xref: /llvm-project/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp (revision 8bc9ccc60a0ae3b38b37bf0916e27bc95e968be2) 
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 const MCSection *TargetLoweringObjectFileELF::
248 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
249                        Mangler &Mang, const TargetMachine &TM) const {
250   unsigned Flags = getELFSectionFlags(Kind);
251 
252   // If we have -ffunction-section or -fdata-section then we should emit the
253   // global value to a uniqued section specifically for it.
254   bool EmitUniqueSection = false;
255   if (!(Flags & ELF::SHF_MERGE) && !Kind.isCommon()) {
256     if (Kind.isText())
257       EmitUniqueSection = TM.getFunctionSections();
258     else
259       EmitUniqueSection = TM.getDataSections();
260   }
261   EmitUniqueSection |= GV->hasComdat();
262 
263   unsigned EntrySize = 0;
264   if (Kind.isMergeableCString()) {
265     if (Kind.isMergeable2ByteCString()) {
266       EntrySize = 2;
267     } else if (Kind.isMergeable4ByteCString()) {
268       EntrySize = 4;
269     } else {
270       EntrySize = 1;
271       assert(Kind.isMergeable1ByteCString() && "unknown string width");
272     }
273   } else if (Kind.isMergeableConst()) {
274     if (Kind.isMergeableConst4()) {
275       EntrySize = 4;
276     } else if (Kind.isMergeableConst8()) {
277       EntrySize = 8;
278     } else {
279       assert(Kind.isMergeableConst16() && "unknown data width");
280       EntrySize = 16;
281     }
282   }
283 
284   StringRef Group = "";
285   if (const Comdat *C = getELFComdat(GV)) {
286     Flags |= ELF::SHF_GROUP;
287     Group = C->getName();
288   }
289 
290   bool UniqueSectionNames = TM.getUniqueSectionNames();
291   SmallString<128> Name;
292   if (Kind.isMergeableCString()) {
293     // We also need alignment here.
294     // FIXME: this is getting the alignment of the character, not the
295     // alignment of the global!
296     unsigned Align =
297         TM.getDataLayout()->getPreferredAlignment(cast<GlobalVariable>(GV));
298 
299     std::string SizeSpec = ".rodata.str" + utostr(EntrySize) + ".";
300     Name = SizeSpec + utostr(Align);
301   } else if (Kind.isMergeableConst()) {
302     Name = ".rodata.cst";
303     Name += utostr(EntrySize);
304   } else {
305     Name = getSectionPrefixForGlobal(Kind);
306   }
307 
308   if (EmitUniqueSection && UniqueSectionNames) {
309     Name.push_back('.');
310     TM.getNameWithPrefix(Name, GV, Mang, true);
311   }
312   return getContext().getELFSection(Name, getELFSectionType(Name, Kind), Flags,
313                                     EntrySize, Group,
314                                     EmitUniqueSection && !UniqueSectionNames);
315 }
316 
317 const MCSection *TargetLoweringObjectFileELF::getSectionForJumpTable(
318     const Function &F, Mangler &Mang, const TargetMachine &TM) const {
319   // If the function can be removed, produce a unique section so that
320   // the table doesn't prevent the removal.
321   const Comdat *C = F.getComdat();
322   bool EmitUniqueSection = TM.getFunctionSections() || C;
323   if (!EmitUniqueSection)
324     return ReadOnlySection;
325 
326   return SelectSectionForGlobal(&F, SectionKind::getReadOnly(), Mang, TM);
327 }
328 
329 bool TargetLoweringObjectFileELF::shouldPutJumpTableInFunctionSection(
330     bool UsesLabelDifference, const Function &F) const {
331   // We can always create relative relocations, so use another section
332   // that can be marked non-executable.
333   return false;
334 }
335 
336 /// getSectionForConstant - Given a mergeable constant with the
337 /// specified size and relocation information, return a section that it
338 /// should be placed in.
339 const MCSection *
340 TargetLoweringObjectFileELF::getSectionForConstant(SectionKind Kind,
341                                                    const Constant *C) const {
342   if (Kind.isMergeableConst4() && MergeableConst4Section)
343     return MergeableConst4Section;
344   if (Kind.isMergeableConst8() && MergeableConst8Section)
345     return MergeableConst8Section;
346   if (Kind.isMergeableConst16() && MergeableConst16Section)
347     return MergeableConst16Section;
348   if (Kind.isReadOnly())
349     return ReadOnlySection;
350 
351   if (Kind.isReadOnlyWithRelLocal()) return DataRelROLocalSection;
352   assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
353   return DataRelROSection;
354 }
355 
356 static const MCSectionELF *getStaticStructorSection(MCContext &Ctx,
357                                                     bool UseInitArray,
358                                                     bool IsCtor,
359                                                     unsigned Priority,
360                                                     const MCSymbol *KeySym) {
361   std::string Name;
362   unsigned Type;
363   unsigned Flags = ELF::SHF_ALLOC | ELF::SHF_WRITE;
364   StringRef COMDAT = KeySym ? KeySym->getName() : "";
365 
366   if (KeySym)
367     Flags |= ELF::SHF_GROUP;
368 
369   if (UseInitArray) {
370     if (IsCtor) {
371       Type = ELF::SHT_INIT_ARRAY;
372       Name = ".init_array";
373     } else {
374       Type = ELF::SHT_FINI_ARRAY;
375       Name = ".fini_array";
376     }
377     if (Priority != 65535) {
378       Name += '.';
379       Name += utostr(Priority);
380     }
381   } else {
382     // The default scheme is .ctor / .dtor, so we have to invert the priority
383     // numbering.
384     if (IsCtor)
385       Name = ".ctors";
386     else
387       Name = ".dtors";
388     if (Priority != 65535) {
389       Name += '.';
390       Name += utostr(65535 - Priority);
391     }
392     Type = ELF::SHT_PROGBITS;
393   }
394 
395   return Ctx.getELFSection(Name, Type, Flags, 0, COMDAT);
396 }
397 
398 const MCSection *TargetLoweringObjectFileELF::getStaticCtorSection(
399     unsigned Priority, const MCSymbol *KeySym) const {
400   return getStaticStructorSection(getContext(), UseInitArray, true, Priority,
401                                   KeySym);
402 }
403 
404 const MCSection *TargetLoweringObjectFileELF::getStaticDtorSection(
405     unsigned Priority, const MCSymbol *KeySym) const {
406   return getStaticStructorSection(getContext(), UseInitArray, false, Priority,
407                                   KeySym);
408 }
409 
410 void
411 TargetLoweringObjectFileELF::InitializeELF(bool UseInitArray_) {
412   UseInitArray = UseInitArray_;
413   if (!UseInitArray)
414     return;
415 
416   StaticCtorSection = getContext().getELFSection(
417       ".init_array", ELF::SHT_INIT_ARRAY, ELF::SHF_WRITE | ELF::SHF_ALLOC);
418   StaticDtorSection = getContext().getELFSection(
419       ".fini_array", ELF::SHT_FINI_ARRAY, ELF::SHF_WRITE | ELF::SHF_ALLOC);
420 }
421 
422 //===----------------------------------------------------------------------===//
423 //                                 MachO
424 //===----------------------------------------------------------------------===//
425 
426 /// getDepLibFromLinkerOpt - Extract the dependent library name from a linker
427 /// option string. Returns StringRef() if the option does not specify a library.
428 StringRef TargetLoweringObjectFileMachO::
429 getDepLibFromLinkerOpt(StringRef LinkerOption) const {
430   const char *LibCmd = "-l";
431   if (LinkerOption.startswith(LibCmd))
432     return LinkerOption.substr(strlen(LibCmd));
433   return StringRef();
434 }
435 
436 /// emitModuleFlags - Perform code emission for module flags.
437 void TargetLoweringObjectFileMachO::
438 emitModuleFlags(MCStreamer &Streamer,
439                 ArrayRef<Module::ModuleFlagEntry> ModuleFlags,
440                 Mangler &Mang, const TargetMachine &TM) const {
441   unsigned VersionVal = 0;
442   unsigned ImageInfoFlags = 0;
443   MDNode *LinkerOptions = nullptr;
444   StringRef SectionVal;
445 
446   for (ArrayRef<Module::ModuleFlagEntry>::iterator
447          i = ModuleFlags.begin(), e = ModuleFlags.end(); i != e; ++i) {
448     const Module::ModuleFlagEntry &MFE = *i;
449 
450     // Ignore flags with 'Require' behavior.
451     if (MFE.Behavior == Module::Require)
452       continue;
453 
454     StringRef Key = MFE.Key->getString();
455     Metadata *Val = MFE.Val;
456 
457     if (Key == "Objective-C Image Info Version") {
458       VersionVal = mdconst::extract<ConstantInt>(Val)->getZExtValue();
459     } else if (Key == "Objective-C Garbage Collection" ||
460                Key == "Objective-C GC Only" ||
461                Key == "Objective-C Is Simulated" ||
462                Key == "Objective-C Image Swift Version") {
463       ImageInfoFlags |= mdconst::extract<ConstantInt>(Val)->getZExtValue();
464     } else if (Key == "Objective-C Image Info Section") {
465       SectionVal = cast<MDString>(Val)->getString();
466     } else if (Key == "Linker Options") {
467       LinkerOptions = cast<MDNode>(Val);
468     }
469   }
470 
471   // Emit the linker options if present.
472   if (LinkerOptions) {
473     for (unsigned i = 0, e = LinkerOptions->getNumOperands(); i != e; ++i) {
474       MDNode *MDOptions = cast<MDNode>(LinkerOptions->getOperand(i));
475       SmallVector<std::string, 4> StrOptions;
476 
477       // Convert to strings.
478       for (unsigned ii = 0, ie = MDOptions->getNumOperands(); ii != ie; ++ii) {
479         MDString *MDOption = cast<MDString>(MDOptions->getOperand(ii));
480         StrOptions.push_back(MDOption->getString());
481       }
482 
483       Streamer.EmitLinkerOptions(StrOptions);
484     }
485   }
486 
487   // The section is mandatory. If we don't have it, then we don't have GC info.
488   if (SectionVal.empty()) return;
489 
490   StringRef Segment, Section;
491   unsigned TAA = 0, StubSize = 0;
492   bool TAAParsed;
493   std::string ErrorCode =
494     MCSectionMachO::ParseSectionSpecifier(SectionVal, Segment, Section,
495                                           TAA, TAAParsed, StubSize);
496   if (!ErrorCode.empty())
497     // If invalid, report the error with report_fatal_error.
498     report_fatal_error("Invalid section specifier '" + Section + "': " +
499                        ErrorCode + ".");
500 
501   // Get the section.
502   const MCSectionMachO *S =
503     getContext().getMachOSection(Segment, Section, TAA, StubSize,
504                                  SectionKind::getDataNoRel());
505   Streamer.SwitchSection(S);
506   Streamer.EmitLabel(getContext().
507                      GetOrCreateSymbol(StringRef("L_OBJC_IMAGE_INFO")));
508   Streamer.EmitIntValue(VersionVal, 4);
509   Streamer.EmitIntValue(ImageInfoFlags, 4);
510   Streamer.AddBlankLine();
511 }
512 
513 static void checkMachOComdat(const GlobalValue *GV) {
514   const Comdat *C = GV->getComdat();
515   if (!C)
516     return;
517 
518   report_fatal_error("MachO doesn't support COMDATs, '" + C->getName() +
519                      "' cannot be lowered.");
520 }
521 
522 const MCSection *TargetLoweringObjectFileMachO::getExplicitSectionGlobal(
523     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
524     const TargetMachine &TM) const {
525   // Parse the section specifier and create it if valid.
526   StringRef Segment, Section;
527   unsigned TAA = 0, StubSize = 0;
528   bool TAAParsed;
529 
530   checkMachOComdat(GV);
531 
532   std::string ErrorCode =
533     MCSectionMachO::ParseSectionSpecifier(GV->getSection(), Segment, Section,
534                                           TAA, TAAParsed, StubSize);
535   if (!ErrorCode.empty()) {
536     // If invalid, report the error with report_fatal_error.
537     report_fatal_error("Global variable '" + GV->getName() +
538                        "' has an invalid section specifier '" +
539                        GV->getSection() + "': " + ErrorCode + ".");
540   }
541 
542   // Get the section.
543   const MCSectionMachO *S =
544     getContext().getMachOSection(Segment, Section, TAA, StubSize, Kind);
545 
546   // If TAA wasn't set by ParseSectionSpecifier() above,
547   // use the value returned by getMachOSection() as a default.
548   if (!TAAParsed)
549     TAA = S->getTypeAndAttributes();
550 
551   // Okay, now that we got the section, verify that the TAA & StubSize agree.
552   // If the user declared multiple globals with different section flags, we need
553   // to reject it here.
554   if (S->getTypeAndAttributes() != TAA || S->getStubSize() != StubSize) {
555     // If invalid, report the error with report_fatal_error.
556     report_fatal_error("Global variable '" + GV->getName() +
557                        "' section type or attributes does not match previous"
558                        " section specifier");
559   }
560 
561   return S;
562 }
563 
564 const MCSection *TargetLoweringObjectFileMachO::
565 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
566                        Mangler &Mang, const TargetMachine &TM) const {
567   checkMachOComdat(GV);
568 
569   // Handle thread local data.
570   if (Kind.isThreadBSS()) return TLSBSSSection;
571   if (Kind.isThreadData()) return TLSDataSection;
572 
573   if (Kind.isText())
574     return GV->isWeakForLinker() ? TextCoalSection : TextSection;
575 
576   // If this is weak/linkonce, put this in a coalescable section, either in text
577   // or data depending on if it is writable.
578   if (GV->isWeakForLinker()) {
579     if (Kind.isReadOnly())
580       return ConstTextCoalSection;
581     return DataCoalSection;
582   }
583 
584   // FIXME: Alignment check should be handled by section classifier.
585   if (Kind.isMergeable1ByteCString() &&
586       TM.getDataLayout()->getPreferredAlignment(cast<GlobalVariable>(GV)) < 32)
587     return CStringSection;
588 
589   // Do not put 16-bit arrays in the UString section if they have an
590   // externally visible label, this runs into issues with certain linker
591   // versions.
592   if (Kind.isMergeable2ByteCString() && !GV->hasExternalLinkage() &&
593       TM.getDataLayout()->getPreferredAlignment(cast<GlobalVariable>(GV)) < 32)
594     return UStringSection;
595 
596   // With MachO only variables whose corresponding symbol starts with 'l' or
597   // 'L' can be merged, so we only try merging GVs with private linkage.
598   if (GV->hasPrivateLinkage() && Kind.isMergeableConst()) {
599     if (Kind.isMergeableConst4())
600       return FourByteConstantSection;
601     if (Kind.isMergeableConst8())
602       return EightByteConstantSection;
603     if (Kind.isMergeableConst16())
604       return SixteenByteConstantSection;
605   }
606 
607   // Otherwise, if it is readonly, but not something we can specially optimize,
608   // just drop it in .const.
609   if (Kind.isReadOnly())
610     return ReadOnlySection;
611 
612   // If this is marked const, put it into a const section.  But if the dynamic
613   // linker needs to write to it, put it in the data segment.
614   if (Kind.isReadOnlyWithRel())
615     return ConstDataSection;
616 
617   // Put zero initialized globals with strong external linkage in the
618   // DATA, __common section with the .zerofill directive.
619   if (Kind.isBSSExtern())
620     return DataCommonSection;
621 
622   // Put zero initialized globals with local linkage in __DATA,__bss directive
623   // with the .zerofill directive (aka .lcomm).
624   if (Kind.isBSSLocal())
625     return DataBSSSection;
626 
627   // Otherwise, just drop the variable in the normal data section.
628   return DataSection;
629 }
630 
631 const MCSection *
632 TargetLoweringObjectFileMachO::getSectionForConstant(SectionKind Kind,
633                                                      const Constant *C) const {
634   // If this constant requires a relocation, we have to put it in the data
635   // segment, not in the text segment.
636   if (Kind.isDataRel() || Kind.isReadOnlyWithRel())
637     return ConstDataSection;
638 
639   if (Kind.isMergeableConst4())
640     return FourByteConstantSection;
641   if (Kind.isMergeableConst8())
642     return EightByteConstantSection;
643   if (Kind.isMergeableConst16())
644     return SixteenByteConstantSection;
645   return ReadOnlySection;  // .const
646 }
647 
648 const MCExpr *TargetLoweringObjectFileMachO::getTTypeGlobalReference(
649     const GlobalValue *GV, unsigned Encoding, Mangler &Mang,
650     const TargetMachine &TM, MachineModuleInfo *MMI,
651     MCStreamer &Streamer) const {
652   // The mach-o version of this method defaults to returning a stub reference.
653 
654   if (Encoding & DW_EH_PE_indirect) {
655     MachineModuleInfoMachO &MachOMMI =
656       MMI->getObjFileInfo<MachineModuleInfoMachO>();
657 
658     MCSymbol *SSym =
659         getSymbolWithGlobalValueBase(GV, "$non_lazy_ptr", Mang, TM);
660 
661     // Add information about the stub reference to MachOMMI so that the stub
662     // gets emitted by the asmprinter.
663     MachineModuleInfoImpl::StubValueTy &StubSym =
664       GV->hasHiddenVisibility() ? MachOMMI.getHiddenGVStubEntry(SSym) :
665                                   MachOMMI.getGVStubEntry(SSym);
666     if (!StubSym.getPointer()) {
667       MCSymbol *Sym = TM.getSymbol(GV, Mang);
668       StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
669     }
670 
671     return TargetLoweringObjectFile::
672       getTTypeReference(MCSymbolRefExpr::Create(SSym, getContext()),
673                         Encoding & ~dwarf::DW_EH_PE_indirect, Streamer);
674   }
675 
676   return TargetLoweringObjectFile::getTTypeGlobalReference(GV, Encoding, Mang,
677                                                            TM, MMI, Streamer);
678 }
679 
680 MCSymbol *TargetLoweringObjectFileMachO::getCFIPersonalitySymbol(
681     const GlobalValue *GV, Mangler &Mang, const TargetMachine &TM,
682     MachineModuleInfo *MMI) const {
683   // The mach-o version of this method defaults to returning a stub reference.
684   MachineModuleInfoMachO &MachOMMI =
685     MMI->getObjFileInfo<MachineModuleInfoMachO>();
686 
687   MCSymbol *SSym = getSymbolWithGlobalValueBase(GV, "$non_lazy_ptr", Mang, TM);
688 
689   // Add information about the stub reference to MachOMMI so that the stub
690   // gets emitted by the asmprinter.
691   MachineModuleInfoImpl::StubValueTy &StubSym = MachOMMI.getGVStubEntry(SSym);
692   if (!StubSym.getPointer()) {
693     MCSymbol *Sym = TM.getSymbol(GV, Mang);
694     StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
695   }
696 
697   return SSym;
698 }
699 
700 //===----------------------------------------------------------------------===//
701 //                                  COFF
702 //===----------------------------------------------------------------------===//
703 
704 static unsigned
705 getCOFFSectionFlags(SectionKind K) {
706   unsigned Flags = 0;
707 
708   if (K.isMetadata())
709     Flags |=
710       COFF::IMAGE_SCN_MEM_DISCARDABLE;
711   else if (K.isText())
712     Flags |=
713       COFF::IMAGE_SCN_MEM_EXECUTE |
714       COFF::IMAGE_SCN_MEM_READ |
715       COFF::IMAGE_SCN_CNT_CODE;
716   else if (K.isBSS())
717     Flags |=
718       COFF::IMAGE_SCN_CNT_UNINITIALIZED_DATA |
719       COFF::IMAGE_SCN_MEM_READ |
720       COFF::IMAGE_SCN_MEM_WRITE;
721   else if (K.isThreadLocal())
722     Flags |=
723       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
724       COFF::IMAGE_SCN_MEM_READ |
725       COFF::IMAGE_SCN_MEM_WRITE;
726   else if (K.isReadOnly() || K.isReadOnlyWithRel())
727     Flags |=
728       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
729       COFF::IMAGE_SCN_MEM_READ;
730   else if (K.isWriteable())
731     Flags |=
732       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
733       COFF::IMAGE_SCN_MEM_READ |
734       COFF::IMAGE_SCN_MEM_WRITE;
735 
736   return Flags;
737 }
738 
739 static const GlobalValue *getComdatGVForCOFF(const GlobalValue *GV) {
740   const Comdat *C = GV->getComdat();
741   assert(C && "expected GV to have a Comdat!");
742 
743   StringRef ComdatGVName = C->getName();
744   const GlobalValue *ComdatGV = GV->getParent()->getNamedValue(ComdatGVName);
745   if (!ComdatGV)
746     report_fatal_error("Associative COMDAT symbol '" + ComdatGVName +
747                        "' does not exist.");
748 
749   if (ComdatGV->getComdat() != C)
750     report_fatal_error("Associative COMDAT symbol '" + ComdatGVName +
751                        "' is not a key for its COMDAT.");
752 
753   return ComdatGV;
754 }
755 
756 static int getSelectionForCOFF(const GlobalValue *GV) {
757   if (const Comdat *C = GV->getComdat()) {
758     const GlobalValue *ComdatKey = getComdatGVForCOFF(GV);
759     if (const auto *GA = dyn_cast<GlobalAlias>(ComdatKey))
760       ComdatKey = GA->getBaseObject();
761     if (ComdatKey == GV) {
762       switch (C->getSelectionKind()) {
763       case Comdat::Any:
764         return COFF::IMAGE_COMDAT_SELECT_ANY;
765       case Comdat::ExactMatch:
766         return COFF::IMAGE_COMDAT_SELECT_EXACT_MATCH;
767       case Comdat::Largest:
768         return COFF::IMAGE_COMDAT_SELECT_LARGEST;
769       case Comdat::NoDuplicates:
770         return COFF::IMAGE_COMDAT_SELECT_NODUPLICATES;
771       case Comdat::SameSize:
772         return COFF::IMAGE_COMDAT_SELECT_SAME_SIZE;
773       }
774     } else {
775       return COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE;
776     }
777   } else if (GV->isWeakForLinker()) {
778     return COFF::IMAGE_COMDAT_SELECT_ANY;
779   }
780   return 0;
781 }
782 
783 const MCSection *TargetLoweringObjectFileCOFF::getExplicitSectionGlobal(
784     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
785     const TargetMachine &TM) const {
786   int Selection = 0;
787   unsigned Characteristics = getCOFFSectionFlags(Kind);
788   StringRef Name = GV->getSection();
789   StringRef COMDATSymName = "";
790   if (GV->hasComdat()) {
791     Selection = getSelectionForCOFF(GV);
792     const GlobalValue *ComdatGV;
793     if (Selection == COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE)
794       ComdatGV = getComdatGVForCOFF(GV);
795     else
796       ComdatGV = GV;
797 
798     if (!ComdatGV->hasPrivateLinkage()) {
799       MCSymbol *Sym = TM.getSymbol(ComdatGV, Mang);
800       COMDATSymName = Sym->getName();
801       Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
802     } else {
803       Selection = 0;
804     }
805   }
806   return getContext().getCOFFSection(Name,
807                                      Characteristics,
808                                      Kind,
809                                      COMDATSymName,
810                                      Selection);
811 }
812 
813 static const char *getCOFFSectionNameForUniqueGlobal(SectionKind Kind) {
814   if (Kind.isText())
815     return ".text";
816   if (Kind.isBSS())
817     return ".bss";
818   if (Kind.isThreadLocal())
819     return ".tls$";
820   if (Kind.isReadOnly() || Kind.isReadOnlyWithRel())
821     return ".rdata";
822   return ".data";
823 }
824 
825 
826 const MCSection *TargetLoweringObjectFileCOFF::
827 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
828                        Mangler &Mang, const TargetMachine &TM) const {
829   // If we have -ffunction-sections then we should emit the global value to a
830   // uniqued section specifically for it.
831   bool EmitUniquedSection;
832   if (Kind.isText())
833     EmitUniquedSection = TM.getFunctionSections();
834   else
835     EmitUniquedSection = TM.getDataSections();
836 
837   if ((EmitUniquedSection && !Kind.isCommon()) || GV->hasComdat()) {
838     const char *Name = getCOFFSectionNameForUniqueGlobal(Kind);
839     unsigned Characteristics = getCOFFSectionFlags(Kind);
840 
841     Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
842     int Selection = getSelectionForCOFF(GV);
843     if (!Selection)
844       Selection = COFF::IMAGE_COMDAT_SELECT_NODUPLICATES;
845     const GlobalValue *ComdatGV;
846     if (GV->hasComdat())
847       ComdatGV = getComdatGVForCOFF(GV);
848     else
849       ComdatGV = GV;
850 
851     if (!ComdatGV->hasPrivateLinkage()) {
852       MCSymbol *Sym = TM.getSymbol(ComdatGV, Mang);
853       StringRef COMDATSymName = Sym->getName();
854       return getContext().getCOFFSection(Name, Characteristics, Kind,
855                                          COMDATSymName, Selection);
856     }
857   }
858 
859   if (Kind.isText())
860     return TextSection;
861 
862   if (Kind.isThreadLocal())
863     return TLSDataSection;
864 
865   if (Kind.isReadOnly() || Kind.isReadOnlyWithRel())
866     return ReadOnlySection;
867 
868   // Note: we claim that common symbols are put in BSSSection, but they are
869   // really emitted with the magic .comm directive, which creates a symbol table
870   // entry but not a section.
871   if (Kind.isBSS() || Kind.isCommon())
872     return BSSSection;
873 
874   return DataSection;
875 }
876 
877 StringRef TargetLoweringObjectFileCOFF::
878 getDepLibFromLinkerOpt(StringRef LinkerOption) const {
879   const char *LibCmd = "/DEFAULTLIB:";
880   if (LinkerOption.startswith(LibCmd))
881     return LinkerOption.substr(strlen(LibCmd));
882   return StringRef();
883 }
884 
885 void TargetLoweringObjectFileCOFF::
886 emitModuleFlags(MCStreamer &Streamer,
887                 ArrayRef<Module::ModuleFlagEntry> ModuleFlags,
888                 Mangler &Mang, const TargetMachine &TM) const {
889   MDNode *LinkerOptions = nullptr;
890 
891   // Look for the "Linker Options" flag, since it's the only one we support.
892   for (ArrayRef<Module::ModuleFlagEntry>::iterator
893        i = ModuleFlags.begin(), e = ModuleFlags.end(); i != e; ++i) {
894     const Module::ModuleFlagEntry &MFE = *i;
895     StringRef Key = MFE.Key->getString();
896     Metadata *Val = MFE.Val;
897     if (Key == "Linker Options") {
898       LinkerOptions = cast<MDNode>(Val);
899       break;
900     }
901   }
902   if (!LinkerOptions)
903     return;
904 
905   // Emit the linker options to the linker .drectve section.  According to the
906   // spec, this section is a space-separated string containing flags for linker.
907   const MCSection *Sec = getDrectveSection();
908   Streamer.SwitchSection(Sec);
909   for (unsigned i = 0, e = LinkerOptions->getNumOperands(); i != e; ++i) {
910     MDNode *MDOptions = cast<MDNode>(LinkerOptions->getOperand(i));
911     for (unsigned ii = 0, ie = MDOptions->getNumOperands(); ii != ie; ++ii) {
912       MDString *MDOption = cast<MDString>(MDOptions->getOperand(ii));
913       // Lead with a space for consistency with our dllexport implementation.
914       std::string Directive(" ");
915       Directive.append(MDOption->getString());
916       Streamer.EmitBytes(Directive);
917     }
918   }
919 }
920 
921 const MCSection *TargetLoweringObjectFileCOFF::getStaticCtorSection(
922     unsigned Priority, const MCSymbol *KeySym) const {
923   return getContext().getAssociativeCOFFSection(
924       cast<MCSectionCOFF>(StaticCtorSection), KeySym);
925 }
926 
927 const MCSection *TargetLoweringObjectFileCOFF::getStaticDtorSection(
928     unsigned Priority, const MCSymbol *KeySym) const {
929   return getContext().getAssociativeCOFFSection(
930       cast<MCSectionCOFF>(StaticDtorSection), KeySym);
931 }
932