xref: /freebsd/contrib/llvm-project/llvm/lib/MC/MCELFStreamer.cpp (revision 0d8fe2373503aeac48492f28073049a8bfa4feb5) 
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::emitLabelAtPos(MCSymbol *S, SMLoc Loc, MCFragment *F,
110                                    uint64_t Offset) {
111   auto *Symbol = cast<MCSymbolELF>(S);
112   MCObjectStreamer::emitLabelAtPos(Symbol, Loc, F, Offset);
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(Align(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_Cold:
206   case MCSA_Extern:
207   case MCSA_LazyReference:
208   case MCSA_Reference:
209   case MCSA_SymbolResolver:
210   case MCSA_PrivateExtern:
211   case MCSA_WeakDefinition:
212   case MCSA_WeakDefAutoPrivate:
213   case MCSA_Invalid:
214   case MCSA_IndirectSymbol:
215     return false;
216 
217   case MCSA_NoDeadStrip:
218     // Ignore for now.
219     break;
220 
221   case MCSA_ELF_TypeGnuUniqueObject:
222     Symbol->setType(CombineSymbolTypes(Symbol->getType(), ELF::STT_OBJECT));
223     Symbol->setBinding(ELF::STB_GNU_UNIQUE);
224     break;
225 
226   case MCSA_Global:
227     // For `.weak x; .global x`, GNU as sets the binding to STB_WEAK while we
228     // traditionally set the binding to STB_GLOBAL. This is error-prone, so we
229     // error on such cases. Note, we also disallow changed binding from .local.
230     if (Symbol->isBindingSet() && Symbol->getBinding() != ELF::STB_GLOBAL)
231       getContext().reportError(getStartTokLoc(),
232                                Symbol->getName() +
233                                    " changed binding to STB_GLOBAL");
234     Symbol->setBinding(ELF::STB_GLOBAL);
235     break;
236 
237   case MCSA_WeakReference:
238   case MCSA_Weak:
239     // For `.global x; .weak x`, both MC and GNU as set the binding to STB_WEAK.
240     // We emit a warning for now but may switch to an error in the future.
241     if (Symbol->isBindingSet() && Symbol->getBinding() != ELF::STB_WEAK)
242       getContext().reportWarning(
243           getStartTokLoc(), Symbol->getName() + " changed binding to STB_WEAK");
244     Symbol->setBinding(ELF::STB_WEAK);
245     break;
246 
247   case MCSA_Local:
248     if (Symbol->isBindingSet() && Symbol->getBinding() != ELF::STB_LOCAL)
249       getContext().reportError(getStartTokLoc(),
250                                Symbol->getName() +
251                                    " changed binding to STB_LOCAL");
252     Symbol->setBinding(ELF::STB_LOCAL);
253     break;
254 
255   case MCSA_ELF_TypeFunction:
256     Symbol->setType(CombineSymbolTypes(Symbol->getType(), ELF::STT_FUNC));
257     break;
258 
259   case MCSA_ELF_TypeIndFunction:
260     Symbol->setType(CombineSymbolTypes(Symbol->getType(), ELF::STT_GNU_IFUNC));
261     break;
262 
263   case MCSA_ELF_TypeObject:
264     Symbol->setType(CombineSymbolTypes(Symbol->getType(), ELF::STT_OBJECT));
265     break;
266 
267   case MCSA_ELF_TypeTLS:
268     Symbol->setType(CombineSymbolTypes(Symbol->getType(), ELF::STT_TLS));
269     break;
270 
271   case MCSA_ELF_TypeCommon:
272     // TODO: Emit these as a common symbol.
273     Symbol->setType(CombineSymbolTypes(Symbol->getType(), ELF::STT_OBJECT));
274     break;
275 
276   case MCSA_ELF_TypeNoType:
277     Symbol->setType(CombineSymbolTypes(Symbol->getType(), ELF::STT_NOTYPE));
278     break;
279 
280   case MCSA_Protected:
281     Symbol->setVisibility(ELF::STV_PROTECTED);
282     break;
283 
284   case MCSA_Hidden:
285     Symbol->setVisibility(ELF::STV_HIDDEN);
286     break;
287 
288   case MCSA_Internal:
289     Symbol->setVisibility(ELF::STV_INTERNAL);
290     break;
291 
292   case MCSA_AltEntry:
293     llvm_unreachable("ELF doesn't support the .alt_entry attribute");
294 
295   case MCSA_LGlobal:
296     llvm_unreachable("ELF doesn't support the .lglobl attribute");
297   }
298 
299   return true;
300 }
301 
302 void MCELFStreamer::emitCommonSymbol(MCSymbol *S, uint64_t Size,
303                                      unsigned ByteAlignment) {
304   auto *Symbol = cast<MCSymbolELF>(S);
305   getAssembler().registerSymbol(*Symbol);
306 
307   if (!Symbol->isBindingSet())
308     Symbol->setBinding(ELF::STB_GLOBAL);
309 
310   Symbol->setType(ELF::STT_OBJECT);
311 
312   if (Symbol->getBinding() == ELF::STB_LOCAL) {
313     MCSection &Section = *getAssembler().getContext().getELFSection(
314         ".bss", ELF::SHT_NOBITS, ELF::SHF_WRITE | ELF::SHF_ALLOC);
315     MCSectionSubPair P = getCurrentSection();
316     SwitchSection(&Section);
317 
318     emitValueToAlignment(ByteAlignment, 0, 1, 0);
319     emitLabel(Symbol);
320     emitZeros(Size);
321 
322     SwitchSection(P.first, P.second);
323   } else {
324     if(Symbol->declareCommon(Size, ByteAlignment))
325       report_fatal_error("Symbol: " + Symbol->getName() +
326                          " redeclared as different type");
327   }
328 
329   cast<MCSymbolELF>(Symbol)
330       ->setSize(MCConstantExpr::create(Size, getContext()));
331 }
332 
333 void MCELFStreamer::emitELFSize(MCSymbol *Symbol, const MCExpr *Value) {
334   cast<MCSymbolELF>(Symbol)->setSize(Value);
335 }
336 
337 void MCELFStreamer::emitELFSymverDirective(StringRef AliasName,
338                                            const MCSymbol *Aliasee) {
339   getAssembler().Symvers.push_back(
340       MCAssembler::Symver{AliasName, Aliasee, getStartTokLoc()});
341 }
342 
343 void MCELFStreamer::emitLocalCommonSymbol(MCSymbol *S, uint64_t Size,
344                                           unsigned ByteAlignment) {
345   auto *Symbol = cast<MCSymbolELF>(S);
346   // FIXME: Should this be caught and done earlier?
347   getAssembler().registerSymbol(*Symbol);
348   Symbol->setBinding(ELF::STB_LOCAL);
349   emitCommonSymbol(Symbol, Size, ByteAlignment);
350 }
351 
352 void MCELFStreamer::emitValueImpl(const MCExpr *Value, unsigned Size,
353                                   SMLoc Loc) {
354   if (isBundleLocked())
355     report_fatal_error("Emitting values inside a locked bundle is forbidden");
356   fixSymbolsInTLSFixups(Value);
357   MCObjectStreamer::emitValueImpl(Value, Size, Loc);
358 }
359 
360 void MCELFStreamer::emitValueToAlignment(unsigned ByteAlignment,
361                                          int64_t Value,
362                                          unsigned ValueSize,
363                                          unsigned MaxBytesToEmit) {
364   if (isBundleLocked())
365     report_fatal_error("Emitting values inside a locked bundle is forbidden");
366   MCObjectStreamer::emitValueToAlignment(ByteAlignment, Value,
367                                          ValueSize, MaxBytesToEmit);
368 }
369 
370 void MCELFStreamer::emitCGProfileEntry(const MCSymbolRefExpr *From,
371                                        const MCSymbolRefExpr *To,
372                                        uint64_t Count) {
373   getAssembler().CGProfile.push_back({From, To, Count});
374 }
375 
376 void MCELFStreamer::emitIdent(StringRef IdentString) {
377   MCSection *Comment = getAssembler().getContext().getELFSection(
378       ".comment", ELF::SHT_PROGBITS, ELF::SHF_MERGE | ELF::SHF_STRINGS, 1, "");
379   PushSection();
380   SwitchSection(Comment);
381   if (!SeenIdent) {
382     emitInt8(0);
383     SeenIdent = true;
384   }
385   emitBytes(IdentString);
386   emitInt8(0);
387   PopSection();
388 }
389 
390 void MCELFStreamer::fixSymbolsInTLSFixups(const MCExpr *expr) {
391   switch (expr->getKind()) {
392   case MCExpr::Target:
393     cast<MCTargetExpr>(expr)->fixELFSymbolsInTLSFixups(getAssembler());
394     break;
395   case MCExpr::Constant:
396     break;
397 
398   case MCExpr::Binary: {
399     const MCBinaryExpr *be = cast<MCBinaryExpr>(expr);
400     fixSymbolsInTLSFixups(be->getLHS());
401     fixSymbolsInTLSFixups(be->getRHS());
402     break;
403   }
404 
405   case MCExpr::SymbolRef: {
406     const MCSymbolRefExpr &symRef = *cast<MCSymbolRefExpr>(expr);
407     switch (symRef.getKind()) {
408     default:
409       return;
410     case MCSymbolRefExpr::VK_GOTTPOFF:
411     case MCSymbolRefExpr::VK_INDNTPOFF:
412     case MCSymbolRefExpr::VK_NTPOFF:
413     case MCSymbolRefExpr::VK_GOTNTPOFF:
414     case MCSymbolRefExpr::VK_TLSCALL:
415     case MCSymbolRefExpr::VK_TLSDESC:
416     case MCSymbolRefExpr::VK_TLSGD:
417     case MCSymbolRefExpr::VK_TLSLD:
418     case MCSymbolRefExpr::VK_TLSLDM:
419     case MCSymbolRefExpr::VK_TPOFF:
420     case MCSymbolRefExpr::VK_TPREL:
421     case MCSymbolRefExpr::VK_DTPOFF:
422     case MCSymbolRefExpr::VK_DTPREL:
423     case MCSymbolRefExpr::VK_PPC_DTPMOD:
424     case MCSymbolRefExpr::VK_PPC_TPREL_LO:
425     case MCSymbolRefExpr::VK_PPC_TPREL_HI:
426     case MCSymbolRefExpr::VK_PPC_TPREL_HA:
427     case MCSymbolRefExpr::VK_PPC_TPREL_HIGH:
428     case MCSymbolRefExpr::VK_PPC_TPREL_HIGHA:
429     case MCSymbolRefExpr::VK_PPC_TPREL_HIGHER:
430     case MCSymbolRefExpr::VK_PPC_TPREL_HIGHERA:
431     case MCSymbolRefExpr::VK_PPC_TPREL_HIGHEST:
432     case MCSymbolRefExpr::VK_PPC_TPREL_HIGHESTA:
433     case MCSymbolRefExpr::VK_PPC_DTPREL_LO:
434     case MCSymbolRefExpr::VK_PPC_DTPREL_HI:
435     case MCSymbolRefExpr::VK_PPC_DTPREL_HA:
436     case MCSymbolRefExpr::VK_PPC_DTPREL_HIGH:
437     case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHA:
438     case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHER:
439     case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHERA:
440     case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHEST:
441     case MCSymbolRefExpr::VK_PPC_DTPREL_HIGHESTA:
442     case MCSymbolRefExpr::VK_PPC_GOT_TPREL:
443     case MCSymbolRefExpr::VK_PPC_GOT_TPREL_LO:
444     case MCSymbolRefExpr::VK_PPC_GOT_TPREL_HI:
445     case MCSymbolRefExpr::VK_PPC_GOT_TPREL_HA:
446     case MCSymbolRefExpr::VK_PPC_GOT_TPREL_PCREL:
447     case MCSymbolRefExpr::VK_PPC_GOT_DTPREL:
448     case MCSymbolRefExpr::VK_PPC_GOT_DTPREL_LO:
449     case MCSymbolRefExpr::VK_PPC_GOT_DTPREL_HI:
450     case MCSymbolRefExpr::VK_PPC_GOT_DTPREL_HA:
451     case MCSymbolRefExpr::VK_PPC_TLS:
452     case MCSymbolRefExpr::VK_PPC_TLS_PCREL:
453     case MCSymbolRefExpr::VK_PPC_GOT_TLSGD:
454     case MCSymbolRefExpr::VK_PPC_GOT_TLSGD_LO:
455     case MCSymbolRefExpr::VK_PPC_GOT_TLSGD_HI:
456     case MCSymbolRefExpr::VK_PPC_GOT_TLSGD_HA:
457     case MCSymbolRefExpr::VK_PPC_GOT_TLSGD_PCREL:
458     case MCSymbolRefExpr::VK_PPC_TLSGD:
459     case MCSymbolRefExpr::VK_PPC_GOT_TLSLD:
460     case MCSymbolRefExpr::VK_PPC_GOT_TLSLD_LO:
461     case MCSymbolRefExpr::VK_PPC_GOT_TLSLD_HI:
462     case MCSymbolRefExpr::VK_PPC_GOT_TLSLD_HA:
463     case MCSymbolRefExpr::VK_PPC_TLSLD:
464       break;
465     }
466     getAssembler().registerSymbol(symRef.getSymbol());
467     cast<MCSymbolELF>(symRef.getSymbol()).setType(ELF::STT_TLS);
468     break;
469   }
470 
471   case MCExpr::Unary:
472     fixSymbolsInTLSFixups(cast<MCUnaryExpr>(expr)->getSubExpr());
473     break;
474   }
475 }
476 
477 void MCELFStreamer::finalizeCGProfileEntry(const MCSymbolRefExpr *&SRE) {
478   const MCSymbol *S = &SRE->getSymbol();
479   if (S->isTemporary()) {
480     if (!S->isInSection()) {
481       getContext().reportError(
482           SRE->getLoc(), Twine("Reference to undefined temporary symbol ") +
483                              "`" + S->getName() + "`");
484       return;
485     }
486     S = S->getSection().getBeginSymbol();
487     S->setUsedInReloc();
488     SRE =
489         MCSymbolRefExpr::create(S, SRE->getKind(), getContext(), SRE->getLoc());
490     return;
491   }
492   // Not a temporary, referece it as a weak undefined.
493   bool Created;
494   getAssembler().registerSymbol(*S, &Created);
495   if (Created)
496     cast<MCSymbolELF>(S)->setBinding(ELF::STB_WEAK);
497 }
498 
499 void MCELFStreamer::finalizeCGProfile() {
500   for (MCAssembler::CGProfileEntry &E : getAssembler().CGProfile) {
501     finalizeCGProfileEntry(E.From);
502     finalizeCGProfileEntry(E.To);
503   }
504 }
505 
506 void MCELFStreamer::emitInstToFragment(const MCInst &Inst,
507                                        const MCSubtargetInfo &STI) {
508   this->MCObjectStreamer::emitInstToFragment(Inst, STI);
509   MCRelaxableFragment &F = *cast<MCRelaxableFragment>(getCurrentFragment());
510 
511   for (unsigned i = 0, e = F.getFixups().size(); i != e; ++i)
512     fixSymbolsInTLSFixups(F.getFixups()[i].getValue());
513 }
514 
515 // A fragment can only have one Subtarget, and when bundling is enabled we
516 // sometimes need to use the same fragment. We give an error if there
517 // are conflicting Subtargets.
518 static void CheckBundleSubtargets(const MCSubtargetInfo *OldSTI,
519                                   const MCSubtargetInfo *NewSTI) {
520   if (OldSTI && NewSTI && OldSTI != NewSTI)
521     report_fatal_error("A Bundle can only have one Subtarget.");
522 }
523 
524 void MCELFStreamer::emitInstToData(const MCInst &Inst,
525                                    const MCSubtargetInfo &STI) {
526   MCAssembler &Assembler = getAssembler();
527   SmallVector<MCFixup, 4> Fixups;
528   SmallString<256> Code;
529   raw_svector_ostream VecOS(Code);
530   Assembler.getEmitter().encodeInstruction(Inst, VecOS, Fixups, STI);
531 
532   for (unsigned i = 0, e = Fixups.size(); i != e; ++i)
533     fixSymbolsInTLSFixups(Fixups[i].getValue());
534 
535   // There are several possibilities here:
536   //
537   // If bundling is disabled, append the encoded instruction to the current data
538   // fragment (or create a new such fragment if the current fragment is not a
539   // data fragment, or the Subtarget has changed).
540   //
541   // If bundling is enabled:
542   // - If we're not in a bundle-locked group, emit the instruction into a
543   //   fragment of its own. If there are no fixups registered for the
544   //   instruction, emit a MCCompactEncodedInstFragment. Otherwise, emit a
545   //   MCDataFragment.
546   // - If we're in a bundle-locked group, append the instruction to the current
547   //   data fragment because we want all the instructions in a group to get into
548   //   the same fragment. Be careful not to do that for the first instruction in
549   //   the group, though.
550   MCDataFragment *DF;
551 
552   if (Assembler.isBundlingEnabled()) {
553     MCSection &Sec = *getCurrentSectionOnly();
554     if (Assembler.getRelaxAll() && isBundleLocked()) {
555       // If the -mc-relax-all flag is used and we are bundle-locked, we re-use
556       // the current bundle group.
557       DF = BundleGroups.back();
558       CheckBundleSubtargets(DF->getSubtargetInfo(), &STI);
559     }
560     else if (Assembler.getRelaxAll() && !isBundleLocked())
561       // When not in a bundle-locked group and the -mc-relax-all flag is used,
562       // we create a new temporary fragment which will be later merged into
563       // the current fragment.
564       DF = new MCDataFragment();
565     else if (isBundleLocked() && !Sec.isBundleGroupBeforeFirstInst()) {
566       // If we are bundle-locked, we re-use the current fragment.
567       // The bundle-locking directive ensures this is a new data fragment.
568       DF = cast<MCDataFragment>(getCurrentFragment());
569       CheckBundleSubtargets(DF->getSubtargetInfo(), &STI);
570     }
571     else if (!isBundleLocked() && Fixups.size() == 0) {
572       // Optimize memory usage by emitting the instruction to a
573       // MCCompactEncodedInstFragment when not in a bundle-locked group and
574       // there are no fixups registered.
575       MCCompactEncodedInstFragment *CEIF = new MCCompactEncodedInstFragment();
576       insert(CEIF);
577       CEIF->getContents().append(Code.begin(), Code.end());
578       CEIF->setHasInstructions(STI);
579       return;
580     } else {
581       DF = new MCDataFragment();
582       insert(DF);
583     }
584     if (Sec.getBundleLockState() == MCSection::BundleLockedAlignToEnd) {
585       // If this fragment is for a group marked "align_to_end", set a flag
586       // in the fragment. This can happen after the fragment has already been
587       // created if there are nested bundle_align groups and an inner one
588       // is the one marked align_to_end.
589       DF->setAlignToBundleEnd(true);
590     }
591 
592     // We're now emitting an instruction in a bundle group, so this flag has
593     // to be turned off.
594     Sec.setBundleGroupBeforeFirstInst(false);
595   } else {
596     DF = getOrCreateDataFragment(&STI);
597   }
598 
599   // Add the fixups and data.
600   for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
601     Fixups[i].setOffset(Fixups[i].getOffset() + DF->getContents().size());
602     DF->getFixups().push_back(Fixups[i]);
603   }
604   DF->setHasInstructions(STI);
605   DF->getContents().append(Code.begin(), Code.end());
606 
607   if (Assembler.isBundlingEnabled() && Assembler.getRelaxAll()) {
608     if (!isBundleLocked()) {
609       mergeFragment(getOrCreateDataFragment(&STI), DF);
610       delete DF;
611     }
612   }
613 }
614 
615 void MCELFStreamer::emitBundleAlignMode(unsigned AlignPow2) {
616   assert(AlignPow2 <= 30 && "Invalid bundle alignment");
617   MCAssembler &Assembler = getAssembler();
618   if (AlignPow2 > 0 && (Assembler.getBundleAlignSize() == 0 ||
619                         Assembler.getBundleAlignSize() == 1U << AlignPow2))
620     Assembler.setBundleAlignSize(1U << AlignPow2);
621   else
622     report_fatal_error(".bundle_align_mode cannot be changed once set");
623 }
624 
625 void MCELFStreamer::emitBundleLock(bool AlignToEnd) {
626   MCSection &Sec = *getCurrentSectionOnly();
627 
628   // Sanity checks
629   //
630   if (!getAssembler().isBundlingEnabled())
631     report_fatal_error(".bundle_lock forbidden when bundling is disabled");
632 
633   if (!isBundleLocked())
634     Sec.setBundleGroupBeforeFirstInst(true);
635 
636   if (getAssembler().getRelaxAll() && !isBundleLocked()) {
637     // TODO: drop the lock state and set directly in the fragment
638     MCDataFragment *DF = new MCDataFragment();
639     BundleGroups.push_back(DF);
640   }
641 
642   Sec.setBundleLockState(AlignToEnd ? MCSection::BundleLockedAlignToEnd
643                                     : MCSection::BundleLocked);
644 }
645 
646 void MCELFStreamer::emitBundleUnlock() {
647   MCSection &Sec = *getCurrentSectionOnly();
648 
649   // Sanity checks
650   if (!getAssembler().isBundlingEnabled())
651     report_fatal_error(".bundle_unlock forbidden when bundling is disabled");
652   else if (!isBundleLocked())
653     report_fatal_error(".bundle_unlock without matching lock");
654   else if (Sec.isBundleGroupBeforeFirstInst())
655     report_fatal_error("Empty bundle-locked group is forbidden");
656 
657   // When the -mc-relax-all flag is used, we emit instructions to fragments
658   // stored on a stack. When the bundle unlock is emitted, we pop a fragment
659   // from the stack a merge it to the one below.
660   if (getAssembler().getRelaxAll()) {
661     assert(!BundleGroups.empty() && "There are no bundle groups");
662     MCDataFragment *DF = BundleGroups.back();
663 
664     // FIXME: Use BundleGroups to track the lock state instead.
665     Sec.setBundleLockState(MCSection::NotBundleLocked);
666 
667     // FIXME: Use more separate fragments for nested groups.
668     if (!isBundleLocked()) {
669       mergeFragment(getOrCreateDataFragment(DF->getSubtargetInfo()), DF);
670       BundleGroups.pop_back();
671       delete DF;
672     }
673 
674     if (Sec.getBundleLockState() != MCSection::BundleLockedAlignToEnd)
675       getOrCreateDataFragment()->setAlignToBundleEnd(false);
676   } else
677     Sec.setBundleLockState(MCSection::NotBundleLocked);
678 }
679 
680 void MCELFStreamer::finishImpl() {
681   // Ensure the last section gets aligned if necessary.
682   MCSection *CurSection = getCurrentSectionOnly();
683   setSectionAlignmentForBundling(getAssembler(), CurSection);
684 
685   finalizeCGProfile();
686   emitFrames(nullptr);
687 
688   this->MCObjectStreamer::finishImpl();
689 }
690 
691 void MCELFStreamer::emitThumbFunc(MCSymbol *Func) {
692   llvm_unreachable("Generic ELF doesn't support this directive");
693 }
694 
695 void MCELFStreamer::emitSymbolDesc(MCSymbol *Symbol, unsigned DescValue) {
696   llvm_unreachable("ELF doesn't support this directive");
697 }
698 
699 void MCELFStreamer::emitZerofill(MCSection *Section, MCSymbol *Symbol,
700                                  uint64_t Size, unsigned ByteAlignment,
701                                  SMLoc Loc) {
702   llvm_unreachable("ELF doesn't support this directive");
703 }
704 
705 void MCELFStreamer::emitTBSSSymbol(MCSection *Section, MCSymbol *Symbol,
706                                    uint64_t Size, unsigned ByteAlignment) {
707   llvm_unreachable("ELF doesn't support this directive");
708 }
709 
710 MCStreamer *llvm::createELFStreamer(MCContext &Context,
711                                     std::unique_ptr<MCAsmBackend> &&MAB,
712                                     std::unique_ptr<MCObjectWriter> &&OW,
713                                     std::unique_ptr<MCCodeEmitter> &&CE,
714                                     bool RelaxAll) {
715   MCELFStreamer *S =
716       new MCELFStreamer(Context, std::move(MAB), std::move(OW), std::move(CE));
717   if (RelaxAll)
718     S->getAssembler().setRelaxAll(true);
719   return S;
720 }
721