xref: /freebsd/contrib/llvm-project/llvm/lib/MC/MCELFStreamer.cpp (revision e40139ff33b48b56a24c808b166b04b8ee6f5b21) 
1 //===- lib/MC/MCELFStreamer.cpp - ELF Object Output -----------------------===//
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 // This file assembles .s files and emits ELF .o object files.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #include "llvm/MC/MCELFStreamer.h"
14 #include "llvm/ADT/SmallString.h"
15 #include "llvm/ADT/SmallVector.h"
16 #include "llvm/BinaryFormat/ELF.h"
17 #include "llvm/MC/MCAsmBackend.h"
18 #include "llvm/MC/MCAsmInfo.h"
19 #include "llvm/MC/MCAssembler.h"
20 #include "llvm/MC/MCCodeEmitter.h"
21 #include "llvm/MC/MCContext.h"
22 #include "llvm/MC/MCExpr.h"
23 #include "llvm/MC/MCFixup.h"
24 #include "llvm/MC/MCFragment.h"
25 #include "llvm/MC/MCObjectFileInfo.h"
26 #include "llvm/MC/MCObjectWriter.h"
27 #include "llvm/MC/MCSection.h"
28 #include "llvm/MC/MCSectionELF.h"
29 #include "llvm/MC/MCStreamer.h"
30 #include "llvm/MC/MCSymbol.h"
31 #include "llvm/MC/MCSymbolELF.h"
32 #include "llvm/Support/Casting.h"
33 #include "llvm/Support/ErrorHandling.h"
34 #include "llvm/Support/TargetRegistry.h"
35 #include "llvm/Support/raw_ostream.h"
36 #include <cassert>
37 #include <cstdint>
38 
39 using namespace llvm;
40 
41 MCELFStreamer::MCELFStreamer(MCContext &Context,
42                              std::unique_ptr<MCAsmBackend> TAB,
43                              std::unique_ptr<MCObjectWriter> OW,
44                              std::unique_ptr<MCCodeEmitter> Emitter)
45     : MCObjectStreamer(Context, std::move(TAB), std::move(OW),
46                        std::move(Emitter)) {}
47 
48 bool MCELFStreamer::isBundleLocked() const {
49   return getCurrentSectionOnly()->isBundleLocked();
50 }
51 
52 void MCELFStreamer::mergeFragment(MCDataFragment *DF,
53                                   MCDataFragment *EF) {
54   MCAssembler &Assembler = getAssembler();
55 
56   if (Assembler.isBundlingEnabled() && Assembler.getRelaxAll()) {
57     uint64_t FSize = EF->getContents().size();
58 
59     if (FSize > Assembler.getBundleAlignSize())
60       report_fatal_error("Fragment can't be larger than a bundle size");
61 
62     uint64_t RequiredBundlePadding = computeBundlePadding(
63         Assembler, EF, DF->getContents().size(), FSize);
64 
65     if (RequiredBundlePadding > UINT8_MAX)
66       report_fatal_error("Padding cannot exceed 255 bytes");
67 
68     if (RequiredBundlePadding > 0) {
69       SmallString<256> Code;
70       raw_svector_ostream VecOS(Code);
71       EF->setBundlePadding(static_cast<uint8_t>(RequiredBundlePadding));
72       Assembler.writeFragmentPadding(VecOS, *EF, FSize);
73 
74       DF->getContents().append(Code.begin(), Code.end());
75     }
76   }
77 
78   flushPendingLabels(DF, DF->getContents().size());
79 
80   for (unsigned i = 0, e = EF->getFixups().size(); i != e; ++i) {
81     EF->getFixups()[i].setOffset(EF->getFixups()[i].getOffset() +
82                                  DF->getContents().size());
83     DF->getFixups().push_back(EF->getFixups()[i]);
84   }
85   if (DF->getSubtargetInfo() == nullptr && EF->getSubtargetInfo())
86     DF->setHasInstructions(*EF->getSubtargetInfo());
87   DF->getContents().append(EF->getContents().begin(), EF->getContents().end());
88 }
89 
90 void MCELFStreamer::InitSections(bool NoExecStack) {
91   MCContext &Ctx = getContext();
92   SwitchSection(Ctx.getObjectFileInfo()->getTextSection());
93   EmitCodeAlignment(4);
94 
95   if (NoExecStack)
96     SwitchSection(Ctx.getAsmInfo()->getNonexecutableStackSection(Ctx));
97 }
98 
99 void MCELFStreamer::EmitLabel(MCSymbol *S, SMLoc Loc) {
100   auto *Symbol = cast<MCSymbolELF>(S);
101   MCObjectStreamer::EmitLabel(Symbol, Loc);
102 
103   const MCSectionELF &Section =
104       static_cast<const MCSectionELF &>(*getCurrentSectionOnly());
105   if (Section.getFlags() & ELF::SHF_TLS)
106     Symbol->setType(ELF::STT_TLS);
107 }
108 
109 void MCELFStreamer::EmitLabel(MCSymbol *S, SMLoc Loc, MCFragment *F) {
110   auto *Symbol = cast<MCSymbolELF>(S);
111   MCObjectStreamer::EmitLabel(Symbol, Loc, F);
112 
113   const MCSectionELF &Section =
114       static_cast<const MCSectionELF &>(*getCurrentSectionOnly());
115   if (Section.getFlags() & ELF::SHF_TLS)
116     Symbol->setType(ELF::STT_TLS);
117 }
118 
119 void MCELFStreamer::EmitAssemblerFlag(MCAssemblerFlag Flag) {
120   // Let the target do whatever target specific stuff it needs to do.
121   getAssembler().getBackend().handleAssemblerFlag(Flag);
122   // Do any generic stuff we need to do.
123   switch (Flag) {
124   case MCAF_SyntaxUnified: return; // no-op here.
125   case MCAF_Code16: return; // Change parsing mode; no-op here.
126   case MCAF_Code32: return; // Change parsing mode; no-op here.
127   case MCAF_Code64: return; // Change parsing mode; no-op here.
128   case MCAF_SubsectionsViaSymbols:
129     getAssembler().setSubsectionsViaSymbols(true);
130     return;
131   }
132 
133   llvm_unreachable("invalid assembler flag!");
134 }
135 
136 // If bundle alignment is used and there are any instructions in the section, it
137 // needs to be aligned to at least the bundle size.
138 static void setSectionAlignmentForBundling(const MCAssembler &Assembler,
139                                            MCSection *Section) {
140   if (Section && Assembler.isBundlingEnabled() && Section->hasInstructions() &&
141       Section->getAlignment() < Assembler.getBundleAlignSize())
142     Section->setAlignment(Align(Assembler.getBundleAlignSize()));
143 }
144 
145 void MCELFStreamer::ChangeSection(MCSection *Section,
146                                   const MCExpr *Subsection) {
147   MCSection *CurSection = getCurrentSectionOnly();
148   if (CurSection && isBundleLocked())
149     report_fatal_error("Unterminated .bundle_lock when changing a section");
150 
151   MCAssembler &Asm = getAssembler();
152   // Ensure the previous section gets aligned if necessary.
153   setSectionAlignmentForBundling(Asm, CurSection);
154   auto *SectionELF = static_cast<const MCSectionELF *>(Section);
155   const MCSymbol *Grp = SectionELF->getGroup();
156   if (Grp)
157     Asm.registerSymbol(*Grp);
158 
159   changeSectionImpl(Section, Subsection);
160   Asm.registerSymbol(*Section->getBeginSymbol());
161 }
162 
163 void MCELFStreamer::EmitWeakReference(MCSymbol *Alias, const MCSymbol *Symbol) {
164   getAssembler().registerSymbol(*Symbol);
165   const MCExpr *Value = MCSymbolRefExpr::create(
166       Symbol, MCSymbolRefExpr::VK_WEAKREF, getContext());
167   Alias->setVariableValue(Value);
168 }
169 
170 // When GNU as encounters more than one .type declaration for an object it seems
171 // to use a mechanism similar to the one below to decide which type is actually
172 // used in the object file.  The greater of T1 and T2 is selected based on the
173 // following ordering:
174 //  STT_NOTYPE < STT_OBJECT < STT_FUNC < STT_GNU_IFUNC < STT_TLS < anything else
175 // If neither T1 < T2 nor T2 < T1 according to this ordering, use T2 (the user
176 // provided type).
177 static unsigned CombineSymbolTypes(unsigned T1, unsigned T2) {
178   for (unsigned Type : {ELF::STT_NOTYPE, ELF::STT_OBJECT, ELF::STT_FUNC,
179                         ELF::STT_GNU_IFUNC, ELF::STT_TLS}) {
180     if (T1 == Type)
181       return T2;
182     if (T2 == Type)
183       return T1;
184   }
185 
186   return T2;
187 }
188 
189 bool MCELFStreamer::EmitSymbolAttribute(MCSymbol *S, MCSymbolAttr Attribute) {
190   auto *Symbol = cast<MCSymbolELF>(S);
191 
192   // Adding a symbol attribute always introduces the symbol, note that an
193   // important side effect of calling registerSymbol here is to register
194   // the symbol with the assembler.
195   getAssembler().registerSymbol(*Symbol);
196 
197   // The implementation of symbol attributes is designed to match 'as', but it
198   // leaves much to desired. It doesn't really make sense to arbitrarily add and
199   // remove flags, but 'as' allows this (in particular, see .desc).
200   //
201   // In the future it might be worth trying to make these operations more well
202   // defined.
203   switch (Attribute) {
204   case MCSA_Cold:
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   case MCSA_LGlobal:
282     llvm_unreachable("ELF doesn't support the .lglobl attribute");
283   }
284 
285   return true;
286 }
287 
288 void MCELFStreamer::EmitCommonSymbol(MCSymbol *S, uint64_t Size,
289                                      unsigned ByteAlignment) {
290   auto *Symbol = cast<MCSymbolELF>(S);
291   getAssembler().registerSymbol(*Symbol);
292 
293   if (!Symbol->isBindingSet()) {
294     Symbol->setBinding(ELF::STB_GLOBAL);
295     Symbol->setExternal(true);
296   }
297 
298   Symbol->setType(ELF::STT_OBJECT);
299 
300   if (Symbol->getBinding() == ELF::STB_LOCAL) {
301     MCSection &Section = *getAssembler().getContext().getELFSection(
302         ".bss", ELF::SHT_NOBITS, ELF::SHF_WRITE | ELF::SHF_ALLOC);
303     MCSectionSubPair P = getCurrentSection();
304     SwitchSection(&Section);
305 
306     EmitValueToAlignment(ByteAlignment, 0, 1, 0);
307     EmitLabel(Symbol);
308     EmitZeros(Size);
309 
310     // Update the maximum alignment of the section if necessary.
311     if (ByteAlignment > Section.getAlignment())
312       Section.setAlignment(Align(ByteAlignment));
313 
314     SwitchSection(P.first, P.second);
315   } else {
316     if(Symbol->declareCommon(Size, ByteAlignment))
317       report_fatal_error("Symbol: " + Symbol->getName() +
318                          " redeclared as different type");
319   }
320 
321   cast<MCSymbolELF>(Symbol)
322       ->setSize(MCConstantExpr::create(Size, getContext()));
323 }
324 
325 void MCELFStreamer::emitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
326   cast<MCSymbolELF>(Symbol)->setSize(Value);
327 }
328 
329 void MCELFStreamer::emitELFSymverDirective(StringRef AliasName,
330                                            const MCSymbol *Aliasee) {
331   getAssembler().Symvers.push_back({AliasName, Aliasee});
332 }
333 
334 void MCELFStreamer::EmitLocalCommonSymbol(MCSymbol *S, uint64_t Size,
335                                           unsigned ByteAlignment) {
336   auto *Symbol = cast<MCSymbolELF>(S);
337   // FIXME: Should this be caught and done earlier?
338   getAssembler().registerSymbol(*Symbol);
339   Symbol->setBinding(ELF::STB_LOCAL);
340   Symbol->setExternal(false);
341   EmitCommonSymbol(Symbol, Size, ByteAlignment);
342 }
343 
344 void MCELFStreamer::EmitValueImpl(const MCExpr *Value, unsigned Size,
345                                   SMLoc Loc) {
346   if (isBundleLocked())
347     report_fatal_error("Emitting values inside a locked bundle is forbidden");
348   fixSymbolsInTLSFixups(Value);
349   MCObjectStreamer::EmitValueImpl(Value, Size, Loc);
350 }
351 
352 void MCELFStreamer::EmitValueToAlignment(unsigned ByteAlignment,
353                                          int64_t Value,
354                                          unsigned ValueSize,
355                                          unsigned MaxBytesToEmit) {
356   if (isBundleLocked())
357     report_fatal_error("Emitting values inside a locked bundle is forbidden");
358   MCObjectStreamer::EmitValueToAlignment(ByteAlignment, Value,
359                                          ValueSize, MaxBytesToEmit);
360 }
361 
362 void MCELFStreamer::emitCGProfileEntry(const MCSymbolRefExpr *From,
363                                        const MCSymbolRefExpr *To,
364                                        uint64_t Count) {
365   getAssembler().CGProfile.push_back({From, To, Count});
366 }
367 
368 void MCELFStreamer::EmitIdent(StringRef IdentString) {
369   MCSection *Comment = getAssembler().getContext().getELFSection(
370       ".comment", ELF::SHT_PROGBITS, ELF::SHF_MERGE | ELF::SHF_STRINGS, 1, "");
371   PushSection();
372   SwitchSection(Comment);
373   if (!SeenIdent) {
374     EmitIntValue(0, 1);
375     SeenIdent = true;
376   }
377   EmitBytes(IdentString);
378   EmitIntValue(0, 1);
379   PopSection();
380 }
381 
382 void MCELFStreamer::fixSymbolsInTLSFixups(const MCExpr *expr) {
383   switch (expr->getKind()) {
384   case MCExpr::Target:
385     cast<MCTargetExpr>(expr)->fixELFSymbolsInTLSFixups(getAssembler());
386     break;
387   case MCExpr::Constant:
388     break;
389 
390   case MCExpr::Binary: {
391     const MCBinaryExpr *be = cast<MCBinaryExpr>(expr);
392     fixSymbolsInTLSFixups(be->getLHS());
393     fixSymbolsInTLSFixups(be->getRHS());
394     break;
395   }
396 
397   case MCExpr::SymbolRef: {
398     const MCSymbolRefExpr &symRef = *cast<MCSymbolRefExpr>(expr);
399     switch (symRef.getKind()) {
400     default:
401       return;
402     case MCSymbolRefExpr::VK_GOTTPOFF:
403     case MCSymbolRefExpr::VK_INDNTPOFF:
404     case MCSymbolRefExpr::VK_NTPOFF:
405     case MCSymbolRefExpr::VK_GOTNTPOFF:
406     case MCSymbolRefExpr::VK_TLSCALL:
407     case MCSymbolRefExpr::VK_TLSDESC:
408     case MCSymbolRefExpr::VK_TLSGD:
409     case MCSymbolRefExpr::VK_TLSLD:
410     case MCSymbolRefExpr::VK_TLSLDM:
411     case MCSymbolRefExpr::VK_TPOFF:
412     case MCSymbolRefExpr::VK_TPREL:
413     case MCSymbolRefExpr::VK_DTPOFF:
414     case MCSymbolRefExpr::VK_DTPREL:
415     case MCSymbolRefExpr::VK_PPC_DTPMOD:
416     case MCSymbolRefExpr::VK_PPC_TPREL_LO:
417     case MCSymbolRefExpr::VK_PPC_TPREL_HI:
418     case MCSymbolRefExpr::VK_PPC_TPREL_HA:
419     case MCSymbolRefExpr::VK_PPC_TPREL_HIGH:
420     case MCSymbolRefExpr::VK_PPC_TPREL_HIGHA:
421     case MCSymbolRefExpr::VK_PPC_TPREL_HIGHER:
422     case MCSymbolRefExpr::VK_PPC_TPREL_HIGHERA:
423     case MCSymbolRefExpr::VK_PPC_TPREL_HIGHEST:
424     case MCSymbolRefExpr::VK_PPC_TPREL_HIGHESTA:
425     case MCSymbolRefExpr::VK_PPC_DTPREL_LO:
426     case MCSymbolRefExpr::VK_PPC_DTPREL_HI:
427     case MCSymbolRefExpr::VK_PPC_DTPREL_HA:
428     case MCSymbolRefExpr::VK_PPC_DTPREL_HIGH:
429     case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHA:
430     case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHER:
431     case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHERA:
432     case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHEST:
433     case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHESTA:
434     case MCSymbolRefExpr::VK_PPC_GOT_TPREL:
435     case MCSymbolRefExpr::VK_PPC_GOT_TPREL_LO:
436     case MCSymbolRefExpr::VK_PPC_GOT_TPREL_HI:
437     case MCSymbolRefExpr::VK_PPC_GOT_TPREL_HA:
438     case MCSymbolRefExpr::VK_PPC_GOT_DTPREL:
439     case MCSymbolRefExpr::VK_PPC_GOT_DTPREL_LO:
440     case MCSymbolRefExpr::VK_PPC_GOT_DTPREL_HI:
441     case MCSymbolRefExpr::VK_PPC_GOT_DTPREL_HA:
442     case MCSymbolRefExpr::VK_PPC_TLS:
443     case MCSymbolRefExpr::VK_PPC_GOT_TLSGD:
444     case MCSymbolRefExpr::VK_PPC_GOT_TLSGD_LO:
445     case MCSymbolRefExpr::VK_PPC_GOT_TLSGD_HI:
446     case MCSymbolRefExpr::VK_PPC_GOT_TLSGD_HA:
447     case MCSymbolRefExpr::VK_PPC_TLSGD:
448     case MCSymbolRefExpr::VK_PPC_GOT_TLSLD:
449     case MCSymbolRefExpr::VK_PPC_GOT_TLSLD_LO:
450     case MCSymbolRefExpr::VK_PPC_GOT_TLSLD_HI:
451     case MCSymbolRefExpr::VK_PPC_GOT_TLSLD_HA:
452     case MCSymbolRefExpr::VK_PPC_TLSLD:
453       break;
454     }
455     getAssembler().registerSymbol(symRef.getSymbol());
456     cast<MCSymbolELF>(symRef.getSymbol()).setType(ELF::STT_TLS);
457     break;
458   }
459 
460   case MCExpr::Unary:
461     fixSymbolsInTLSFixups(cast<MCUnaryExpr>(expr)->getSubExpr());
462     break;
463   }
464 }
465 
466 void MCELFStreamer::finalizeCGProfileEntry(const MCSymbolRefExpr *&SRE) {
467   const MCSymbol *S = &SRE->getSymbol();
468   if (S->isTemporary()) {
469     if (!S->isInSection()) {
470       getContext().reportError(
471           SRE->getLoc(), Twine("Reference to undefined temporary symbol ") +
472                              "`" + S->getName() + "`");
473       return;
474     }
475     S = S->getSection().getBeginSymbol();
476     S->setUsedInReloc();
477     SRE =
478         MCSymbolRefExpr::create(S, SRE->getKind(), getContext(), SRE->getLoc());
479     return;
480   }
481   // Not a temporary, referece it as a weak undefined.
482   bool Created;
483   getAssembler().registerSymbol(*S, &Created);
484   if (Created) {
485     cast<MCSymbolELF>(S)->setBinding(ELF::STB_WEAK);
486     cast<MCSymbolELF>(S)->setExternal(true);
487   }
488 }
489 
490 void MCELFStreamer::finalizeCGProfile() {
491   for (MCAssembler::CGProfileEntry &E : getAssembler().CGProfile) {
492     finalizeCGProfileEntry(E.From);
493     finalizeCGProfileEntry(E.To);
494   }
495 }
496 
497 void MCELFStreamer::EmitInstToFragment(const MCInst &Inst,
498                                        const MCSubtargetInfo &STI) {
499   this->MCObjectStreamer::EmitInstToFragment(Inst, STI);
500   MCRelaxableFragment &F = *cast<MCRelaxableFragment>(getCurrentFragment());
501 
502   for (unsigned i = 0, e = F.getFixups().size(); i != e; ++i)
503     fixSymbolsInTLSFixups(F.getFixups()[i].getValue());
504 }
505 
506 // A fragment can only have one Subtarget, and when bundling is enabled we
507 // sometimes need to use the same fragment. We give an error if there
508 // are conflicting Subtargets.
509 static void CheckBundleSubtargets(const MCSubtargetInfo *OldSTI,
510                                   const MCSubtargetInfo *NewSTI) {
511   if (OldSTI && NewSTI && OldSTI != NewSTI)
512     report_fatal_error("A Bundle can only have one Subtarget.");
513 }
514 
515 void MCELFStreamer::EmitInstToData(const MCInst &Inst,
516                                    const MCSubtargetInfo &STI) {
517   MCAssembler &Assembler = getAssembler();
518   SmallVector<MCFixup, 4> Fixups;
519   SmallString<256> Code;
520   raw_svector_ostream VecOS(Code);
521   Assembler.getEmitter().encodeInstruction(Inst, VecOS, Fixups, STI);
522 
523   for (unsigned i = 0, e = Fixups.size(); i != e; ++i)
524     fixSymbolsInTLSFixups(Fixups[i].getValue());
525 
526   // There are several possibilities here:
527   //
528   // If bundling is disabled, append the encoded instruction to the current data
529   // fragment (or create a new such fragment if the current fragment is not a
530   // data fragment, or the Subtarget has changed).
531   //
532   // If bundling is enabled:
533   // - If we're not in a bundle-locked group, emit the instruction into a
534   //   fragment of its own. If there are no fixups registered for the
535   //   instruction, emit a MCCompactEncodedInstFragment. Otherwise, emit a
536   //   MCDataFragment.
537   // - If we're in a bundle-locked group, append the instruction to the current
538   //   data fragment because we want all the instructions in a group to get into
539   //   the same fragment. Be careful not to do that for the first instruction in
540   //   the group, though.
541   MCDataFragment *DF;
542 
543   if (Assembler.isBundlingEnabled()) {
544     MCSection &Sec = *getCurrentSectionOnly();
545     if (Assembler.getRelaxAll() && isBundleLocked()) {
546       // If the -mc-relax-all flag is used and we are bundle-locked, we re-use
547       // the current bundle group.
548       DF = BundleGroups.back();
549       CheckBundleSubtargets(DF->getSubtargetInfo(), &STI);
550     }
551     else if (Assembler.getRelaxAll() && !isBundleLocked())
552       // When not in a bundle-locked group and the -mc-relax-all flag is used,
553       // we create a new temporary fragment which will be later merged into
554       // the current fragment.
555       DF = new MCDataFragment();
556     else if (isBundleLocked() && !Sec.isBundleGroupBeforeFirstInst()) {
557       // If we are bundle-locked, we re-use the current fragment.
558       // The bundle-locking directive ensures this is a new data fragment.
559       DF = cast<MCDataFragment>(getCurrentFragment());
560       CheckBundleSubtargets(DF->getSubtargetInfo(), &STI);
561     }
562     else if (!isBundleLocked() && Fixups.size() == 0) {
563       // Optimize memory usage by emitting the instruction to a
564       // MCCompactEncodedInstFragment when not in a bundle-locked group and
565       // there are no fixups registered.
566       MCCompactEncodedInstFragment *CEIF = new MCCompactEncodedInstFragment();
567       insert(CEIF);
568       CEIF->getContents().append(Code.begin(), Code.end());
569       CEIF->setHasInstructions(STI);
570       return;
571     } else {
572       DF = new MCDataFragment();
573       insert(DF);
574     }
575     if (Sec.getBundleLockState() == MCSection::BundleLockedAlignToEnd) {
576       // If this fragment is for a group marked "align_to_end", set a flag
577       // in the fragment. This can happen after the fragment has already been
578       // created if there are nested bundle_align groups and an inner one
579       // is the one marked align_to_end.
580       DF->setAlignToBundleEnd(true);
581     }
582 
583     // We're now emitting an instruction in a bundle group, so this flag has
584     // to be turned off.
585     Sec.setBundleGroupBeforeFirstInst(false);
586   } else {
587     DF = getOrCreateDataFragment(&STI);
588   }
589 
590   // Add the fixups and data.
591   for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
592     Fixups[i].setOffset(Fixups[i].getOffset() + DF->getContents().size());
593     DF->getFixups().push_back(Fixups[i]);
594   }
595   DF->setHasInstructions(STI);
596   DF->getContents().append(Code.begin(), Code.end());
597 
598   if (Assembler.isBundlingEnabled() && Assembler.getRelaxAll()) {
599     if (!isBundleLocked()) {
600       mergeFragment(getOrCreateDataFragment(&STI), DF);
601       delete DF;
602     }
603   }
604 }
605 
606 void MCELFStreamer::EmitBundleAlignMode(unsigned AlignPow2) {
607   assert(AlignPow2 <= 30 && "Invalid bundle alignment");
608   MCAssembler &Assembler = getAssembler();
609   if (AlignPow2 > 0 && (Assembler.getBundleAlignSize() == 0 ||
610                         Assembler.getBundleAlignSize() == 1U << AlignPow2))
611     Assembler.setBundleAlignSize(1U << AlignPow2);
612   else
613     report_fatal_error(".bundle_align_mode cannot be changed once set");
614 }
615 
616 void MCELFStreamer::EmitBundleLock(bool AlignToEnd) {
617   MCSection &Sec = *getCurrentSectionOnly();
618 
619   // Sanity checks
620   //
621   if (!getAssembler().isBundlingEnabled())
622     report_fatal_error(".bundle_lock forbidden when bundling is disabled");
623 
624   if (!isBundleLocked())
625     Sec.setBundleGroupBeforeFirstInst(true);
626 
627   if (getAssembler().getRelaxAll() && !isBundleLocked()) {
628     // TODO: drop the lock state and set directly in the fragment
629     MCDataFragment *DF = new MCDataFragment();
630     BundleGroups.push_back(DF);
631   }
632 
633   Sec.setBundleLockState(AlignToEnd ? MCSection::BundleLockedAlignToEnd
634                                     : MCSection::BundleLocked);
635 }
636 
637 void MCELFStreamer::EmitBundleUnlock() {
638   MCSection &Sec = *getCurrentSectionOnly();
639 
640   // Sanity checks
641   if (!getAssembler().isBundlingEnabled())
642     report_fatal_error(".bundle_unlock forbidden when bundling is disabled");
643   else if (!isBundleLocked())
644     report_fatal_error(".bundle_unlock without matching lock");
645   else if (Sec.isBundleGroupBeforeFirstInst())
646     report_fatal_error("Empty bundle-locked group is forbidden");
647 
648   // When the -mc-relax-all flag is used, we emit instructions to fragments
649   // stored on a stack. When the bundle unlock is emitted, we pop a fragment
650   // from the stack a merge it to the one below.
651   if (getAssembler().getRelaxAll()) {
652     assert(!BundleGroups.empty() && "There are no bundle groups");
653     MCDataFragment *DF = BundleGroups.back();
654 
655     // FIXME: Use BundleGroups to track the lock state instead.
656     Sec.setBundleLockState(MCSection::NotBundleLocked);
657 
658     // FIXME: Use more separate fragments for nested groups.
659     if (!isBundleLocked()) {
660       mergeFragment(getOrCreateDataFragment(DF->getSubtargetInfo()), DF);
661       BundleGroups.pop_back();
662       delete DF;
663     }
664 
665     if (Sec.getBundleLockState() != MCSection::BundleLockedAlignToEnd)
666       getOrCreateDataFragment()->setAlignToBundleEnd(false);
667   } else
668     Sec.setBundleLockState(MCSection::NotBundleLocked);
669 }
670 
671 void MCELFStreamer::FinishImpl() {
672   // Ensure the last section gets aligned if necessary.
673   MCSection *CurSection = getCurrentSectionOnly();
674   setSectionAlignmentForBundling(getAssembler(), CurSection);
675 
676   finalizeCGProfile();
677   EmitFrames(nullptr);
678 
679   this->MCObjectStreamer::FinishImpl();
680 }
681 
682 void MCELFStreamer::EmitThumbFunc(MCSymbol *Func) {
683   llvm_unreachable("Generic ELF doesn't support this directive");
684 }
685 
686 void MCELFStreamer::EmitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
687   llvm_unreachable("ELF doesn't support this directive");
688 }
689 
690 void MCELFStreamer::EmitZerofill(MCSection *Section, MCSymbol *Symbol,
691                                  uint64_t Size, unsigned ByteAlignment,
692                                  SMLoc Loc) {
693   llvm_unreachable("ELF doesn't support this directive");
694 }
695 
696 void MCELFStreamer::EmitTBSSSymbol(MCSection *Section, MCSymbol *Symbol,
697                                    uint64_t Size, unsigned ByteAlignment) {
698   llvm_unreachable("ELF doesn't support this directive");
699 }
700 
701 MCStreamer *llvm::createELFStreamer(MCContext &Context,
702                                     std::unique_ptr<MCAsmBackend> &&MAB,
703                                     std::unique_ptr<MCObjectWriter> &&OW,
704                                     std::unique_ptr<MCCodeEmitter> &&CE,
705                                     bool RelaxAll) {
706   MCELFStreamer *S =
707       new MCELFStreamer(Context, std::move(MAB), std::move(OW), std::move(CE));
708   if (RelaxAll)
709     S->getAssembler().setRelaxAll(true);
710   return S;
711 }
712