xref: /llvm-project/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp (revision 1a6a2b642bd61910424cb7244f547c02460f18db) 
1 //===- llvm/CodeGen/TargetLoweringObjectFileImpl.cpp - Object File Info ---===//
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 implements classes used to handle lowerings specific to common
11 // object file formats.
12 //
13 //===----------------------------------------------------------------------===//
14 
15 #include "llvm/ADT/SmallString.h"
16 #include "llvm/ADT/SmallVector.h"
17 #include "llvm/ADT/StringExtras.h"
18 #include "llvm/ADT/StringRef.h"
19 #include "llvm/ADT/Triple.h"
20 #include "llvm/CodeGen/MachineModuleInfo.h"
21 #include "llvm/CodeGen/MachineModuleInfoImpls.h"
22 #include "llvm/CodeGen/TargetLoweringObjectFileImpl.h"
23 #include "llvm/IR/Comdat.h"
24 #include "llvm/IR/Constants.h"
25 #include "llvm/IR/DataLayout.h"
26 #include "llvm/IR/DerivedTypes.h"
27 #include "llvm/IR/Function.h"
28 #include "llvm/IR/GlobalAlias.h"
29 #include "llvm/IR/GlobalObject.h"
30 #include "llvm/IR/GlobalValue.h"
31 #include "llvm/IR/GlobalVariable.h"
32 #include "llvm/IR/Mangler.h"
33 #include "llvm/IR/Metadata.h"
34 #include "llvm/IR/Module.h"
35 #include "llvm/IR/Type.h"
36 #include "llvm/MC/MCAsmInfo.h"
37 #include "llvm/MC/MCContext.h"
38 #include "llvm/MC/MCExpr.h"
39 #include "llvm/MC/MCSectionCOFF.h"
40 #include "llvm/MC/MCSectionELF.h"
41 #include "llvm/MC/MCSectionMachO.h"
42 #include "llvm/MC/MCSectionWasm.h"
43 #include "llvm/MC/MCStreamer.h"
44 #include "llvm/MC/MCSymbol.h"
45 #include "llvm/MC/MCSymbolELF.h"
46 #include "llvm/MC/MCValue.h"
47 #include "llvm/MC/SectionKind.h"
48 #include "llvm/ProfileData/InstrProf.h"
49 #include "llvm/Support/Casting.h"
50 #include "llvm/Support/CodeGen.h"
51 #include "llvm/Support/COFF.h"
52 #include "llvm/Support/Dwarf.h"
53 #include "llvm/Support/ELF.h"
54 #include "llvm/Support/ErrorHandling.h"
55 #include "llvm/Support/MachO.h"
56 #include "llvm/Support/raw_ostream.h"
57 #include "llvm/Target/TargetMachine.h"
58 #include <cassert>
59 #include <string>
60 
61 using namespace llvm;
62 using namespace dwarf;
63 
64 //===----------------------------------------------------------------------===//
65 //                                  ELF
66 //===----------------------------------------------------------------------===//
67 
68 MCSymbol *TargetLoweringObjectFileELF::getCFIPersonalitySymbol(
69     const GlobalValue *GV, const TargetMachine &TM,
70     MachineModuleInfo *MMI) const {
71   unsigned Encoding = getPersonalityEncoding();
72   if ((Encoding & 0x80) == DW_EH_PE_indirect)
73     return getContext().getOrCreateSymbol(StringRef("DW.ref.") +
74                                           TM.getSymbol(GV)->getName());
75   if ((Encoding & 0x70) == DW_EH_PE_absptr)
76     return TM.getSymbol(GV);
77   report_fatal_error("We do not support this DWARF encoding yet!");
78 }
79 
80 void TargetLoweringObjectFileELF::emitPersonalityValue(
81     MCStreamer &Streamer, const DataLayout &DL, const MCSymbol *Sym) const {
82   SmallString<64> NameData("DW.ref.");
83   NameData += Sym->getName();
84   MCSymbolELF *Label =
85       cast<MCSymbolELF>(getContext().getOrCreateSymbol(NameData));
86   Streamer.EmitSymbolAttribute(Label, MCSA_Hidden);
87   Streamer.EmitSymbolAttribute(Label, MCSA_Weak);
88   unsigned Flags = ELF::SHF_ALLOC | ELF::SHF_WRITE | ELF::SHF_GROUP;
89   MCSection *Sec = getContext().getELFNamedSection(".data", Label->getName(),
90                                                    ELF::SHT_PROGBITS, Flags, 0);
91   unsigned Size = DL.getPointerSize();
92   Streamer.SwitchSection(Sec);
93   Streamer.EmitValueToAlignment(DL.getPointerABIAlignment());
94   Streamer.EmitSymbolAttribute(Label, MCSA_ELF_TypeObject);
95   const MCExpr *E = MCConstantExpr::create(Size, getContext());
96   Streamer.emitELFSize(Label, E);
97   Streamer.EmitLabel(Label);
98 
99   Streamer.EmitSymbolValue(Sym, Size);
100 }
101 
102 const MCExpr *TargetLoweringObjectFileELF::getTTypeGlobalReference(
103     const GlobalValue *GV, unsigned Encoding, const TargetMachine &TM,
104     MachineModuleInfo *MMI, MCStreamer &Streamer) const {
105   if (Encoding & DW_EH_PE_indirect) {
106     MachineModuleInfoELF &ELFMMI = MMI->getObjFileInfo<MachineModuleInfoELF>();
107 
108     MCSymbol *SSym = getSymbolWithGlobalValueBase(GV, ".DW.stub", TM);
109 
110     // Add information about the stub reference to ELFMMI so that the stub
111     // gets emitted by the asmprinter.
112     MachineModuleInfoImpl::StubValueTy &StubSym = ELFMMI.getGVStubEntry(SSym);
113     if (!StubSym.getPointer()) {
114       MCSymbol *Sym = TM.getSymbol(GV);
115       StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
116     }
117 
118     return TargetLoweringObjectFile::
119       getTTypeReference(MCSymbolRefExpr::create(SSym, getContext()),
120                         Encoding & ~DW_EH_PE_indirect, Streamer);
121   }
122 
123   return TargetLoweringObjectFile::getTTypeGlobalReference(GV, Encoding, TM,
124                                                            MMI, Streamer);
125 }
126 
127 static SectionKind
128 getELFKindForNamedSection(StringRef Name, SectionKind K) {
129   // N.B.: The defaults used in here are no the same ones used in MC.
130   // We follow gcc, MC follows gas. For example, given ".section .eh_frame",
131   // both gas and MC will produce a section with no flags. Given
132   // section(".eh_frame") gcc will produce:
133   //
134   //   .section   .eh_frame,"a",@progbits
135 
136   if (Name == getInstrProfSectionName(IPSK_covmap, Triple::ELF,
137                                       /*AddSegmentInfo=*/false))
138     return SectionKind::getMetadata();
139 
140   if (Name.empty() || Name[0] != '.') return K;
141 
142   // Some lame default implementation based on some magic section names.
143   if (Name == ".bss" ||
144       Name.startswith(".bss.") ||
145       Name.startswith(".gnu.linkonce.b.") ||
146       Name.startswith(".llvm.linkonce.b.") ||
147       Name == ".sbss" ||
148       Name.startswith(".sbss.") ||
149       Name.startswith(".gnu.linkonce.sb.") ||
150       Name.startswith(".llvm.linkonce.sb."))
151     return SectionKind::getBSS();
152 
153   if (Name == ".tdata" ||
154       Name.startswith(".tdata.") ||
155       Name.startswith(".gnu.linkonce.td.") ||
156       Name.startswith(".llvm.linkonce.td."))
157     return SectionKind::getThreadData();
158 
159   if (Name == ".tbss" ||
160       Name.startswith(".tbss.") ||
161       Name.startswith(".gnu.linkonce.tb.") ||
162       Name.startswith(".llvm.linkonce.tb."))
163     return SectionKind::getThreadBSS();
164 
165   return K;
166 }
167 
168 static unsigned getELFSectionType(StringRef Name, SectionKind K) {
169   // Use SHT_NOTE for section whose name starts with ".note" to allow
170   // emitting ELF notes from C variable declaration.
171   // See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77609
172   if (Name.startswith(".note"))
173     return ELF::SHT_NOTE;
174 
175   if (Name == ".init_array")
176     return ELF::SHT_INIT_ARRAY;
177 
178   if (Name == ".fini_array")
179     return ELF::SHT_FINI_ARRAY;
180 
181   if (Name == ".preinit_array")
182     return ELF::SHT_PREINIT_ARRAY;
183 
184   if (K.isBSS() || K.isThreadBSS())
185     return ELF::SHT_NOBITS;
186 
187   return ELF::SHT_PROGBITS;
188 }
189 
190 static unsigned getELFSectionFlags(SectionKind K) {
191   unsigned Flags = 0;
192 
193   if (!K.isMetadata())
194     Flags |= ELF::SHF_ALLOC;
195 
196   if (K.isText())
197     Flags |= ELF::SHF_EXECINSTR;
198 
199   if (K.isExecuteOnly())
200     Flags |= ELF::SHF_ARM_PURECODE;
201 
202   if (K.isWriteable())
203     Flags |= ELF::SHF_WRITE;
204 
205   if (K.isThreadLocal())
206     Flags |= ELF::SHF_TLS;
207 
208   if (K.isMergeableCString() || K.isMergeableConst())
209     Flags |= ELF::SHF_MERGE;
210 
211   if (K.isMergeableCString())
212     Flags |= ELF::SHF_STRINGS;
213 
214   return Flags;
215 }
216 
217 static const Comdat *getELFComdat(const GlobalValue *GV) {
218   const Comdat *C = GV->getComdat();
219   if (!C)
220     return nullptr;
221 
222   if (C->getSelectionKind() != Comdat::Any)
223     report_fatal_error("ELF COMDATs only support SelectionKind::Any, '" +
224                        C->getName() + "' cannot be lowered.");
225 
226   return C;
227 }
228 
229 static const MCSymbolELF *getAssociatedSymbol(const GlobalObject *GO,
230                                               const TargetMachine &TM) {
231   MDNode *MD = GO->getMetadata(LLVMContext::MD_associated);
232   if (!MD)
233     return nullptr;
234 
235   auto *VM = dyn_cast<ValueAsMetadata>(MD->getOperand(0));
236   if (!VM)
237     report_fatal_error("MD_associated operand is not ValueAsMetadata");
238 
239   GlobalObject *OtherGO = dyn_cast<GlobalObject>(VM->getValue());
240   return OtherGO ? dyn_cast<MCSymbolELF>(TM.getSymbol(OtherGO)) : nullptr;
241 }
242 
243 MCSection *TargetLoweringObjectFileELF::getExplicitSectionGlobal(
244     const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
245   StringRef SectionName = GO->getSection();
246 
247   // Infer section flags from the section name if we can.
248   Kind = getELFKindForNamedSection(SectionName, Kind);
249 
250   StringRef Group = "";
251   unsigned Flags = getELFSectionFlags(Kind);
252   if (const Comdat *C = getELFComdat(GO)) {
253     Group = C->getName();
254     Flags |= ELF::SHF_GROUP;
255   }
256 
257   // A section can have at most one associated section. Put each global with
258   // MD_associated in a unique section.
259   unsigned UniqueID = MCContext::GenericSectionID;
260   const MCSymbolELF *AssociatedSymbol = getAssociatedSymbol(GO, TM);
261   if (AssociatedSymbol) {
262     UniqueID = NextUniqueID++;
263     Flags |= ELF::SHF_LINK_ORDER;
264   }
265 
266   MCSectionELF *Section = getContext().getELFSection(
267       SectionName, getELFSectionType(SectionName, Kind), Flags,
268       /*EntrySize=*/0, Group, UniqueID, AssociatedSymbol);
269   // Make sure that we did not get some other section with incompatible sh_link.
270   // This should not be possible due to UniqueID code above.
271   assert(Section->getAssociatedSymbol() == AssociatedSymbol);
272   return Section;
273 }
274 
275 /// Return the section prefix name used by options FunctionsSections and
276 /// DataSections.
277 static StringRef getSectionPrefixForGlobal(SectionKind Kind) {
278   if (Kind.isText())
279     return ".text";
280   if (Kind.isReadOnly())
281     return ".rodata";
282   if (Kind.isBSS())
283     return ".bss";
284   if (Kind.isThreadData())
285     return ".tdata";
286   if (Kind.isThreadBSS())
287     return ".tbss";
288   if (Kind.isData())
289     return ".data";
290   assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
291   return ".data.rel.ro";
292 }
293 
294 static MCSectionELF *selectELFSectionForGlobal(
295     MCContext &Ctx, const GlobalObject *GO, SectionKind Kind, Mangler &Mang,
296     const TargetMachine &TM, bool EmitUniqueSection, unsigned Flags,
297     unsigned *NextUniqueID, const MCSymbolELF *AssociatedSymbol) {
298   unsigned EntrySize = 0;
299   if (Kind.isMergeableCString()) {
300     if (Kind.isMergeable2ByteCString()) {
301       EntrySize = 2;
302     } else if (Kind.isMergeable4ByteCString()) {
303       EntrySize = 4;
304     } else {
305       EntrySize = 1;
306       assert(Kind.isMergeable1ByteCString() && "unknown string width");
307     }
308   } else if (Kind.isMergeableConst()) {
309     if (Kind.isMergeableConst4()) {
310       EntrySize = 4;
311     } else if (Kind.isMergeableConst8()) {
312       EntrySize = 8;
313     } else if (Kind.isMergeableConst16()) {
314       EntrySize = 16;
315     } else {
316       assert(Kind.isMergeableConst32() && "unknown data width");
317       EntrySize = 32;
318     }
319   }
320 
321   StringRef Group = "";
322   if (const Comdat *C = getELFComdat(GO)) {
323     Flags |= ELF::SHF_GROUP;
324     Group = C->getName();
325   }
326 
327   bool UniqueSectionNames = TM.getUniqueSectionNames();
328   SmallString<128> Name;
329   if (Kind.isMergeableCString()) {
330     // We also need alignment here.
331     // FIXME: this is getting the alignment of the character, not the
332     // alignment of the global!
333     unsigned Align = GO->getParent()->getDataLayout().getPreferredAlignment(
334         cast<GlobalVariable>(GO));
335 
336     std::string SizeSpec = ".rodata.str" + utostr(EntrySize) + ".";
337     Name = SizeSpec + utostr(Align);
338   } else if (Kind.isMergeableConst()) {
339     Name = ".rodata.cst";
340     Name += utostr(EntrySize);
341   } else {
342     Name = getSectionPrefixForGlobal(Kind);
343   }
344 
345   if (const auto *F = dyn_cast<Function>(GO)) {
346     const auto &OptionalPrefix = F->getSectionPrefix();
347     if (OptionalPrefix)
348       Name += *OptionalPrefix;
349   }
350 
351   if (EmitUniqueSection && UniqueSectionNames) {
352     Name.push_back('.');
353     TM.getNameWithPrefix(Name, GO, Mang, true);
354   }
355   unsigned UniqueID = MCContext::GenericSectionID;
356   if (EmitUniqueSection && !UniqueSectionNames) {
357     UniqueID = *NextUniqueID;
358     (*NextUniqueID)++;
359   }
360   // Use 0 as the unique ID for execute-only text
361   if (Kind.isExecuteOnly())
362     UniqueID = 0;
363   return Ctx.getELFSection(Name, getELFSectionType(Name, Kind), Flags,
364                            EntrySize, Group, UniqueID, AssociatedSymbol);
365 }
366 
367 MCSection *TargetLoweringObjectFileELF::SelectSectionForGlobal(
368     const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
369   unsigned Flags = getELFSectionFlags(Kind);
370 
371   // If we have -ffunction-section or -fdata-section then we should emit the
372   // global value to a uniqued section specifically for it.
373   bool EmitUniqueSection = false;
374   if (!(Flags & ELF::SHF_MERGE) && !Kind.isCommon()) {
375     if (Kind.isText())
376       EmitUniqueSection = TM.getFunctionSections();
377     else
378       EmitUniqueSection = TM.getDataSections();
379   }
380   EmitUniqueSection |= GO->hasComdat();
381 
382   const MCSymbolELF *AssociatedSymbol = getAssociatedSymbol(GO, TM);
383   if (AssociatedSymbol) {
384     EmitUniqueSection = true;
385     Flags |= ELF::SHF_LINK_ORDER;
386   }
387 
388   MCSectionELF *Section = selectELFSectionForGlobal(
389       getContext(), GO, Kind, getMangler(), TM, EmitUniqueSection, Flags,
390       &NextUniqueID, AssociatedSymbol);
391   assert(Section->getAssociatedSymbol() == AssociatedSymbol);
392   return Section;
393 }
394 
395 MCSection *TargetLoweringObjectFileELF::getSectionForJumpTable(
396     const Function &F, const TargetMachine &TM) const {
397   // If the function can be removed, produce a unique section so that
398   // the table doesn't prevent the removal.
399   const Comdat *C = F.getComdat();
400   bool EmitUniqueSection = TM.getFunctionSections() || C;
401   if (!EmitUniqueSection)
402     return ReadOnlySection;
403 
404   return selectELFSectionForGlobal(getContext(), &F, SectionKind::getReadOnly(),
405                                    getMangler(), TM, EmitUniqueSection,
406                                    ELF::SHF_ALLOC, &NextUniqueID,
407                                    /* AssociatedSymbol */ nullptr);
408 }
409 
410 bool TargetLoweringObjectFileELF::shouldPutJumpTableInFunctionSection(
411     bool UsesLabelDifference, const Function &F) const {
412   // We can always create relative relocations, so use another section
413   // that can be marked non-executable.
414   return false;
415 }
416 
417 /// Given a mergeable constant with the specified size and relocation
418 /// information, return a section that it should be placed in.
419 MCSection *TargetLoweringObjectFileELF::getSectionForConstant(
420     const DataLayout &DL, SectionKind Kind, const Constant *C,
421     unsigned &Align) const {
422   if (Kind.isMergeableConst4() && MergeableConst4Section)
423     return MergeableConst4Section;
424   if (Kind.isMergeableConst8() && MergeableConst8Section)
425     return MergeableConst8Section;
426   if (Kind.isMergeableConst16() && MergeableConst16Section)
427     return MergeableConst16Section;
428   if (Kind.isMergeableConst32() && MergeableConst32Section)
429     return MergeableConst32Section;
430   if (Kind.isReadOnly())
431     return ReadOnlySection;
432 
433   assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
434   return DataRelROSection;
435 }
436 
437 static MCSectionELF *getStaticStructorSection(MCContext &Ctx, bool UseInitArray,
438                                               bool IsCtor, unsigned Priority,
439                                               const MCSymbol *KeySym) {
440   std::string Name;
441   unsigned Type;
442   unsigned Flags = ELF::SHF_ALLOC | ELF::SHF_WRITE;
443   StringRef COMDAT = KeySym ? KeySym->getName() : "";
444 
445   if (KeySym)
446     Flags |= ELF::SHF_GROUP;
447 
448   if (UseInitArray) {
449     if (IsCtor) {
450       Type = ELF::SHT_INIT_ARRAY;
451       Name = ".init_array";
452     } else {
453       Type = ELF::SHT_FINI_ARRAY;
454       Name = ".fini_array";
455     }
456     if (Priority != 65535) {
457       Name += '.';
458       Name += utostr(Priority);
459     }
460   } else {
461     // The default scheme is .ctor / .dtor, so we have to invert the priority
462     // numbering.
463     if (IsCtor)
464       Name = ".ctors";
465     else
466       Name = ".dtors";
467     if (Priority != 65535) {
468       Name += '.';
469       Name += utostr(65535 - Priority);
470     }
471     Type = ELF::SHT_PROGBITS;
472   }
473 
474   return Ctx.getELFSection(Name, Type, Flags, 0, COMDAT);
475 }
476 
477 MCSection *TargetLoweringObjectFileELF::getStaticCtorSection(
478     unsigned Priority, const MCSymbol *KeySym) const {
479   return getStaticStructorSection(getContext(), UseInitArray, true, Priority,
480                                   KeySym);
481 }
482 
483 MCSection *TargetLoweringObjectFileELF::getStaticDtorSection(
484     unsigned Priority, const MCSymbol *KeySym) const {
485   return getStaticStructorSection(getContext(), UseInitArray, false, Priority,
486                                   KeySym);
487 }
488 
489 const MCExpr *TargetLoweringObjectFileELF::lowerRelativeReference(
490     const GlobalValue *LHS, const GlobalValue *RHS,
491     const TargetMachine &TM) const {
492   // We may only use a PLT-relative relocation to refer to unnamed_addr
493   // functions.
494   if (!LHS->hasGlobalUnnamedAddr() || !LHS->getValueType()->isFunctionTy())
495     return nullptr;
496 
497   // Basic sanity checks.
498   if (LHS->getType()->getPointerAddressSpace() != 0 ||
499       RHS->getType()->getPointerAddressSpace() != 0 || LHS->isThreadLocal() ||
500       RHS->isThreadLocal())
501     return nullptr;
502 
503   return MCBinaryExpr::createSub(
504       MCSymbolRefExpr::create(TM.getSymbol(LHS), PLTRelativeVariantKind,
505                               getContext()),
506       MCSymbolRefExpr::create(TM.getSymbol(RHS), getContext()), getContext());
507 }
508 
509 void
510 TargetLoweringObjectFileELF::InitializeELF(bool UseInitArray_) {
511   UseInitArray = UseInitArray_;
512   MCContext &Ctx = getContext();
513   if (!UseInitArray) {
514     StaticCtorSection = Ctx.getELFSection(".ctors", ELF::SHT_PROGBITS,
515                                           ELF::SHF_ALLOC | ELF::SHF_WRITE);
516 
517     StaticDtorSection = Ctx.getELFSection(".dtors", ELF::SHT_PROGBITS,
518                                           ELF::SHF_ALLOC | ELF::SHF_WRITE);
519     return;
520   }
521 
522   StaticCtorSection = Ctx.getELFSection(".init_array", ELF::SHT_INIT_ARRAY,
523                                         ELF::SHF_WRITE | ELF::SHF_ALLOC);
524   StaticDtorSection = Ctx.getELFSection(".fini_array", ELF::SHT_FINI_ARRAY,
525                                         ELF::SHF_WRITE | ELF::SHF_ALLOC);
526 }
527 
528 //===----------------------------------------------------------------------===//
529 //                                 MachO
530 //===----------------------------------------------------------------------===//
531 
532 TargetLoweringObjectFileMachO::TargetLoweringObjectFileMachO()
533   : TargetLoweringObjectFile() {
534   SupportIndirectSymViaGOTPCRel = true;
535 }
536 
537 void TargetLoweringObjectFileMachO::Initialize(MCContext &Ctx,
538                                                const TargetMachine &TM) {
539   TargetLoweringObjectFile::Initialize(Ctx, TM);
540   if (TM.getRelocationModel() == Reloc::Static) {
541     StaticCtorSection = Ctx.getMachOSection("__TEXT", "__constructor", 0,
542                                             SectionKind::getData());
543     StaticDtorSection = Ctx.getMachOSection("__TEXT", "__destructor", 0,
544                                             SectionKind::getData());
545   } else {
546     StaticCtorSection = Ctx.getMachOSection("__DATA", "__mod_init_func",
547                                             MachO::S_MOD_INIT_FUNC_POINTERS,
548                                             SectionKind::getData());
549     StaticDtorSection = Ctx.getMachOSection("__DATA", "__mod_term_func",
550                                             MachO::S_MOD_TERM_FUNC_POINTERS,
551                                             SectionKind::getData());
552   }
553 }
554 
555 /// emitModuleFlags - Perform code emission for module flags.
556 void TargetLoweringObjectFileMachO::emitModuleFlags(
557     MCStreamer &Streamer, ArrayRef<Module::ModuleFlagEntry> ModuleFlags,
558     const TargetMachine &TM) const {
559   unsigned VersionVal = 0;
560   unsigned ImageInfoFlags = 0;
561   MDNode *LinkerOptions = nullptr;
562   StringRef SectionVal;
563 
564   for (const auto &MFE : ModuleFlags) {
565     // Ignore flags with 'Require' behavior.
566     if (MFE.Behavior == Module::Require)
567       continue;
568 
569     StringRef Key = MFE.Key->getString();
570     Metadata *Val = MFE.Val;
571 
572     if (Key == "Objective-C Image Info Version") {
573       VersionVal = mdconst::extract<ConstantInt>(Val)->getZExtValue();
574     } else if (Key == "Objective-C Garbage Collection" ||
575                Key == "Objective-C GC Only" ||
576                Key == "Objective-C Is Simulated" ||
577                Key == "Objective-C Class Properties" ||
578                Key == "Objective-C Image Swift Version") {
579       ImageInfoFlags |= mdconst::extract<ConstantInt>(Val)->getZExtValue();
580     } else if (Key == "Objective-C Image Info Section") {
581       SectionVal = cast<MDString>(Val)->getString();
582     } else if (Key == "Linker Options") {
583       LinkerOptions = cast<MDNode>(Val);
584     }
585   }
586 
587   // Emit the linker options if present.
588   if (LinkerOptions) {
589     for (const auto &Option : LinkerOptions->operands()) {
590       SmallVector<std::string, 4> StrOptions;
591       for (const auto &Piece : cast<MDNode>(Option)->operands())
592         StrOptions.push_back(cast<MDString>(Piece)->getString());
593       Streamer.EmitLinkerOptions(StrOptions);
594     }
595   }
596 
597   // The section is mandatory. If we don't have it, then we don't have GC info.
598   if (SectionVal.empty()) return;
599 
600   StringRef Segment, Section;
601   unsigned TAA = 0, StubSize = 0;
602   bool TAAParsed;
603   std::string ErrorCode =
604     MCSectionMachO::ParseSectionSpecifier(SectionVal, Segment, Section,
605                                           TAA, TAAParsed, StubSize);
606   if (!ErrorCode.empty())
607     // If invalid, report the error with report_fatal_error.
608     report_fatal_error("Invalid section specifier '" + Section + "': " +
609                        ErrorCode + ".");
610 
611   // Get the section.
612   MCSectionMachO *S = getContext().getMachOSection(
613       Segment, Section, TAA, StubSize, SectionKind::getData());
614   Streamer.SwitchSection(S);
615   Streamer.EmitLabel(getContext().
616                      getOrCreateSymbol(StringRef("L_OBJC_IMAGE_INFO")));
617   Streamer.EmitIntValue(VersionVal, 4);
618   Streamer.EmitIntValue(ImageInfoFlags, 4);
619   Streamer.AddBlankLine();
620 }
621 
622 static void checkMachOComdat(const GlobalValue *GV) {
623   const Comdat *C = GV->getComdat();
624   if (!C)
625     return;
626 
627   report_fatal_error("MachO doesn't support COMDATs, '" + C->getName() +
628                      "' cannot be lowered.");
629 }
630 
631 MCSection *TargetLoweringObjectFileMachO::getExplicitSectionGlobal(
632     const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
633   // Parse the section specifier and create it if valid.
634   StringRef Segment, Section;
635   unsigned TAA = 0, StubSize = 0;
636   bool TAAParsed;
637 
638   checkMachOComdat(GO);
639 
640   std::string ErrorCode =
641     MCSectionMachO::ParseSectionSpecifier(GO->getSection(), Segment, Section,
642                                           TAA, TAAParsed, StubSize);
643   if (!ErrorCode.empty()) {
644     // If invalid, report the error with report_fatal_error.
645     report_fatal_error("Global variable '" + GO->getName() +
646                        "' has an invalid section specifier '" +
647                        GO->getSection() + "': " + ErrorCode + ".");
648   }
649 
650   // Get the section.
651   MCSectionMachO *S =
652       getContext().getMachOSection(Segment, Section, TAA, StubSize, Kind);
653 
654   // If TAA wasn't set by ParseSectionSpecifier() above,
655   // use the value returned by getMachOSection() as a default.
656   if (!TAAParsed)
657     TAA = S->getTypeAndAttributes();
658 
659   // Okay, now that we got the section, verify that the TAA & StubSize agree.
660   // If the user declared multiple globals with different section flags, we need
661   // to reject it here.
662   if (S->getTypeAndAttributes() != TAA || S->getStubSize() != StubSize) {
663     // If invalid, report the error with report_fatal_error.
664     report_fatal_error("Global variable '" + GO->getName() +
665                        "' section type or attributes does not match previous"
666                        " section specifier");
667   }
668 
669   return S;
670 }
671 
672 MCSection *TargetLoweringObjectFileMachO::SelectSectionForGlobal(
673     const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
674   checkMachOComdat(GO);
675 
676   // Handle thread local data.
677   if (Kind.isThreadBSS()) return TLSBSSSection;
678   if (Kind.isThreadData()) return TLSDataSection;
679 
680   if (Kind.isText())
681     return GO->isWeakForLinker() ? TextCoalSection : TextSection;
682 
683   // If this is weak/linkonce, put this in a coalescable section, either in text
684   // or data depending on if it is writable.
685   if (GO->isWeakForLinker()) {
686     if (Kind.isReadOnly())
687       return ConstTextCoalSection;
688     return DataCoalSection;
689   }
690 
691   // FIXME: Alignment check should be handled by section classifier.
692   if (Kind.isMergeable1ByteCString() &&
693       GO->getParent()->getDataLayout().getPreferredAlignment(
694           cast<GlobalVariable>(GO)) < 32)
695     return CStringSection;
696 
697   // Do not put 16-bit arrays in the UString section if they have an
698   // externally visible label, this runs into issues with certain linker
699   // versions.
700   if (Kind.isMergeable2ByteCString() && !GO->hasExternalLinkage() &&
701       GO->getParent()->getDataLayout().getPreferredAlignment(
702           cast<GlobalVariable>(GO)) < 32)
703     return UStringSection;
704 
705   // With MachO only variables whose corresponding symbol starts with 'l' or
706   // 'L' can be merged, so we only try merging GVs with private linkage.
707   if (GO->hasPrivateLinkage() && Kind.isMergeableConst()) {
708     if (Kind.isMergeableConst4())
709       return FourByteConstantSection;
710     if (Kind.isMergeableConst8())
711       return EightByteConstantSection;
712     if (Kind.isMergeableConst16())
713       return SixteenByteConstantSection;
714   }
715 
716   // Otherwise, if it is readonly, but not something we can specially optimize,
717   // just drop it in .const.
718   if (Kind.isReadOnly())
719     return ReadOnlySection;
720 
721   // If this is marked const, put it into a const section.  But if the dynamic
722   // linker needs to write to it, put it in the data segment.
723   if (Kind.isReadOnlyWithRel())
724     return ConstDataSection;
725 
726   // Put zero initialized globals with strong external linkage in the
727   // DATA, __common section with the .zerofill directive.
728   if (Kind.isBSSExtern())
729     return DataCommonSection;
730 
731   // Put zero initialized globals with local linkage in __DATA,__bss directive
732   // with the .zerofill directive (aka .lcomm).
733   if (Kind.isBSSLocal())
734     return DataBSSSection;
735 
736   // Otherwise, just drop the variable in the normal data section.
737   return DataSection;
738 }
739 
740 MCSection *TargetLoweringObjectFileMachO::getSectionForConstant(
741     const DataLayout &DL, SectionKind Kind, const Constant *C,
742     unsigned &Align) const {
743   // If this constant requires a relocation, we have to put it in the data
744   // segment, not in the text segment.
745   if (Kind.isData() || Kind.isReadOnlyWithRel())
746     return ConstDataSection;
747 
748   if (Kind.isMergeableConst4())
749     return FourByteConstantSection;
750   if (Kind.isMergeableConst8())
751     return EightByteConstantSection;
752   if (Kind.isMergeableConst16())
753     return SixteenByteConstantSection;
754   return ReadOnlySection;  // .const
755 }
756 
757 const MCExpr *TargetLoweringObjectFileMachO::getTTypeGlobalReference(
758     const GlobalValue *GV, unsigned Encoding, const TargetMachine &TM,
759     MachineModuleInfo *MMI, MCStreamer &Streamer) const {
760   // The mach-o version of this method defaults to returning a stub reference.
761 
762   if (Encoding & DW_EH_PE_indirect) {
763     MachineModuleInfoMachO &MachOMMI =
764       MMI->getObjFileInfo<MachineModuleInfoMachO>();
765 
766     MCSymbol *SSym = getSymbolWithGlobalValueBase(GV, "$non_lazy_ptr", TM);
767 
768     // Add information about the stub reference to MachOMMI so that the stub
769     // gets emitted by the asmprinter.
770     MachineModuleInfoImpl::StubValueTy &StubSym = MachOMMI.getGVStubEntry(SSym);
771     if (!StubSym.getPointer()) {
772       MCSymbol *Sym = TM.getSymbol(GV);
773       StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
774     }
775 
776     return TargetLoweringObjectFile::
777       getTTypeReference(MCSymbolRefExpr::create(SSym, getContext()),
778                         Encoding & ~DW_EH_PE_indirect, Streamer);
779   }
780 
781   return TargetLoweringObjectFile::getTTypeGlobalReference(GV, Encoding, TM,
782                                                            MMI, Streamer);
783 }
784 
785 MCSymbol *TargetLoweringObjectFileMachO::getCFIPersonalitySymbol(
786     const GlobalValue *GV, const TargetMachine &TM,
787     MachineModuleInfo *MMI) const {
788   // The mach-o version of this method defaults to returning a stub reference.
789   MachineModuleInfoMachO &MachOMMI =
790     MMI->getObjFileInfo<MachineModuleInfoMachO>();
791 
792   MCSymbol *SSym = getSymbolWithGlobalValueBase(GV, "$non_lazy_ptr", TM);
793 
794   // Add information about the stub reference to MachOMMI so that the stub
795   // gets emitted by the asmprinter.
796   MachineModuleInfoImpl::StubValueTy &StubSym = MachOMMI.getGVStubEntry(SSym);
797   if (!StubSym.getPointer()) {
798     MCSymbol *Sym = TM.getSymbol(GV);
799     StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
800   }
801 
802   return SSym;
803 }
804 
805 const MCExpr *TargetLoweringObjectFileMachO::getIndirectSymViaGOTPCRel(
806     const MCSymbol *Sym, const MCValue &MV, int64_t Offset,
807     MachineModuleInfo *MMI, MCStreamer &Streamer) const {
808   // Although MachO 32-bit targets do not explicitly have a GOTPCREL relocation
809   // as 64-bit do, we replace the GOT equivalent by accessing the final symbol
810   // through a non_lazy_ptr stub instead. One advantage is that it allows the
811   // computation of deltas to final external symbols. Example:
812   //
813   //    _extgotequiv:
814   //       .long   _extfoo
815   //
816   //    _delta:
817   //       .long   _extgotequiv-_delta
818   //
819   // is transformed to:
820   //
821   //    _delta:
822   //       .long   L_extfoo$non_lazy_ptr-(_delta+0)
823   //
824   //       .section        __IMPORT,__pointers,non_lazy_symbol_pointers
825   //    L_extfoo$non_lazy_ptr:
826   //       .indirect_symbol        _extfoo
827   //       .long   0
828   //
829   MachineModuleInfoMachO &MachOMMI =
830     MMI->getObjFileInfo<MachineModuleInfoMachO>();
831   MCContext &Ctx = getContext();
832 
833   // The offset must consider the original displacement from the base symbol
834   // since 32-bit targets don't have a GOTPCREL to fold the PC displacement.
835   Offset = -MV.getConstant();
836   const MCSymbol *BaseSym = &MV.getSymB()->getSymbol();
837 
838   // Access the final symbol via sym$non_lazy_ptr and generate the appropriated
839   // non_lazy_ptr stubs.
840   SmallString<128> Name;
841   StringRef Suffix = "$non_lazy_ptr";
842   Name += MMI->getModule()->getDataLayout().getPrivateGlobalPrefix();
843   Name += Sym->getName();
844   Name += Suffix;
845   MCSymbol *Stub = Ctx.getOrCreateSymbol(Name);
846 
847   MachineModuleInfoImpl::StubValueTy &StubSym = MachOMMI.getGVStubEntry(Stub);
848   if (!StubSym.getPointer())
849     StubSym = MachineModuleInfoImpl::
850       StubValueTy(const_cast<MCSymbol *>(Sym), true /* access indirectly */);
851 
852   const MCExpr *BSymExpr =
853     MCSymbolRefExpr::create(BaseSym, MCSymbolRefExpr::VK_None, Ctx);
854   const MCExpr *LHS =
855     MCSymbolRefExpr::create(Stub, MCSymbolRefExpr::VK_None, Ctx);
856 
857   if (!Offset)
858     return MCBinaryExpr::createSub(LHS, BSymExpr, Ctx);
859 
860   const MCExpr *RHS =
861     MCBinaryExpr::createAdd(BSymExpr, MCConstantExpr::create(Offset, Ctx), Ctx);
862   return MCBinaryExpr::createSub(LHS, RHS, Ctx);
863 }
864 
865 static bool canUsePrivateLabel(const MCAsmInfo &AsmInfo,
866                                const MCSection &Section) {
867   if (!AsmInfo.isSectionAtomizableBySymbols(Section))
868     return true;
869 
870   // If it is not dead stripped, it is safe to use private labels.
871   const MCSectionMachO &SMO = cast<MCSectionMachO>(Section);
872   if (SMO.hasAttribute(MachO::S_ATTR_NO_DEAD_STRIP))
873     return true;
874 
875   return false;
876 }
877 
878 void TargetLoweringObjectFileMachO::getNameWithPrefix(
879     SmallVectorImpl<char> &OutName, const GlobalValue *GV,
880     const TargetMachine &TM) const {
881   bool CannotUsePrivateLabel = true;
882   if (auto *GO = GV->getBaseObject()) {
883     SectionKind GOKind = TargetLoweringObjectFile::getKindForGlobal(GO, TM);
884     const MCSection *TheSection = SectionForGlobal(GO, GOKind, TM);
885     CannotUsePrivateLabel =
886         !canUsePrivateLabel(*TM.getMCAsmInfo(), *TheSection);
887   }
888   getMangler().getNameWithPrefix(OutName, GV, CannotUsePrivateLabel);
889 }
890 
891 //===----------------------------------------------------------------------===//
892 //                                  COFF
893 //===----------------------------------------------------------------------===//
894 
895 static unsigned
896 getCOFFSectionFlags(SectionKind K, const TargetMachine &TM) {
897   unsigned Flags = 0;
898   bool isThumb = TM.getTargetTriple().getArch() == Triple::thumb;
899 
900   if (K.isMetadata())
901     Flags |=
902       COFF::IMAGE_SCN_MEM_DISCARDABLE;
903   else if (K.isText())
904     Flags |=
905       COFF::IMAGE_SCN_MEM_EXECUTE |
906       COFF::IMAGE_SCN_MEM_READ |
907       COFF::IMAGE_SCN_CNT_CODE |
908       (isThumb ? COFF::IMAGE_SCN_MEM_16BIT : (COFF::SectionCharacteristics)0);
909   else if (K.isBSS())
910     Flags |=
911       COFF::IMAGE_SCN_CNT_UNINITIALIZED_DATA |
912       COFF::IMAGE_SCN_MEM_READ |
913       COFF::IMAGE_SCN_MEM_WRITE;
914   else if (K.isThreadLocal())
915     Flags |=
916       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
917       COFF::IMAGE_SCN_MEM_READ |
918       COFF::IMAGE_SCN_MEM_WRITE;
919   else if (K.isReadOnly() || K.isReadOnlyWithRel())
920     Flags |=
921       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
922       COFF::IMAGE_SCN_MEM_READ;
923   else if (K.isWriteable())
924     Flags |=
925       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
926       COFF::IMAGE_SCN_MEM_READ |
927       COFF::IMAGE_SCN_MEM_WRITE;
928 
929   return Flags;
930 }
931 
932 static const GlobalValue *getComdatGVForCOFF(const GlobalValue *GV) {
933   const Comdat *C = GV->getComdat();
934   assert(C && "expected GV to have a Comdat!");
935 
936   StringRef ComdatGVName = C->getName();
937   const GlobalValue *ComdatGV = GV->getParent()->getNamedValue(ComdatGVName);
938   if (!ComdatGV)
939     report_fatal_error("Associative COMDAT symbol '" + ComdatGVName +
940                        "' does not exist.");
941 
942   if (ComdatGV->getComdat() != C)
943     report_fatal_error("Associative COMDAT symbol '" + ComdatGVName +
944                        "' is not a key for its COMDAT.");
945 
946   return ComdatGV;
947 }
948 
949 static int getSelectionForCOFF(const GlobalValue *GV) {
950   if (const Comdat *C = GV->getComdat()) {
951     const GlobalValue *ComdatKey = getComdatGVForCOFF(GV);
952     if (const auto *GA = dyn_cast<GlobalAlias>(ComdatKey))
953       ComdatKey = GA->getBaseObject();
954     if (ComdatKey == GV) {
955       switch (C->getSelectionKind()) {
956       case Comdat::Any:
957         return COFF::IMAGE_COMDAT_SELECT_ANY;
958       case Comdat::ExactMatch:
959         return COFF::IMAGE_COMDAT_SELECT_EXACT_MATCH;
960       case Comdat::Largest:
961         return COFF::IMAGE_COMDAT_SELECT_LARGEST;
962       case Comdat::NoDuplicates:
963         return COFF::IMAGE_COMDAT_SELECT_NODUPLICATES;
964       case Comdat::SameSize:
965         return COFF::IMAGE_COMDAT_SELECT_SAME_SIZE;
966       }
967     } else {
968       return COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE;
969     }
970   }
971   return 0;
972 }
973 
974 MCSection *TargetLoweringObjectFileCOFF::getExplicitSectionGlobal(
975     const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
976   int Selection = 0;
977   unsigned Characteristics = getCOFFSectionFlags(Kind, TM);
978   StringRef Name = GO->getSection();
979   StringRef COMDATSymName = "";
980   if (GO->hasComdat()) {
981     Selection = getSelectionForCOFF(GO);
982     const GlobalValue *ComdatGV;
983     if (Selection == COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE)
984       ComdatGV = getComdatGVForCOFF(GO);
985     else
986       ComdatGV = GO;
987 
988     if (!ComdatGV->hasPrivateLinkage()) {
989       MCSymbol *Sym = TM.getSymbol(ComdatGV);
990       COMDATSymName = Sym->getName();
991       Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
992     } else {
993       Selection = 0;
994     }
995   }
996 
997   return getContext().getCOFFSection(Name, Characteristics, Kind, COMDATSymName,
998                                      Selection);
999 }
1000 
1001 static const char *getCOFFSectionNameForUniqueGlobal(SectionKind Kind) {
1002   if (Kind.isText())
1003     return ".text";
1004   if (Kind.isBSS())
1005     return ".bss";
1006   if (Kind.isThreadLocal())
1007     return ".tls$";
1008   if (Kind.isReadOnly() || Kind.isReadOnlyWithRel())
1009     return ".rdata";
1010   return ".data";
1011 }
1012 
1013 MCSection *TargetLoweringObjectFileCOFF::SelectSectionForGlobal(
1014     const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
1015   // If we have -ffunction-sections then we should emit the global value to a
1016   // uniqued section specifically for it.
1017   bool EmitUniquedSection;
1018   if (Kind.isText())
1019     EmitUniquedSection = TM.getFunctionSections();
1020   else
1021     EmitUniquedSection = TM.getDataSections();
1022 
1023   if ((EmitUniquedSection && !Kind.isCommon()) || GO->hasComdat()) {
1024     const char *Name = getCOFFSectionNameForUniqueGlobal(Kind);
1025     unsigned Characteristics = getCOFFSectionFlags(Kind, TM);
1026 
1027     Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
1028     int Selection = getSelectionForCOFF(GO);
1029     if (!Selection)
1030       Selection = COFF::IMAGE_COMDAT_SELECT_NODUPLICATES;
1031     const GlobalValue *ComdatGV;
1032     if (GO->hasComdat())
1033       ComdatGV = getComdatGVForCOFF(GO);
1034     else
1035       ComdatGV = GO;
1036 
1037     unsigned UniqueID = MCContext::GenericSectionID;
1038     if (EmitUniquedSection)
1039       UniqueID = NextUniqueID++;
1040 
1041     if (!ComdatGV->hasPrivateLinkage()) {
1042       MCSymbol *Sym = TM.getSymbol(ComdatGV);
1043       StringRef COMDATSymName = Sym->getName();
1044       return getContext().getCOFFSection(Name, Characteristics, Kind,
1045                                          COMDATSymName, Selection, UniqueID);
1046     } else {
1047       SmallString<256> TmpData;
1048       getMangler().getNameWithPrefix(TmpData, GO, /*CannotUsePrivateLabel=*/true);
1049       return getContext().getCOFFSection(Name, Characteristics, Kind, TmpData,
1050                                          Selection, UniqueID);
1051     }
1052   }
1053 
1054   if (Kind.isText())
1055     return TextSection;
1056 
1057   if (Kind.isThreadLocal())
1058     return TLSDataSection;
1059 
1060   if (Kind.isReadOnly() || Kind.isReadOnlyWithRel())
1061     return ReadOnlySection;
1062 
1063   // Note: we claim that common symbols are put in BSSSection, but they are
1064   // really emitted with the magic .comm directive, which creates a symbol table
1065   // entry but not a section.
1066   if (Kind.isBSS() || Kind.isCommon())
1067     return BSSSection;
1068 
1069   return DataSection;
1070 }
1071 
1072 void TargetLoweringObjectFileCOFF::getNameWithPrefix(
1073     SmallVectorImpl<char> &OutName, const GlobalValue *GV,
1074     const TargetMachine &TM) const {
1075   bool CannotUsePrivateLabel = false;
1076   if (GV->hasPrivateLinkage() &&
1077       ((isa<Function>(GV) && TM.getFunctionSections()) ||
1078        (isa<GlobalVariable>(GV) && TM.getDataSections())))
1079     CannotUsePrivateLabel = true;
1080 
1081   getMangler().getNameWithPrefix(OutName, GV, CannotUsePrivateLabel);
1082 }
1083 
1084 MCSection *TargetLoweringObjectFileCOFF::getSectionForJumpTable(
1085     const Function &F, const TargetMachine &TM) const {
1086   // If the function can be removed, produce a unique section so that
1087   // the table doesn't prevent the removal.
1088   const Comdat *C = F.getComdat();
1089   bool EmitUniqueSection = TM.getFunctionSections() || C;
1090   if (!EmitUniqueSection)
1091     return ReadOnlySection;
1092 
1093   // FIXME: we should produce a symbol for F instead.
1094   if (F.hasPrivateLinkage())
1095     return ReadOnlySection;
1096 
1097   MCSymbol *Sym = TM.getSymbol(&F);
1098   StringRef COMDATSymName = Sym->getName();
1099 
1100   SectionKind Kind = SectionKind::getReadOnly();
1101   const char *Name = getCOFFSectionNameForUniqueGlobal(Kind);
1102   unsigned Characteristics = getCOFFSectionFlags(Kind, TM);
1103   Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
1104   unsigned UniqueID = NextUniqueID++;
1105 
1106   return getContext().getCOFFSection(Name, Characteristics, Kind, COMDATSymName,
1107                                      COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE, UniqueID);
1108 }
1109 
1110 void TargetLoweringObjectFileCOFF::emitModuleFlags(
1111     MCStreamer &Streamer, ArrayRef<Module::ModuleFlagEntry> ModuleFlags,
1112     const TargetMachine &TM) const {
1113   MDNode *LinkerOptions = nullptr;
1114 
1115   for (const auto &MFE : ModuleFlags) {
1116     StringRef Key = MFE.Key->getString();
1117     if (Key == "Linker Options")
1118       LinkerOptions = cast<MDNode>(MFE.Val);
1119   }
1120 
1121   if (LinkerOptions) {
1122     // Emit the linker options to the linker .drectve section.  According to the
1123     // spec, this section is a space-separated string containing flags for
1124     // linker.
1125     MCSection *Sec = getDrectveSection();
1126     Streamer.SwitchSection(Sec);
1127     for (const auto &Option : LinkerOptions->operands()) {
1128       for (const auto &Piece : cast<MDNode>(Option)->operands()) {
1129         // Lead with a space for consistency with our dllexport implementation.
1130         std::string Directive(" ");
1131         Directive.append(cast<MDString>(Piece)->getString());
1132         Streamer.EmitBytes(Directive);
1133       }
1134     }
1135   }
1136 }
1137 
1138 void TargetLoweringObjectFileCOFF::Initialize(MCContext &Ctx,
1139                                               const TargetMachine &TM) {
1140   TargetLoweringObjectFile::Initialize(Ctx, TM);
1141   const Triple &T = TM.getTargetTriple();
1142   if (T.isKnownWindowsMSVCEnvironment() || T.isWindowsItaniumEnvironment()) {
1143     StaticCtorSection =
1144         Ctx.getCOFFSection(".CRT$XCU", COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
1145                                            COFF::IMAGE_SCN_MEM_READ,
1146                            SectionKind::getReadOnly());
1147     StaticDtorSection =
1148         Ctx.getCOFFSection(".CRT$XTX", COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
1149                                            COFF::IMAGE_SCN_MEM_READ,
1150                            SectionKind::getReadOnly());
1151   } else {
1152     StaticCtorSection = Ctx.getCOFFSection(
1153         ".ctors", COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
1154                       COFF::IMAGE_SCN_MEM_READ | COFF::IMAGE_SCN_MEM_WRITE,
1155         SectionKind::getData());
1156     StaticDtorSection = Ctx.getCOFFSection(
1157         ".dtors", COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
1158                       COFF::IMAGE_SCN_MEM_READ | COFF::IMAGE_SCN_MEM_WRITE,
1159         SectionKind::getData());
1160   }
1161 }
1162 
1163 MCSection *TargetLoweringObjectFileCOFF::getStaticCtorSection(
1164     unsigned Priority, const MCSymbol *KeySym) const {
1165   return getContext().getAssociativeCOFFSection(
1166       cast<MCSectionCOFF>(StaticCtorSection), KeySym, 0);
1167 }
1168 
1169 MCSection *TargetLoweringObjectFileCOFF::getStaticDtorSection(
1170     unsigned Priority, const MCSymbol *KeySym) const {
1171   return getContext().getAssociativeCOFFSection(
1172       cast<MCSectionCOFF>(StaticDtorSection), KeySym, 0);
1173 }
1174 
1175 void TargetLoweringObjectFileCOFF::emitLinkerFlagsForGlobal(
1176     raw_ostream &OS, const GlobalValue *GV) const {
1177   emitLinkerFlagsForGlobalCOFF(OS, GV, getTargetTriple(), getMangler());
1178 }
1179 
1180 //===----------------------------------------------------------------------===//
1181 //                                  Wasm
1182 //===----------------------------------------------------------------------===//
1183 
1184 static const Comdat *getWasmComdat(const GlobalValue *GV) {
1185   const Comdat *C = GV->getComdat();
1186   if (!C)
1187     return nullptr;
1188 
1189   if (C->getSelectionKind() != Comdat::Any)
1190     report_fatal_error("Wasm COMDATs only support SelectionKind::Any, '" +
1191                        C->getName() + "' cannot be lowered.");
1192 
1193   return C;
1194 }
1195 
1196 MCSection *TargetLoweringObjectFileWasm::getExplicitSectionGlobal(
1197     const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
1198   llvm_unreachable("getExplicitSectionGlobal not yet implemented");
1199   return nullptr;
1200 }
1201 
1202 static MCSectionWasm *
1203 selectWasmSectionForGlobal(MCContext &Ctx, const GlobalObject *GO,
1204                            SectionKind Kind, Mangler &Mang,
1205                            const TargetMachine &TM, bool EmitUniqueSection,
1206                            unsigned Flags, unsigned *NextUniqueID) {
1207   StringRef Group = "";
1208   if (getWasmComdat(GO))
1209     llvm_unreachable("comdat not yet supported for wasm");
1210 
1211   bool UniqueSectionNames = TM.getUniqueSectionNames();
1212   SmallString<128> Name = getSectionPrefixForGlobal(Kind);
1213 
1214   if (const auto *F = dyn_cast<Function>(GO)) {
1215     const auto &OptionalPrefix = F->getSectionPrefix();
1216     if (OptionalPrefix)
1217       Name += *OptionalPrefix;
1218   }
1219 
1220   if (EmitUniqueSection && UniqueSectionNames) {
1221     Name.push_back('.');
1222     TM.getNameWithPrefix(Name, GO, Mang, true);
1223   }
1224   unsigned UniqueID = MCContext::GenericSectionID;
1225   if (EmitUniqueSection && !UniqueSectionNames) {
1226     UniqueID = *NextUniqueID;
1227     (*NextUniqueID)++;
1228   }
1229   return Ctx.getWasmSection(Name, /*Type=*/0, Flags,
1230                             Group, UniqueID);
1231 }
1232 
1233 MCSection *TargetLoweringObjectFileWasm::SelectSectionForGlobal(
1234     const GlobalObject *GO, SectionKind Kind, const TargetMachine &TM) const {
1235 
1236   if (Kind.isCommon())
1237     report_fatal_error("mergable sections not supported yet on wasm");
1238 
1239   // If we have -ffunction-section or -fdata-section then we should emit the
1240   // global value to a uniqued section specifically for it.
1241   bool EmitUniqueSection = false;
1242   if (Kind.isText())
1243     EmitUniqueSection = TM.getFunctionSections();
1244   else
1245     EmitUniqueSection = TM.getDataSections();
1246   EmitUniqueSection |= GO->hasComdat();
1247 
1248   return selectWasmSectionForGlobal(getContext(), GO, Kind, getMangler(), TM,
1249                                     EmitUniqueSection, /*Flags=*/0,
1250                                     &NextUniqueID);
1251 }
1252 
1253 bool TargetLoweringObjectFileWasm::shouldPutJumpTableInFunctionSection(
1254     bool UsesLabelDifference, const Function &F) const {
1255   // We can always create relative relocations, so use another section
1256   // that can be marked non-executable.
1257   return false;
1258 }
1259 
1260 const MCExpr *TargetLoweringObjectFileWasm::lowerRelativeReference(
1261     const GlobalValue *LHS, const GlobalValue *RHS,
1262     const TargetMachine &TM) const {
1263   // We may only use a PLT-relative relocation to refer to unnamed_addr
1264   // functions.
1265   if (!LHS->hasGlobalUnnamedAddr() || !LHS->getValueType()->isFunctionTy())
1266     return nullptr;
1267 
1268   // Basic sanity checks.
1269   if (LHS->getType()->getPointerAddressSpace() != 0 ||
1270       RHS->getType()->getPointerAddressSpace() != 0 || LHS->isThreadLocal() ||
1271       RHS->isThreadLocal())
1272     return nullptr;
1273 
1274   return MCBinaryExpr::createSub(
1275       MCSymbolRefExpr::create(TM.getSymbol(LHS), MCSymbolRefExpr::VK_None,
1276                               getContext()),
1277       MCSymbolRefExpr::create(TM.getSymbol(RHS), getContext()), getContext());
1278 }
1279 
1280 void
1281 TargetLoweringObjectFileWasm::InitializeWasm() {
1282   // TODO: Initialize StaticCtorSection and StaticDtorSection.
1283 }
1284