xref: /llvm-project/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp (revision b6a812ebb10c074266d6e4f9d2e2405bf57e4788) 
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 
168 static unsigned
169 getELFSectionFlags(SectionKind K, bool InCOMDAT) {
170   unsigned Flags = 0;
171 
172   if (!K.isMetadata())
173     Flags |= ELF::SHF_ALLOC;
174 
175   if (K.isText())
176     Flags |= ELF::SHF_EXECINSTR;
177 
178   if (K.isWriteable())
179     Flags |= ELF::SHF_WRITE;
180 
181   if (K.isThreadLocal())
182     Flags |= ELF::SHF_TLS;
183 
184   // FIXME: There is nothing in ELF preventing an SHF_MERGE from being
185   // in a comdat. We just avoid it for now because we don't print
186   // those .sections correctly.
187   if (!InCOMDAT && (K.isMergeableCString() || K.isMergeableConst()))
188     Flags |= ELF::SHF_MERGE;
189 
190   if (K.isMergeableCString())
191     Flags |= ELF::SHF_STRINGS;
192 
193   return Flags;
194 }
195 
196 static const Comdat *getELFComdat(const GlobalValue *GV) {
197   const Comdat *C = GV->getComdat();
198   if (!C)
199     return nullptr;
200 
201   if (C->getSelectionKind() != Comdat::Any)
202     report_fatal_error("ELF COMDATs only support SelectionKind::Any, '" +
203                        C->getName() + "' cannot be lowered.");
204 
205   return C;
206 }
207 
208 const MCSection *TargetLoweringObjectFileELF::getExplicitSectionGlobal(
209     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
210     const TargetMachine &TM) const {
211   StringRef SectionName = GV->getSection();
212 
213   // Infer section flags from the section name if we can.
214   Kind = getELFKindForNamedSection(SectionName, Kind);
215 
216   StringRef Group = "";
217   unsigned Flags = getELFSectionFlags(Kind, GV->hasComdat());
218   if (const Comdat *C = getELFComdat(GV)) {
219     Group = C->getName();
220     Flags |= ELF::SHF_GROUP;
221   }
222   return getContext().getELFSection(SectionName,
223                                     getELFSectionType(SectionName, Kind), Flags,
224                                     /*EntrySize=*/0, Group);
225 }
226 
227 /// Return the section prefix name used by options FunctionsSections and
228 /// DataSections.
229 static StringRef getSectionPrefixForGlobal(SectionKind Kind) {
230   if (Kind.isText())
231     return ".text";
232   if (Kind.isReadOnly())
233     return ".rodata";
234   if (Kind.isBSS())
235     return ".bss";
236   if (Kind.isThreadData())
237     return ".tdata";
238   if (Kind.isThreadBSS())
239     return ".tbss";
240   if (Kind.isDataNoRel())
241     return ".data";
242   if (Kind.isDataRelLocal())
243     return ".data.rel.local";
244   if (Kind.isDataRel())
245     return ".data.rel";
246   if (Kind.isReadOnlyWithRelLocal())
247     return ".data.rel.ro.local";
248   assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
249   return ".data.rel.ro";
250 }
251 
252 const MCSection *TargetLoweringObjectFileELF::
253 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
254                        Mangler &Mang, const TargetMachine &TM) const {
255   unsigned Flags = getELFSectionFlags(Kind, GV->hasComdat());
256 
257   // If we have -ffunction-section or -fdata-section then we should emit the
258   // global value to a uniqued section specifically for it.
259   bool EmitUniquedSection = false;
260   if (!(Flags & ELF::SHF_MERGE) && !Kind.isCommon()) {
261     if (Kind.isText())
262       EmitUniquedSection = TM.getFunctionSections();
263     else
264       EmitUniquedSection = TM.getDataSections();
265   }
266 
267   if (EmitUniquedSection || GV->hasComdat()) {
268     StringRef Prefix = getSectionPrefixForGlobal(Kind);
269 
270     SmallString<128> Name(Prefix);
271     bool UniqueSectionNames = TM.getUniqueSectionNames();
272     if (UniqueSectionNames) {
273       Name.push_back('.');
274       TM.getNameWithPrefix(Name, GV, Mang, true);
275     }
276     StringRef Group = "";
277     if (const Comdat *C = getELFComdat(GV)) {
278       Flags |= ELF::SHF_GROUP;
279       Group = C->getName();
280     }
281 
282     return getContext().getELFSection(Name, getELFSectionType(Name, Kind),
283                                       Flags, 0, Group, !UniqueSectionNames);
284   }
285 
286   if (Kind.isText()) return TextSection;
287 
288   if (Kind.isMergeableCString()) {
289 
290     // We also need alignment here.
291     // FIXME: this is getting the alignment of the character, not the
292     // alignment of the global!
293     unsigned Align =
294         TM.getDataLayout()->getPreferredAlignment(cast<GlobalVariable>(GV));
295 
296     unsigned EntrySize = 1;
297     if (Kind.isMergeable2ByteCString())
298       EntrySize = 2;
299     else if (Kind.isMergeable4ByteCString())
300       EntrySize = 4;
301     else
302       assert(Kind.isMergeable1ByteCString() && "unknown string width");
303 
304     std::string SizeSpec = ".rodata.str" + utostr(EntrySize) + ".";
305     std::string Name = SizeSpec + utostr(Align);
306     return getContext().getELFSection(
307         Name, ELF::SHT_PROGBITS,
308         ELF::SHF_ALLOC | ELF::SHF_MERGE | ELF::SHF_STRINGS, EntrySize, "");
309   }
310 
311   if (Kind.isMergeableConst()) {
312     if (Kind.isMergeableConst4() && MergeableConst4Section)
313       return MergeableConst4Section;
314     if (Kind.isMergeableConst8() && MergeableConst8Section)
315       return MergeableConst8Section;
316     if (Kind.isMergeableConst16() && MergeableConst16Section)
317       return MergeableConst16Section;
318     return ReadOnlySection;  // .const
319   }
320 
321   if (Kind.isReadOnly())             return ReadOnlySection;
322 
323   if (Kind.isThreadData())           return TLSDataSection;
324   if (Kind.isThreadBSS())            return TLSBSSSection;
325 
326   // Note: we claim that common symbols are put in BSSSection, but they are
327   // really emitted with the magic .comm directive, which creates a symbol table
328   // entry but not a section.
329   if (Kind.isBSS() || Kind.isCommon()) return BSSSection;
330 
331   if (Kind.isDataNoRel())            return DataSection;
332   if (Kind.isDataRelLocal())         return DataRelLocalSection;
333   if (Kind.isDataRel())              return DataRelSection;
334   if (Kind.isReadOnlyWithRelLocal()) return DataRelROLocalSection;
335 
336   assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
337   return DataRelROSection;
338 }
339 
340 const MCSection *TargetLoweringObjectFileELF::getSectionForJumpTable(
341     const Function &F, Mangler &Mang, const TargetMachine &TM) const {
342   // If the function can be removed, produce a unique section so that
343   // the table doesn't prevent the removal.
344   const Comdat *C = F.getComdat();
345   bool EmitUniqueSection = TM.getFunctionSections() || C;
346   if (!EmitUniqueSection)
347     return ReadOnlySection;
348 
349   SmallString<128> Name(".rodata.");
350   TM.getNameWithPrefix(Name, &F, Mang, true);
351 
352   unsigned Flags = ELF::SHF_ALLOC;
353   StringRef Group = "";
354   if (C) {
355     Flags |= ELF::SHF_GROUP;
356     Group = C->getName();
357   }
358 
359   return getContext().getELFSection(Name, ELF::SHT_PROGBITS, Flags, 0, Group);
360 }
361 
362 bool TargetLoweringObjectFileELF::shouldPutJumpTableInFunctionSection(
363     bool UsesLabelDifference, const Function &F) const {
364   // We can always create relative relocations, so use another section
365   // that can be marked non-executable.
366   return false;
367 }
368 
369 /// getSectionForConstant - Given a mergeable constant with the
370 /// specified size and relocation information, return a section that it
371 /// should be placed in.
372 const MCSection *
373 TargetLoweringObjectFileELF::getSectionForConstant(SectionKind Kind,
374                                                    const Constant *C) const {
375   if (Kind.isMergeableConst4() && MergeableConst4Section)
376     return MergeableConst4Section;
377   if (Kind.isMergeableConst8() && MergeableConst8Section)
378     return MergeableConst8Section;
379   if (Kind.isMergeableConst16() && MergeableConst16Section)
380     return MergeableConst16Section;
381   if (Kind.isReadOnly())
382     return ReadOnlySection;
383 
384   if (Kind.isReadOnlyWithRelLocal()) return DataRelROLocalSection;
385   assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
386   return DataRelROSection;
387 }
388 
389 static const MCSectionELF *getStaticStructorSection(MCContext &Ctx,
390                                                     bool UseInitArray,
391                                                     bool IsCtor,
392                                                     unsigned Priority,
393                                                     const MCSymbol *KeySym) {
394   std::string Name;
395   unsigned Type;
396   unsigned Flags = ELF::SHF_ALLOC | ELF::SHF_WRITE;
397   StringRef COMDAT = KeySym ? KeySym->getName() : "";
398 
399   if (KeySym)
400     Flags |= ELF::SHF_GROUP;
401 
402   if (UseInitArray) {
403     if (IsCtor) {
404       Type = ELF::SHT_INIT_ARRAY;
405       Name = ".init_array";
406     } else {
407       Type = ELF::SHT_FINI_ARRAY;
408       Name = ".fini_array";
409     }
410     if (Priority != 65535) {
411       Name += '.';
412       Name += utostr(Priority);
413     }
414   } else {
415     // The default scheme is .ctor / .dtor, so we have to invert the priority
416     // numbering.
417     if (IsCtor)
418       Name = ".ctors";
419     else
420       Name = ".dtors";
421     if (Priority != 65535) {
422       Name += '.';
423       Name += utostr(65535 - Priority);
424     }
425     Type = ELF::SHT_PROGBITS;
426   }
427 
428   return Ctx.getELFSection(Name, Type, Flags, 0, COMDAT);
429 }
430 
431 const MCSection *TargetLoweringObjectFileELF::getStaticCtorSection(
432     unsigned Priority, const MCSymbol *KeySym) const {
433   return getStaticStructorSection(getContext(), UseInitArray, true, Priority,
434                                   KeySym);
435 }
436 
437 const MCSection *TargetLoweringObjectFileELF::getStaticDtorSection(
438     unsigned Priority, const MCSymbol *KeySym) const {
439   return getStaticStructorSection(getContext(), UseInitArray, false, Priority,
440                                   KeySym);
441 }
442 
443 void
444 TargetLoweringObjectFileELF::InitializeELF(bool UseInitArray_) {
445   UseInitArray = UseInitArray_;
446   if (!UseInitArray)
447     return;
448 
449   StaticCtorSection = getContext().getELFSection(
450       ".init_array", ELF::SHT_INIT_ARRAY, ELF::SHF_WRITE | ELF::SHF_ALLOC);
451   StaticDtorSection = getContext().getELFSection(
452       ".fini_array", ELF::SHT_FINI_ARRAY, ELF::SHF_WRITE | ELF::SHF_ALLOC);
453 }
454 
455 //===----------------------------------------------------------------------===//
456 //                                 MachO
457 //===----------------------------------------------------------------------===//
458 
459 /// getDepLibFromLinkerOpt - Extract the dependent library name from a linker
460 /// option string. Returns StringRef() if the option does not specify a library.
461 StringRef TargetLoweringObjectFileMachO::
462 getDepLibFromLinkerOpt(StringRef LinkerOption) const {
463   const char *LibCmd = "-l";
464   if (LinkerOption.startswith(LibCmd))
465     return LinkerOption.substr(strlen(LibCmd));
466   return StringRef();
467 }
468 
469 /// emitModuleFlags - Perform code emission for module flags.
470 void TargetLoweringObjectFileMachO::
471 emitModuleFlags(MCStreamer &Streamer,
472                 ArrayRef<Module::ModuleFlagEntry> ModuleFlags,
473                 Mangler &Mang, const TargetMachine &TM) const {
474   unsigned VersionVal = 0;
475   unsigned ImageInfoFlags = 0;
476   MDNode *LinkerOptions = nullptr;
477   StringRef SectionVal;
478 
479   for (ArrayRef<Module::ModuleFlagEntry>::iterator
480          i = ModuleFlags.begin(), e = ModuleFlags.end(); i != e; ++i) {
481     const Module::ModuleFlagEntry &MFE = *i;
482 
483     // Ignore flags with 'Require' behavior.
484     if (MFE.Behavior == Module::Require)
485       continue;
486 
487     StringRef Key = MFE.Key->getString();
488     Metadata *Val = MFE.Val;
489 
490     if (Key == "Objective-C Image Info Version") {
491       VersionVal = mdconst::extract<ConstantInt>(Val)->getZExtValue();
492     } else if (Key == "Objective-C Garbage Collection" ||
493                Key == "Objective-C GC Only" ||
494                Key == "Objective-C Is Simulated" ||
495                Key == "Objective-C Image Swift Version") {
496       ImageInfoFlags |= mdconst::extract<ConstantInt>(Val)->getZExtValue();
497     } else if (Key == "Objective-C Image Info Section") {
498       SectionVal = cast<MDString>(Val)->getString();
499     } else if (Key == "Linker Options") {
500       LinkerOptions = cast<MDNode>(Val);
501     }
502   }
503 
504   // Emit the linker options if present.
505   if (LinkerOptions) {
506     for (unsigned i = 0, e = LinkerOptions->getNumOperands(); i != e; ++i) {
507       MDNode *MDOptions = cast<MDNode>(LinkerOptions->getOperand(i));
508       SmallVector<std::string, 4> StrOptions;
509 
510       // Convert to strings.
511       for (unsigned ii = 0, ie = MDOptions->getNumOperands(); ii != ie; ++ii) {
512         MDString *MDOption = cast<MDString>(MDOptions->getOperand(ii));
513         StrOptions.push_back(MDOption->getString());
514       }
515 
516       Streamer.EmitLinkerOptions(StrOptions);
517     }
518   }
519 
520   // The section is mandatory. If we don't have it, then we don't have GC info.
521   if (SectionVal.empty()) return;
522 
523   StringRef Segment, Section;
524   unsigned TAA = 0, StubSize = 0;
525   bool TAAParsed;
526   std::string ErrorCode =
527     MCSectionMachO::ParseSectionSpecifier(SectionVal, Segment, Section,
528                                           TAA, TAAParsed, StubSize);
529   if (!ErrorCode.empty())
530     // If invalid, report the error with report_fatal_error.
531     report_fatal_error("Invalid section specifier '" + Section + "': " +
532                        ErrorCode + ".");
533 
534   // Get the section.
535   const MCSectionMachO *S =
536     getContext().getMachOSection(Segment, Section, TAA, StubSize,
537                                  SectionKind::getDataNoRel());
538   Streamer.SwitchSection(S);
539   Streamer.EmitLabel(getContext().
540                      GetOrCreateSymbol(StringRef("L_OBJC_IMAGE_INFO")));
541   Streamer.EmitIntValue(VersionVal, 4);
542   Streamer.EmitIntValue(ImageInfoFlags, 4);
543   Streamer.AddBlankLine();
544 }
545 
546 static void checkMachOComdat(const GlobalValue *GV) {
547   const Comdat *C = GV->getComdat();
548   if (!C)
549     return;
550 
551   report_fatal_error("MachO doesn't support COMDATs, '" + C->getName() +
552                      "' cannot be lowered.");
553 }
554 
555 const MCSection *TargetLoweringObjectFileMachO::getExplicitSectionGlobal(
556     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
557     const TargetMachine &TM) const {
558   // Parse the section specifier and create it if valid.
559   StringRef Segment, Section;
560   unsigned TAA = 0, StubSize = 0;
561   bool TAAParsed;
562 
563   checkMachOComdat(GV);
564 
565   std::string ErrorCode =
566     MCSectionMachO::ParseSectionSpecifier(GV->getSection(), Segment, Section,
567                                           TAA, TAAParsed, StubSize);
568   if (!ErrorCode.empty()) {
569     // If invalid, report the error with report_fatal_error.
570     report_fatal_error("Global variable '" + GV->getName() +
571                        "' has an invalid section specifier '" +
572                        GV->getSection() + "': " + ErrorCode + ".");
573   }
574 
575   // Get the section.
576   const MCSectionMachO *S =
577     getContext().getMachOSection(Segment, Section, TAA, StubSize, Kind);
578 
579   // If TAA wasn't set by ParseSectionSpecifier() above,
580   // use the value returned by getMachOSection() as a default.
581   if (!TAAParsed)
582     TAA = S->getTypeAndAttributes();
583 
584   // Okay, now that we got the section, verify that the TAA & StubSize agree.
585   // If the user declared multiple globals with different section flags, we need
586   // to reject it here.
587   if (S->getTypeAndAttributes() != TAA || S->getStubSize() != StubSize) {
588     // If invalid, report the error with report_fatal_error.
589     report_fatal_error("Global variable '" + GV->getName() +
590                        "' section type or attributes does not match previous"
591                        " section specifier");
592   }
593 
594   return S;
595 }
596 
597 const MCSection *TargetLoweringObjectFileMachO::
598 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
599                        Mangler &Mang, const TargetMachine &TM) const {
600   checkMachOComdat(GV);
601 
602   // Handle thread local data.
603   if (Kind.isThreadBSS()) return TLSBSSSection;
604   if (Kind.isThreadData()) return TLSDataSection;
605 
606   if (Kind.isText())
607     return GV->isWeakForLinker() ? TextCoalSection : TextSection;
608 
609   // If this is weak/linkonce, put this in a coalescable section, either in text
610   // or data depending on if it is writable.
611   if (GV->isWeakForLinker()) {
612     if (Kind.isReadOnly())
613       return ConstTextCoalSection;
614     return DataCoalSection;
615   }
616 
617   // FIXME: Alignment check should be handled by section classifier.
618   if (Kind.isMergeable1ByteCString() &&
619       TM.getDataLayout()->getPreferredAlignment(cast<GlobalVariable>(GV)) < 32)
620     return CStringSection;
621 
622   // Do not put 16-bit arrays in the UString section if they have an
623   // externally visible label, this runs into issues with certain linker
624   // versions.
625   if (Kind.isMergeable2ByteCString() && !GV->hasExternalLinkage() &&
626       TM.getDataLayout()->getPreferredAlignment(cast<GlobalVariable>(GV)) < 32)
627     return UStringSection;
628 
629   // With MachO only variables whose corresponding symbol starts with 'l' or
630   // 'L' can be merged, so we only try merging GVs with private linkage.
631   if (GV->hasPrivateLinkage() && Kind.isMergeableConst()) {
632     if (Kind.isMergeableConst4())
633       return FourByteConstantSection;
634     if (Kind.isMergeableConst8())
635       return EightByteConstantSection;
636     if (Kind.isMergeableConst16())
637       return SixteenByteConstantSection;
638   }
639 
640   // Otherwise, if it is readonly, but not something we can specially optimize,
641   // just drop it in .const.
642   if (Kind.isReadOnly())
643     return ReadOnlySection;
644 
645   // If this is marked const, put it into a const section.  But if the dynamic
646   // linker needs to write to it, put it in the data segment.
647   if (Kind.isReadOnlyWithRel())
648     return ConstDataSection;
649 
650   // Put zero initialized globals with strong external linkage in the
651   // DATA, __common section with the .zerofill directive.
652   if (Kind.isBSSExtern())
653     return DataCommonSection;
654 
655   // Put zero initialized globals with local linkage in __DATA,__bss directive
656   // with the .zerofill directive (aka .lcomm).
657   if (Kind.isBSSLocal())
658     return DataBSSSection;
659 
660   // Otherwise, just drop the variable in the normal data section.
661   return DataSection;
662 }
663 
664 const MCSection *
665 TargetLoweringObjectFileMachO::getSectionForConstant(SectionKind Kind,
666                                                      const Constant *C) const {
667   // If this constant requires a relocation, we have to put it in the data
668   // segment, not in the text segment.
669   if (Kind.isDataRel() || Kind.isReadOnlyWithRel())
670     return ConstDataSection;
671 
672   if (Kind.isMergeableConst4())
673     return FourByteConstantSection;
674   if (Kind.isMergeableConst8())
675     return EightByteConstantSection;
676   if (Kind.isMergeableConst16())
677     return SixteenByteConstantSection;
678   return ReadOnlySection;  // .const
679 }
680 
681 const MCExpr *TargetLoweringObjectFileMachO::getTTypeGlobalReference(
682     const GlobalValue *GV, unsigned Encoding, Mangler &Mang,
683     const TargetMachine &TM, MachineModuleInfo *MMI,
684     MCStreamer &Streamer) const {
685   // The mach-o version of this method defaults to returning a stub reference.
686 
687   if (Encoding & DW_EH_PE_indirect) {
688     MachineModuleInfoMachO &MachOMMI =
689       MMI->getObjFileInfo<MachineModuleInfoMachO>();
690 
691     MCSymbol *SSym =
692         getSymbolWithGlobalValueBase(GV, "$non_lazy_ptr", Mang, TM);
693 
694     // Add information about the stub reference to MachOMMI so that the stub
695     // gets emitted by the asmprinter.
696     MachineModuleInfoImpl::StubValueTy &StubSym =
697       GV->hasHiddenVisibility() ? MachOMMI.getHiddenGVStubEntry(SSym) :
698                                   MachOMMI.getGVStubEntry(SSym);
699     if (!StubSym.getPointer()) {
700       MCSymbol *Sym = TM.getSymbol(GV, Mang);
701       StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
702     }
703 
704     return TargetLoweringObjectFile::
705       getTTypeReference(MCSymbolRefExpr::Create(SSym, getContext()),
706                         Encoding & ~dwarf::DW_EH_PE_indirect, Streamer);
707   }
708 
709   return TargetLoweringObjectFile::getTTypeGlobalReference(GV, Encoding, Mang,
710                                                            TM, MMI, Streamer);
711 }
712 
713 MCSymbol *TargetLoweringObjectFileMachO::getCFIPersonalitySymbol(
714     const GlobalValue *GV, Mangler &Mang, const TargetMachine &TM,
715     MachineModuleInfo *MMI) const {
716   // The mach-o version of this method defaults to returning a stub reference.
717   MachineModuleInfoMachO &MachOMMI =
718     MMI->getObjFileInfo<MachineModuleInfoMachO>();
719 
720   MCSymbol *SSym = getSymbolWithGlobalValueBase(GV, "$non_lazy_ptr", Mang, TM);
721 
722   // Add information about the stub reference to MachOMMI so that the stub
723   // gets emitted by the asmprinter.
724   MachineModuleInfoImpl::StubValueTy &StubSym = MachOMMI.getGVStubEntry(SSym);
725   if (!StubSym.getPointer()) {
726     MCSymbol *Sym = TM.getSymbol(GV, Mang);
727     StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
728   }
729 
730   return SSym;
731 }
732 
733 //===----------------------------------------------------------------------===//
734 //                                  COFF
735 //===----------------------------------------------------------------------===//
736 
737 static unsigned
738 getCOFFSectionFlags(SectionKind K) {
739   unsigned Flags = 0;
740 
741   if (K.isMetadata())
742     Flags |=
743       COFF::IMAGE_SCN_MEM_DISCARDABLE;
744   else if (K.isText())
745     Flags |=
746       COFF::IMAGE_SCN_MEM_EXECUTE |
747       COFF::IMAGE_SCN_MEM_READ |
748       COFF::IMAGE_SCN_CNT_CODE;
749   else if (K.isBSS())
750     Flags |=
751       COFF::IMAGE_SCN_CNT_UNINITIALIZED_DATA |
752       COFF::IMAGE_SCN_MEM_READ |
753       COFF::IMAGE_SCN_MEM_WRITE;
754   else if (K.isThreadLocal())
755     Flags |=
756       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
757       COFF::IMAGE_SCN_MEM_READ |
758       COFF::IMAGE_SCN_MEM_WRITE;
759   else if (K.isReadOnly() || K.isReadOnlyWithRel())
760     Flags |=
761       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
762       COFF::IMAGE_SCN_MEM_READ;
763   else if (K.isWriteable())
764     Flags |=
765       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
766       COFF::IMAGE_SCN_MEM_READ |
767       COFF::IMAGE_SCN_MEM_WRITE;
768 
769   return Flags;
770 }
771 
772 static const GlobalValue *getComdatGVForCOFF(const GlobalValue *GV) {
773   const Comdat *C = GV->getComdat();
774   assert(C && "expected GV to have a Comdat!");
775 
776   StringRef ComdatGVName = C->getName();
777   const GlobalValue *ComdatGV = GV->getParent()->getNamedValue(ComdatGVName);
778   if (!ComdatGV)
779     report_fatal_error("Associative COMDAT symbol '" + ComdatGVName +
780                        "' does not exist.");
781 
782   if (ComdatGV->getComdat() != C)
783     report_fatal_error("Associative COMDAT symbol '" + ComdatGVName +
784                        "' is not a key for its COMDAT.");
785 
786   return ComdatGV;
787 }
788 
789 static int getSelectionForCOFF(const GlobalValue *GV) {
790   if (const Comdat *C = GV->getComdat()) {
791     const GlobalValue *ComdatKey = getComdatGVForCOFF(GV);
792     if (const auto *GA = dyn_cast<GlobalAlias>(ComdatKey))
793       ComdatKey = GA->getBaseObject();
794     if (ComdatKey == GV) {
795       switch (C->getSelectionKind()) {
796       case Comdat::Any:
797         return COFF::IMAGE_COMDAT_SELECT_ANY;
798       case Comdat::ExactMatch:
799         return COFF::IMAGE_COMDAT_SELECT_EXACT_MATCH;
800       case Comdat::Largest:
801         return COFF::IMAGE_COMDAT_SELECT_LARGEST;
802       case Comdat::NoDuplicates:
803         return COFF::IMAGE_COMDAT_SELECT_NODUPLICATES;
804       case Comdat::SameSize:
805         return COFF::IMAGE_COMDAT_SELECT_SAME_SIZE;
806       }
807     } else {
808       return COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE;
809     }
810   } else if (GV->isWeakForLinker()) {
811     return COFF::IMAGE_COMDAT_SELECT_ANY;
812   }
813   return 0;
814 }
815 
816 const MCSection *TargetLoweringObjectFileCOFF::getExplicitSectionGlobal(
817     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
818     const TargetMachine &TM) const {
819   int Selection = 0;
820   unsigned Characteristics = getCOFFSectionFlags(Kind);
821   StringRef Name = GV->getSection();
822   StringRef COMDATSymName = "";
823   if (GV->hasComdat()) {
824     Selection = getSelectionForCOFF(GV);
825     const GlobalValue *ComdatGV;
826     if (Selection == COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE)
827       ComdatGV = getComdatGVForCOFF(GV);
828     else
829       ComdatGV = GV;
830 
831     if (!ComdatGV->hasPrivateLinkage()) {
832       MCSymbol *Sym = TM.getSymbol(ComdatGV, Mang);
833       COMDATSymName = Sym->getName();
834       Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
835     } else {
836       Selection = 0;
837     }
838   }
839   return getContext().getCOFFSection(Name,
840                                      Characteristics,
841                                      Kind,
842                                      COMDATSymName,
843                                      Selection);
844 }
845 
846 static const char *getCOFFSectionNameForUniqueGlobal(SectionKind Kind) {
847   if (Kind.isText())
848     return ".text";
849   if (Kind.isBSS())
850     return ".bss";
851   if (Kind.isThreadLocal())
852     return ".tls$";
853   if (Kind.isReadOnly() || Kind.isReadOnlyWithRel())
854     return ".rdata";
855   return ".data";
856 }
857 
858 
859 const MCSection *TargetLoweringObjectFileCOFF::
860 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
861                        Mangler &Mang, const TargetMachine &TM) const {
862   // If we have -ffunction-sections then we should emit the global value to a
863   // uniqued section specifically for it.
864   bool EmitUniquedSection;
865   if (Kind.isText())
866     EmitUniquedSection = TM.getFunctionSections();
867   else
868     EmitUniquedSection = TM.getDataSections();
869 
870   if ((EmitUniquedSection && !Kind.isCommon()) || GV->hasComdat()) {
871     const char *Name = getCOFFSectionNameForUniqueGlobal(Kind);
872     unsigned Characteristics = getCOFFSectionFlags(Kind);
873 
874     Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
875     int Selection = getSelectionForCOFF(GV);
876     if (!Selection)
877       Selection = COFF::IMAGE_COMDAT_SELECT_NODUPLICATES;
878     const GlobalValue *ComdatGV;
879     if (GV->hasComdat())
880       ComdatGV = getComdatGVForCOFF(GV);
881     else
882       ComdatGV = GV;
883 
884     if (!ComdatGV->hasPrivateLinkage()) {
885       MCSymbol *Sym = TM.getSymbol(ComdatGV, Mang);
886       StringRef COMDATSymName = Sym->getName();
887       return getContext().getCOFFSection(Name, Characteristics, Kind,
888                                          COMDATSymName, Selection);
889     }
890   }
891 
892   if (Kind.isText())
893     return TextSection;
894 
895   if (Kind.isThreadLocal())
896     return TLSDataSection;
897 
898   if (Kind.isReadOnly() || Kind.isReadOnlyWithRel())
899     return ReadOnlySection;
900 
901   // Note: we claim that common symbols are put in BSSSection, but they are
902   // really emitted with the magic .comm directive, which creates a symbol table
903   // entry but not a section.
904   if (Kind.isBSS() || Kind.isCommon())
905     return BSSSection;
906 
907   return DataSection;
908 }
909 
910 StringRef TargetLoweringObjectFileCOFF::
911 getDepLibFromLinkerOpt(StringRef LinkerOption) const {
912   const char *LibCmd = "/DEFAULTLIB:";
913   if (LinkerOption.startswith(LibCmd))
914     return LinkerOption.substr(strlen(LibCmd));
915   return StringRef();
916 }
917 
918 void TargetLoweringObjectFileCOFF::
919 emitModuleFlags(MCStreamer &Streamer,
920                 ArrayRef<Module::ModuleFlagEntry> ModuleFlags,
921                 Mangler &Mang, const TargetMachine &TM) const {
922   MDNode *LinkerOptions = nullptr;
923 
924   // Look for the "Linker Options" flag, since it's the only one we support.
925   for (ArrayRef<Module::ModuleFlagEntry>::iterator
926        i = ModuleFlags.begin(), e = ModuleFlags.end(); i != e; ++i) {
927     const Module::ModuleFlagEntry &MFE = *i;
928     StringRef Key = MFE.Key->getString();
929     Metadata *Val = MFE.Val;
930     if (Key == "Linker Options") {
931       LinkerOptions = cast<MDNode>(Val);
932       break;
933     }
934   }
935   if (!LinkerOptions)
936     return;
937 
938   // Emit the linker options to the linker .drectve section.  According to the
939   // spec, this section is a space-separated string containing flags for linker.
940   const MCSection *Sec = getDrectveSection();
941   Streamer.SwitchSection(Sec);
942   for (unsigned i = 0, e = LinkerOptions->getNumOperands(); i != e; ++i) {
943     MDNode *MDOptions = cast<MDNode>(LinkerOptions->getOperand(i));
944     for (unsigned ii = 0, ie = MDOptions->getNumOperands(); ii != ie; ++ii) {
945       MDString *MDOption = cast<MDString>(MDOptions->getOperand(ii));
946       StringRef Op = MDOption->getString();
947       // Lead with a space for consistency with our dllexport implementation.
948       std::string Escaped(" ");
949       if (!Op.startswith("\"") && (Op.find(" ") != StringRef::npos)) {
950         // The PE-COFF spec says args with spaces must be quoted.  It doesn't say
951         // how to escape quotes, but it probably uses this algorithm:
952         // http://msdn.microsoft.com/en-us/library/17w5ykft(v=vs.85).aspx
953         // FIXME: Reuse escaping code from Support/Windows/Program.inc
954         Escaped.push_back('\"');
955         Escaped.append(Op);
956         Escaped.push_back('\"');
957       } else {
958         Escaped.append(Op);
959       }
960       Streamer.EmitBytes(Escaped);
961     }
962   }
963 }
964 
965 const MCSection *TargetLoweringObjectFileCOFF::getStaticCtorSection(
966     unsigned Priority, const MCSymbol *KeySym) const {
967   return getContext().getAssociativeCOFFSection(
968       cast<MCSectionCOFF>(StaticCtorSection), KeySym);
969 }
970 
971 const MCSection *TargetLoweringObjectFileCOFF::getStaticDtorSection(
972     unsigned Priority, const MCSymbol *KeySym) const {
973   return getContext().getAssociativeCOFFSection(
974       cast<MCSectionCOFF>(StaticDtorSection), KeySym);
975 }
976