
    692                                    uint64_t Size, unsigned ByteAlignment) {
    693   llvm_unreachable("ELF doesn't support this directive");
    694 }
    695 
    696 MCStreamer *llvm::createELFStreamer(MCContext &Context,
    697                                     std::unique_ptr<MCAsmBackend> &&MAB,
    698                                     std::unique_ptr<MCObjectWriter> &&OW,
    699                                     std::unique_ptr<MCCodeEmitter> &&CE,
    700                                     bool RelaxAll) {
    701   MCELFStreamer *S =
    702       new MCELFStreamer(Context, std::move(MAB), std::move(OW), std::move(CE));
    703   if (RelaxAll)
    704     S->getAssembler().setRelaxAll(true);
    705   return S;
    706 }
    707