xref: /llvm-project/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp (revision a869576008864fe061b0a6e8f50d7489aaf88f1b) 
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/MCSymbolELF.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   MCSymbolELF *Label =
67       cast<MCSymbolELF>(getContext().getOrCreateSymbol(NameData));
68   Streamer.EmitSymbolAttribute(Label, MCSA_Hidden);
69   Streamer.EmitSymbolAttribute(Label, MCSA_Weak);
70   StringRef Prefix = ".data.";
71   NameData.insert(NameData.begin(), Prefix.begin(), Prefix.end());
72   unsigned Flags = ELF::SHF_ALLOC | ELF::SHF_WRITE | ELF::SHF_GROUP;
73   MCSection *Sec = getContext().getELFSection(NameData, ELF::SHT_PROGBITS,
74                                               Flags, 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 MCSection *TargetLoweringObjectFileELF::getExplicitSectionGlobal(
204     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
205     const TargetMachine &TM) const {
206   StringRef SectionName = GV->getSection();
207 
208   // Infer section flags from the section name if we can.
209   Kind = getELFKindForNamedSection(SectionName, Kind);
210 
211   StringRef Group = "";
212   unsigned Flags = getELFSectionFlags(Kind);
213   if (const Comdat *C = getELFComdat(GV)) {
214     Group = C->getName();
215     Flags |= ELF::SHF_GROUP;
216   }
217   return getContext().getELFSection(SectionName,
218                                     getELFSectionType(SectionName, Kind), Flags,
219                                     /*EntrySize=*/0, Group);
220 }
221 
222 /// Return the section prefix name used by options FunctionsSections and
223 /// DataSections.
224 static StringRef getSectionPrefixForGlobal(SectionKind Kind) {
225   if (Kind.isText())
226     return ".text";
227   if (Kind.isReadOnly())
228     return ".rodata";
229   if (Kind.isBSS())
230     return ".bss";
231   if (Kind.isThreadData())
232     return ".tdata";
233   if (Kind.isThreadBSS())
234     return ".tbss";
235   if (Kind.isDataNoRel())
236     return ".data";
237   if (Kind.isDataRelLocal())
238     return ".data.rel.local";
239   if (Kind.isDataRel())
240     return ".data.rel";
241   if (Kind.isReadOnlyWithRelLocal())
242     return ".data.rel.ro.local";
243   assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
244   return ".data.rel.ro";
245 }
246 
247 static MCSectionELF *
248 selectELFSectionForGlobal(MCContext &Ctx, const GlobalValue *GV,
249                           SectionKind Kind, Mangler &Mang,
250                           const TargetMachine &TM, bool EmitUniqueSection,
251                           unsigned Flags, unsigned *NextUniqueID) {
252   unsigned EntrySize = 0;
253   if (Kind.isMergeableCString()) {
254     if (Kind.isMergeable2ByteCString()) {
255       EntrySize = 2;
256     } else if (Kind.isMergeable4ByteCString()) {
257       EntrySize = 4;
258     } else {
259       EntrySize = 1;
260       assert(Kind.isMergeable1ByteCString() && "unknown string width");
261     }
262   } else if (Kind.isMergeableConst()) {
263     if (Kind.isMergeableConst4()) {
264       EntrySize = 4;
265     } else if (Kind.isMergeableConst8()) {
266       EntrySize = 8;
267     } else {
268       assert(Kind.isMergeableConst16() && "unknown data width");
269       EntrySize = 16;
270     }
271   }
272 
273   StringRef Group = "";
274   if (const Comdat *C = getELFComdat(GV)) {
275     Flags |= ELF::SHF_GROUP;
276     Group = C->getName();
277   }
278 
279   bool UniqueSectionNames = TM.getUniqueSectionNames();
280   SmallString<128> Name;
281   if (Kind.isMergeableCString()) {
282     // We also need alignment here.
283     // FIXME: this is getting the alignment of the character, not the
284     // alignment of the global!
285     unsigned Align =
286         TM.getDataLayout()->getPreferredAlignment(cast<GlobalVariable>(GV));
287 
288     std::string SizeSpec = ".rodata.str" + utostr(EntrySize) + ".";
289     Name = SizeSpec + utostr(Align);
290   } else if (Kind.isMergeableConst()) {
291     Name = ".rodata.cst";
292     Name += utostr(EntrySize);
293   } else {
294     Name = getSectionPrefixForGlobal(Kind);
295   }
296 
297   if (EmitUniqueSection && UniqueSectionNames) {
298     Name.push_back('.');
299     TM.getNameWithPrefix(Name, GV, Mang, true);
300   }
301   unsigned UniqueID = ~0;
302   if (EmitUniqueSection && !UniqueSectionNames) {
303     UniqueID = *NextUniqueID;
304     (*NextUniqueID)++;
305   }
306   return Ctx.getELFSection(Name, getELFSectionType(Name, Kind), Flags,
307                            EntrySize, Group, UniqueID);
308 }
309 
310 MCSection *TargetLoweringObjectFileELF::SelectSectionForGlobal(
311     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
312     const TargetMachine &TM) const {
313   unsigned Flags = getELFSectionFlags(Kind);
314 
315   // If we have -ffunction-section or -fdata-section then we should emit the
316   // global value to a uniqued section specifically for it.
317   bool EmitUniqueSection = false;
318   if (!(Flags & ELF::SHF_MERGE) && !Kind.isCommon()) {
319     if (Kind.isText())
320       EmitUniqueSection = TM.getFunctionSections();
321     else
322       EmitUniqueSection = TM.getDataSections();
323   }
324   EmitUniqueSection |= GV->hasComdat();
325 
326   return selectELFSectionForGlobal(getContext(), GV, Kind, Mang, TM,
327                                    EmitUniqueSection, Flags, &NextUniqueID);
328 }
329 
330 MCSection *TargetLoweringObjectFileELF::getSectionForJumpTable(
331     const Function &F, Mangler &Mang, const TargetMachine &TM) const {
332   // If the function can be removed, produce a unique section so that
333   // the table doesn't prevent the removal.
334   const Comdat *C = F.getComdat();
335   bool EmitUniqueSection = TM.getFunctionSections() || C;
336   if (!EmitUniqueSection)
337     return ReadOnlySection;
338 
339   return selectELFSectionForGlobal(getContext(), &F, SectionKind::getReadOnly(),
340                                    Mang, TM, EmitUniqueSection, ELF::SHF_ALLOC,
341                                    &NextUniqueID);
342 }
343 
344 bool TargetLoweringObjectFileELF::shouldPutJumpTableInFunctionSection(
345     bool UsesLabelDifference, const Function &F) const {
346   // We can always create relative relocations, so use another section
347   // that can be marked non-executable.
348   return false;
349 }
350 
351 /// Given a mergeable constant with the specified size and relocation
352 /// information, return a section that it should be placed in.
353 MCSection *
354 TargetLoweringObjectFileELF::getSectionForConstant(SectionKind Kind,
355                                                    const Constant *C) const {
356   if (Kind.isMergeableConst4() && MergeableConst4Section)
357     return MergeableConst4Section;
358   if (Kind.isMergeableConst8() && MergeableConst8Section)
359     return MergeableConst8Section;
360   if (Kind.isMergeableConst16() && MergeableConst16Section)
361     return MergeableConst16Section;
362   if (Kind.isReadOnly())
363     return ReadOnlySection;
364 
365   if (Kind.isReadOnlyWithRelLocal()) return DataRelROLocalSection;
366   assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
367   return DataRelROSection;
368 }
369 
370 static MCSectionELF *getStaticStructorSection(MCContext &Ctx, bool UseInitArray,
371                                               bool IsCtor, unsigned Priority,
372                                               const MCSymbol *KeySym) {
373   std::string Name;
374   unsigned Type;
375   unsigned Flags = ELF::SHF_ALLOC | ELF::SHF_WRITE;
376   StringRef COMDAT = KeySym ? KeySym->getName() : "";
377 
378   if (KeySym)
379     Flags |= ELF::SHF_GROUP;
380 
381   if (UseInitArray) {
382     if (IsCtor) {
383       Type = ELF::SHT_INIT_ARRAY;
384       Name = ".init_array";
385     } else {
386       Type = ELF::SHT_FINI_ARRAY;
387       Name = ".fini_array";
388     }
389     if (Priority != 65535) {
390       Name += '.';
391       Name += utostr(Priority);
392     }
393   } else {
394     // The default scheme is .ctor / .dtor, so we have to invert the priority
395     // numbering.
396     if (IsCtor)
397       Name = ".ctors";
398     else
399       Name = ".dtors";
400     if (Priority != 65535) {
401       Name += '.';
402       Name += utostr(65535 - Priority);
403     }
404     Type = ELF::SHT_PROGBITS;
405   }
406 
407   return Ctx.getELFSection(Name, Type, Flags, 0, COMDAT);
408 }
409 
410 MCSection *TargetLoweringObjectFileELF::getStaticCtorSection(
411     unsigned Priority, const MCSymbol *KeySym) const {
412   return getStaticStructorSection(getContext(), UseInitArray, true, Priority,
413                                   KeySym);
414 }
415 
416 MCSection *TargetLoweringObjectFileELF::getStaticDtorSection(
417     unsigned Priority, const MCSymbol *KeySym) const {
418   return getStaticStructorSection(getContext(), UseInitArray, false, Priority,
419                                   KeySym);
420 }
421 
422 void
423 TargetLoweringObjectFileELF::InitializeELF(bool UseInitArray_) {
424   UseInitArray = UseInitArray_;
425   if (!UseInitArray)
426     return;
427 
428   StaticCtorSection = getContext().getELFSection(
429       ".init_array", ELF::SHT_INIT_ARRAY, ELF::SHF_WRITE | ELF::SHF_ALLOC);
430   StaticDtorSection = getContext().getELFSection(
431       ".fini_array", ELF::SHT_FINI_ARRAY, ELF::SHF_WRITE | ELF::SHF_ALLOC);
432 }
433 
434 //===----------------------------------------------------------------------===//
435 //                                 MachO
436 //===----------------------------------------------------------------------===//
437 
438 TargetLoweringObjectFileMachO::TargetLoweringObjectFileMachO()
439   : TargetLoweringObjectFile() {
440   SupportIndirectSymViaGOTPCRel = true;
441 }
442 
443 /// getDepLibFromLinkerOpt - Extract the dependent library name from a linker
444 /// option string. Returns StringRef() if the option does not specify a library.
445 StringRef TargetLoweringObjectFileMachO::
446 getDepLibFromLinkerOpt(StringRef LinkerOption) const {
447   const char *LibCmd = "-l";
448   if (LinkerOption.startswith(LibCmd))
449     return LinkerOption.substr(strlen(LibCmd));
450   return StringRef();
451 }
452 
453 /// emitModuleFlags - Perform code emission for module flags.
454 void TargetLoweringObjectFileMachO::
455 emitModuleFlags(MCStreamer &Streamer,
456                 ArrayRef<Module::ModuleFlagEntry> ModuleFlags,
457                 Mangler &Mang, const TargetMachine &TM) const {
458   unsigned VersionVal = 0;
459   unsigned ImageInfoFlags = 0;
460   MDNode *LinkerOptions = nullptr;
461   StringRef SectionVal;
462 
463   for (ArrayRef<Module::ModuleFlagEntry>::iterator
464          i = ModuleFlags.begin(), e = ModuleFlags.end(); i != e; ++i) {
465     const Module::ModuleFlagEntry &MFE = *i;
466 
467     // Ignore flags with 'Require' behavior.
468     if (MFE.Behavior == Module::Require)
469       continue;
470 
471     StringRef Key = MFE.Key->getString();
472     Metadata *Val = MFE.Val;
473 
474     if (Key == "Objective-C Image Info Version") {
475       VersionVal = mdconst::extract<ConstantInt>(Val)->getZExtValue();
476     } else if (Key == "Objective-C Garbage Collection" ||
477                Key == "Objective-C GC Only" ||
478                Key == "Objective-C Is Simulated" ||
479                Key == "Objective-C Image Swift Version") {
480       ImageInfoFlags |= mdconst::extract<ConstantInt>(Val)->getZExtValue();
481     } else if (Key == "Objective-C Image Info Section") {
482       SectionVal = cast<MDString>(Val)->getString();
483     } else if (Key == "Linker Options") {
484       LinkerOptions = cast<MDNode>(Val);
485     }
486   }
487 
488   // Emit the linker options if present.
489   if (LinkerOptions) {
490     for (unsigned i = 0, e = LinkerOptions->getNumOperands(); i != e; ++i) {
491       MDNode *MDOptions = cast<MDNode>(LinkerOptions->getOperand(i));
492       SmallVector<std::string, 4> StrOptions;
493 
494       // Convert to strings.
495       for (unsigned ii = 0, ie = MDOptions->getNumOperands(); ii != ie; ++ii) {
496         MDString *MDOption = cast<MDString>(MDOptions->getOperand(ii));
497         StrOptions.push_back(MDOption->getString());
498       }
499 
500       Streamer.EmitLinkerOptions(StrOptions);
501     }
502   }
503 
504   // The section is mandatory. If we don't have it, then we don't have GC info.
505   if (SectionVal.empty()) return;
506 
507   StringRef Segment, Section;
508   unsigned TAA = 0, StubSize = 0;
509   bool TAAParsed;
510   std::string ErrorCode =
511     MCSectionMachO::ParseSectionSpecifier(SectionVal, Segment, Section,
512                                           TAA, TAAParsed, StubSize);
513   if (!ErrorCode.empty())
514     // If invalid, report the error with report_fatal_error.
515     report_fatal_error("Invalid section specifier '" + Section + "': " +
516                        ErrorCode + ".");
517 
518   // Get the section.
519   MCSectionMachO *S = getContext().getMachOSection(
520       Segment, Section, TAA, StubSize, SectionKind::getDataNoRel());
521   Streamer.SwitchSection(S);
522   Streamer.EmitLabel(getContext().
523                      getOrCreateSymbol(StringRef("L_OBJC_IMAGE_INFO")));
524   Streamer.EmitIntValue(VersionVal, 4);
525   Streamer.EmitIntValue(ImageInfoFlags, 4);
526   Streamer.AddBlankLine();
527 }
528 
529 static void checkMachOComdat(const GlobalValue *GV) {
530   const Comdat *C = GV->getComdat();
531   if (!C)
532     return;
533 
534   report_fatal_error("MachO doesn't support COMDATs, '" + C->getName() +
535                      "' cannot be lowered.");
536 }
537 
538 MCSection *TargetLoweringObjectFileMachO::getExplicitSectionGlobal(
539     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
540     const TargetMachine &TM) const {
541   // Parse the section specifier and create it if valid.
542   StringRef Segment, Section;
543   unsigned TAA = 0, StubSize = 0;
544   bool TAAParsed;
545 
546   checkMachOComdat(GV);
547 
548   std::string ErrorCode =
549     MCSectionMachO::ParseSectionSpecifier(GV->getSection(), Segment, Section,
550                                           TAA, TAAParsed, StubSize);
551   if (!ErrorCode.empty()) {
552     // If invalid, report the error with report_fatal_error.
553     report_fatal_error("Global variable '" + GV->getName() +
554                        "' has an invalid section specifier '" +
555                        GV->getSection() + "': " + ErrorCode + ".");
556   }
557 
558   // Get the section.
559   MCSectionMachO *S =
560       getContext().getMachOSection(Segment, Section, TAA, StubSize, Kind);
561 
562   // If TAA wasn't set by ParseSectionSpecifier() above,
563   // use the value returned by getMachOSection() as a default.
564   if (!TAAParsed)
565     TAA = S->getTypeAndAttributes();
566 
567   // Okay, now that we got the section, verify that the TAA & StubSize agree.
568   // If the user declared multiple globals with different section flags, we need
569   // to reject it here.
570   if (S->getTypeAndAttributes() != TAA || S->getStubSize() != StubSize) {
571     // If invalid, report the error with report_fatal_error.
572     report_fatal_error("Global variable '" + GV->getName() +
573                        "' section type or attributes does not match previous"
574                        " section specifier");
575   }
576 
577   return S;
578 }
579 
580 MCSection *TargetLoweringObjectFileMachO::SelectSectionForGlobal(
581     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
582     const TargetMachine &TM) const {
583   checkMachOComdat(GV);
584 
585   // Handle thread local data.
586   if (Kind.isThreadBSS()) return TLSBSSSection;
587   if (Kind.isThreadData()) return TLSDataSection;
588 
589   if (Kind.isText())
590     return GV->isWeakForLinker() ? TextCoalSection : TextSection;
591 
592   // If this is weak/linkonce, put this in a coalescable section, either in text
593   // or data depending on if it is writable.
594   if (GV->isWeakForLinker()) {
595     if (Kind.isReadOnly())
596       return ConstTextCoalSection;
597     return DataCoalSection;
598   }
599 
600   // FIXME: Alignment check should be handled by section classifier.
601   if (Kind.isMergeable1ByteCString() &&
602       TM.getDataLayout()->getPreferredAlignment(cast<GlobalVariable>(GV)) < 32)
603     return CStringSection;
604 
605   // Do not put 16-bit arrays in the UString section if they have an
606   // externally visible label, this runs into issues with certain linker
607   // versions.
608   if (Kind.isMergeable2ByteCString() && !GV->hasExternalLinkage() &&
609       TM.getDataLayout()->getPreferredAlignment(cast<GlobalVariable>(GV)) < 32)
610     return UStringSection;
611 
612   // With MachO only variables whose corresponding symbol starts with 'l' or
613   // 'L' can be merged, so we only try merging GVs with private linkage.
614   if (GV->hasPrivateLinkage() && Kind.isMergeableConst()) {
615     if (Kind.isMergeableConst4())
616       return FourByteConstantSection;
617     if (Kind.isMergeableConst8())
618       return EightByteConstantSection;
619     if (Kind.isMergeableConst16())
620       return SixteenByteConstantSection;
621   }
622 
623   // Otherwise, if it is readonly, but not something we can specially optimize,
624   // just drop it in .const.
625   if (Kind.isReadOnly())
626     return ReadOnlySection;
627 
628   // If this is marked const, put it into a const section.  But if the dynamic
629   // linker needs to write to it, put it in the data segment.
630   if (Kind.isReadOnlyWithRel())
631     return ConstDataSection;
632 
633   // Put zero initialized globals with strong external linkage in the
634   // DATA, __common section with the .zerofill directive.
635   if (Kind.isBSSExtern())
636     return DataCommonSection;
637 
638   // Put zero initialized globals with local linkage in __DATA,__bss directive
639   // with the .zerofill directive (aka .lcomm).
640   if (Kind.isBSSLocal())
641     return DataBSSSection;
642 
643   // Otherwise, just drop the variable in the normal data section.
644   return DataSection;
645 }
646 
647 MCSection *
648 TargetLoweringObjectFileMachO::getSectionForConstant(SectionKind Kind,
649                                                      const Constant *C) const {
650   // If this constant requires a relocation, we have to put it in the data
651   // segment, not in the text segment.
652   if (Kind.isDataRel() || Kind.isReadOnlyWithRel())
653     return ConstDataSection;
654 
655   if (Kind.isMergeableConst4())
656     return FourByteConstantSection;
657   if (Kind.isMergeableConst8())
658     return EightByteConstantSection;
659   if (Kind.isMergeableConst16())
660     return SixteenByteConstantSection;
661   return ReadOnlySection;  // .const
662 }
663 
664 const MCExpr *TargetLoweringObjectFileMachO::getTTypeGlobalReference(
665     const GlobalValue *GV, unsigned Encoding, Mangler &Mang,
666     const TargetMachine &TM, MachineModuleInfo *MMI,
667     MCStreamer &Streamer) const {
668   // The mach-o version of this method defaults to returning a stub reference.
669 
670   if (Encoding & DW_EH_PE_indirect) {
671     MachineModuleInfoMachO &MachOMMI =
672       MMI->getObjFileInfo<MachineModuleInfoMachO>();
673 
674     MCSymbol *SSym =
675         getSymbolWithGlobalValueBase(GV, "$non_lazy_ptr", Mang, TM);
676 
677     // Add information about the stub reference to MachOMMI so that the stub
678     // gets emitted by the asmprinter.
679     MachineModuleInfoImpl::StubValueTy &StubSym =
680       GV->hasHiddenVisibility() ? MachOMMI.getHiddenGVStubEntry(SSym) :
681                                   MachOMMI.getGVStubEntry(SSym);
682     if (!StubSym.getPointer()) {
683       MCSymbol *Sym = TM.getSymbol(GV, Mang);
684       StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
685     }
686 
687     return TargetLoweringObjectFile::
688       getTTypeReference(MCSymbolRefExpr::create(SSym, getContext()),
689                         Encoding & ~dwarf::DW_EH_PE_indirect, Streamer);
690   }
691 
692   return TargetLoweringObjectFile::getTTypeGlobalReference(GV, Encoding, Mang,
693                                                            TM, MMI, Streamer);
694 }
695 
696 MCSymbol *TargetLoweringObjectFileMachO::getCFIPersonalitySymbol(
697     const GlobalValue *GV, Mangler &Mang, const TargetMachine &TM,
698     MachineModuleInfo *MMI) const {
699   // The mach-o version of this method defaults to returning a stub reference.
700   MachineModuleInfoMachO &MachOMMI =
701     MMI->getObjFileInfo<MachineModuleInfoMachO>();
702 
703   MCSymbol *SSym = getSymbolWithGlobalValueBase(GV, "$non_lazy_ptr", Mang, TM);
704 
705   // Add information about the stub reference to MachOMMI so that the stub
706   // gets emitted by the asmprinter.
707   MachineModuleInfoImpl::StubValueTy &StubSym = MachOMMI.getGVStubEntry(SSym);
708   if (!StubSym.getPointer()) {
709     MCSymbol *Sym = TM.getSymbol(GV, Mang);
710     StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
711   }
712 
713   return SSym;
714 }
715 
716 const MCExpr *TargetLoweringObjectFileMachO::getIndirectSymViaGOTPCRel(
717     const MCSymbol *Sym, const MCValue &MV, int64_t Offset,
718     MachineModuleInfo *MMI, MCStreamer &Streamer) const {
719   // Although MachO 32-bit targets do not explictly have a GOTPCREL relocation
720   // as 64-bit do, we replace the GOT equivalent by accessing the final symbol
721   // through a non_lazy_ptr stub instead. One advantage is that it allows the
722   // computation of deltas to final external symbols. Example:
723   //
724   //    _extgotequiv:
725   //       .long   _extfoo
726   //
727   //    _delta:
728   //       .long   _extgotequiv-_delta
729   //
730   // is transformed to:
731   //
732   //    _delta:
733   //       .long   L_extfoo$non_lazy_ptr-(_delta+0)
734   //
735   //       .section        __IMPORT,__pointers,non_lazy_symbol_pointers
736   //    L_extfoo$non_lazy_ptr:
737   //       .indirect_symbol        _extfoo
738   //       .long   0
739   //
740   MachineModuleInfoMachO &MachOMMI =
741     MMI->getObjFileInfo<MachineModuleInfoMachO>();
742   MCContext &Ctx = getContext();
743 
744   // The offset must consider the original displacement from the base symbol
745   // since 32-bit targets don't have a GOTPCREL to fold the PC displacement.
746   Offset = -MV.getConstant();
747   const MCSymbol *BaseSym = &MV.getSymB()->getSymbol();
748 
749   // Access the final symbol via sym$non_lazy_ptr and generate the appropriated
750   // non_lazy_ptr stubs.
751   SmallString<128> Name;
752   StringRef Suffix = "$non_lazy_ptr";
753   Name += DL->getPrivateGlobalPrefix();
754   Name += Sym->getName();
755   Name += Suffix;
756   MCSymbol *Stub = Ctx.getOrCreateSymbol(Name);
757 
758   MachineModuleInfoImpl::StubValueTy &StubSym = MachOMMI.getGVStubEntry(Stub);
759   if (!StubSym.getPointer())
760     StubSym = MachineModuleInfoImpl::
761       StubValueTy(const_cast<MCSymbol *>(Sym), true /* access indirectly */);
762 
763   const MCExpr *BSymExpr =
764     MCSymbolRefExpr::create(BaseSym, MCSymbolRefExpr::VK_None, Ctx);
765   const MCExpr *LHS =
766     MCSymbolRefExpr::create(Stub, MCSymbolRefExpr::VK_None, Ctx);
767 
768   if (!Offset)
769     return MCBinaryExpr::createSub(LHS, BSymExpr, Ctx);
770 
771   const MCExpr *RHS =
772     MCBinaryExpr::createAdd(BSymExpr, MCConstantExpr::create(Offset, Ctx), Ctx);
773   return MCBinaryExpr::createSub(LHS, RHS, Ctx);
774 }
775 
776 //===----------------------------------------------------------------------===//
777 //                                  COFF
778 //===----------------------------------------------------------------------===//
779 
780 static unsigned
781 getCOFFSectionFlags(SectionKind K) {
782   unsigned Flags = 0;
783 
784   if (K.isMetadata())
785     Flags |=
786       COFF::IMAGE_SCN_MEM_DISCARDABLE;
787   else if (K.isText())
788     Flags |=
789       COFF::IMAGE_SCN_MEM_EXECUTE |
790       COFF::IMAGE_SCN_MEM_READ |
791       COFF::IMAGE_SCN_CNT_CODE;
792   else if (K.isBSS())
793     Flags |=
794       COFF::IMAGE_SCN_CNT_UNINITIALIZED_DATA |
795       COFF::IMAGE_SCN_MEM_READ |
796       COFF::IMAGE_SCN_MEM_WRITE;
797   else if (K.isThreadLocal())
798     Flags |=
799       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
800       COFF::IMAGE_SCN_MEM_READ |
801       COFF::IMAGE_SCN_MEM_WRITE;
802   else if (K.isReadOnly() || K.isReadOnlyWithRel())
803     Flags |=
804       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
805       COFF::IMAGE_SCN_MEM_READ;
806   else if (K.isWriteable())
807     Flags |=
808       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
809       COFF::IMAGE_SCN_MEM_READ |
810       COFF::IMAGE_SCN_MEM_WRITE;
811 
812   return Flags;
813 }
814 
815 static const GlobalValue *getComdatGVForCOFF(const GlobalValue *GV) {
816   const Comdat *C = GV->getComdat();
817   assert(C && "expected GV to have a Comdat!");
818 
819   StringRef ComdatGVName = C->getName();
820   const GlobalValue *ComdatGV = GV->getParent()->getNamedValue(ComdatGVName);
821   if (!ComdatGV)
822     report_fatal_error("Associative COMDAT symbol '" + ComdatGVName +
823                        "' does not exist.");
824 
825   if (ComdatGV->getComdat() != C)
826     report_fatal_error("Associative COMDAT symbol '" + ComdatGVName +
827                        "' is not a key for its COMDAT.");
828 
829   return ComdatGV;
830 }
831 
832 static int getSelectionForCOFF(const GlobalValue *GV) {
833   if (const Comdat *C = GV->getComdat()) {
834     const GlobalValue *ComdatKey = getComdatGVForCOFF(GV);
835     if (const auto *GA = dyn_cast<GlobalAlias>(ComdatKey))
836       ComdatKey = GA->getBaseObject();
837     if (ComdatKey == GV) {
838       switch (C->getSelectionKind()) {
839       case Comdat::Any:
840         return COFF::IMAGE_COMDAT_SELECT_ANY;
841       case Comdat::ExactMatch:
842         return COFF::IMAGE_COMDAT_SELECT_EXACT_MATCH;
843       case Comdat::Largest:
844         return COFF::IMAGE_COMDAT_SELECT_LARGEST;
845       case Comdat::NoDuplicates:
846         return COFF::IMAGE_COMDAT_SELECT_NODUPLICATES;
847       case Comdat::SameSize:
848         return COFF::IMAGE_COMDAT_SELECT_SAME_SIZE;
849       }
850     } else {
851       return COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE;
852     }
853   } else if (GV->isWeakForLinker()) {
854     return COFF::IMAGE_COMDAT_SELECT_ANY;
855   }
856   return 0;
857 }
858 
859 MCSection *TargetLoweringObjectFileCOFF::getExplicitSectionGlobal(
860     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
861     const TargetMachine &TM) const {
862   int Selection = 0;
863   unsigned Characteristics = getCOFFSectionFlags(Kind);
864   StringRef Name = GV->getSection();
865   StringRef COMDATSymName = "";
866   if (GV->hasComdat()) {
867     Selection = getSelectionForCOFF(GV);
868     const GlobalValue *ComdatGV;
869     if (Selection == COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE)
870       ComdatGV = getComdatGVForCOFF(GV);
871     else
872       ComdatGV = GV;
873 
874     if (!ComdatGV->hasPrivateLinkage()) {
875       MCSymbol *Sym = TM.getSymbol(ComdatGV, Mang);
876       COMDATSymName = Sym->getName();
877       Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
878     } else {
879       Selection = 0;
880     }
881   }
882   return getContext().getCOFFSection(Name,
883                                      Characteristics,
884                                      Kind,
885                                      COMDATSymName,
886                                      Selection);
887 }
888 
889 static const char *getCOFFSectionNameForUniqueGlobal(SectionKind Kind) {
890   if (Kind.isText())
891     return ".text";
892   if (Kind.isBSS())
893     return ".bss";
894   if (Kind.isThreadLocal())
895     return ".tls$";
896   if (Kind.isReadOnly() || Kind.isReadOnlyWithRel())
897     return ".rdata";
898   return ".data";
899 }
900 
901 MCSection *TargetLoweringObjectFileCOFF::SelectSectionForGlobal(
902     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
903     const TargetMachine &TM) const {
904   // If we have -ffunction-sections then we should emit the global value to a
905   // uniqued section specifically for it.
906   bool EmitUniquedSection;
907   if (Kind.isText())
908     EmitUniquedSection = TM.getFunctionSections();
909   else
910     EmitUniquedSection = TM.getDataSections();
911 
912   if ((EmitUniquedSection && !Kind.isCommon()) || GV->hasComdat()) {
913     const char *Name = getCOFFSectionNameForUniqueGlobal(Kind);
914     unsigned Characteristics = getCOFFSectionFlags(Kind);
915 
916     Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
917     int Selection = getSelectionForCOFF(GV);
918     if (!Selection)
919       Selection = COFF::IMAGE_COMDAT_SELECT_NODUPLICATES;
920     const GlobalValue *ComdatGV;
921     if (GV->hasComdat())
922       ComdatGV = getComdatGVForCOFF(GV);
923     else
924       ComdatGV = GV;
925 
926     if (!ComdatGV->hasPrivateLinkage()) {
927       MCSymbol *Sym = TM.getSymbol(ComdatGV, Mang);
928       StringRef COMDATSymName = Sym->getName();
929       return getContext().getCOFFSection(Name, Characteristics, Kind,
930                                          COMDATSymName, Selection);
931     } else {
932       SmallString<256> TmpData;
933       getNameWithPrefix(TmpData, GV, /*CannotUsePrivateLabel=*/true, Mang, TM);
934       return getContext().getCOFFSection(Name, Characteristics, Kind, TmpData,
935                                          Selection);
936     }
937   }
938 
939   if (Kind.isText())
940     return TextSection;
941 
942   if (Kind.isThreadLocal())
943     return TLSDataSection;
944 
945   if (Kind.isReadOnly() || Kind.isReadOnlyWithRel())
946     return ReadOnlySection;
947 
948   // Note: we claim that common symbols are put in BSSSection, but they are
949   // really emitted with the magic .comm directive, which creates a symbol table
950   // entry but not a section.
951   if (Kind.isBSS() || Kind.isCommon())
952     return BSSSection;
953 
954   return DataSection;
955 }
956 
957 void TargetLoweringObjectFileCOFF::getNameWithPrefix(
958     SmallVectorImpl<char> &OutName, const GlobalValue *GV,
959     bool CannotUsePrivateLabel, Mangler &Mang, const TargetMachine &TM) const {
960   if (GV->hasPrivateLinkage() &&
961       ((isa<Function>(GV) && TM.getFunctionSections()) ||
962        (isa<GlobalVariable>(GV) && TM.getDataSections())))
963     CannotUsePrivateLabel = true;
964 
965   Mang.getNameWithPrefix(OutName, GV, CannotUsePrivateLabel);
966 }
967 
968 MCSection *TargetLoweringObjectFileCOFF::getSectionForJumpTable(
969     const Function &F, Mangler &Mang, const TargetMachine &TM) const {
970   // If the function can be removed, produce a unique section so that
971   // the table doesn't prevent the removal.
972   const Comdat *C = F.getComdat();
973   bool EmitUniqueSection = TM.getFunctionSections() || C;
974   if (!EmitUniqueSection)
975     return ReadOnlySection;
976 
977   // FIXME: we should produce a symbol for F instead.
978   if (F.hasPrivateLinkage())
979     return ReadOnlySection;
980 
981   MCSymbol *Sym = TM.getSymbol(&F, Mang);
982   StringRef COMDATSymName = Sym->getName();
983 
984   SectionKind Kind = SectionKind::getReadOnly();
985   const char *Name = getCOFFSectionNameForUniqueGlobal(Kind);
986   unsigned Characteristics = getCOFFSectionFlags(Kind);
987   Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
988 
989   return getContext().getCOFFSection(Name, Characteristics, Kind, COMDATSymName,
990                                      COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE);
991 }
992 
993 StringRef TargetLoweringObjectFileCOFF::
994 getDepLibFromLinkerOpt(StringRef LinkerOption) const {
995   const char *LibCmd = "/DEFAULTLIB:";
996   if (LinkerOption.startswith(LibCmd))
997     return LinkerOption.substr(strlen(LibCmd));
998   return StringRef();
999 }
1000 
1001 void TargetLoweringObjectFileCOFF::
1002 emitModuleFlags(MCStreamer &Streamer,
1003                 ArrayRef<Module::ModuleFlagEntry> ModuleFlags,
1004                 Mangler &Mang, const TargetMachine &TM) const {
1005   MDNode *LinkerOptions = nullptr;
1006 
1007   // Look for the "Linker Options" flag, since it's the only one we support.
1008   for (ArrayRef<Module::ModuleFlagEntry>::iterator
1009        i = ModuleFlags.begin(), e = ModuleFlags.end(); i != e; ++i) {
1010     const Module::ModuleFlagEntry &MFE = *i;
1011     StringRef Key = MFE.Key->getString();
1012     Metadata *Val = MFE.Val;
1013     if (Key == "Linker Options") {
1014       LinkerOptions = cast<MDNode>(Val);
1015       break;
1016     }
1017   }
1018   if (!LinkerOptions)
1019     return;
1020 
1021   // Emit the linker options to the linker .drectve section.  According to the
1022   // spec, this section is a space-separated string containing flags for linker.
1023   MCSection *Sec = getDrectveSection();
1024   Streamer.SwitchSection(Sec);
1025   for (unsigned i = 0, e = LinkerOptions->getNumOperands(); i != e; ++i) {
1026     MDNode *MDOptions = cast<MDNode>(LinkerOptions->getOperand(i));
1027     for (unsigned ii = 0, ie = MDOptions->getNumOperands(); ii != ie; ++ii) {
1028       MDString *MDOption = cast<MDString>(MDOptions->getOperand(ii));
1029       // Lead with a space for consistency with our dllexport implementation.
1030       std::string Directive(" ");
1031       Directive.append(MDOption->getString());
1032       Streamer.EmitBytes(Directive);
1033     }
1034   }
1035 }
1036 
1037 MCSection *TargetLoweringObjectFileCOFF::getStaticCtorSection(
1038     unsigned Priority, const MCSymbol *KeySym) const {
1039   return getContext().getAssociativeCOFFSection(
1040       cast<MCSectionCOFF>(StaticCtorSection), KeySym);
1041 }
1042 
1043 MCSection *TargetLoweringObjectFileCOFF::getStaticDtorSection(
1044     unsigned Priority, const MCSymbol *KeySym) const {
1045   return getContext().getAssociativeCOFFSection(
1046       cast<MCSectionCOFF>(StaticDtorSection), KeySym);
1047 }
1048