MCELFStreamer.cpp revision cd81d94322a39503e4a3e87b6ee03d4fcb3465fb 
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/STLExtras.h"
16#include "llvm/ADT/SmallPtrSet.h"
17#include "llvm/MC/MCAsmBackend.h"
18#include "llvm/MC/MCAssembler.h"
19#include "llvm/MC/MCCodeEmitter.h"
20#include "llvm/MC/MCContext.h"
21#include "llvm/MC/MCELF.h"
22#include "llvm/MC/MCELFSymbolFlags.h"
23#include "llvm/MC/MCExpr.h"
24#include "llvm/MC/MCInst.h"
25#include "llvm/MC/MCObjectFileInfo.h"
26#include "llvm/MC/MCObjectStreamer.h"
27#include "llvm/MC/MCSection.h"
28#include "llvm/MC/MCSectionELF.h"
29#include "llvm/MC/MCSymbol.h"
30#include "llvm/MC/MCValue.h"
31#include "llvm/Support/Debug.h"
32#include "llvm/Support/ELF.h"
33#include "llvm/Support/ErrorHandling.h"
34#include "llvm/Support/raw_ostream.h"
35
36using namespace llvm;
37
38MCELFStreamer::~MCELFStreamer() {
39}
40
41void MCELFStreamer::InitSections() {
42  // This emulates the same behavior of GNU as. This makes it easier
43  // to compare the output as the major sections are in the same order.
44  SwitchSection(getContext().getObjectFileInfo()->getTextSection());
45  EmitCodeAlignment(4);
46
47  SwitchSection(getContext().getObjectFileInfo()->getDataSection());
48  EmitCodeAlignment(4);
49
50  SwitchSection(getContext().getObjectFileInfo()->getBSSSection());
51  EmitCodeAlignment(4);
52
53  SwitchSection(getContext().getObjectFileInfo()->getTextSection());
54}
55
56void MCELFStreamer::EmitLabel(MCSymbol *Symbol) {
57  assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
58
59  MCObjectStreamer::EmitLabel(Symbol);
60
61  const MCSectionELF &Section =
62    static_cast<const MCSectionELF&>(Symbol->getSection());
63  MCSymbolData &SD = getAssembler().getSymbolData(*Symbol);
64  if (Section.getFlags() & ELF::SHF_TLS)
65    MCELF::SetType(SD, ELF::STT_TLS);
66}
67
68void MCELFStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
69  // Let the target do whatever target specific stuff it needs to do.
70  getAssembler().getBackend().handleAssemblerFlag(Flag);
71  // Do any generic stuff we need to do.
72  switch (Flag) {
73  case MCAF_SyntaxUnified: return; // no-op here.
74  case MCAF_Code16: return; // Change parsing mode; no-op here.
75  case MCAF_Code32: return; // Change parsing mode; no-op here.
76  case MCAF_Code64: return; // Change parsing mode; no-op here.
77  case MCAF_SubsectionsViaSymbols:
78    getAssembler().setSubsectionsViaSymbols(true);
79    return;
80  }
81
82  llvm_unreachable("invalid assembler flag!");
83}
84
85void MCELFStreamer::ChangeSection(const MCSection *Section,
86                                  const MCExpr *Subsection) {
87  MCSectionData *CurSection = getCurrentSectionData();
88  if (CurSection && CurSection->isBundleLocked())
89    report_fatal_error("Unterminated .bundle_lock when changing a section");
90  const MCSymbol *Grp = static_cast<const MCSectionELF *>(Section)->getGroup();
91  if (Grp)
92    getAssembler().getOrCreateSymbolData(*Grp);
93  this->MCObjectStreamer::ChangeSection(Section, Subsection);
94}
95
96void MCELFStreamer::EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) {
97  getAssembler().getOrCreateSymbolData(*Symbol);
98  const MCExpr *Value = MCSymbolRefExpr::Create(
99      Symbol, MCSymbolRefExpr::VK_WEAKREF, getContext());
100  Alias->setVariableValue(Value);
101}
102
103// When GNU as encounters more than one .type declaration for an object it seems
104// to use a mechanism similar to the one below to decide which type is actually
105// used in the object file.  The greater of T1 and T2 is selected based on the
106// following ordering:
107//  STT_NOTYPE < STT_OBJECT < STT_FUNC < STT_GNU_IFUNC < STT_TLS < anything else
108// If neither T1 < T2 nor T2 < T1 according to this ordering, use T2 (the user
109// provided type).
110static unsigned CombineSymbolTypes(unsigned T1, unsigned T2) {
111  unsigned TypeOrdering[] = {ELF::STT_NOTYPE, ELF::STT_OBJECT, ELF::STT_FUNC,
112                             ELF::STT_GNU_IFUNC, ELF::STT_TLS};
113  for (unsigned i = 0; i != array_lengthof(TypeOrdering); ++i) {
114    if (T1 == TypeOrdering[i])
115      return T2;
116    if (T2 == TypeOrdering[i])
117      return T1;
118  }
119
120  return T2;
121}
122
123bool MCELFStreamer::EmitSymbolAttribute(MCSymbol *Symbol,
124                                        MCSymbolAttr Attribute) {
125  // Indirect symbols are handled differently, to match how 'as' handles
126  // them. This makes writing matching .o files easier.
127  if (Attribute == MCSA_IndirectSymbol) {
128    // Note that we intentionally cannot use the symbol data here; this is
129    // important for matching the string table that 'as' generates.
130    IndirectSymbolData ISD;
131    ISD.Symbol = Symbol;
132    ISD.SectionData = getCurrentSectionData();
133    getAssembler().getIndirectSymbols().push_back(ISD);
134    return true;
135  }
136
137  // Adding a symbol attribute always introduces the symbol, note that an
138  // important side effect of calling getOrCreateSymbolData here is to register
139  // the symbol with the assembler.
140  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
141
142  // The implementation of symbol attributes is designed to match 'as', but it
143  // leaves much to desired. It doesn't really make sense to arbitrarily add and
144  // remove flags, but 'as' allows this (in particular, see .desc).
145  //
146  // In the future it might be worth trying to make these operations more well
147  // defined.
148  switch (Attribute) {
149  case MCSA_LazyReference:
150  case MCSA_Reference:
151  case MCSA_SymbolResolver:
152  case MCSA_PrivateExtern:
153  case MCSA_WeakDefinition:
154  case MCSA_WeakDefAutoPrivate:
155  case MCSA_Invalid:
156  case MCSA_IndirectSymbol:
157    return false;
158
159  case MCSA_NoDeadStrip:
160  case MCSA_ELF_TypeGnuUniqueObject:
161    // Ignore for now.
162    break;
163
164  case MCSA_Global:
165    MCELF::SetBinding(SD, ELF::STB_GLOBAL);
166    SD.setExternal(true);
167    BindingExplicitlySet.insert(Symbol);
168    break;
169
170  case MCSA_WeakReference:
171  case MCSA_Weak:
172    MCELF::SetBinding(SD, ELF::STB_WEAK);
173    SD.setExternal(true);
174    BindingExplicitlySet.insert(Symbol);
175    break;
176
177  case MCSA_Local:
178    MCELF::SetBinding(SD, ELF::STB_LOCAL);
179    SD.setExternal(false);
180    BindingExplicitlySet.insert(Symbol);
181    break;
182
183  case MCSA_ELF_TypeFunction:
184    MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
185                                          ELF::STT_FUNC));
186    break;
187
188  case MCSA_ELF_TypeIndFunction:
189    MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
190                                          ELF::STT_GNU_IFUNC));
191    break;
192
193  case MCSA_ELF_TypeObject:
194    MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
195                                          ELF::STT_OBJECT));
196    break;
197
198  case MCSA_ELF_TypeTLS:
199    MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
200                                          ELF::STT_TLS));
201    break;
202
203  case MCSA_ELF_TypeCommon:
204    // TODO: Emit these as a common symbol.
205    MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
206                                          ELF::STT_OBJECT));
207    break;
208
209  case MCSA_ELF_TypeNoType:
210    MCELF::SetType(SD, CombineSymbolTypes(MCELF::GetType(SD),
211                                          ELF::STT_NOTYPE));
212    break;
213
214  case MCSA_Protected:
215    MCELF::SetVisibility(SD, ELF::STV_PROTECTED);
216    break;
217
218  case MCSA_Hidden:
219    MCELF::SetVisibility(SD, ELF::STV_HIDDEN);
220    break;
221
222  case MCSA_Internal:
223    MCELF::SetVisibility(SD, ELF::STV_INTERNAL);
224    break;
225  }
226
227  return true;
228}
229
230void MCELFStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
231                                       unsigned ByteAlignment) {
232  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
233
234  if (!BindingExplicitlySet.count(Symbol)) {
235    MCELF::SetBinding(SD, ELF::STB_GLOBAL);
236    SD.setExternal(true);
237  }
238
239  MCELF::SetType(SD, ELF::STT_OBJECT);
240
241  if (MCELF::GetBinding(SD) == ELF_STB_Local) {
242    const MCSection *Section = getAssembler().getContext().getELFSection(".bss",
243                                                         ELF::SHT_NOBITS,
244                                                         ELF::SHF_WRITE |
245                                                         ELF::SHF_ALLOC,
246                                                         SectionKind::getBSS());
247
248    AssignSection(Symbol, Section);
249
250    struct LocalCommon L = {&SD, Size, ByteAlignment};
251    LocalCommons.push_back(L);
252  } else {
253    SD.setCommon(Size, ByteAlignment);
254  }
255
256  SD.setSize(MCConstantExpr::Create(Size, getContext()));
257}
258
259void MCELFStreamer::EmitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
260  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
261  SD.setSize(Value);
262}
263
264void MCELFStreamer::EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
265                                          unsigned ByteAlignment) {
266  // FIXME: Should this be caught and done earlier?
267  MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
268  MCELF::SetBinding(SD, ELF::STB_LOCAL);
269  SD.setExternal(false);
270  BindingExplicitlySet.insert(Symbol);
271  EmitCommonSymbol(Symbol, Size, ByteAlignment);
272}
273
274void MCELFStreamer::EmitValueImpl(const MCExpr *Value, unsigned Size,
275                                  const SMLoc &Loc) {
276  if (getCurrentSectionData()->isBundleLocked())
277    report_fatal_error("Emitting values inside a locked bundle is forbidden");
278  fixSymbolsInTLSFixups(Value);
279  MCObjectStreamer::EmitValueImpl(Value, Size, Loc);
280}
281
282void MCELFStreamer::EmitValueToAlignment(unsigned ByteAlignment,
283                                         int64_t Value,
284                                         unsigned ValueSize,
285                                         unsigned MaxBytesToEmit) {
286  if (getCurrentSectionData()->isBundleLocked())
287    report_fatal_error("Emitting values inside a locked bundle is forbidden");
288  MCObjectStreamer::EmitValueToAlignment(ByteAlignment, Value,
289                                         ValueSize, MaxBytesToEmit);
290}
291
292// Add a symbol for the file name of this module. They start after the
293// null symbol and don't count as normal symbol, i.e. a non-STT_FILE symbol
294// with the same name may appear.
295void MCELFStreamer::EmitFileDirective(StringRef Filename) {
296  getAssembler().addFileName(Filename);
297}
298
299void MCELFStreamer::EmitIdent(StringRef IdentString) {
300  const MCSection *Comment = getAssembler().getContext().getELFSection(
301      ".comment", ELF::SHT_PROGBITS, ELF::SHF_MERGE | ELF::SHF_STRINGS,
302      SectionKind::getReadOnly(), 1, "");
303  PushSection();
304  SwitchSection(Comment);
305  if (!SeenIdent) {
306    EmitIntValue(0, 1);
307    SeenIdent = true;
308  }
309  EmitBytes(IdentString);
310  EmitIntValue(0, 1);
311  PopSection();
312}
313
314void MCELFStreamer::fixSymbolsInTLSFixups(const MCExpr *expr) {
315  switch (expr->getKind()) {
316  case MCExpr::Target:
317    cast<MCTargetExpr>(expr)->fixELFSymbolsInTLSFixups(getAssembler());
318    break;
319  case MCExpr::Constant:
320    break;
321
322  case MCExpr::Binary: {
323    const MCBinaryExpr *be = cast<MCBinaryExpr>(expr);
324    fixSymbolsInTLSFixups(be->getLHS());
325    fixSymbolsInTLSFixups(be->getRHS());
326    break;
327  }
328
329  case MCExpr::SymbolRef: {
330    const MCSymbolRefExpr &symRef = *cast<MCSymbolRefExpr>(expr);
331    switch (symRef.getKind()) {
332    default:
333      return;
334    case MCSymbolRefExpr::VK_GOTTPOFF:
335    case MCSymbolRefExpr::VK_INDNTPOFF:
336    case MCSymbolRefExpr::VK_NTPOFF:
337    case MCSymbolRefExpr::VK_GOTNTPOFF:
338    case MCSymbolRefExpr::VK_TLSGD:
339    case MCSymbolRefExpr::VK_TLSLD:
340    case MCSymbolRefExpr::VK_TLSLDM:
341    case MCSymbolRefExpr::VK_TPOFF:
342    case MCSymbolRefExpr::VK_DTPOFF:
343    case MCSymbolRefExpr::VK_Mips_TLSGD:
344    case MCSymbolRefExpr::VK_Mips_GOTTPREL:
345    case MCSymbolRefExpr::VK_Mips_TPREL_HI:
346    case MCSymbolRefExpr::VK_Mips_TPREL_LO:
347    case MCSymbolRefExpr::VK_PPC_DTPMOD:
348    case MCSymbolRefExpr::VK_PPC_TPREL:
349    case MCSymbolRefExpr::VK_PPC_TPREL_LO:
350    case MCSymbolRefExpr::VK_PPC_TPREL_HI:
351    case MCSymbolRefExpr::VK_PPC_TPREL_HA:
352    case MCSymbolRefExpr::VK_PPC_TPREL_HIGHER:
353    case MCSymbolRefExpr::VK_PPC_TPREL_HIGHERA:
354    case MCSymbolRefExpr::VK_PPC_TPREL_HIGHEST:
355    case MCSymbolRefExpr::VK_PPC_TPREL_HIGHESTA:
356    case MCSymbolRefExpr::VK_PPC_DTPREL:
357    case MCSymbolRefExpr::VK_PPC_DTPREL_LO:
358    case MCSymbolRefExpr::VK_PPC_DTPREL_HI:
359    case MCSymbolRefExpr::VK_PPC_DTPREL_HA:
360    case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHER:
361    case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHERA:
362    case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHEST:
363    case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHESTA:
364    case MCSymbolRefExpr::VK_PPC_GOT_TPREL:
365    case MCSymbolRefExpr::VK_PPC_GOT_TPREL_LO:
366    case MCSymbolRefExpr::VK_PPC_GOT_TPREL_HI:
367    case MCSymbolRefExpr::VK_PPC_GOT_TPREL_HA:
368    case MCSymbolRefExpr::VK_PPC_GOT_DTPREL:
369    case MCSymbolRefExpr::VK_PPC_GOT_DTPREL_LO:
370    case MCSymbolRefExpr::VK_PPC_GOT_DTPREL_HI:
371    case MCSymbolRefExpr::VK_PPC_GOT_DTPREL_HA:
372    case MCSymbolRefExpr::VK_PPC_TLS:
373    case MCSymbolRefExpr::VK_PPC_GOT_TLSGD:
374    case MCSymbolRefExpr::VK_PPC_GOT_TLSGD_LO:
375    case MCSymbolRefExpr::VK_PPC_GOT_TLSGD_HI:
376    case MCSymbolRefExpr::VK_PPC_GOT_TLSGD_HA:
377    case MCSymbolRefExpr::VK_PPC_TLSGD:
378    case MCSymbolRefExpr::VK_PPC_GOT_TLSLD:
379    case MCSymbolRefExpr::VK_PPC_GOT_TLSLD_LO:
380    case MCSymbolRefExpr::VK_PPC_GOT_TLSLD_HI:
381    case MCSymbolRefExpr::VK_PPC_GOT_TLSLD_HA:
382    case MCSymbolRefExpr::VK_PPC_TLSLD:
383      break;
384    }
385    MCSymbolData &SD = getAssembler().getOrCreateSymbolData(symRef.getSymbol());
386    MCELF::SetType(SD, ELF::STT_TLS);
387    break;
388  }
389
390  case MCExpr::Unary:
391    fixSymbolsInTLSFixups(cast<MCUnaryExpr>(expr)->getSubExpr());
392    break;
393  }
394}
395
396void MCELFStreamer::EmitInstToFragment(const MCInst &Inst,
397                                       const MCSubtargetInfo &STI) {
398  this->MCObjectStreamer::EmitInstToFragment(Inst, STI);
399  MCRelaxableFragment &F = *cast<MCRelaxableFragment>(getCurrentFragment());
400
401  for (unsigned i = 0, e = F.getFixups().size(); i != e; ++i)
402    fixSymbolsInTLSFixups(F.getFixups()[i].getValue());
403}
404
405void MCELFStreamer::EmitInstToData(const MCInst &Inst,
406                                   const MCSubtargetInfo &STI) {
407  MCAssembler &Assembler = getAssembler();
408  SmallVector<MCFixup, 4> Fixups;
409  SmallString<256> Code;
410  raw_svector_ostream VecOS(Code);
411  Assembler.getEmitter().EncodeInstruction(Inst, VecOS, Fixups, STI);
412  VecOS.flush();
413
414  for (unsigned i = 0, e = Fixups.size(); i != e; ++i)
415    fixSymbolsInTLSFixups(Fixups[i].getValue());
416
417  // There are several possibilities here:
418  //
419  // If bundling is disabled, append the encoded instruction to the current data
420  // fragment (or create a new such fragment if the current fragment is not a
421  // data fragment).
422  //
423  // If bundling is enabled:
424  // - If we're not in a bundle-locked group, emit the instruction into a
425  //   fragment of its own. If there are no fixups registered for the
426  //   instruction, emit a MCCompactEncodedInstFragment. Otherwise, emit a
427  //   MCDataFragment.
428  // - If we're in a bundle-locked group, append the instruction to the current
429  //   data fragment because we want all the instructions in a group to get into
430  //   the same fragment. Be careful not to do that for the first instruction in
431  //   the group, though.
432  MCDataFragment *DF;
433
434  if (Assembler.isBundlingEnabled()) {
435    MCSectionData *SD = getCurrentSectionData();
436    if (SD->isBundleLocked() && !SD->isBundleGroupBeforeFirstInst())
437      // If we are bundle-locked, we re-use the current fragment.
438      // The bundle-locking directive ensures this is a new data fragment.
439      DF = cast<MCDataFragment>(getCurrentFragment());
440    else if (!SD->isBundleLocked() && Fixups.size() == 0) {
441      // Optimize memory usage by emitting the instruction to a
442      // MCCompactEncodedInstFragment when not in a bundle-locked group and
443      // there are no fixups registered.
444      MCCompactEncodedInstFragment *CEIF = new MCCompactEncodedInstFragment();
445      insert(CEIF);
446      CEIF->getContents().append(Code.begin(), Code.end());
447      return;
448    } else {
449      DF = new MCDataFragment();
450      insert(DF);
451      if (SD->getBundleLockState() == MCSectionData::BundleLockedAlignToEnd) {
452        // If this is a new fragment created for a bundle-locked group, and the
453        // group was marked as "align_to_end", set a flag in the fragment.
454        DF->setAlignToBundleEnd(true);
455      }
456    }
457
458    // We're now emitting an instruction in a bundle group, so this flag has
459    // to be turned off.
460    SD->setBundleGroupBeforeFirstInst(false);
461  } else {
462    DF = getOrCreateDataFragment();
463  }
464
465  // Add the fixups and data.
466  for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
467    Fixups[i].setOffset(Fixups[i].getOffset() + DF->getContents().size());
468    DF->getFixups().push_back(Fixups[i]);
469  }
470  DF->setHasInstructions(true);
471  DF->getContents().append(Code.begin(), Code.end());
472}
473
474void MCELFStreamer::EmitBundleAlignMode(unsigned AlignPow2) {
475  assert(AlignPow2 <= 30 && "Invalid bundle alignment");
476  MCAssembler &Assembler = getAssembler();
477  if (Assembler.getBundleAlignSize() == 0 && AlignPow2 > 0)
478    Assembler.setBundleAlignSize(1 << AlignPow2);
479  else
480    report_fatal_error(".bundle_align_mode should be only set once per file");
481}
482
483void MCELFStreamer::EmitBundleLock(bool AlignToEnd) {
484  MCSectionData *SD = getCurrentSectionData();
485
486  // Sanity checks
487  //
488  if (!getAssembler().isBundlingEnabled())
489    report_fatal_error(".bundle_lock forbidden when bundling is disabled");
490  else if (SD->isBundleLocked())
491    report_fatal_error("Nesting of .bundle_lock is forbidden");
492
493  SD->setBundleLockState(AlignToEnd ? MCSectionData::BundleLockedAlignToEnd :
494                                      MCSectionData::BundleLocked);
495  SD->setBundleGroupBeforeFirstInst(true);
496}
497
498void MCELFStreamer::EmitBundleUnlock() {
499  MCSectionData *SD = getCurrentSectionData();
500
501  // Sanity checks
502  if (!getAssembler().isBundlingEnabled())
503    report_fatal_error(".bundle_unlock forbidden when bundling is disabled");
504  else if (!SD->isBundleLocked())
505    report_fatal_error(".bundle_unlock without matching lock");
506  else if (SD->isBundleGroupBeforeFirstInst())
507    report_fatal_error("Empty bundle-locked group is forbidden");
508
509  SD->setBundleLockState(MCSectionData::NotBundleLocked);
510}
511
512void MCELFStreamer::Flush() {
513  for (std::vector<LocalCommon>::const_iterator i = LocalCommons.begin(),
514                                                e = LocalCommons.end();
515       i != e; ++i) {
516    MCSymbolData *SD = i->SD;
517    uint64_t Size = i->Size;
518    unsigned ByteAlignment = i->ByteAlignment;
519    const MCSymbol &Symbol = SD->getSymbol();
520    const MCSection &Section = Symbol.getSection();
521
522    MCSectionData &SectData = getAssembler().getOrCreateSectionData(Section);
523    new MCAlignFragment(ByteAlignment, 0, 1, ByteAlignment, &SectData);
524
525    MCFragment *F = new MCFillFragment(0, 0, Size, &SectData);
526    SD->setFragment(F);
527
528    // Update the maximum alignment of the section if necessary.
529    if (ByteAlignment > SectData.getAlignment())
530      SectData.setAlignment(ByteAlignment);
531  }
532
533  LocalCommons.clear();
534}
535
536void MCELFStreamer::FinishImpl() {
537  EmitFrames(nullptr);
538
539  Flush();
540
541  this->MCObjectStreamer::FinishImpl();
542}
543
544MCStreamer *llvm::createELFStreamer(MCContext &Context, MCAsmBackend &MAB,
545                                    raw_ostream &OS, MCCodeEmitter *CE,
546                                    bool RelaxAll, bool NoExecStack) {
547  MCELFStreamer *S = new MCELFStreamer(Context, MAB, OS, CE);
548  if (RelaxAll)
549    S->getAssembler().setRelaxAll(true);
550  if (NoExecStack)
551    S->getAssembler().setNoExecStack(true);
552  return S;
553}
554
555void MCELFStreamer::EmitThumbFunc(MCSymbol *Func) {
556  llvm_unreachable("Generic ELF doesn't support this directive");
557}
558
559void MCELFStreamer::EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
560  llvm_unreachable("ELF doesn't support this directive");
561}
562
563void MCELFStreamer::BeginCOFFSymbolDef(const MCSymbol *Symbol) {
564  llvm_unreachable("ELF doesn't support this directive");
565}
566
567void MCELFStreamer::EmitCOFFSymbolStorageClass(int StorageClass) {
568  llvm_unreachable("ELF doesn't support this directive");
569}
570
571void MCELFStreamer::EmitCOFFSymbolType(int Type) {
572  llvm_unreachable("ELF doesn't support this directive");
573}
574
575void MCELFStreamer::EndCOFFSymbolDef() {
576  llvm_unreachable("ELF doesn't support this directive");
577}
578
579void MCELFStreamer::EmitZerofill(const MCSection *Section, MCSymbol *Symbol,
580                                 uint64_t Size, unsigned ByteAlignment) {
581  llvm_unreachable("ELF doesn't support this directive");
582}
583
584void MCELFStreamer::EmitTBSSSymbol(const MCSection *Section, MCSymbol *Symbol,
585                                   uint64_t Size, unsigned ByteAlignment) {
586  llvm_unreachable("ELF doesn't support this directive");
587}
588