xref: /llvm-project/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp (revision 65e49021565e84ba4e96a0627a946b2211d79c59) 
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/MCAsmInfo.h"
28 #include "llvm/MC/MCContext.h"
29 #include "llvm/MC/MCExpr.h"
30 #include "llvm/MC/MCSectionCOFF.h"
31 #include "llvm/MC/MCSectionELF.h"
32 #include "llvm/MC/MCSectionMachO.h"
33 #include "llvm/MC/MCStreamer.h"
34 #include "llvm/MC/MCSymbolELF.h"
35 #include "llvm/MC/MCValue.h"
36 #include "llvm/Support/COFF.h"
37 #include "llvm/Support/Dwarf.h"
38 #include "llvm/Support/ELF.h"
39 #include "llvm/Support/ErrorHandling.h"
40 #include "llvm/Support/raw_ostream.h"
41 #include "llvm/Target/TargetLowering.h"
42 #include "llvm/Target/TargetMachine.h"
43 #include "llvm/Target/TargetSubtargetInfo.h"
44 using namespace llvm;
45 using namespace dwarf;
46 
47 //===----------------------------------------------------------------------===//
48 //                                  ELF
49 //===----------------------------------------------------------------------===//
50 
51 MCSymbol *TargetLoweringObjectFileELF::getCFIPersonalitySymbol(
52     const GlobalValue *GV, Mangler &Mang, const TargetMachine &TM,
53     MachineModuleInfo *MMI) const {
54   unsigned Encoding = getPersonalityEncoding();
55   if ((Encoding & 0x80) == dwarf::DW_EH_PE_indirect)
56     return getContext().getOrCreateSymbol(StringRef("DW.ref.") +
57                                           TM.getSymbol(GV, Mang)->getName());
58   if ((Encoding & 0x70) == dwarf::DW_EH_PE_absptr)
59     return TM.getSymbol(GV, Mang);
60   report_fatal_error("We do not support this DWARF encoding yet!");
61 }
62 
63 void TargetLoweringObjectFileELF::emitPersonalityValue(
64     MCStreamer &Streamer, const DataLayout &DL, const MCSymbol *Sym) const {
65   SmallString<64> NameData("DW.ref.");
66   NameData += Sym->getName();
67   MCSymbolELF *Label =
68       cast<MCSymbolELF>(getContext().getOrCreateSymbol(NameData));
69   Streamer.EmitSymbolAttribute(Label, MCSA_Hidden);
70   Streamer.EmitSymbolAttribute(Label, MCSA_Weak);
71   StringRef Prefix = ".data.";
72   NameData.insert(NameData.begin(), Prefix.begin(), Prefix.end());
73   unsigned Flags = ELF::SHF_ALLOC | ELF::SHF_WRITE | ELF::SHF_GROUP;
74   MCSection *Sec = getContext().getELFSection(NameData, ELF::SHT_PROGBITS,
75                                               Flags, 0, Label->getName());
76   unsigned Size = DL.getPointerSize();
77   Streamer.SwitchSection(Sec);
78   Streamer.EmitValueToAlignment(DL.getPointerABIAlignment());
79   Streamer.EmitSymbolAttribute(Label, MCSA_ELF_TypeObject);
80   const MCExpr *E = MCConstantExpr::create(Size, getContext());
81   Streamer.emitELFSize(Label, E);
82   Streamer.EmitLabel(Label);
83 
84   Streamer.EmitSymbolValue(Sym, Size);
85 }
86 
87 const MCExpr *TargetLoweringObjectFileELF::getTTypeGlobalReference(
88     const GlobalValue *GV, unsigned Encoding, Mangler &Mang,
89     const TargetMachine &TM, MachineModuleInfo *MMI,
90     MCStreamer &Streamer) const {
91 
92   if (Encoding & dwarf::DW_EH_PE_indirect) {
93     MachineModuleInfoELF &ELFMMI = MMI->getObjFileInfo<MachineModuleInfoELF>();
94 
95     MCSymbol *SSym = getSymbolWithGlobalValueBase(GV, ".DW.stub", Mang, TM);
96 
97     // Add information about the stub reference to ELFMMI so that the stub
98     // gets emitted by the asmprinter.
99     MachineModuleInfoImpl::StubValueTy &StubSym = ELFMMI.getGVStubEntry(SSym);
100     if (!StubSym.getPointer()) {
101       MCSymbol *Sym = TM.getSymbol(GV, Mang);
102       StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
103     }
104 
105     return TargetLoweringObjectFile::
106       getTTypeReference(MCSymbolRefExpr::create(SSym, getContext()),
107                         Encoding & ~dwarf::DW_EH_PE_indirect, Streamer);
108   }
109 
110   return TargetLoweringObjectFile::
111     getTTypeGlobalReference(GV, Encoding, Mang, TM, MMI, Streamer);
112 }
113 
114 static SectionKind
115 getELFKindForNamedSection(StringRef Name, SectionKind K) {
116   // N.B.: The defaults used in here are no the same ones used in MC.
117   // We follow gcc, MC follows gas. For example, given ".section .eh_frame",
118   // both gas and MC will produce a section with no flags. Given
119   // section(".eh_frame") gcc will produce:
120   //
121   //   .section   .eh_frame,"a",@progbits
122   if (Name.empty() || Name[0] != '.') return K;
123 
124   // Some lame default implementation based on some magic section names.
125   if (Name == ".bss" ||
126       Name.startswith(".bss.") ||
127       Name.startswith(".gnu.linkonce.b.") ||
128       Name.startswith(".llvm.linkonce.b.") ||
129       Name == ".sbss" ||
130       Name.startswith(".sbss.") ||
131       Name.startswith(".gnu.linkonce.sb.") ||
132       Name.startswith(".llvm.linkonce.sb."))
133     return SectionKind::getBSS();
134 
135   if (Name == ".tdata" ||
136       Name.startswith(".tdata.") ||
137       Name.startswith(".gnu.linkonce.td.") ||
138       Name.startswith(".llvm.linkonce.td."))
139     return SectionKind::getThreadData();
140 
141   if (Name == ".tbss" ||
142       Name.startswith(".tbss.") ||
143       Name.startswith(".gnu.linkonce.tb.") ||
144       Name.startswith(".llvm.linkonce.tb."))
145     return SectionKind::getThreadBSS();
146 
147   return K;
148 }
149 
150 
151 static unsigned getELFSectionType(StringRef Name, SectionKind K) {
152 
153   if (Name == ".init_array")
154     return ELF::SHT_INIT_ARRAY;
155 
156   if (Name == ".fini_array")
157     return ELF::SHT_FINI_ARRAY;
158 
159   if (Name == ".preinit_array")
160     return ELF::SHT_PREINIT_ARRAY;
161 
162   if (K.isBSS() || K.isThreadBSS())
163     return ELF::SHT_NOBITS;
164 
165   return ELF::SHT_PROGBITS;
166 }
167 
168 static unsigned getELFSectionFlags(SectionKind K) {
169   unsigned Flags = 0;
170 
171   if (!K.isMetadata())
172     Flags |= ELF::SHF_ALLOC;
173 
174   if (K.isText())
175     Flags |= ELF::SHF_EXECINSTR;
176 
177   if (K.isWriteable())
178     Flags |= ELF::SHF_WRITE;
179 
180   if (K.isThreadLocal())
181     Flags |= ELF::SHF_TLS;
182 
183   if (K.isMergeableCString() || K.isMergeableConst())
184     Flags |= ELF::SHF_MERGE;
185 
186   if (K.isMergeableCString())
187     Flags |= ELF::SHF_STRINGS;
188 
189   return Flags;
190 }
191 
192 static const Comdat *getELFComdat(const GlobalValue *GV) {
193   const Comdat *C = GV->getComdat();
194   if (!C)
195     return nullptr;
196 
197   if (C->getSelectionKind() != Comdat::Any)
198     report_fatal_error("ELF COMDATs only support SelectionKind::Any, '" +
199                        C->getName() + "' cannot be lowered.");
200 
201   return C;
202 }
203 
204 MCSection *TargetLoweringObjectFileELF::getExplicitSectionGlobal(
205     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
206     const TargetMachine &TM) const {
207   StringRef SectionName = GV->getSection();
208 
209   // Infer section flags from the section name if we can.
210   Kind = getELFKindForNamedSection(SectionName, Kind);
211 
212   StringRef Group = "";
213   unsigned Flags = getELFSectionFlags(Kind);
214   if (const Comdat *C = getELFComdat(GV)) {
215     Group = C->getName();
216     Flags |= ELF::SHF_GROUP;
217   }
218   return getContext().getELFSection(SectionName,
219                                     getELFSectionType(SectionName, Kind), Flags,
220                                     /*EntrySize=*/0, Group);
221 }
222 
223 /// Return the section prefix name used by options FunctionsSections and
224 /// DataSections.
225 static StringRef getSectionPrefixForGlobal(SectionKind Kind) {
226   if (Kind.isText())
227     return ".text";
228   if (Kind.isReadOnly())
229     return ".rodata";
230   if (Kind.isBSS())
231     return ".bss";
232   if (Kind.isThreadData())
233     return ".tdata";
234   if (Kind.isThreadBSS())
235     return ".tbss";
236   if (Kind.isDataNoRel())
237     return ".data";
238   if (Kind.isDataRel())
239     return ".data.rel";
240   assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
241   return ".data.rel.ro";
242 }
243 
244 static MCSectionELF *
245 selectELFSectionForGlobal(MCContext &Ctx, const GlobalValue *GV,
246                           SectionKind Kind, Mangler &Mang,
247                           const TargetMachine &TM, bool EmitUniqueSection,
248                           unsigned Flags, unsigned *NextUniqueID) {
249   unsigned EntrySize = 0;
250   if (Kind.isMergeableCString()) {
251     if (Kind.isMergeable2ByteCString()) {
252       EntrySize = 2;
253     } else if (Kind.isMergeable4ByteCString()) {
254       EntrySize = 4;
255     } else {
256       EntrySize = 1;
257       assert(Kind.isMergeable1ByteCString() && "unknown string width");
258     }
259   } else if (Kind.isMergeableConst()) {
260     if (Kind.isMergeableConst4()) {
261       EntrySize = 4;
262     } else if (Kind.isMergeableConst8()) {
263       EntrySize = 8;
264     } else {
265       assert(Kind.isMergeableConst16() && "unknown data width");
266       EntrySize = 16;
267     }
268   }
269 
270   StringRef Group = "";
271   if (const Comdat *C = getELFComdat(GV)) {
272     Flags |= ELF::SHF_GROUP;
273     Group = C->getName();
274   }
275 
276   bool UniqueSectionNames = TM.getUniqueSectionNames();
277   SmallString<128> Name;
278   if (Kind.isMergeableCString()) {
279     // We also need alignment here.
280     // FIXME: this is getting the alignment of the character, not the
281     // alignment of the global!
282     unsigned Align = GV->getParent()->getDataLayout().getPreferredAlignment(
283         cast<GlobalVariable>(GV));
284 
285     std::string SizeSpec = ".rodata.str" + utostr(EntrySize) + ".";
286     Name = SizeSpec + utostr(Align);
287   } else if (Kind.isMergeableConst()) {
288     Name = ".rodata.cst";
289     Name += utostr(EntrySize);
290   } else {
291     Name = getSectionPrefixForGlobal(Kind);
292   }
293 
294   if (EmitUniqueSection && UniqueSectionNames) {
295     Name.push_back('.');
296     TM.getNameWithPrefix(Name, GV, Mang, true);
297   }
298   unsigned UniqueID = ~0;
299   if (EmitUniqueSection && !UniqueSectionNames) {
300     UniqueID = *NextUniqueID;
301     (*NextUniqueID)++;
302   }
303   return Ctx.getELFSection(Name, getELFSectionType(Name, Kind), Flags,
304                            EntrySize, Group, UniqueID);
305 }
306 
307 MCSection *TargetLoweringObjectFileELF::SelectSectionForGlobal(
308     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
309     const TargetMachine &TM) const {
310   unsigned Flags = getELFSectionFlags(Kind);
311 
312   // If we have -ffunction-section or -fdata-section then we should emit the
313   // global value to a uniqued section specifically for it.
314   bool EmitUniqueSection = false;
315   if (!(Flags & ELF::SHF_MERGE) && !Kind.isCommon()) {
316     if (Kind.isText())
317       EmitUniqueSection = TM.getFunctionSections();
318     else
319       EmitUniqueSection = TM.getDataSections();
320   }
321   EmitUniqueSection |= GV->hasComdat();
322 
323   return selectELFSectionForGlobal(getContext(), GV, Kind, Mang, TM,
324                                    EmitUniqueSection, Flags, &NextUniqueID);
325 }
326 
327 MCSection *TargetLoweringObjectFileELF::getSectionForJumpTable(
328     const Function &F, Mangler &Mang, const TargetMachine &TM) const {
329   // If the function can be removed, produce a unique section so that
330   // the table doesn't prevent the removal.
331   const Comdat *C = F.getComdat();
332   bool EmitUniqueSection = TM.getFunctionSections() || C;
333   if (!EmitUniqueSection)
334     return ReadOnlySection;
335 
336   return selectELFSectionForGlobal(getContext(), &F, SectionKind::getReadOnly(),
337                                    Mang, TM, EmitUniqueSection, ELF::SHF_ALLOC,
338                                    &NextUniqueID);
339 }
340 
341 bool TargetLoweringObjectFileELF::shouldPutJumpTableInFunctionSection(
342     bool UsesLabelDifference, const Function &F) const {
343   // We can always create relative relocations, so use another section
344   // that can be marked non-executable.
345   return false;
346 }
347 
348 /// Given a mergeable constant with the specified size and relocation
349 /// information, return a section that it should be placed in.
350 MCSection *TargetLoweringObjectFileELF::getSectionForConstant(
351     const DataLayout &DL, SectionKind Kind, const Constant *C) const {
352   if (Kind.isMergeableConst4() && MergeableConst4Section)
353     return MergeableConst4Section;
354   if (Kind.isMergeableConst8() && MergeableConst8Section)
355     return MergeableConst8Section;
356   if (Kind.isMergeableConst16() && MergeableConst16Section)
357     return MergeableConst16Section;
358   if (Kind.isReadOnly())
359     return ReadOnlySection;
360 
361   assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
362   return DataRelROSection;
363 }
364 
365 static MCSectionELF *getStaticStructorSection(MCContext &Ctx, bool UseInitArray,
366                                               bool IsCtor, unsigned Priority,
367                                               const MCSymbol *KeySym) {
368   std::string Name;
369   unsigned Type;
370   unsigned Flags = ELF::SHF_ALLOC | ELF::SHF_WRITE;
371   StringRef COMDAT = KeySym ? KeySym->getName() : "";
372 
373   if (KeySym)
374     Flags |= ELF::SHF_GROUP;
375 
376   if (UseInitArray) {
377     if (IsCtor) {
378       Type = ELF::SHT_INIT_ARRAY;
379       Name = ".init_array";
380     } else {
381       Type = ELF::SHT_FINI_ARRAY;
382       Name = ".fini_array";
383     }
384     if (Priority != 65535) {
385       Name += '.';
386       Name += utostr(Priority);
387     }
388   } else {
389     // The default scheme is .ctor / .dtor, so we have to invert the priority
390     // numbering.
391     if (IsCtor)
392       Name = ".ctors";
393     else
394       Name = ".dtors";
395     if (Priority != 65535) {
396       Name += '.';
397       Name += utostr(65535 - Priority);
398     }
399     Type = ELF::SHT_PROGBITS;
400   }
401 
402   return Ctx.getELFSection(Name, Type, Flags, 0, COMDAT);
403 }
404 
405 MCSection *TargetLoweringObjectFileELF::getStaticCtorSection(
406     unsigned Priority, const MCSymbol *KeySym) const {
407   return getStaticStructorSection(getContext(), UseInitArray, true, Priority,
408                                   KeySym);
409 }
410 
411 MCSection *TargetLoweringObjectFileELF::getStaticDtorSection(
412     unsigned Priority, const MCSymbol *KeySym) const {
413   return getStaticStructorSection(getContext(), UseInitArray, false, Priority,
414                                   KeySym);
415 }
416 
417 void
418 TargetLoweringObjectFileELF::InitializeELF(bool UseInitArray_) {
419   UseInitArray = UseInitArray_;
420   if (!UseInitArray)
421     return;
422 
423   StaticCtorSection = getContext().getELFSection(
424       ".init_array", ELF::SHT_INIT_ARRAY, ELF::SHF_WRITE | ELF::SHF_ALLOC);
425   StaticDtorSection = getContext().getELFSection(
426       ".fini_array", ELF::SHT_FINI_ARRAY, ELF::SHF_WRITE | ELF::SHF_ALLOC);
427 }
428 
429 //===----------------------------------------------------------------------===//
430 //                                 MachO
431 //===----------------------------------------------------------------------===//
432 
433 TargetLoweringObjectFileMachO::TargetLoweringObjectFileMachO()
434   : TargetLoweringObjectFile() {
435   SupportIndirectSymViaGOTPCRel = true;
436 }
437 
438 /// emitModuleFlags - Perform code emission for module flags.
439 void TargetLoweringObjectFileMachO::
440 emitModuleFlags(MCStreamer &Streamer,
441                 ArrayRef<Module::ModuleFlagEntry> ModuleFlags,
442                 Mangler &Mang, const TargetMachine &TM) const {
443   unsigned VersionVal = 0;
444   unsigned ImageInfoFlags = 0;
445   MDNode *LinkerOptions = nullptr;
446   StringRef SectionVal;
447 
448   for (ArrayRef<Module::ModuleFlagEntry>::iterator
449          i = ModuleFlags.begin(), e = ModuleFlags.end(); i != e; ++i) {
450     const Module::ModuleFlagEntry &MFE = *i;
451 
452     // Ignore flags with 'Require' behavior.
453     if (MFE.Behavior == Module::Require)
454       continue;
455 
456     StringRef Key = MFE.Key->getString();
457     Metadata *Val = MFE.Val;
458 
459     if (Key == "Objective-C Image Info Version") {
460       VersionVal = mdconst::extract<ConstantInt>(Val)->getZExtValue();
461     } else if (Key == "Objective-C Garbage Collection" ||
462                Key == "Objective-C GC Only" ||
463                Key == "Objective-C Is Simulated" ||
464                Key == "Objective-C Image Swift Version") {
465       ImageInfoFlags |= mdconst::extract<ConstantInt>(Val)->getZExtValue();
466     } else if (Key == "Objective-C Image Info Section") {
467       SectionVal = cast<MDString>(Val)->getString();
468     } else if (Key == "Linker Options") {
469       LinkerOptions = cast<MDNode>(Val);
470     }
471   }
472 
473   // Emit the linker options if present.
474   if (LinkerOptions) {
475     for (unsigned i = 0, e = LinkerOptions->getNumOperands(); i != e; ++i) {
476       MDNode *MDOptions = cast<MDNode>(LinkerOptions->getOperand(i));
477       SmallVector<std::string, 4> StrOptions;
478 
479       // Convert to strings.
480       for (unsigned ii = 0, ie = MDOptions->getNumOperands(); ii != ie; ++ii) {
481         MDString *MDOption = cast<MDString>(MDOptions->getOperand(ii));
482         StrOptions.push_back(MDOption->getString());
483       }
484 
485       Streamer.EmitLinkerOptions(StrOptions);
486     }
487   }
488 
489   // The section is mandatory. If we don't have it, then we don't have GC info.
490   if (SectionVal.empty()) return;
491 
492   StringRef Segment, Section;
493   unsigned TAA = 0, StubSize = 0;
494   bool TAAParsed;
495   std::string ErrorCode =
496     MCSectionMachO::ParseSectionSpecifier(SectionVal, Segment, Section,
497                                           TAA, TAAParsed, StubSize);
498   if (!ErrorCode.empty())
499     // If invalid, report the error with report_fatal_error.
500     report_fatal_error("Invalid section specifier '" + Section + "': " +
501                        ErrorCode + ".");
502 
503   // Get the section.
504   MCSectionMachO *S = getContext().getMachOSection(
505       Segment, Section, TAA, StubSize, SectionKind::getDataNoRel());
506   Streamer.SwitchSection(S);
507   Streamer.EmitLabel(getContext().
508                      getOrCreateSymbol(StringRef("L_OBJC_IMAGE_INFO")));
509   Streamer.EmitIntValue(VersionVal, 4);
510   Streamer.EmitIntValue(ImageInfoFlags, 4);
511   Streamer.AddBlankLine();
512 }
513 
514 static void checkMachOComdat(const GlobalValue *GV) {
515   const Comdat *C = GV->getComdat();
516   if (!C)
517     return;
518 
519   report_fatal_error("MachO doesn't support COMDATs, '" + C->getName() +
520                      "' cannot be lowered.");
521 }
522 
523 MCSection *TargetLoweringObjectFileMachO::getExplicitSectionGlobal(
524     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
525     const TargetMachine &TM) const {
526   // Parse the section specifier and create it if valid.
527   StringRef Segment, Section;
528   unsigned TAA = 0, StubSize = 0;
529   bool TAAParsed;
530 
531   checkMachOComdat(GV);
532 
533   std::string ErrorCode =
534     MCSectionMachO::ParseSectionSpecifier(GV->getSection(), Segment, Section,
535                                           TAA, TAAParsed, StubSize);
536   if (!ErrorCode.empty()) {
537     // If invalid, report the error with report_fatal_error.
538     report_fatal_error("Global variable '" + GV->getName() +
539                        "' has an invalid section specifier '" +
540                        GV->getSection() + "': " + ErrorCode + ".");
541   }
542 
543   // Get the section.
544   MCSectionMachO *S =
545       getContext().getMachOSection(Segment, Section, TAA, StubSize, Kind);
546 
547   // If TAA wasn't set by ParseSectionSpecifier() above,
548   // use the value returned by getMachOSection() as a default.
549   if (!TAAParsed)
550     TAA = S->getTypeAndAttributes();
551 
552   // Okay, now that we got the section, verify that the TAA & StubSize agree.
553   // If the user declared multiple globals with different section flags, we need
554   // to reject it here.
555   if (S->getTypeAndAttributes() != TAA || S->getStubSize() != StubSize) {
556     // If invalid, report the error with report_fatal_error.
557     report_fatal_error("Global variable '" + GV->getName() +
558                        "' section type or attributes does not match previous"
559                        " section specifier");
560   }
561 
562   return S;
563 }
564 
565 MCSection *TargetLoweringObjectFileMachO::SelectSectionForGlobal(
566     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
567     const TargetMachine &TM) const {
568   checkMachOComdat(GV);
569 
570   // Handle thread local data.
571   if (Kind.isThreadBSS()) return TLSBSSSection;
572   if (Kind.isThreadData()) return TLSDataSection;
573 
574   if (Kind.isText())
575     return GV->isWeakForLinker() ? TextCoalSection : TextSection;
576 
577   // If this is weak/linkonce, put this in a coalescable section, either in text
578   // or data depending on if it is writable.
579   if (GV->isWeakForLinker()) {
580     if (Kind.isReadOnly())
581       return ConstTextCoalSection;
582     return DataCoalSection;
583   }
584 
585   // FIXME: Alignment check should be handled by section classifier.
586   if (Kind.isMergeable1ByteCString() &&
587       GV->getParent()->getDataLayout().getPreferredAlignment(
588           cast<GlobalVariable>(GV)) < 32)
589     return CStringSection;
590 
591   // Do not put 16-bit arrays in the UString section if they have an
592   // externally visible label, this runs into issues with certain linker
593   // versions.
594   if (Kind.isMergeable2ByteCString() && !GV->hasExternalLinkage() &&
595       GV->getParent()->getDataLayout().getPreferredAlignment(
596           cast<GlobalVariable>(GV)) < 32)
597     return UStringSection;
598 
599   // With MachO only variables whose corresponding symbol starts with 'l' or
600   // 'L' can be merged, so we only try merging GVs with private linkage.
601   if (GV->hasPrivateLinkage() && Kind.isMergeableConst()) {
602     if (Kind.isMergeableConst4())
603       return FourByteConstantSection;
604     if (Kind.isMergeableConst8())
605       return EightByteConstantSection;
606     if (Kind.isMergeableConst16())
607       return SixteenByteConstantSection;
608   }
609 
610   // Otherwise, if it is readonly, but not something we can specially optimize,
611   // just drop it in .const.
612   if (Kind.isReadOnly())
613     return ReadOnlySection;
614 
615   // If this is marked const, put it into a const section.  But if the dynamic
616   // linker needs to write to it, put it in the data segment.
617   if (Kind.isReadOnlyWithRel())
618     return ConstDataSection;
619 
620   // Put zero initialized globals with strong external linkage in the
621   // DATA, __common section with the .zerofill directive.
622   if (Kind.isBSSExtern())
623     return DataCommonSection;
624 
625   // Put zero initialized globals with local linkage in __DATA,__bss directive
626   // with the .zerofill directive (aka .lcomm).
627   if (Kind.isBSSLocal())
628     return DataBSSSection;
629 
630   // Otherwise, just drop the variable in the normal data section.
631   return DataSection;
632 }
633 
634 MCSection *TargetLoweringObjectFileMachO::getSectionForConstant(
635     const DataLayout &DL, SectionKind Kind, const Constant *C) const {
636   // If this constant requires a relocation, we have to put it in the data
637   // segment, not in the text segment.
638   if (Kind.isDataRel() || Kind.isReadOnlyWithRel())
639     return ConstDataSection;
640 
641   if (Kind.isMergeableConst4())
642     return FourByteConstantSection;
643   if (Kind.isMergeableConst8())
644     return EightByteConstantSection;
645   if (Kind.isMergeableConst16())
646     return SixteenByteConstantSection;
647   return ReadOnlySection;  // .const
648 }
649 
650 const MCExpr *TargetLoweringObjectFileMachO::getTTypeGlobalReference(
651     const GlobalValue *GV, unsigned Encoding, Mangler &Mang,
652     const TargetMachine &TM, MachineModuleInfo *MMI,
653     MCStreamer &Streamer) const {
654   // The mach-o version of this method defaults to returning a stub reference.
655 
656   if (Encoding & DW_EH_PE_indirect) {
657     MachineModuleInfoMachO &MachOMMI =
658       MMI->getObjFileInfo<MachineModuleInfoMachO>();
659 
660     MCSymbol *SSym =
661         getSymbolWithGlobalValueBase(GV, "$non_lazy_ptr", Mang, TM);
662 
663     // Add information about the stub reference to MachOMMI so that the stub
664     // gets emitted by the asmprinter.
665     MachineModuleInfoImpl::StubValueTy &StubSym =
666       GV->hasHiddenVisibility() ? MachOMMI.getHiddenGVStubEntry(SSym) :
667                                   MachOMMI.getGVStubEntry(SSym);
668     if (!StubSym.getPointer()) {
669       MCSymbol *Sym = TM.getSymbol(GV, Mang);
670       StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
671     }
672 
673     return TargetLoweringObjectFile::
674       getTTypeReference(MCSymbolRefExpr::create(SSym, getContext()),
675                         Encoding & ~dwarf::DW_EH_PE_indirect, Streamer);
676   }
677 
678   return TargetLoweringObjectFile::getTTypeGlobalReference(GV, Encoding, Mang,
679                                                            TM, MMI, Streamer);
680 }
681 
682 MCSymbol *TargetLoweringObjectFileMachO::getCFIPersonalitySymbol(
683     const GlobalValue *GV, Mangler &Mang, const TargetMachine &TM,
684     MachineModuleInfo *MMI) const {
685   // The mach-o version of this method defaults to returning a stub reference.
686   MachineModuleInfoMachO &MachOMMI =
687     MMI->getObjFileInfo<MachineModuleInfoMachO>();
688 
689   MCSymbol *SSym = getSymbolWithGlobalValueBase(GV, "$non_lazy_ptr", Mang, TM);
690 
691   // Add information about the stub reference to MachOMMI so that the stub
692   // gets emitted by the asmprinter.
693   MachineModuleInfoImpl::StubValueTy &StubSym = MachOMMI.getGVStubEntry(SSym);
694   if (!StubSym.getPointer()) {
695     MCSymbol *Sym = TM.getSymbol(GV, Mang);
696     StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
697   }
698 
699   return SSym;
700 }
701 
702 const MCExpr *TargetLoweringObjectFileMachO::getIndirectSymViaGOTPCRel(
703     const MCSymbol *Sym, const MCValue &MV, int64_t Offset,
704     MachineModuleInfo *MMI, MCStreamer &Streamer) const {
705   // Although MachO 32-bit targets do not explicitly have a GOTPCREL relocation
706   // as 64-bit do, we replace the GOT equivalent by accessing the final symbol
707   // through a non_lazy_ptr stub instead. One advantage is that it allows the
708   // computation of deltas to final external symbols. Example:
709   //
710   //    _extgotequiv:
711   //       .long   _extfoo
712   //
713   //    _delta:
714   //       .long   _extgotequiv-_delta
715   //
716   // is transformed to:
717   //
718   //    _delta:
719   //       .long   L_extfoo$non_lazy_ptr-(_delta+0)
720   //
721   //       .section        __IMPORT,__pointers,non_lazy_symbol_pointers
722   //    L_extfoo$non_lazy_ptr:
723   //       .indirect_symbol        _extfoo
724   //       .long   0
725   //
726   MachineModuleInfoMachO &MachOMMI =
727     MMI->getObjFileInfo<MachineModuleInfoMachO>();
728   MCContext &Ctx = getContext();
729 
730   // The offset must consider the original displacement from the base symbol
731   // since 32-bit targets don't have a GOTPCREL to fold the PC displacement.
732   Offset = -MV.getConstant();
733   const MCSymbol *BaseSym = &MV.getSymB()->getSymbol();
734 
735   // Access the final symbol via sym$non_lazy_ptr and generate the appropriated
736   // non_lazy_ptr stubs.
737   SmallString<128> Name;
738   StringRef Suffix = "$non_lazy_ptr";
739   Name += MMI->getModule()->getDataLayout().getPrivateGlobalPrefix();
740   Name += Sym->getName();
741   Name += Suffix;
742   MCSymbol *Stub = Ctx.getOrCreateSymbol(Name);
743 
744   MachineModuleInfoImpl::StubValueTy &StubSym = MachOMMI.getGVStubEntry(Stub);
745   if (!StubSym.getPointer())
746     StubSym = MachineModuleInfoImpl::
747       StubValueTy(const_cast<MCSymbol *>(Sym), true /* access indirectly */);
748 
749   const MCExpr *BSymExpr =
750     MCSymbolRefExpr::create(BaseSym, MCSymbolRefExpr::VK_None, Ctx);
751   const MCExpr *LHS =
752     MCSymbolRefExpr::create(Stub, MCSymbolRefExpr::VK_None, Ctx);
753 
754   if (!Offset)
755     return MCBinaryExpr::createSub(LHS, BSymExpr, Ctx);
756 
757   const MCExpr *RHS =
758     MCBinaryExpr::createAdd(BSymExpr, MCConstantExpr::create(Offset, Ctx), Ctx);
759   return MCBinaryExpr::createSub(LHS, RHS, Ctx);
760 }
761 
762 static bool canUsePrivateLabel(const MCAsmInfo &AsmInfo,
763                                const MCSection &Section) {
764   if (!AsmInfo.isSectionAtomizableBySymbols(Section))
765     return true;
766 
767   // If it is not dead stripped, it is safe to use private labels.
768   const MCSectionMachO &SMO = cast<MCSectionMachO>(Section);
769   if (SMO.hasAttribute(MachO::S_ATTR_NO_DEAD_STRIP))
770     return true;
771 
772   return false;
773 }
774 
775 void TargetLoweringObjectFileMachO::getNameWithPrefix(
776     SmallVectorImpl<char> &OutName, const GlobalValue *GV, Mangler &Mang,
777     const TargetMachine &TM) const {
778   SectionKind GVKind = TargetLoweringObjectFile::getKindForGlobal(GV, TM);
779   const MCSection *TheSection = SectionForGlobal(GV, GVKind, Mang, TM);
780   bool CannotUsePrivateLabel =
781       !canUsePrivateLabel(*TM.getMCAsmInfo(), *TheSection);
782   Mang.getNameWithPrefix(OutName, GV, CannotUsePrivateLabel);
783 }
784 
785 //===----------------------------------------------------------------------===//
786 //                                  COFF
787 //===----------------------------------------------------------------------===//
788 
789 static unsigned
790 getCOFFSectionFlags(SectionKind K) {
791   unsigned Flags = 0;
792 
793   if (K.isMetadata())
794     Flags |=
795       COFF::IMAGE_SCN_MEM_DISCARDABLE;
796   else if (K.isText())
797     Flags |=
798       COFF::IMAGE_SCN_MEM_EXECUTE |
799       COFF::IMAGE_SCN_MEM_READ |
800       COFF::IMAGE_SCN_CNT_CODE;
801   else if (K.isBSS())
802     Flags |=
803       COFF::IMAGE_SCN_CNT_UNINITIALIZED_DATA |
804       COFF::IMAGE_SCN_MEM_READ |
805       COFF::IMAGE_SCN_MEM_WRITE;
806   else if (K.isThreadLocal())
807     Flags |=
808       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
809       COFF::IMAGE_SCN_MEM_READ |
810       COFF::IMAGE_SCN_MEM_WRITE;
811   else if (K.isReadOnly() || K.isReadOnlyWithRel())
812     Flags |=
813       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
814       COFF::IMAGE_SCN_MEM_READ;
815   else if (K.isWriteable())
816     Flags |=
817       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
818       COFF::IMAGE_SCN_MEM_READ |
819       COFF::IMAGE_SCN_MEM_WRITE;
820 
821   return Flags;
822 }
823 
824 static const GlobalValue *getComdatGVForCOFF(const GlobalValue *GV) {
825   const Comdat *C = GV->getComdat();
826   assert(C && "expected GV to have a Comdat!");
827 
828   StringRef ComdatGVName = C->getName();
829   const GlobalValue *ComdatGV = GV->getParent()->getNamedValue(ComdatGVName);
830   if (!ComdatGV)
831     report_fatal_error("Associative COMDAT symbol '" + ComdatGVName +
832                        "' does not exist.");
833 
834   if (ComdatGV->getComdat() != C)
835     report_fatal_error("Associative COMDAT symbol '" + ComdatGVName +
836                        "' is not a key for its COMDAT.");
837 
838   return ComdatGV;
839 }
840 
841 static int getSelectionForCOFF(const GlobalValue *GV) {
842   if (const Comdat *C = GV->getComdat()) {
843     const GlobalValue *ComdatKey = getComdatGVForCOFF(GV);
844     if (const auto *GA = dyn_cast<GlobalAlias>(ComdatKey))
845       ComdatKey = GA->getBaseObject();
846     if (ComdatKey == GV) {
847       switch (C->getSelectionKind()) {
848       case Comdat::Any:
849         return COFF::IMAGE_COMDAT_SELECT_ANY;
850       case Comdat::ExactMatch:
851         return COFF::IMAGE_COMDAT_SELECT_EXACT_MATCH;
852       case Comdat::Largest:
853         return COFF::IMAGE_COMDAT_SELECT_LARGEST;
854       case Comdat::NoDuplicates:
855         return COFF::IMAGE_COMDAT_SELECT_NODUPLICATES;
856       case Comdat::SameSize:
857         return COFF::IMAGE_COMDAT_SELECT_SAME_SIZE;
858       }
859     } else {
860       return COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE;
861     }
862   }
863   return 0;
864 }
865 
866 MCSection *TargetLoweringObjectFileCOFF::getExplicitSectionGlobal(
867     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
868     const TargetMachine &TM) const {
869   int Selection = 0;
870   unsigned Characteristics = getCOFFSectionFlags(Kind);
871   StringRef Name = GV->getSection();
872   StringRef COMDATSymName = "";
873   if (GV->hasComdat()) {
874     Selection = getSelectionForCOFF(GV);
875     const GlobalValue *ComdatGV;
876     if (Selection == COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE)
877       ComdatGV = getComdatGVForCOFF(GV);
878     else
879       ComdatGV = GV;
880 
881     if (!ComdatGV->hasPrivateLinkage()) {
882       MCSymbol *Sym = TM.getSymbol(ComdatGV, Mang);
883       COMDATSymName = Sym->getName();
884       Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
885     } else {
886       Selection = 0;
887     }
888   }
889   return getContext().getCOFFSection(Name,
890                                      Characteristics,
891                                      Kind,
892                                      COMDATSymName,
893                                      Selection);
894 }
895 
896 static const char *getCOFFSectionNameForUniqueGlobal(SectionKind Kind) {
897   if (Kind.isText())
898     return ".text";
899   if (Kind.isBSS())
900     return ".bss";
901   if (Kind.isThreadLocal())
902     return ".tls$";
903   if (Kind.isReadOnly() || Kind.isReadOnlyWithRel())
904     return ".rdata";
905   return ".data";
906 }
907 
908 MCSection *TargetLoweringObjectFileCOFF::SelectSectionForGlobal(
909     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
910     const TargetMachine &TM) const {
911   // If we have -ffunction-sections then we should emit the global value to a
912   // uniqued section specifically for it.
913   bool EmitUniquedSection;
914   if (Kind.isText())
915     EmitUniquedSection = TM.getFunctionSections();
916   else
917     EmitUniquedSection = TM.getDataSections();
918 
919   if ((EmitUniquedSection && !Kind.isCommon()) || GV->hasComdat()) {
920     const char *Name = getCOFFSectionNameForUniqueGlobal(Kind);
921     unsigned Characteristics = getCOFFSectionFlags(Kind);
922 
923     Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
924     int Selection = getSelectionForCOFF(GV);
925     if (!Selection)
926       Selection = COFF::IMAGE_COMDAT_SELECT_NODUPLICATES;
927     const GlobalValue *ComdatGV;
928     if (GV->hasComdat())
929       ComdatGV = getComdatGVForCOFF(GV);
930     else
931       ComdatGV = GV;
932 
933     if (!ComdatGV->hasPrivateLinkage()) {
934       MCSymbol *Sym = TM.getSymbol(ComdatGV, Mang);
935       StringRef COMDATSymName = Sym->getName();
936       return getContext().getCOFFSection(Name, Characteristics, Kind,
937                                          COMDATSymName, Selection);
938     } else {
939       SmallString<256> TmpData;
940       Mang.getNameWithPrefix(TmpData, GV, /*CannotUsePrivateLabel=*/true);
941       return getContext().getCOFFSection(Name, Characteristics, Kind, TmpData,
942                                          Selection);
943     }
944   }
945 
946   if (Kind.isText())
947     return TextSection;
948 
949   if (Kind.isThreadLocal())
950     return TLSDataSection;
951 
952   if (Kind.isReadOnly() || Kind.isReadOnlyWithRel())
953     return ReadOnlySection;
954 
955   // Note: we claim that common symbols are put in BSSSection, but they are
956   // really emitted with the magic .comm directive, which creates a symbol table
957   // entry but not a section.
958   if (Kind.isBSS() || Kind.isCommon())
959     return BSSSection;
960 
961   return DataSection;
962 }
963 
964 void TargetLoweringObjectFileCOFF::getNameWithPrefix(
965     SmallVectorImpl<char> &OutName, const GlobalValue *GV, Mangler &Mang,
966     const TargetMachine &TM) const {
967   bool CannotUsePrivateLabel = false;
968   if (GV->hasPrivateLinkage() &&
969       ((isa<Function>(GV) && TM.getFunctionSections()) ||
970        (isa<GlobalVariable>(GV) && TM.getDataSections())))
971     CannotUsePrivateLabel = true;
972 
973   Mang.getNameWithPrefix(OutName, GV, CannotUsePrivateLabel);
974 }
975 
976 MCSection *TargetLoweringObjectFileCOFF::getSectionForJumpTable(
977     const Function &F, Mangler &Mang, const TargetMachine &TM) const {
978   // If the function can be removed, produce a unique section so that
979   // the table doesn't prevent the removal.
980   const Comdat *C = F.getComdat();
981   bool EmitUniqueSection = TM.getFunctionSections() || C;
982   if (!EmitUniqueSection)
983     return ReadOnlySection;
984 
985   // FIXME: we should produce a symbol for F instead.
986   if (F.hasPrivateLinkage())
987     return ReadOnlySection;
988 
989   MCSymbol *Sym = TM.getSymbol(&F, Mang);
990   StringRef COMDATSymName = Sym->getName();
991 
992   SectionKind Kind = SectionKind::getReadOnly();
993   const char *Name = getCOFFSectionNameForUniqueGlobal(Kind);
994   unsigned Characteristics = getCOFFSectionFlags(Kind);
995   Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
996 
997   return getContext().getCOFFSection(Name, Characteristics, Kind, COMDATSymName,
998                                      COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE);
999 }
1000 
1001 void TargetLoweringObjectFileCOFF::
1002 emitModuleFlags(MCStreamer &Streamer,
1003                 ArrayRef<Module::ModuleFlagEntry> ModuleFlags,
1004                 Mangler &Mang, const TargetMachine &TM) const {
1005   MDNode *LinkerOptions = nullptr;
1006 
1007   // Look for the "Linker Options" flag, since it's the only one we support.
1008   for (ArrayRef<Module::ModuleFlagEntry>::iterator
1009        i = ModuleFlags.begin(), e = ModuleFlags.end(); i != e; ++i) {
1010     const Module::ModuleFlagEntry &MFE = *i;
1011     StringRef Key = MFE.Key->getString();
1012     Metadata *Val = MFE.Val;
1013     if (Key == "Linker Options") {
1014       LinkerOptions = cast<MDNode>(Val);
1015       break;
1016     }
1017   }
1018   if (!LinkerOptions)
1019     return;
1020 
1021   // Emit the linker options to the linker .drectve section.  According to the
1022   // spec, this section is a space-separated string containing flags for linker.
1023   MCSection *Sec = getDrectveSection();
1024   Streamer.SwitchSection(Sec);
1025   for (unsigned i = 0, e = LinkerOptions->getNumOperands(); i != e; ++i) {
1026     MDNode *MDOptions = cast<MDNode>(LinkerOptions->getOperand(i));
1027     for (unsigned ii = 0, ie = MDOptions->getNumOperands(); ii != ie; ++ii) {
1028       MDString *MDOption = cast<MDString>(MDOptions->getOperand(ii));
1029       // Lead with a space for consistency with our dllexport implementation.
1030       std::string Directive(" ");
1031       Directive.append(MDOption->getString());
1032       Streamer.EmitBytes(Directive);
1033     }
1034   }
1035 }
1036 
1037 MCSection *TargetLoweringObjectFileCOFF::getStaticCtorSection(
1038     unsigned Priority, const MCSymbol *KeySym) const {
1039   return getContext().getAssociativeCOFFSection(
1040       cast<MCSectionCOFF>(StaticCtorSection), KeySym);
1041 }
1042 
1043 MCSection *TargetLoweringObjectFileCOFF::getStaticDtorSection(
1044     unsigned Priority, const MCSymbol *KeySym) const {
1045   return getContext().getAssociativeCOFFSection(
1046       cast<MCSectionCOFF>(StaticDtorSection), KeySym);
1047 }
1048 
1049 void TargetLoweringObjectFileCOFF::emitLinkerFlagsForGlobal(
1050     raw_ostream &OS, const GlobalValue *GV, const Mangler &Mang) const {
1051   if (!GV->hasDLLExportStorageClass() || GV->isDeclaration())
1052     return;
1053 
1054   const Triple &TT = getTargetTriple();
1055 
1056   if (TT.isKnownWindowsMSVCEnvironment())
1057     OS << " /EXPORT:";
1058   else
1059     OS << " -export:";
1060 
1061   if (TT.isWindowsGNUEnvironment() || TT.isWindowsCygwinEnvironment()) {
1062     std::string Flag;
1063     raw_string_ostream FlagOS(Flag);
1064     Mang.getNameWithPrefix(FlagOS, GV, false);
1065     FlagOS.flush();
1066     if (Flag[0] == GV->getParent()->getDataLayout().getGlobalPrefix())
1067       OS << Flag.substr(1);
1068     else
1069       OS << Flag;
1070   } else {
1071     Mang.getNameWithPrefix(OS, GV, false);
1072   }
1073 
1074   if (!GV->getValueType()->isFunctionTy()) {
1075     if (TT.isKnownWindowsMSVCEnvironment())
1076       OS << ",DATA";
1077     else
1078       OS << ",data";
1079   }
1080 }
1081