xref: /llvm-project/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp (revision 4491d0d337a42f34cf5f51a7324ee6e8af8eb5c2) 
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/CodeGen/TargetLoweringObjectFileImpl.h"
16 #include "llvm/ADT/SmallString.h"
17 #include "llvm/ADT/StringExtras.h"
18 #include "llvm/ADT/Triple.h"
19 #include "llvm/CodeGen/MachineModuleInfoImpls.h"
20 #include "llvm/IR/Constants.h"
21 #include "llvm/IR/DataLayout.h"
22 #include "llvm/IR/DerivedTypes.h"
23 #include "llvm/IR/Function.h"
24 #include "llvm/IR/GlobalVariable.h"
25 #include "llvm/IR/Mangler.h"
26 #include "llvm/IR/Module.h"
27 #include "llvm/MC/MCContext.h"
28 #include "llvm/MC/MCExpr.h"
29 #include "llvm/MC/MCSectionCOFF.h"
30 #include "llvm/MC/MCSectionELF.h"
31 #include "llvm/MC/MCSectionMachO.h"
32 #include "llvm/MC/MCStreamer.h"
33 #include "llvm/MC/MCSymbol.h"
34 #include "llvm/Support/Dwarf.h"
35 #include "llvm/Support/ELF.h"
36 #include "llvm/Support/ErrorHandling.h"
37 #include "llvm/Support/raw_ostream.h"
38 #include "llvm/Target/TargetLowering.h"
39 #include "llvm/Target/TargetMachine.h"
40 #include "llvm/Target/TargetSubtargetInfo.h"
41 using namespace llvm;
42 using namespace dwarf;
43 
44 //===----------------------------------------------------------------------===//
45 //                                  ELF
46 //===----------------------------------------------------------------------===//
47 
48 MCSymbol *TargetLoweringObjectFileELF::getCFIPersonalitySymbol(
49     const GlobalValue *GV, Mangler &Mang, const TargetMachine &TM,
50     MachineModuleInfo *MMI) const {
51   unsigned Encoding = getPersonalityEncoding();
52   if ((Encoding & 0x80) == dwarf::DW_EH_PE_indirect)
53     return getContext().GetOrCreateSymbol(StringRef("DW.ref.") +
54                                           TM.getSymbol(GV, Mang)->getName());
55   if ((Encoding & 0x70) == dwarf::DW_EH_PE_absptr)
56     return TM.getSymbol(GV, Mang);
57   report_fatal_error("We do not support this DWARF encoding yet!");
58 }
59 
60 void TargetLoweringObjectFileELF::emitPersonalityValue(MCStreamer &Streamer,
61                                                        const TargetMachine &TM,
62                                                        const MCSymbol *Sym) const {
63   SmallString<64> NameData("DW.ref.");
64   NameData += Sym->getName();
65   MCSymbol *Label = getContext().GetOrCreateSymbol(NameData);
66   Streamer.EmitSymbolAttribute(Label, MCSA_Hidden);
67   Streamer.EmitSymbolAttribute(Label, MCSA_Weak);
68   StringRef Prefix = ".data.";
69   NameData.insert(NameData.begin(), Prefix.begin(), Prefix.end());
70   unsigned Flags = ELF::SHF_ALLOC | ELF::SHF_WRITE | ELF::SHF_GROUP;
71   const MCSection *Sec = getContext().getELFSection(NameData,
72                                                     ELF::SHT_PROGBITS,
73                                                     Flags,
74                                                     0, Label->getName());
75   unsigned Size = TM.getDataLayout()->getPointerSize();
76   Streamer.SwitchSection(Sec);
77   Streamer.EmitValueToAlignment(TM.getDataLayout()->getPointerABIAlignment());
78   Streamer.EmitSymbolAttribute(Label, MCSA_ELF_TypeObject);
79   const MCExpr *E = MCConstantExpr::Create(Size, getContext());
80   Streamer.EmitELFSize(Label, E);
81   Streamer.EmitLabel(Label);
82 
83   Streamer.EmitSymbolValue(Sym, Size);
84 }
85 
86 const MCExpr *TargetLoweringObjectFileELF::getTTypeGlobalReference(
87     const GlobalValue *GV, unsigned Encoding, Mangler &Mang,
88     const TargetMachine &TM, MachineModuleInfo *MMI,
89     MCStreamer &Streamer) const {
90 
91   if (Encoding & dwarf::DW_EH_PE_indirect) {
92     MachineModuleInfoELF &ELFMMI = MMI->getObjFileInfo<MachineModuleInfoELF>();
93 
94     MCSymbol *SSym = getSymbolWithGlobalValueBase(GV, ".DW.stub", Mang, TM);
95 
96     // Add information about the stub reference to ELFMMI so that the stub
97     // gets emitted by the asmprinter.
98     MachineModuleInfoImpl::StubValueTy &StubSym = ELFMMI.getGVStubEntry(SSym);
99     if (!StubSym.getPointer()) {
100       MCSymbol *Sym = TM.getSymbol(GV, Mang);
101       StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
102     }
103 
104     return TargetLoweringObjectFile::
105       getTTypeReference(MCSymbolRefExpr::Create(SSym, getContext()),
106                         Encoding & ~dwarf::DW_EH_PE_indirect, Streamer);
107   }
108 
109   return TargetLoweringObjectFile::
110     getTTypeGlobalReference(GV, Encoding, Mang, TM, MMI, Streamer);
111 }
112 
113 static SectionKind
114 getELFKindForNamedSection(StringRef Name, SectionKind K) {
115   // N.B.: The defaults used in here are no the same ones used in MC.
116   // We follow gcc, MC follows gas. For example, given ".section .eh_frame",
117   // both gas and MC will produce a section with no flags. Given
118   // section(".eh_frame") gcc will produce:
119   //
120   //   .section   .eh_frame,"a",@progbits
121   if (Name.empty() || Name[0] != '.') return K;
122 
123   // Some lame default implementation based on some magic section names.
124   if (Name == ".bss" ||
125       Name.startswith(".bss.") ||
126       Name.startswith(".gnu.linkonce.b.") ||
127       Name.startswith(".llvm.linkonce.b.") ||
128       Name == ".sbss" ||
129       Name.startswith(".sbss.") ||
130       Name.startswith(".gnu.linkonce.sb.") ||
131       Name.startswith(".llvm.linkonce.sb."))
132     return SectionKind::getBSS();
133 
134   if (Name == ".tdata" ||
135       Name.startswith(".tdata.") ||
136       Name.startswith(".gnu.linkonce.td.") ||
137       Name.startswith(".llvm.linkonce.td."))
138     return SectionKind::getThreadData();
139 
140   if (Name == ".tbss" ||
141       Name.startswith(".tbss.") ||
142       Name.startswith(".gnu.linkonce.tb.") ||
143       Name.startswith(".llvm.linkonce.tb."))
144     return SectionKind::getThreadBSS();
145 
146   return K;
147 }
148 
149 
150 static unsigned getELFSectionType(StringRef Name, SectionKind K) {
151 
152   if (Name == ".init_array")
153     return ELF::SHT_INIT_ARRAY;
154 
155   if (Name == ".fini_array")
156     return ELF::SHT_FINI_ARRAY;
157 
158   if (Name == ".preinit_array")
159     return ELF::SHT_PREINIT_ARRAY;
160 
161   if (K.isBSS() || K.isThreadBSS())
162     return ELF::SHT_NOBITS;
163 
164   return ELF::SHT_PROGBITS;
165 }
166 
167 static unsigned getELFSectionFlags(SectionKind K) {
168   unsigned Flags = 0;
169 
170   if (!K.isMetadata())
171     Flags |= ELF::SHF_ALLOC;
172 
173   if (K.isText())
174     Flags |= ELF::SHF_EXECINSTR;
175 
176   if (K.isWriteable())
177     Flags |= ELF::SHF_WRITE;
178 
179   if (K.isThreadLocal())
180     Flags |= ELF::SHF_TLS;
181 
182   if (K.isMergeableCString() || K.isMergeableConst())
183     Flags |= ELF::SHF_MERGE;
184 
185   if (K.isMergeableCString())
186     Flags |= ELF::SHF_STRINGS;
187 
188   return Flags;
189 }
190 
191 static const Comdat *getELFComdat(const GlobalValue *GV) {
192   const Comdat *C = GV->getComdat();
193   if (!C)
194     return nullptr;
195 
196   if (C->getSelectionKind() != Comdat::Any)
197     report_fatal_error("ELF COMDATs only support SelectionKind::Any, '" +
198                        C->getName() + "' cannot be lowered.");
199 
200   return C;
201 }
202 
203 const MCSection *TargetLoweringObjectFileELF::getExplicitSectionGlobal(
204     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
205     const TargetMachine &TM) const {
206   StringRef SectionName = GV->getSection();
207 
208   // Infer section flags from the section name if we can.
209   Kind = getELFKindForNamedSection(SectionName, Kind);
210 
211   StringRef Group = "";
212   unsigned Flags = getELFSectionFlags(Kind);
213   if (const Comdat *C = getELFComdat(GV)) {
214     Group = C->getName();
215     Flags |= ELF::SHF_GROUP;
216   }
217   return getContext().getELFSection(SectionName,
218                                     getELFSectionType(SectionName, Kind), Flags,
219                                     /*EntrySize=*/0, Group);
220 }
221 
222 /// Return the section prefix name used by options FunctionsSections and
223 /// DataSections.
224 static StringRef getSectionPrefixForGlobal(SectionKind Kind) {
225   if (Kind.isText())
226     return ".text";
227   if (Kind.isReadOnly())
228     return ".rodata";
229   if (Kind.isBSS())
230     return ".bss";
231   if (Kind.isThreadData())
232     return ".tdata";
233   if (Kind.isThreadBSS())
234     return ".tbss";
235   if (Kind.isDataNoRel())
236     return ".data";
237   if (Kind.isDataRelLocal())
238     return ".data.rel.local";
239   if (Kind.isDataRel())
240     return ".data.rel";
241   if (Kind.isReadOnlyWithRelLocal())
242     return ".data.rel.ro.local";
243   assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
244   return ".data.rel.ro";
245 }
246 
247 static const MCSectionELF *selectELFSectionForGlobal(
248     MCContext &Ctx, const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
249     const TargetMachine &TM, bool EmitUniqueSection, unsigned Flags) {
250   unsigned EntrySize = 0;
251   if (Kind.isMergeableCString()) {
252     if (Kind.isMergeable2ByteCString()) {
253       EntrySize = 2;
254     } else if (Kind.isMergeable4ByteCString()) {
255       EntrySize = 4;
256     } else {
257       EntrySize = 1;
258       assert(Kind.isMergeable1ByteCString() && "unknown string width");
259     }
260   } else if (Kind.isMergeableConst()) {
261     if (Kind.isMergeableConst4()) {
262       EntrySize = 4;
263     } else if (Kind.isMergeableConst8()) {
264       EntrySize = 8;
265     } else {
266       assert(Kind.isMergeableConst16() && "unknown data width");
267       EntrySize = 16;
268     }
269   }
270 
271   StringRef Group = "";
272   if (const Comdat *C = getELFComdat(GV)) {
273     Flags |= ELF::SHF_GROUP;
274     Group = C->getName();
275   }
276 
277   bool UniqueSectionNames = TM.getUniqueSectionNames();
278   SmallString<128> Name;
279   if (Kind.isMergeableCString()) {
280     // We also need alignment here.
281     // FIXME: this is getting the alignment of the character, not the
282     // alignment of the global!
283     unsigned Align =
284         TM.getDataLayout()->getPreferredAlignment(cast<GlobalVariable>(GV));
285 
286     std::string SizeSpec = ".rodata.str" + utostr(EntrySize) + ".";
287     Name = SizeSpec + utostr(Align);
288   } else if (Kind.isMergeableConst()) {
289     Name = ".rodata.cst";
290     Name += utostr(EntrySize);
291   } else {
292     Name = getSectionPrefixForGlobal(Kind);
293   }
294 
295   if (EmitUniqueSection && UniqueSectionNames) {
296     Name.push_back('.');
297     TM.getNameWithPrefix(Name, GV, Mang, true);
298   }
299   return Ctx.getELFSection(Name, getELFSectionType(Name, Kind), Flags,
300                            EntrySize, Group,
301                            EmitUniqueSection && !UniqueSectionNames);
302 }
303 
304 const MCSection *TargetLoweringObjectFileELF::SelectSectionForGlobal(
305     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
306     const TargetMachine &TM) const {
307   unsigned Flags = getELFSectionFlags(Kind);
308 
309   // If we have -ffunction-section or -fdata-section then we should emit the
310   // global value to a uniqued section specifically for it.
311   bool EmitUniqueSection = false;
312   if (!(Flags & ELF::SHF_MERGE) && !Kind.isCommon()) {
313     if (Kind.isText())
314       EmitUniqueSection = TM.getFunctionSections();
315     else
316       EmitUniqueSection = TM.getDataSections();
317   }
318   EmitUniqueSection |= GV->hasComdat();
319 
320   return selectELFSectionForGlobal(getContext(), GV, Kind, Mang, TM,
321                                    EmitUniqueSection, Flags);
322 }
323 
324 const MCSection *TargetLoweringObjectFileELF::getSectionForJumpTable(
325     const Function &F, Mangler &Mang, const TargetMachine &TM) const {
326   // If the function can be removed, produce a unique section so that
327   // the table doesn't prevent the removal.
328   const Comdat *C = F.getComdat();
329   bool EmitUniqueSection = TM.getFunctionSections() || C;
330   if (!EmitUniqueSection)
331     return ReadOnlySection;
332 
333   return selectELFSectionForGlobal(getContext(), &F, SectionKind::getReadOnly(),
334                                    Mang, TM, EmitUniqueSection, ELF::SHF_ALLOC);
335 }
336 
337 bool TargetLoweringObjectFileELF::shouldPutJumpTableInFunctionSection(
338     bool UsesLabelDifference, const Function &F) const {
339   // We can always create relative relocations, so use another section
340   // that can be marked non-executable.
341   return false;
342 }
343 
344 /// getSectionForConstant - Given a mergeable constant with the
345 /// specified size and relocation information, return a section that it
346 /// should be placed in.
347 const MCSection *
348 TargetLoweringObjectFileELF::getSectionForConstant(SectionKind Kind,
349                                                    const Constant *C) const {
350   if (Kind.isMergeableConst4() && MergeableConst4Section)
351     return MergeableConst4Section;
352   if (Kind.isMergeableConst8() && MergeableConst8Section)
353     return MergeableConst8Section;
354   if (Kind.isMergeableConst16() && MergeableConst16Section)
355     return MergeableConst16Section;
356   if (Kind.isReadOnly())
357     return ReadOnlySection;
358 
359   if (Kind.isReadOnlyWithRelLocal()) return DataRelROLocalSection;
360   assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
361   return DataRelROSection;
362 }
363 
364 static const MCSectionELF *getStaticStructorSection(MCContext &Ctx,
365                                                     bool UseInitArray,
366                                                     bool IsCtor,
367                                                     unsigned Priority,
368                                                     const MCSymbol *KeySym) {
369   std::string Name;
370   unsigned Type;
371   unsigned Flags = ELF::SHF_ALLOC | ELF::SHF_WRITE;
372   StringRef COMDAT = KeySym ? KeySym->getName() : "";
373 
374   if (KeySym)
375     Flags |= ELF::SHF_GROUP;
376 
377   if (UseInitArray) {
378     if (IsCtor) {
379       Type = ELF::SHT_INIT_ARRAY;
380       Name = ".init_array";
381     } else {
382       Type = ELF::SHT_FINI_ARRAY;
383       Name = ".fini_array";
384     }
385     if (Priority != 65535) {
386       Name += '.';
387       Name += utostr(Priority);
388     }
389   } else {
390     // The default scheme is .ctor / .dtor, so we have to invert the priority
391     // numbering.
392     if (IsCtor)
393       Name = ".ctors";
394     else
395       Name = ".dtors";
396     if (Priority != 65535) {
397       Name += '.';
398       Name += utostr(65535 - Priority);
399     }
400     Type = ELF::SHT_PROGBITS;
401   }
402 
403   return Ctx.getELFSection(Name, Type, Flags, 0, COMDAT);
404 }
405 
406 const MCSection *TargetLoweringObjectFileELF::getStaticCtorSection(
407     unsigned Priority, const MCSymbol *KeySym) const {
408   return getStaticStructorSection(getContext(), UseInitArray, true, Priority,
409                                   KeySym);
410 }
411 
412 const MCSection *TargetLoweringObjectFileELF::getStaticDtorSection(
413     unsigned Priority, const MCSymbol *KeySym) const {
414   return getStaticStructorSection(getContext(), UseInitArray, false, Priority,
415                                   KeySym);
416 }
417 
418 void
419 TargetLoweringObjectFileELF::InitializeELF(bool UseInitArray_) {
420   UseInitArray = UseInitArray_;
421   if (!UseInitArray)
422     return;
423 
424   StaticCtorSection = getContext().getELFSection(
425       ".init_array", ELF::SHT_INIT_ARRAY, ELF::SHF_WRITE | ELF::SHF_ALLOC);
426   StaticDtorSection = getContext().getELFSection(
427       ".fini_array", ELF::SHT_FINI_ARRAY, ELF::SHF_WRITE | ELF::SHF_ALLOC);
428 }
429 
430 //===----------------------------------------------------------------------===//
431 //                                 MachO
432 //===----------------------------------------------------------------------===//
433 
434 /// getDepLibFromLinkerOpt - Extract the dependent library name from a linker
435 /// option string. Returns StringRef() if the option does not specify a library.
436 StringRef TargetLoweringObjectFileMachO::
437 getDepLibFromLinkerOpt(StringRef LinkerOption) const {
438   const char *LibCmd = "-l";
439   if (LinkerOption.startswith(LibCmd))
440     return LinkerOption.substr(strlen(LibCmd));
441   return StringRef();
442 }
443 
444 /// emitModuleFlags - Perform code emission for module flags.
445 void TargetLoweringObjectFileMachO::
446 emitModuleFlags(MCStreamer &Streamer,
447                 ArrayRef<Module::ModuleFlagEntry> ModuleFlags,
448                 Mangler &Mang, const TargetMachine &TM) const {
449   unsigned VersionVal = 0;
450   unsigned ImageInfoFlags = 0;
451   MDNode *LinkerOptions = nullptr;
452   StringRef SectionVal;
453 
454   for (ArrayRef<Module::ModuleFlagEntry>::iterator
455          i = ModuleFlags.begin(), e = ModuleFlags.end(); i != e; ++i) {
456     const Module::ModuleFlagEntry &MFE = *i;
457 
458     // Ignore flags with 'Require' behavior.
459     if (MFE.Behavior == Module::Require)
460       continue;
461 
462     StringRef Key = MFE.Key->getString();
463     Metadata *Val = MFE.Val;
464 
465     if (Key == "Objective-C Image Info Version") {
466       VersionVal = mdconst::extract<ConstantInt>(Val)->getZExtValue();
467     } else if (Key == "Objective-C Garbage Collection" ||
468                Key == "Objective-C GC Only" ||
469                Key == "Objective-C Is Simulated" ||
470                Key == "Objective-C Image Swift Version") {
471       ImageInfoFlags |= mdconst::extract<ConstantInt>(Val)->getZExtValue();
472     } else if (Key == "Objective-C Image Info Section") {
473       SectionVal = cast<MDString>(Val)->getString();
474     } else if (Key == "Linker Options") {
475       LinkerOptions = cast<MDNode>(Val);
476     }
477   }
478 
479   // Emit the linker options if present.
480   if (LinkerOptions) {
481     for (unsigned i = 0, e = LinkerOptions->getNumOperands(); i != e; ++i) {
482       MDNode *MDOptions = cast<MDNode>(LinkerOptions->getOperand(i));
483       SmallVector<std::string, 4> StrOptions;
484 
485       // Convert to strings.
486       for (unsigned ii = 0, ie = MDOptions->getNumOperands(); ii != ie; ++ii) {
487         MDString *MDOption = cast<MDString>(MDOptions->getOperand(ii));
488         StrOptions.push_back(MDOption->getString());
489       }
490 
491       Streamer.EmitLinkerOptions(StrOptions);
492     }
493   }
494 
495   // The section is mandatory. If we don't have it, then we don't have GC info.
496   if (SectionVal.empty()) return;
497 
498   StringRef Segment, Section;
499   unsigned TAA = 0, StubSize = 0;
500   bool TAAParsed;
501   std::string ErrorCode =
502     MCSectionMachO::ParseSectionSpecifier(SectionVal, Segment, Section,
503                                           TAA, TAAParsed, StubSize);
504   if (!ErrorCode.empty())
505     // If invalid, report the error with report_fatal_error.
506     report_fatal_error("Invalid section specifier '" + Section + "': " +
507                        ErrorCode + ".");
508 
509   // Get the section.
510   const MCSectionMachO *S =
511     getContext().getMachOSection(Segment, Section, TAA, StubSize,
512                                  SectionKind::getDataNoRel());
513   Streamer.SwitchSection(S);
514   Streamer.EmitLabel(getContext().
515                      GetOrCreateSymbol(StringRef("L_OBJC_IMAGE_INFO")));
516   Streamer.EmitIntValue(VersionVal, 4);
517   Streamer.EmitIntValue(ImageInfoFlags, 4);
518   Streamer.AddBlankLine();
519 }
520 
521 static void checkMachOComdat(const GlobalValue *GV) {
522   const Comdat *C = GV->getComdat();
523   if (!C)
524     return;
525 
526   report_fatal_error("MachO doesn't support COMDATs, '" + C->getName() +
527                      "' cannot be lowered.");
528 }
529 
530 const MCSection *TargetLoweringObjectFileMachO::getExplicitSectionGlobal(
531     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
532     const TargetMachine &TM) const {
533   // Parse the section specifier and create it if valid.
534   StringRef Segment, Section;
535   unsigned TAA = 0, StubSize = 0;
536   bool TAAParsed;
537 
538   checkMachOComdat(GV);
539 
540   std::string ErrorCode =
541     MCSectionMachO::ParseSectionSpecifier(GV->getSection(), Segment, Section,
542                                           TAA, TAAParsed, StubSize);
543   if (!ErrorCode.empty()) {
544     // If invalid, report the error with report_fatal_error.
545     report_fatal_error("Global variable '" + GV->getName() +
546                        "' has an invalid section specifier '" +
547                        GV->getSection() + "': " + ErrorCode + ".");
548   }
549 
550   // Get the section.
551   const MCSectionMachO *S =
552     getContext().getMachOSection(Segment, Section, TAA, StubSize, Kind);
553 
554   // If TAA wasn't set by ParseSectionSpecifier() above,
555   // use the value returned by getMachOSection() as a default.
556   if (!TAAParsed)
557     TAA = S->getTypeAndAttributes();
558 
559   // Okay, now that we got the section, verify that the TAA & StubSize agree.
560   // If the user declared multiple globals with different section flags, we need
561   // to reject it here.
562   if (S->getTypeAndAttributes() != TAA || S->getStubSize() != StubSize) {
563     // If invalid, report the error with report_fatal_error.
564     report_fatal_error("Global variable '" + GV->getName() +
565                        "' section type or attributes does not match previous"
566                        " section specifier");
567   }
568 
569   return S;
570 }
571 
572 const MCSection *TargetLoweringObjectFileMachO::
573 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
574                        Mangler &Mang, const TargetMachine &TM) const {
575   checkMachOComdat(GV);
576 
577   // Handle thread local data.
578   if (Kind.isThreadBSS()) return TLSBSSSection;
579   if (Kind.isThreadData()) return TLSDataSection;
580 
581   if (Kind.isText())
582     return GV->isWeakForLinker() ? TextCoalSection : TextSection;
583 
584   // If this is weak/linkonce, put this in a coalescable section, either in text
585   // or data depending on if it is writable.
586   if (GV->isWeakForLinker()) {
587     if (Kind.isReadOnly())
588       return ConstTextCoalSection;
589     return DataCoalSection;
590   }
591 
592   // FIXME: Alignment check should be handled by section classifier.
593   if (Kind.isMergeable1ByteCString() &&
594       TM.getDataLayout()->getPreferredAlignment(cast<GlobalVariable>(GV)) < 32)
595     return CStringSection;
596 
597   // Do not put 16-bit arrays in the UString section if they have an
598   // externally visible label, this runs into issues with certain linker
599   // versions.
600   if (Kind.isMergeable2ByteCString() && !GV->hasExternalLinkage() &&
601       TM.getDataLayout()->getPreferredAlignment(cast<GlobalVariable>(GV)) < 32)
602     return UStringSection;
603 
604   // With MachO only variables whose corresponding symbol starts with 'l' or
605   // 'L' can be merged, so we only try merging GVs with private linkage.
606   if (GV->hasPrivateLinkage() && Kind.isMergeableConst()) {
607     if (Kind.isMergeableConst4())
608       return FourByteConstantSection;
609     if (Kind.isMergeableConst8())
610       return EightByteConstantSection;
611     if (Kind.isMergeableConst16())
612       return SixteenByteConstantSection;
613   }
614 
615   // Otherwise, if it is readonly, but not something we can specially optimize,
616   // just drop it in .const.
617   if (Kind.isReadOnly())
618     return ReadOnlySection;
619 
620   // If this is marked const, put it into a const section.  But if the dynamic
621   // linker needs to write to it, put it in the data segment.
622   if (Kind.isReadOnlyWithRel())
623     return ConstDataSection;
624 
625   // Put zero initialized globals with strong external linkage in the
626   // DATA, __common section with the .zerofill directive.
627   if (Kind.isBSSExtern())
628     return DataCommonSection;
629 
630   // Put zero initialized globals with local linkage in __DATA,__bss directive
631   // with the .zerofill directive (aka .lcomm).
632   if (Kind.isBSSLocal())
633     return DataBSSSection;
634 
635   // Otherwise, just drop the variable in the normal data section.
636   return DataSection;
637 }
638 
639 const MCSection *
640 TargetLoweringObjectFileMachO::getSectionForConstant(SectionKind Kind,
641                                                      const Constant *C) const {
642   // If this constant requires a relocation, we have to put it in the data
643   // segment, not in the text segment.
644   if (Kind.isDataRel() || Kind.isReadOnlyWithRel())
645     return ConstDataSection;
646 
647   if (Kind.isMergeableConst4())
648     return FourByteConstantSection;
649   if (Kind.isMergeableConst8())
650     return EightByteConstantSection;
651   if (Kind.isMergeableConst16())
652     return SixteenByteConstantSection;
653   return ReadOnlySection;  // .const
654 }
655 
656 const MCExpr *TargetLoweringObjectFileMachO::getTTypeGlobalReference(
657     const GlobalValue *GV, unsigned Encoding, Mangler &Mang,
658     const TargetMachine &TM, MachineModuleInfo *MMI,
659     MCStreamer &Streamer) const {
660   // The mach-o version of this method defaults to returning a stub reference.
661 
662   if (Encoding & DW_EH_PE_indirect) {
663     MachineModuleInfoMachO &MachOMMI =
664       MMI->getObjFileInfo<MachineModuleInfoMachO>();
665 
666     MCSymbol *SSym =
667         getSymbolWithGlobalValueBase(GV, "$non_lazy_ptr", Mang, TM);
668 
669     // Add information about the stub reference to MachOMMI so that the stub
670     // gets emitted by the asmprinter.
671     MachineModuleInfoImpl::StubValueTy &StubSym =
672       GV->hasHiddenVisibility() ? MachOMMI.getHiddenGVStubEntry(SSym) :
673                                   MachOMMI.getGVStubEntry(SSym);
674     if (!StubSym.getPointer()) {
675       MCSymbol *Sym = TM.getSymbol(GV, Mang);
676       StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
677     }
678 
679     return TargetLoweringObjectFile::
680       getTTypeReference(MCSymbolRefExpr::Create(SSym, getContext()),
681                         Encoding & ~dwarf::DW_EH_PE_indirect, Streamer);
682   }
683 
684   return TargetLoweringObjectFile::getTTypeGlobalReference(GV, Encoding, Mang,
685                                                            TM, MMI, Streamer);
686 }
687 
688 MCSymbol *TargetLoweringObjectFileMachO::getCFIPersonalitySymbol(
689     const GlobalValue *GV, Mangler &Mang, const TargetMachine &TM,
690     MachineModuleInfo *MMI) const {
691   // The mach-o version of this method defaults to returning a stub reference.
692   MachineModuleInfoMachO &MachOMMI =
693     MMI->getObjFileInfo<MachineModuleInfoMachO>();
694 
695   MCSymbol *SSym = getSymbolWithGlobalValueBase(GV, "$non_lazy_ptr", Mang, TM);
696 
697   // Add information about the stub reference to MachOMMI so that the stub
698   // gets emitted by the asmprinter.
699   MachineModuleInfoImpl::StubValueTy &StubSym = MachOMMI.getGVStubEntry(SSym);
700   if (!StubSym.getPointer()) {
701     MCSymbol *Sym = TM.getSymbol(GV, Mang);
702     StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
703   }
704 
705   return SSym;
706 }
707 
708 //===----------------------------------------------------------------------===//
709 //                                  COFF
710 //===----------------------------------------------------------------------===//
711 
712 static unsigned
713 getCOFFSectionFlags(SectionKind K) {
714   unsigned Flags = 0;
715 
716   if (K.isMetadata())
717     Flags |=
718       COFF::IMAGE_SCN_MEM_DISCARDABLE;
719   else if (K.isText())
720     Flags |=
721       COFF::IMAGE_SCN_MEM_EXECUTE |
722       COFF::IMAGE_SCN_MEM_READ |
723       COFF::IMAGE_SCN_CNT_CODE;
724   else if (K.isBSS())
725     Flags |=
726       COFF::IMAGE_SCN_CNT_UNINITIALIZED_DATA |
727       COFF::IMAGE_SCN_MEM_READ |
728       COFF::IMAGE_SCN_MEM_WRITE;
729   else if (K.isThreadLocal())
730     Flags |=
731       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
732       COFF::IMAGE_SCN_MEM_READ |
733       COFF::IMAGE_SCN_MEM_WRITE;
734   else if (K.isReadOnly() || K.isReadOnlyWithRel())
735     Flags |=
736       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
737       COFF::IMAGE_SCN_MEM_READ;
738   else if (K.isWriteable())
739     Flags |=
740       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
741       COFF::IMAGE_SCN_MEM_READ |
742       COFF::IMAGE_SCN_MEM_WRITE;
743 
744   return Flags;
745 }
746 
747 static const GlobalValue *getComdatGVForCOFF(const GlobalValue *GV) {
748   const Comdat *C = GV->getComdat();
749   assert(C && "expected GV to have a Comdat!");
750 
751   StringRef ComdatGVName = C->getName();
752   const GlobalValue *ComdatGV = GV->getParent()->getNamedValue(ComdatGVName);
753   if (!ComdatGV)
754     report_fatal_error("Associative COMDAT symbol '" + ComdatGVName +
755                        "' does not exist.");
756 
757   if (ComdatGV->getComdat() != C)
758     report_fatal_error("Associative COMDAT symbol '" + ComdatGVName +
759                        "' is not a key for its COMDAT.");
760 
761   return ComdatGV;
762 }
763 
764 static int getSelectionForCOFF(const GlobalValue *GV) {
765   if (const Comdat *C = GV->getComdat()) {
766     const GlobalValue *ComdatKey = getComdatGVForCOFF(GV);
767     if (const auto *GA = dyn_cast<GlobalAlias>(ComdatKey))
768       ComdatKey = GA->getBaseObject();
769     if (ComdatKey == GV) {
770       switch (C->getSelectionKind()) {
771       case Comdat::Any:
772         return COFF::IMAGE_COMDAT_SELECT_ANY;
773       case Comdat::ExactMatch:
774         return COFF::IMAGE_COMDAT_SELECT_EXACT_MATCH;
775       case Comdat::Largest:
776         return COFF::IMAGE_COMDAT_SELECT_LARGEST;
777       case Comdat::NoDuplicates:
778         return COFF::IMAGE_COMDAT_SELECT_NODUPLICATES;
779       case Comdat::SameSize:
780         return COFF::IMAGE_COMDAT_SELECT_SAME_SIZE;
781       }
782     } else {
783       return COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE;
784     }
785   } else if (GV->isWeakForLinker()) {
786     return COFF::IMAGE_COMDAT_SELECT_ANY;
787   }
788   return 0;
789 }
790 
791 const MCSection *TargetLoweringObjectFileCOFF::getExplicitSectionGlobal(
792     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
793     const TargetMachine &TM) const {
794   int Selection = 0;
795   unsigned Characteristics = getCOFFSectionFlags(Kind);
796   StringRef Name = GV->getSection();
797   StringRef COMDATSymName = "";
798   if (GV->hasComdat()) {
799     Selection = getSelectionForCOFF(GV);
800     const GlobalValue *ComdatGV;
801     if (Selection == COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE)
802       ComdatGV = getComdatGVForCOFF(GV);
803     else
804       ComdatGV = GV;
805 
806     if (!ComdatGV->hasPrivateLinkage()) {
807       MCSymbol *Sym = TM.getSymbol(ComdatGV, Mang);
808       COMDATSymName = Sym->getName();
809       Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
810     } else {
811       Selection = 0;
812     }
813   }
814   return getContext().getCOFFSection(Name,
815                                      Characteristics,
816                                      Kind,
817                                      COMDATSymName,
818                                      Selection);
819 }
820 
821 static const char *getCOFFSectionNameForUniqueGlobal(SectionKind Kind) {
822   if (Kind.isText())
823     return ".text";
824   if (Kind.isBSS())
825     return ".bss";
826   if (Kind.isThreadLocal())
827     return ".tls$";
828   if (Kind.isReadOnly() || Kind.isReadOnlyWithRel())
829     return ".rdata";
830   return ".data";
831 }
832 
833 
834 const MCSection *TargetLoweringObjectFileCOFF::
835 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
836                        Mangler &Mang, const TargetMachine &TM) const {
837   // If we have -ffunction-sections then we should emit the global value to a
838   // uniqued section specifically for it.
839   bool EmitUniquedSection;
840   if (Kind.isText())
841     EmitUniquedSection = TM.getFunctionSections();
842   else
843     EmitUniquedSection = TM.getDataSections();
844 
845   if ((EmitUniquedSection && !Kind.isCommon()) || GV->hasComdat()) {
846     const char *Name = getCOFFSectionNameForUniqueGlobal(Kind);
847     unsigned Characteristics = getCOFFSectionFlags(Kind);
848 
849     Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
850     int Selection = getSelectionForCOFF(GV);
851     if (!Selection)
852       Selection = COFF::IMAGE_COMDAT_SELECT_NODUPLICATES;
853     const GlobalValue *ComdatGV;
854     if (GV->hasComdat())
855       ComdatGV = getComdatGVForCOFF(GV);
856     else
857       ComdatGV = GV;
858 
859     if (!ComdatGV->hasPrivateLinkage()) {
860       MCSymbol *Sym = TM.getSymbol(ComdatGV, Mang);
861       StringRef COMDATSymName = Sym->getName();
862       return getContext().getCOFFSection(Name, Characteristics, Kind,
863                                          COMDATSymName, Selection);
864     }
865   }
866 
867   if (Kind.isText())
868     return TextSection;
869 
870   if (Kind.isThreadLocal())
871     return TLSDataSection;
872 
873   if (Kind.isReadOnly() || Kind.isReadOnlyWithRel())
874     return ReadOnlySection;
875 
876   // Note: we claim that common symbols are put in BSSSection, but they are
877   // really emitted with the magic .comm directive, which creates a symbol table
878   // entry but not a section.
879   if (Kind.isBSS() || Kind.isCommon())
880     return BSSSection;
881 
882   return DataSection;
883 }
884 
885 StringRef TargetLoweringObjectFileCOFF::
886 getDepLibFromLinkerOpt(StringRef LinkerOption) const {
887   const char *LibCmd = "/DEFAULTLIB:";
888   if (LinkerOption.startswith(LibCmd))
889     return LinkerOption.substr(strlen(LibCmd));
890   return StringRef();
891 }
892 
893 void TargetLoweringObjectFileCOFF::
894 emitModuleFlags(MCStreamer &Streamer,
895                 ArrayRef<Module::ModuleFlagEntry> ModuleFlags,
896                 Mangler &Mang, const TargetMachine &TM) const {
897   MDNode *LinkerOptions = nullptr;
898 
899   // Look for the "Linker Options" flag, since it's the only one we support.
900   for (ArrayRef<Module::ModuleFlagEntry>::iterator
901        i = ModuleFlags.begin(), e = ModuleFlags.end(); i != e; ++i) {
902     const Module::ModuleFlagEntry &MFE = *i;
903     StringRef Key = MFE.Key->getString();
904     Metadata *Val = MFE.Val;
905     if (Key == "Linker Options") {
906       LinkerOptions = cast<MDNode>(Val);
907       break;
908     }
909   }
910   if (!LinkerOptions)
911     return;
912 
913   // Emit the linker options to the linker .drectve section.  According to the
914   // spec, this section is a space-separated string containing flags for linker.
915   const MCSection *Sec = getDrectveSection();
916   Streamer.SwitchSection(Sec);
917   for (unsigned i = 0, e = LinkerOptions->getNumOperands(); i != e; ++i) {
918     MDNode *MDOptions = cast<MDNode>(LinkerOptions->getOperand(i));
919     for (unsigned ii = 0, ie = MDOptions->getNumOperands(); ii != ie; ++ii) {
920       MDString *MDOption = cast<MDString>(MDOptions->getOperand(ii));
921       // Lead with a space for consistency with our dllexport implementation.
922       std::string Directive(" ");
923       Directive.append(MDOption->getString());
924       Streamer.EmitBytes(Directive);
925     }
926   }
927 }
928 
929 const MCSection *TargetLoweringObjectFileCOFF::getStaticCtorSection(
930     unsigned Priority, const MCSymbol *KeySym) const {
931   return getContext().getAssociativeCOFFSection(
932       cast<MCSectionCOFF>(StaticCtorSection), KeySym);
933 }
934 
935 const MCSection *TargetLoweringObjectFileCOFF::getStaticDtorSection(
936     unsigned Priority, const MCSymbol *KeySym) const {
937   return getContext().getAssociativeCOFFSection(
938       cast<MCSectionCOFF>(StaticDtorSection), KeySym);
939 }
940