xref: /llvm-project/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp (revision 47e384298245b707d6dd986f5eb0646103cf06fd) 
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/MC/MCValue.h"
35 #include "llvm/Support/Dwarf.h"
36 #include "llvm/Support/ELF.h"
37 #include "llvm/Support/ErrorHandling.h"
38 #include "llvm/Support/raw_ostream.h"
39 #include "llvm/Target/TargetLowering.h"
40 #include "llvm/Target/TargetMachine.h"
41 #include "llvm/Target/TargetSubtargetInfo.h"
42 using namespace llvm;
43 using namespace dwarf;
44 
45 //===----------------------------------------------------------------------===//
46 //                                  ELF
47 //===----------------------------------------------------------------------===//
48 
49 MCSymbol *TargetLoweringObjectFileELF::getCFIPersonalitySymbol(
50     const GlobalValue *GV, Mangler &Mang, const TargetMachine &TM,
51     MachineModuleInfo *MMI) const {
52   unsigned Encoding = getPersonalityEncoding();
53   if ((Encoding & 0x80) == dwarf::DW_EH_PE_indirect)
54     return getContext().GetOrCreateSymbol(StringRef("DW.ref.") +
55                                           TM.getSymbol(GV, Mang)->getName());
56   if ((Encoding & 0x70) == dwarf::DW_EH_PE_absptr)
57     return TM.getSymbol(GV, Mang);
58   report_fatal_error("We do not support this DWARF encoding yet!");
59 }
60 
61 void TargetLoweringObjectFileELF::emitPersonalityValue(MCStreamer &Streamer,
62                                                        const TargetMachine &TM,
63                                                        const MCSymbol *Sym) const {
64   SmallString<64> NameData("DW.ref.");
65   NameData += Sym->getName();
66   MCSymbol *Label = getContext().GetOrCreateSymbol(NameData);
67   Streamer.EmitSymbolAttribute(Label, MCSA_Hidden);
68   Streamer.EmitSymbolAttribute(Label, MCSA_Weak);
69   StringRef Prefix = ".data.";
70   NameData.insert(NameData.begin(), Prefix.begin(), Prefix.end());
71   unsigned Flags = ELF::SHF_ALLOC | ELF::SHF_WRITE | ELF::SHF_GROUP;
72   const MCSection *Sec = getContext().getELFSection(NameData,
73                                                     ELF::SHT_PROGBITS,
74                                                     Flags,
75                                                     0, Label->getName());
76   unsigned Size = TM.getDataLayout()->getPointerSize();
77   Streamer.SwitchSection(Sec);
78   Streamer.EmitValueToAlignment(TM.getDataLayout()->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 const 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.isDataRelLocal())
239     return ".data.rel.local";
240   if (Kind.isDataRel())
241     return ".data.rel";
242   if (Kind.isReadOnlyWithRelLocal())
243     return ".data.rel.ro.local";
244   assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
245   return ".data.rel.ro";
246 }
247 
248 static const MCSectionELF *selectELFSectionForGlobal(
249     MCContext &Ctx, const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
250     const TargetMachine &TM, bool EmitUniqueSection, unsigned Flags) {
251   unsigned EntrySize = 0;
252   if (Kind.isMergeableCString()) {
253     if (Kind.isMergeable2ByteCString()) {
254       EntrySize = 2;
255     } else if (Kind.isMergeable4ByteCString()) {
256       EntrySize = 4;
257     } else {
258       EntrySize = 1;
259       assert(Kind.isMergeable1ByteCString() && "unknown string width");
260     }
261   } else if (Kind.isMergeableConst()) {
262     if (Kind.isMergeableConst4()) {
263       EntrySize = 4;
264     } else if (Kind.isMergeableConst8()) {
265       EntrySize = 8;
266     } else {
267       assert(Kind.isMergeableConst16() && "unknown data width");
268       EntrySize = 16;
269     }
270   }
271 
272   StringRef Group = "";
273   if (const Comdat *C = getELFComdat(GV)) {
274     Flags |= ELF::SHF_GROUP;
275     Group = C->getName();
276   }
277 
278   bool UniqueSectionNames = TM.getUniqueSectionNames();
279   SmallString<128> Name;
280   if (Kind.isMergeableCString()) {
281     // We also need alignment here.
282     // FIXME: this is getting the alignment of the character, not the
283     // alignment of the global!
284     unsigned Align =
285         TM.getDataLayout()->getPreferredAlignment(cast<GlobalVariable>(GV));
286 
287     std::string SizeSpec = ".rodata.str" + utostr(EntrySize) + ".";
288     Name = SizeSpec + utostr(Align);
289   } else if (Kind.isMergeableConst()) {
290     Name = ".rodata.cst";
291     Name += utostr(EntrySize);
292   } else {
293     Name = getSectionPrefixForGlobal(Kind);
294   }
295 
296   if (EmitUniqueSection && UniqueSectionNames) {
297     Name.push_back('.');
298     TM.getNameWithPrefix(Name, GV, Mang, true);
299   }
300   return Ctx.getELFSection(Name, getELFSectionType(Name, Kind), Flags,
301                            EntrySize, Group,
302                            EmitUniqueSection && !UniqueSectionNames);
303 }
304 
305 const MCSection *TargetLoweringObjectFileELF::SelectSectionForGlobal(
306     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
307     const TargetMachine &TM) const {
308   unsigned Flags = getELFSectionFlags(Kind);
309 
310   // If we have -ffunction-section or -fdata-section then we should emit the
311   // global value to a uniqued section specifically for it.
312   bool EmitUniqueSection = false;
313   if (!(Flags & ELF::SHF_MERGE) && !Kind.isCommon()) {
314     if (Kind.isText())
315       EmitUniqueSection = TM.getFunctionSections();
316     else
317       EmitUniqueSection = TM.getDataSections();
318   }
319   EmitUniqueSection |= GV->hasComdat();
320 
321   return selectELFSectionForGlobal(getContext(), GV, Kind, Mang, TM,
322                                    EmitUniqueSection, Flags);
323 }
324 
325 const MCSection *TargetLoweringObjectFileELF::getSectionForJumpTable(
326     const Function &F, Mangler &Mang, const TargetMachine &TM) const {
327   // If the function can be removed, produce a unique section so that
328   // the table doesn't prevent the removal.
329   const Comdat *C = F.getComdat();
330   bool EmitUniqueSection = TM.getFunctionSections() || C;
331   if (!EmitUniqueSection)
332     return ReadOnlySection;
333 
334   return selectELFSectionForGlobal(getContext(), &F, SectionKind::getReadOnly(),
335                                    Mang, TM, EmitUniqueSection, ELF::SHF_ALLOC);
336 }
337 
338 bool TargetLoweringObjectFileELF::shouldPutJumpTableInFunctionSection(
339     bool UsesLabelDifference, const Function &F) const {
340   // We can always create relative relocations, so use another section
341   // that can be marked non-executable.
342   return false;
343 }
344 
345 /// getSectionForConstant - Given a mergeable constant with the
346 /// specified size and relocation information, return a section that it
347 /// should be placed in.
348 const MCSection *
349 TargetLoweringObjectFileELF::getSectionForConstant(SectionKind Kind,
350                                                    const Constant *C) const {
351   if (Kind.isMergeableConst4() && MergeableConst4Section)
352     return MergeableConst4Section;
353   if (Kind.isMergeableConst8() && MergeableConst8Section)
354     return MergeableConst8Section;
355   if (Kind.isMergeableConst16() && MergeableConst16Section)
356     return MergeableConst16Section;
357   if (Kind.isReadOnly())
358     return ReadOnlySection;
359 
360   if (Kind.isReadOnlyWithRelLocal()) return DataRelROLocalSection;
361   assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
362   return DataRelROSection;
363 }
364 
365 static const MCSectionELF *getStaticStructorSection(MCContext &Ctx,
366                                                     bool UseInitArray,
367                                                     bool IsCtor,
368                                                     unsigned Priority,
369                                                     const MCSymbol *KeySym) {
370   std::string Name;
371   unsigned Type;
372   unsigned Flags = ELF::SHF_ALLOC | ELF::SHF_WRITE;
373   StringRef COMDAT = KeySym ? KeySym->getName() : "";
374 
375   if (KeySym)
376     Flags |= ELF::SHF_GROUP;
377 
378   if (UseInitArray) {
379     if (IsCtor) {
380       Type = ELF::SHT_INIT_ARRAY;
381       Name = ".init_array";
382     } else {
383       Type = ELF::SHT_FINI_ARRAY;
384       Name = ".fini_array";
385     }
386     if (Priority != 65535) {
387       Name += '.';
388       Name += utostr(Priority);
389     }
390   } else {
391     // The default scheme is .ctor / .dtor, so we have to invert the priority
392     // numbering.
393     if (IsCtor)
394       Name = ".ctors";
395     else
396       Name = ".dtors";
397     if (Priority != 65535) {
398       Name += '.';
399       Name += utostr(65535 - Priority);
400     }
401     Type = ELF::SHT_PROGBITS;
402   }
403 
404   return Ctx.getELFSection(Name, Type, Flags, 0, COMDAT);
405 }
406 
407 const MCSection *TargetLoweringObjectFileELF::getStaticCtorSection(
408     unsigned Priority, const MCSymbol *KeySym) const {
409   return getStaticStructorSection(getContext(), UseInitArray, true, Priority,
410                                   KeySym);
411 }
412 
413 const MCSection *TargetLoweringObjectFileELF::getStaticDtorSection(
414     unsigned Priority, const MCSymbol *KeySym) const {
415   return getStaticStructorSection(getContext(), UseInitArray, false, Priority,
416                                   KeySym);
417 }
418 
419 void
420 TargetLoweringObjectFileELF::InitializeELF(bool UseInitArray_) {
421   UseInitArray = UseInitArray_;
422   if (!UseInitArray)
423     return;
424 
425   StaticCtorSection = getContext().getELFSection(
426       ".init_array", ELF::SHT_INIT_ARRAY, ELF::SHF_WRITE | ELF::SHF_ALLOC);
427   StaticDtorSection = getContext().getELFSection(
428       ".fini_array", ELF::SHT_FINI_ARRAY, ELF::SHF_WRITE | ELF::SHF_ALLOC);
429 }
430 
431 //===----------------------------------------------------------------------===//
432 //                                 MachO
433 //===----------------------------------------------------------------------===//
434 
435 TargetLoweringObjectFileMachO::TargetLoweringObjectFileMachO()
436   : TargetLoweringObjectFile() {
437   SupportIndirectSymViaGOTPCRel = true;
438 }
439 
440 /// getDepLibFromLinkerOpt - Extract the dependent library name from a linker
441 /// option string. Returns StringRef() if the option does not specify a library.
442 StringRef TargetLoweringObjectFileMachO::
443 getDepLibFromLinkerOpt(StringRef LinkerOption) const {
444   const char *LibCmd = "-l";
445   if (LinkerOption.startswith(LibCmd))
446     return LinkerOption.substr(strlen(LibCmd));
447   return StringRef();
448 }
449 
450 /// emitModuleFlags - Perform code emission for module flags.
451 void TargetLoweringObjectFileMachO::
452 emitModuleFlags(MCStreamer &Streamer,
453                 ArrayRef<Module::ModuleFlagEntry> ModuleFlags,
454                 Mangler &Mang, const TargetMachine &TM) const {
455   unsigned VersionVal = 0;
456   unsigned ImageInfoFlags = 0;
457   MDNode *LinkerOptions = nullptr;
458   StringRef SectionVal;
459 
460   for (ArrayRef<Module::ModuleFlagEntry>::iterator
461          i = ModuleFlags.begin(), e = ModuleFlags.end(); i != e; ++i) {
462     const Module::ModuleFlagEntry &MFE = *i;
463 
464     // Ignore flags with 'Require' behavior.
465     if (MFE.Behavior == Module::Require)
466       continue;
467 
468     StringRef Key = MFE.Key->getString();
469     Metadata *Val = MFE.Val;
470 
471     if (Key == "Objective-C Image Info Version") {
472       VersionVal = mdconst::extract<ConstantInt>(Val)->getZExtValue();
473     } else if (Key == "Objective-C Garbage Collection" ||
474                Key == "Objective-C GC Only" ||
475                Key == "Objective-C Is Simulated" ||
476                Key == "Objective-C Image Swift Version") {
477       ImageInfoFlags |= mdconst::extract<ConstantInt>(Val)->getZExtValue();
478     } else if (Key == "Objective-C Image Info Section") {
479       SectionVal = cast<MDString>(Val)->getString();
480     } else if (Key == "Linker Options") {
481       LinkerOptions = cast<MDNode>(Val);
482     }
483   }
484 
485   // Emit the linker options if present.
486   if (LinkerOptions) {
487     for (unsigned i = 0, e = LinkerOptions->getNumOperands(); i != e; ++i) {
488       MDNode *MDOptions = cast<MDNode>(LinkerOptions->getOperand(i));
489       SmallVector<std::string, 4> StrOptions;
490 
491       // Convert to strings.
492       for (unsigned ii = 0, ie = MDOptions->getNumOperands(); ii != ie; ++ii) {
493         MDString *MDOption = cast<MDString>(MDOptions->getOperand(ii));
494         StrOptions.push_back(MDOption->getString());
495       }
496 
497       Streamer.EmitLinkerOptions(StrOptions);
498     }
499   }
500 
501   // The section is mandatory. If we don't have it, then we don't have GC info.
502   if (SectionVal.empty()) return;
503 
504   StringRef Segment, Section;
505   unsigned TAA = 0, StubSize = 0;
506   bool TAAParsed;
507   std::string ErrorCode =
508     MCSectionMachO::ParseSectionSpecifier(SectionVal, Segment, Section,
509                                           TAA, TAAParsed, StubSize);
510   if (!ErrorCode.empty())
511     // If invalid, report the error with report_fatal_error.
512     report_fatal_error("Invalid section specifier '" + Section + "': " +
513                        ErrorCode + ".");
514 
515   // Get the section.
516   const MCSectionMachO *S =
517     getContext().getMachOSection(Segment, Section, TAA, StubSize,
518                                  SectionKind::getDataNoRel());
519   Streamer.SwitchSection(S);
520   Streamer.EmitLabel(getContext().
521                      GetOrCreateSymbol(StringRef("L_OBJC_IMAGE_INFO")));
522   Streamer.EmitIntValue(VersionVal, 4);
523   Streamer.EmitIntValue(ImageInfoFlags, 4);
524   Streamer.AddBlankLine();
525 }
526 
527 static void checkMachOComdat(const GlobalValue *GV) {
528   const Comdat *C = GV->getComdat();
529   if (!C)
530     return;
531 
532   report_fatal_error("MachO doesn't support COMDATs, '" + C->getName() +
533                      "' cannot be lowered.");
534 }
535 
536 const MCSection *TargetLoweringObjectFileMachO::getExplicitSectionGlobal(
537     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
538     const TargetMachine &TM) const {
539   // Parse the section specifier and create it if valid.
540   StringRef Segment, Section;
541   unsigned TAA = 0, StubSize = 0;
542   bool TAAParsed;
543 
544   checkMachOComdat(GV);
545 
546   std::string ErrorCode =
547     MCSectionMachO::ParseSectionSpecifier(GV->getSection(), Segment, Section,
548                                           TAA, TAAParsed, StubSize);
549   if (!ErrorCode.empty()) {
550     // If invalid, report the error with report_fatal_error.
551     report_fatal_error("Global variable '" + GV->getName() +
552                        "' has an invalid section specifier '" +
553                        GV->getSection() + "': " + ErrorCode + ".");
554   }
555 
556   // Get the section.
557   const MCSectionMachO *S =
558     getContext().getMachOSection(Segment, Section, TAA, StubSize, Kind);
559 
560   // If TAA wasn't set by ParseSectionSpecifier() above,
561   // use the value returned by getMachOSection() as a default.
562   if (!TAAParsed)
563     TAA = S->getTypeAndAttributes();
564 
565   // Okay, now that we got the section, verify that the TAA & StubSize agree.
566   // If the user declared multiple globals with different section flags, we need
567   // to reject it here.
568   if (S->getTypeAndAttributes() != TAA || S->getStubSize() != StubSize) {
569     // If invalid, report the error with report_fatal_error.
570     report_fatal_error("Global variable '" + GV->getName() +
571                        "' section type or attributes does not match previous"
572                        " section specifier");
573   }
574 
575   return S;
576 }
577 
578 const MCSection *TargetLoweringObjectFileMachO::
579 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
580                        Mangler &Mang, const TargetMachine &TM) const {
581   checkMachOComdat(GV);
582 
583   // Handle thread local data.
584   if (Kind.isThreadBSS()) return TLSBSSSection;
585   if (Kind.isThreadData()) return TLSDataSection;
586 
587   if (Kind.isText())
588     return GV->isWeakForLinker() ? TextCoalSection : TextSection;
589 
590   // If this is weak/linkonce, put this in a coalescable section, either in text
591   // or data depending on if it is writable.
592   if (GV->isWeakForLinker()) {
593     if (Kind.isReadOnly())
594       return ConstTextCoalSection;
595     return DataCoalSection;
596   }
597 
598   // FIXME: Alignment check should be handled by section classifier.
599   if (Kind.isMergeable1ByteCString() &&
600       TM.getDataLayout()->getPreferredAlignment(cast<GlobalVariable>(GV)) < 32)
601     return CStringSection;
602 
603   // Do not put 16-bit arrays in the UString section if they have an
604   // externally visible label, this runs into issues with certain linker
605   // versions.
606   if (Kind.isMergeable2ByteCString() && !GV->hasExternalLinkage() &&
607       TM.getDataLayout()->getPreferredAlignment(cast<GlobalVariable>(GV)) < 32)
608     return UStringSection;
609 
610   // With MachO only variables whose corresponding symbol starts with 'l' or
611   // 'L' can be merged, so we only try merging GVs with private linkage.
612   if (GV->hasPrivateLinkage() && Kind.isMergeableConst()) {
613     if (Kind.isMergeableConst4())
614       return FourByteConstantSection;
615     if (Kind.isMergeableConst8())
616       return EightByteConstantSection;
617     if (Kind.isMergeableConst16())
618       return SixteenByteConstantSection;
619   }
620 
621   // Otherwise, if it is readonly, but not something we can specially optimize,
622   // just drop it in .const.
623   if (Kind.isReadOnly())
624     return ReadOnlySection;
625 
626   // If this is marked const, put it into a const section.  But if the dynamic
627   // linker needs to write to it, put it in the data segment.
628   if (Kind.isReadOnlyWithRel())
629     return ConstDataSection;
630 
631   // Put zero initialized globals with strong external linkage in the
632   // DATA, __common section with the .zerofill directive.
633   if (Kind.isBSSExtern())
634     return DataCommonSection;
635 
636   // Put zero initialized globals with local linkage in __DATA,__bss directive
637   // with the .zerofill directive (aka .lcomm).
638   if (Kind.isBSSLocal())
639     return DataBSSSection;
640 
641   // Otherwise, just drop the variable in the normal data section.
642   return DataSection;
643 }
644 
645 const MCSection *
646 TargetLoweringObjectFileMachO::getSectionForConstant(SectionKind Kind,
647                                                      const Constant *C) const {
648   // If this constant requires a relocation, we have to put it in the data
649   // segment, not in the text segment.
650   if (Kind.isDataRel() || Kind.isReadOnlyWithRel())
651     return ConstDataSection;
652 
653   if (Kind.isMergeableConst4())
654     return FourByteConstantSection;
655   if (Kind.isMergeableConst8())
656     return EightByteConstantSection;
657   if (Kind.isMergeableConst16())
658     return SixteenByteConstantSection;
659   return ReadOnlySection;  // .const
660 }
661 
662 const MCExpr *TargetLoweringObjectFileMachO::getTTypeGlobalReference(
663     const GlobalValue *GV, unsigned Encoding, Mangler &Mang,
664     const TargetMachine &TM, MachineModuleInfo *MMI,
665     MCStreamer &Streamer) const {
666   // The mach-o version of this method defaults to returning a stub reference.
667 
668   if (Encoding & DW_EH_PE_indirect) {
669     MachineModuleInfoMachO &MachOMMI =
670       MMI->getObjFileInfo<MachineModuleInfoMachO>();
671 
672     MCSymbol *SSym =
673         getSymbolWithGlobalValueBase(GV, "$non_lazy_ptr", Mang, TM);
674 
675     // Add information about the stub reference to MachOMMI so that the stub
676     // gets emitted by the asmprinter.
677     MachineModuleInfoImpl::StubValueTy &StubSym =
678       GV->hasHiddenVisibility() ? MachOMMI.getHiddenGVStubEntry(SSym) :
679                                   MachOMMI.getGVStubEntry(SSym);
680     if (!StubSym.getPointer()) {
681       MCSymbol *Sym = TM.getSymbol(GV, Mang);
682       StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
683     }
684 
685     return TargetLoweringObjectFile::
686       getTTypeReference(MCSymbolRefExpr::Create(SSym, getContext()),
687                         Encoding & ~dwarf::DW_EH_PE_indirect, Streamer);
688   }
689 
690   return TargetLoweringObjectFile::getTTypeGlobalReference(GV, Encoding, Mang,
691                                                            TM, MMI, Streamer);
692 }
693 
694 MCSymbol *TargetLoweringObjectFileMachO::getCFIPersonalitySymbol(
695     const GlobalValue *GV, Mangler &Mang, const TargetMachine &TM,
696     MachineModuleInfo *MMI) const {
697   // The mach-o version of this method defaults to returning a stub reference.
698   MachineModuleInfoMachO &MachOMMI =
699     MMI->getObjFileInfo<MachineModuleInfoMachO>();
700 
701   MCSymbol *SSym = getSymbolWithGlobalValueBase(GV, "$non_lazy_ptr", Mang, TM);
702 
703   // Add information about the stub reference to MachOMMI so that the stub
704   // gets emitted by the asmprinter.
705   MachineModuleInfoImpl::StubValueTy &StubSym = MachOMMI.getGVStubEntry(SSym);
706   if (!StubSym.getPointer()) {
707     MCSymbol *Sym = TM.getSymbol(GV, Mang);
708     StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
709   }
710 
711   return SSym;
712 }
713 
714 const MCExpr *TargetLoweringObjectFileMachO::getIndirectSymViaGOTPCRel(
715     const MCSymbol *Sym, const MCValue &MV, int64_t Offset,
716     MachineModuleInfo *MMI, MCStreamer &Streamer) const {
717   // Although MachO 32-bit targets do not explictly have a GOTPCREL relocation
718   // as 64-bit do, we replace the GOT equivalent by accessing the final symbol
719   // through a non_lazy_ptr stub instead. One advantage is that it allows the
720   // computation of deltas to final external symbols. Example:
721   //
722   //    _extgotequiv:
723   //       .long   _extfoo
724   //
725   //    _delta:
726   //       .long   _extgotequiv-_delta
727   //
728   // is transformed to:
729   //
730   //    _delta:
731   //       .long   L_extfoo$non_lazy_ptr-(_delta+0)
732   //
733   //       .section        __IMPORT,__pointers,non_lazy_symbol_pointers
734   //    L_extfoo$non_lazy_ptr:
735   //       .indirect_symbol        _extfoo
736   //       .long   0
737   //
738   MachineModuleInfoMachO &MachOMMI =
739     MMI->getObjFileInfo<MachineModuleInfoMachO>();
740   MCContext &Ctx = getContext();
741 
742   // The offset must consider the original displacement from the base symbol
743   // since 32-bit targets don't have a GOTPCREL to fold the PC displacement.
744   Offset = -MV.getConstant();
745   const MCSymbol *BaseSym = &MV.getSymB()->getSymbol();
746 
747   // Access the final symbol via sym$non_lazy_ptr and generate the appropriated
748   // non_lazy_ptr stubs.
749   SmallString<128> Name;
750   StringRef Suffix = "$non_lazy_ptr";
751   Name += DL->getPrivateGlobalPrefix();
752   Name += Sym->getName();
753   Name += Suffix;
754   MCSymbol *Stub = Ctx.GetOrCreateSymbol(Name);
755 
756   MachineModuleInfoImpl::StubValueTy &StubSym = MachOMMI.getGVStubEntry(Stub);
757   if (!StubSym.getPointer())
758     StubSym = MachineModuleInfoImpl::
759       StubValueTy(const_cast<MCSymbol *>(Sym), true /* access indirectly */);
760 
761   const MCExpr *BSymExpr =
762     MCSymbolRefExpr::Create(BaseSym, MCSymbolRefExpr::VK_None, Ctx);
763   const MCExpr *LHS =
764     MCSymbolRefExpr::Create(Stub, MCSymbolRefExpr::VK_None, Ctx);
765 
766   if (!Offset)
767     return MCBinaryExpr::CreateSub(LHS, BSymExpr, Ctx);
768 
769   const MCExpr *RHS =
770     MCBinaryExpr::CreateAdd(BSymExpr, MCConstantExpr::Create(Offset, Ctx), Ctx);
771   return MCBinaryExpr::CreateSub(LHS, RHS, Ctx);
772 }
773 
774 //===----------------------------------------------------------------------===//
775 //                                  COFF
776 //===----------------------------------------------------------------------===//
777 
778 static unsigned
779 getCOFFSectionFlags(SectionKind K) {
780   unsigned Flags = 0;
781 
782   if (K.isMetadata())
783     Flags |=
784       COFF::IMAGE_SCN_MEM_DISCARDABLE;
785   else if (K.isText())
786     Flags |=
787       COFF::IMAGE_SCN_MEM_EXECUTE |
788       COFF::IMAGE_SCN_MEM_READ |
789       COFF::IMAGE_SCN_CNT_CODE;
790   else if (K.isBSS())
791     Flags |=
792       COFF::IMAGE_SCN_CNT_UNINITIALIZED_DATA |
793       COFF::IMAGE_SCN_MEM_READ |
794       COFF::IMAGE_SCN_MEM_WRITE;
795   else if (K.isThreadLocal())
796     Flags |=
797       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
798       COFF::IMAGE_SCN_MEM_READ |
799       COFF::IMAGE_SCN_MEM_WRITE;
800   else if (K.isReadOnly() || K.isReadOnlyWithRel())
801     Flags |=
802       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
803       COFF::IMAGE_SCN_MEM_READ;
804   else if (K.isWriteable())
805     Flags |=
806       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
807       COFF::IMAGE_SCN_MEM_READ |
808       COFF::IMAGE_SCN_MEM_WRITE;
809 
810   return Flags;
811 }
812 
813 static const GlobalValue *getComdatGVForCOFF(const GlobalValue *GV) {
814   const Comdat *C = GV->getComdat();
815   assert(C && "expected GV to have a Comdat!");
816 
817   StringRef ComdatGVName = C->getName();
818   const GlobalValue *ComdatGV = GV->getParent()->getNamedValue(ComdatGVName);
819   if (!ComdatGV)
820     report_fatal_error("Associative COMDAT symbol '" + ComdatGVName +
821                        "' does not exist.");
822 
823   if (ComdatGV->getComdat() != C)
824     report_fatal_error("Associative COMDAT symbol '" + ComdatGVName +
825                        "' is not a key for its COMDAT.");
826 
827   return ComdatGV;
828 }
829 
830 static int getSelectionForCOFF(const GlobalValue *GV) {
831   if (const Comdat *C = GV->getComdat()) {
832     const GlobalValue *ComdatKey = getComdatGVForCOFF(GV);
833     if (const auto *GA = dyn_cast<GlobalAlias>(ComdatKey))
834       ComdatKey = GA->getBaseObject();
835     if (ComdatKey == GV) {
836       switch (C->getSelectionKind()) {
837       case Comdat::Any:
838         return COFF::IMAGE_COMDAT_SELECT_ANY;
839       case Comdat::ExactMatch:
840         return COFF::IMAGE_COMDAT_SELECT_EXACT_MATCH;
841       case Comdat::Largest:
842         return COFF::IMAGE_COMDAT_SELECT_LARGEST;
843       case Comdat::NoDuplicates:
844         return COFF::IMAGE_COMDAT_SELECT_NODUPLICATES;
845       case Comdat::SameSize:
846         return COFF::IMAGE_COMDAT_SELECT_SAME_SIZE;
847       }
848     } else {
849       return COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE;
850     }
851   } else if (GV->isWeakForLinker()) {
852     return COFF::IMAGE_COMDAT_SELECT_ANY;
853   }
854   return 0;
855 }
856 
857 const MCSection *TargetLoweringObjectFileCOFF::getExplicitSectionGlobal(
858     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
859     const TargetMachine &TM) const {
860   int Selection = 0;
861   unsigned Characteristics = getCOFFSectionFlags(Kind);
862   StringRef Name = GV->getSection();
863   StringRef COMDATSymName = "";
864   if (GV->hasComdat()) {
865     Selection = getSelectionForCOFF(GV);
866     const GlobalValue *ComdatGV;
867     if (Selection == COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE)
868       ComdatGV = getComdatGVForCOFF(GV);
869     else
870       ComdatGV = GV;
871 
872     if (!ComdatGV->hasPrivateLinkage()) {
873       MCSymbol *Sym = TM.getSymbol(ComdatGV, Mang);
874       COMDATSymName = Sym->getName();
875       Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
876     } else {
877       Selection = 0;
878     }
879   }
880   return getContext().getCOFFSection(Name,
881                                      Characteristics,
882                                      Kind,
883                                      COMDATSymName,
884                                      Selection);
885 }
886 
887 static const char *getCOFFSectionNameForUniqueGlobal(SectionKind Kind) {
888   if (Kind.isText())
889     return ".text";
890   if (Kind.isBSS())
891     return ".bss";
892   if (Kind.isThreadLocal())
893     return ".tls$";
894   if (Kind.isReadOnly() || Kind.isReadOnlyWithRel())
895     return ".rdata";
896   return ".data";
897 }
898 
899 
900 const MCSection *TargetLoweringObjectFileCOFF::
901 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
902                        Mangler &Mang, const TargetMachine &TM) const {
903   // If we have -ffunction-sections then we should emit the global value to a
904   // uniqued section specifically for it.
905   bool EmitUniquedSection;
906   if (Kind.isText())
907     EmitUniquedSection = TM.getFunctionSections();
908   else
909     EmitUniquedSection = TM.getDataSections();
910 
911   if ((EmitUniquedSection && !Kind.isCommon()) || GV->hasComdat()) {
912     const char *Name = getCOFFSectionNameForUniqueGlobal(Kind);
913     unsigned Characteristics = getCOFFSectionFlags(Kind);
914 
915     Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
916     int Selection = getSelectionForCOFF(GV);
917     if (!Selection)
918       Selection = COFF::IMAGE_COMDAT_SELECT_NODUPLICATES;
919     const GlobalValue *ComdatGV;
920     if (GV->hasComdat())
921       ComdatGV = getComdatGVForCOFF(GV);
922     else
923       ComdatGV = GV;
924 
925     if (!ComdatGV->hasPrivateLinkage()) {
926       MCSymbol *Sym = TM.getSymbol(ComdatGV, Mang);
927       StringRef COMDATSymName = Sym->getName();
928       return getContext().getCOFFSection(Name, Characteristics, Kind,
929                                          COMDATSymName, Selection);
930     } else {
931       SmallString<256> TmpData;
932       getNameWithPrefix(TmpData, GV, true, Mang, TM);
933       return getContext().getCOFFSection(Name, Characteristics, Kind, TmpData,
934                                          Selection);
935     }
936   }
937 
938   if (Kind.isText())
939     return TextSection;
940 
941   if (Kind.isThreadLocal())
942     return TLSDataSection;
943 
944   if (Kind.isReadOnly() || Kind.isReadOnlyWithRel())
945     return ReadOnlySection;
946 
947   // Note: we claim that common symbols are put in BSSSection, but they are
948   // really emitted with the magic .comm directive, which creates a symbol table
949   // entry but not a section.
950   if (Kind.isBSS() || Kind.isCommon())
951     return BSSSection;
952 
953   return DataSection;
954 }
955 
956 void TargetLoweringObjectFileCOFF::getNameWithPrefix(
957     SmallVectorImpl<char> &OutName, const GlobalValue *GV,
958     bool CannotUsePrivateLabel, Mangler &Mang, const TargetMachine &TM) const {
959   if (GV->hasPrivateLinkage() &&
960       ((isa<Function>(GV) && TM.getFunctionSections()) ||
961        (isa<GlobalVariable>(GV) && TM.getDataSections()))) {
962     SmallString<256> Tmp;
963     Mang.getNameWithPrefix(Tmp, GV, /*CannotUsePrivateLabel=*/false);
964     if (Tmp.startswith(".L"))
965       OutName.append(Tmp.begin() + 2, Tmp.end());
966     else if (Tmp.startswith("L"))
967       OutName.append(Tmp.begin() + 1, Tmp.end());
968     else
969       OutName.append(Tmp.begin(), Tmp.end());
970     return;
971   }
972   Mang.getNameWithPrefix(OutName, GV, CannotUsePrivateLabel);
973 }
974 
975 const MCSection *TargetLoweringObjectFileCOFF::getSectionForJumpTable(
976     const Function &F, Mangler &Mang, const TargetMachine &TM) const {
977   // If the function can be removed, produce a unique section so that
978   // the table doesn't prevent the removal.
979   const Comdat *C = F.getComdat();
980   bool EmitUniqueSection = TM.getFunctionSections() || C;
981   if (!EmitUniqueSection)
982     return ReadOnlySection;
983 
984   // FIXME: we should produce a symbol for F instead.
985   if (F.hasPrivateLinkage())
986     return ReadOnlySection;
987 
988   MCSymbol *Sym = TM.getSymbol(&F, Mang);
989   StringRef COMDATSymName = Sym->getName();
990 
991   SectionKind Kind = SectionKind::getReadOnly();
992   const char *Name = getCOFFSectionNameForUniqueGlobal(Kind);
993   unsigned Characteristics = getCOFFSectionFlags(Kind);
994   Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
995 
996   return getContext().getCOFFSection(Name, Characteristics, Kind, COMDATSymName,
997                                      COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE);
998 }
999 
1000 StringRef TargetLoweringObjectFileCOFF::
1001 getDepLibFromLinkerOpt(StringRef LinkerOption) const {
1002   const char *LibCmd = "/DEFAULTLIB:";
1003   if (LinkerOption.startswith(LibCmd))
1004     return LinkerOption.substr(strlen(LibCmd));
1005   return StringRef();
1006 }
1007 
1008 void TargetLoweringObjectFileCOFF::
1009 emitModuleFlags(MCStreamer &Streamer,
1010                 ArrayRef<Module::ModuleFlagEntry> ModuleFlags,
1011                 Mangler &Mang, const TargetMachine &TM) const {
1012   MDNode *LinkerOptions = nullptr;
1013 
1014   // Look for the "Linker Options" flag, since it's the only one we support.
1015   for (ArrayRef<Module::ModuleFlagEntry>::iterator
1016        i = ModuleFlags.begin(), e = ModuleFlags.end(); i != e; ++i) {
1017     const Module::ModuleFlagEntry &MFE = *i;
1018     StringRef Key = MFE.Key->getString();
1019     Metadata *Val = MFE.Val;
1020     if (Key == "Linker Options") {
1021       LinkerOptions = cast<MDNode>(Val);
1022       break;
1023     }
1024   }
1025   if (!LinkerOptions)
1026     return;
1027 
1028   // Emit the linker options to the linker .drectve section.  According to the
1029   // spec, this section is a space-separated string containing flags for linker.
1030   const MCSection *Sec = getDrectveSection();
1031   Streamer.SwitchSection(Sec);
1032   for (unsigned i = 0, e = LinkerOptions->getNumOperands(); i != e; ++i) {
1033     MDNode *MDOptions = cast<MDNode>(LinkerOptions->getOperand(i));
1034     for (unsigned ii = 0, ie = MDOptions->getNumOperands(); ii != ie; ++ii) {
1035       MDString *MDOption = cast<MDString>(MDOptions->getOperand(ii));
1036       // Lead with a space for consistency with our dllexport implementation.
1037       std::string Directive(" ");
1038       Directive.append(MDOption->getString());
1039       Streamer.EmitBytes(Directive);
1040     }
1041   }
1042 }
1043 
1044 const MCSection *TargetLoweringObjectFileCOFF::getStaticCtorSection(
1045     unsigned Priority, const MCSymbol *KeySym) const {
1046   return getContext().getAssociativeCOFFSection(
1047       cast<MCSectionCOFF>(StaticCtorSection), KeySym);
1048 }
1049 
1050 const MCSection *TargetLoweringObjectFileCOFF::getStaticDtorSection(
1051     unsigned Priority, const MCSymbol *KeySym) const {
1052   return getContext().getAssociativeCOFFSection(
1053       cast<MCSectionCOFF>(StaticDtorSection), KeySym);
1054 }
1055