xref: /llvm-project/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp (revision ba31e27f0adb88edffeacd8c18fc760ce7e0a640) 
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) {
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   if (K.isMergeableCString() || K.isMergeableConst())
185     Flags |= ELF::SHF_MERGE;
186 
187   if (K.isMergeableCString())
188     Flags |= ELF::SHF_STRINGS;
189 
190   return Flags;
191 }
192 
193 static const Comdat *getELFComdat(const GlobalValue *GV) {
194   const Comdat *C = GV->getComdat();
195   if (!C)
196     return nullptr;
197 
198   if (C->getSelectionKind() != Comdat::Any)
199     report_fatal_error("ELF COMDATs only support SelectionKind::Any, '" +
200                        C->getName() + "' cannot be lowered.");
201 
202   return C;
203 }
204 
205 const MCSection *TargetLoweringObjectFileELF::getExplicitSectionGlobal(
206     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
207     const TargetMachine &TM) const {
208   StringRef SectionName = GV->getSection();
209 
210   // Infer section flags from the section name if we can.
211   Kind = getELFKindForNamedSection(SectionName, Kind);
212 
213   StringRef Group = "";
214   unsigned Flags = getELFSectionFlags(Kind);
215   if (const Comdat *C = getELFComdat(GV)) {
216     Group = C->getName();
217     Flags |= ELF::SHF_GROUP;
218   }
219   return getContext().getELFSection(SectionName,
220                                     getELFSectionType(SectionName, Kind), Flags,
221                                     /*EntrySize=*/0, Group);
222 }
223 
224 /// getSectionPrefixForGlobal - Return the section prefix name used by options
225 /// FunctionsSections and DataSections.
226 static StringRef getSectionPrefixForGlobal(SectionKind Kind) {
227   if (Kind.isText())                 return ".text.";
228   if (Kind.isReadOnly())             return ".rodata.";
229   if (Kind.isBSS())                  return ".bss.";
230 
231   if (Kind.isThreadData())           return ".tdata.";
232   if (Kind.isThreadBSS())            return ".tbss.";
233 
234   if (Kind.isDataNoRel())            return ".data.";
235   if (Kind.isDataRelLocal())         return ".data.rel.local.";
236   if (Kind.isDataRel())              return ".data.rel.";
237   if (Kind.isReadOnlyWithRelLocal()) return ".data.rel.ro.local.";
238 
239   assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
240   return ".data.rel.ro.";
241 }
242 
243 const MCSection *TargetLoweringObjectFileELF::
244 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
245                        Mangler &Mang, const TargetMachine &TM) const {
246   unsigned Flags = getELFSectionFlags(Kind);
247 
248   // If we have -ffunction-section or -fdata-section then we should emit the
249   // global value to a uniqued section specifically for it.
250   bool EmitUniquedSection = false;
251   if (!(Flags & ELF::SHF_MERGE) && !Kind.isCommon()) {
252     if (Kind.isText())
253       EmitUniquedSection = TM.getFunctionSections();
254     else
255       EmitUniquedSection = TM.getDataSections();
256   }
257 
258   if (EmitUniquedSection || GV->hasComdat()) {
259     StringRef Prefix = getSectionPrefixForGlobal(Kind);
260 
261     SmallString<128> Name(Prefix);
262     TM.getNameWithPrefix(Name, GV, Mang, true);
263 
264     StringRef Group = "";
265     if (const Comdat *C = getELFComdat(GV)) {
266       Flags |= ELF::SHF_GROUP;
267       Group = C->getName();
268     }
269 
270     return getContext().getELFSection(
271         Name.str(), getELFSectionType(Name.str(), Kind), Flags, 0, Group);
272   }
273 
274   if (Kind.isText()) return TextSection;
275 
276   if (Kind.isMergeableCString()) {
277 
278     // We also need alignment here.
279     // FIXME: this is getting the alignment of the character, not the
280     // alignment of the global!
281     unsigned Align =
282         TM.getDataLayout()->getPreferredAlignment(cast<GlobalVariable>(GV));
283 
284     unsigned EntrySize = 1;
285     if (Kind.isMergeable2ByteCString())
286       EntrySize = 2;
287     else if (Kind.isMergeable4ByteCString())
288       EntrySize = 4;
289     else
290       assert(Kind.isMergeable1ByteCString() && "unknown string width");
291 
292     std::string SizeSpec = ".rodata.str" + utostr(EntrySize) + ".";
293     std::string Name = SizeSpec + utostr(Align);
294     return getContext().getELFSection(
295         Name, ELF::SHT_PROGBITS,
296         ELF::SHF_ALLOC | ELF::SHF_MERGE | ELF::SHF_STRINGS, EntrySize, "");
297   }
298 
299   if (Kind.isMergeableConst()) {
300     if (Kind.isMergeableConst4() && MergeableConst4Section)
301       return MergeableConst4Section;
302     if (Kind.isMergeableConst8() && MergeableConst8Section)
303       return MergeableConst8Section;
304     if (Kind.isMergeableConst16() && MergeableConst16Section)
305       return MergeableConst16Section;
306     return ReadOnlySection;  // .const
307   }
308 
309   if (Kind.isReadOnly())             return ReadOnlySection;
310 
311   if (Kind.isThreadData())           return TLSDataSection;
312   if (Kind.isThreadBSS())            return TLSBSSSection;
313 
314   // Note: we claim that common symbols are put in BSSSection, but they are
315   // really emitted with the magic .comm directive, which creates a symbol table
316   // entry but not a section.
317   if (Kind.isBSS() || Kind.isCommon()) return BSSSection;
318 
319   if (Kind.isDataNoRel())            return DataSection;
320   if (Kind.isDataRelLocal())         return DataRelLocalSection;
321   if (Kind.isDataRel())              return DataRelSection;
322   if (Kind.isReadOnlyWithRelLocal()) return DataRelROLocalSection;
323 
324   assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
325   return DataRelROSection;
326 }
327 
328 /// getSectionForConstant - Given a mergeable constant with the
329 /// specified size and relocation information, return a section that it
330 /// should be placed in.
331 const MCSection *
332 TargetLoweringObjectFileELF::getSectionForConstant(SectionKind Kind,
333                                                    const Constant *C) const {
334   if (Kind.isMergeableConst4() && MergeableConst4Section)
335     return MergeableConst4Section;
336   if (Kind.isMergeableConst8() && MergeableConst8Section)
337     return MergeableConst8Section;
338   if (Kind.isMergeableConst16() && MergeableConst16Section)
339     return MergeableConst16Section;
340   if (Kind.isReadOnly())
341     return ReadOnlySection;
342 
343   if (Kind.isReadOnlyWithRelLocal()) return DataRelROLocalSection;
344   assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
345   return DataRelROSection;
346 }
347 
348 static const MCSectionELF *getStaticStructorSection(MCContext &Ctx,
349                                                     bool UseInitArray,
350                                                     bool IsCtor,
351                                                     unsigned Priority,
352                                                     const MCSymbol *KeySym) {
353   std::string Name;
354   unsigned Type;
355   unsigned Flags = ELF::SHF_ALLOC | ELF::SHF_WRITE;
356   StringRef COMDAT = KeySym ? KeySym->getName() : "";
357 
358   if (KeySym)
359     Flags |= ELF::SHF_GROUP;
360 
361   if (UseInitArray) {
362     if (IsCtor) {
363       Type = ELF::SHT_INIT_ARRAY;
364       Name = ".init_array";
365     } else {
366       Type = ELF::SHT_FINI_ARRAY;
367       Name = ".fini_array";
368     }
369     if (Priority != 65535) {
370       Name += '.';
371       Name += utostr(Priority);
372     }
373   } else {
374     // The default scheme is .ctor / .dtor, so we have to invert the priority
375     // numbering.
376     if (IsCtor)
377       Name = ".ctors";
378     else
379       Name = ".dtors";
380     if (Priority != 65535) {
381       Name += '.';
382       Name += utostr(65535 - Priority);
383     }
384     Type = ELF::SHT_PROGBITS;
385   }
386 
387   return Ctx.getELFSection(Name, Type, Flags, 0, COMDAT);
388 }
389 
390 const MCSection *TargetLoweringObjectFileELF::getStaticCtorSection(
391     unsigned Priority, const MCSymbol *KeySym) const {
392   return getStaticStructorSection(getContext(), UseInitArray, true, Priority,
393                                   KeySym);
394 }
395 
396 const MCSection *TargetLoweringObjectFileELF::getStaticDtorSection(
397     unsigned Priority, const MCSymbol *KeySym) const {
398   return getStaticStructorSection(getContext(), UseInitArray, false, Priority,
399                                   KeySym);
400 }
401 
402 void
403 TargetLoweringObjectFileELF::InitializeELF(bool UseInitArray_) {
404   UseInitArray = UseInitArray_;
405   if (!UseInitArray)
406     return;
407 
408   StaticCtorSection = getContext().getELFSection(
409       ".init_array", ELF::SHT_INIT_ARRAY, ELF::SHF_WRITE | ELF::SHF_ALLOC);
410   StaticDtorSection = getContext().getELFSection(
411       ".fini_array", ELF::SHT_FINI_ARRAY, ELF::SHF_WRITE | ELF::SHF_ALLOC);
412 }
413 
414 //===----------------------------------------------------------------------===//
415 //                                 MachO
416 //===----------------------------------------------------------------------===//
417 
418 /// getDepLibFromLinkerOpt - Extract the dependent library name from a linker
419 /// option string. Returns StringRef() if the option does not specify a library.
420 StringRef TargetLoweringObjectFileMachO::
421 getDepLibFromLinkerOpt(StringRef LinkerOption) const {
422   const char *LibCmd = "-l";
423   if (LinkerOption.startswith(LibCmd))
424     return LinkerOption.substr(strlen(LibCmd));
425   return StringRef();
426 }
427 
428 /// emitModuleFlags - Perform code emission for module flags.
429 void TargetLoweringObjectFileMachO::
430 emitModuleFlags(MCStreamer &Streamer,
431                 ArrayRef<Module::ModuleFlagEntry> ModuleFlags,
432                 Mangler &Mang, const TargetMachine &TM) const {
433   unsigned VersionVal = 0;
434   unsigned ImageInfoFlags = 0;
435   MDNode *LinkerOptions = nullptr;
436   StringRef SectionVal;
437 
438   for (ArrayRef<Module::ModuleFlagEntry>::iterator
439          i = ModuleFlags.begin(), e = ModuleFlags.end(); i != e; ++i) {
440     const Module::ModuleFlagEntry &MFE = *i;
441 
442     // Ignore flags with 'Require' behavior.
443     if (MFE.Behavior == Module::Require)
444       continue;
445 
446     StringRef Key = MFE.Key->getString();
447     Metadata *Val = MFE.Val;
448 
449     if (Key == "Objective-C Image Info Version") {
450       VersionVal = mdconst::extract<ConstantInt>(Val)->getZExtValue();
451     } else if (Key == "Objective-C Garbage Collection" ||
452                Key == "Objective-C GC Only" ||
453                Key == "Objective-C Is Simulated" ||
454                Key == "Objective-C Image Swift Version") {
455       ImageInfoFlags |= mdconst::extract<ConstantInt>(Val)->getZExtValue();
456     } else if (Key == "Objective-C Image Info Section") {
457       SectionVal = cast<MDString>(Val)->getString();
458     } else if (Key == "Linker Options") {
459       LinkerOptions = cast<MDNode>(Val);
460     }
461   }
462 
463   // Emit the linker options if present.
464   if (LinkerOptions) {
465     for (unsigned i = 0, e = LinkerOptions->getNumOperands(); i != e; ++i) {
466       MDNode *MDOptions = cast<MDNode>(LinkerOptions->getOperand(i));
467       SmallVector<std::string, 4> StrOptions;
468 
469       // Convert to strings.
470       for (unsigned ii = 0, ie = MDOptions->getNumOperands(); ii != ie; ++ii) {
471         MDString *MDOption = cast<MDString>(MDOptions->getOperand(ii));
472         StrOptions.push_back(MDOption->getString());
473       }
474 
475       Streamer.EmitLinkerOptions(StrOptions);
476     }
477   }
478 
479   // The section is mandatory. If we don't have it, then we don't have GC info.
480   if (SectionVal.empty()) return;
481 
482   StringRef Segment, Section;
483   unsigned TAA = 0, StubSize = 0;
484   bool TAAParsed;
485   std::string ErrorCode =
486     MCSectionMachO::ParseSectionSpecifier(SectionVal, Segment, Section,
487                                           TAA, TAAParsed, StubSize);
488   if (!ErrorCode.empty())
489     // If invalid, report the error with report_fatal_error.
490     report_fatal_error("Invalid section specifier '" + Section + "': " +
491                        ErrorCode + ".");
492 
493   // Get the section.
494   const MCSectionMachO *S =
495     getContext().getMachOSection(Segment, Section, TAA, StubSize,
496                                  SectionKind::getDataNoRel());
497   Streamer.SwitchSection(S);
498   Streamer.EmitLabel(getContext().
499                      GetOrCreateSymbol(StringRef("L_OBJC_IMAGE_INFO")));
500   Streamer.EmitIntValue(VersionVal, 4);
501   Streamer.EmitIntValue(ImageInfoFlags, 4);
502   Streamer.AddBlankLine();
503 }
504 
505 static void checkMachOComdat(const GlobalValue *GV) {
506   const Comdat *C = GV->getComdat();
507   if (!C)
508     return;
509 
510   report_fatal_error("MachO doesn't support COMDATs, '" + C->getName() +
511                      "' cannot be lowered.");
512 }
513 
514 const MCSection *TargetLoweringObjectFileMachO::getExplicitSectionGlobal(
515     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
516     const TargetMachine &TM) const {
517   // Parse the section specifier and create it if valid.
518   StringRef Segment, Section;
519   unsigned TAA = 0, StubSize = 0;
520   bool TAAParsed;
521 
522   checkMachOComdat(GV);
523 
524   std::string ErrorCode =
525     MCSectionMachO::ParseSectionSpecifier(GV->getSection(), Segment, Section,
526                                           TAA, TAAParsed, StubSize);
527   if (!ErrorCode.empty()) {
528     // If invalid, report the error with report_fatal_error.
529     report_fatal_error("Global variable '" + GV->getName() +
530                        "' has an invalid section specifier '" +
531                        GV->getSection() + "': " + ErrorCode + ".");
532   }
533 
534   // Get the section.
535   const MCSectionMachO *S =
536     getContext().getMachOSection(Segment, Section, TAA, StubSize, Kind);
537 
538   // If TAA wasn't set by ParseSectionSpecifier() above,
539   // use the value returned by getMachOSection() as a default.
540   if (!TAAParsed)
541     TAA = S->getTypeAndAttributes();
542 
543   // Okay, now that we got the section, verify that the TAA & StubSize agree.
544   // If the user declared multiple globals with different section flags, we need
545   // to reject it here.
546   if (S->getTypeAndAttributes() != TAA || S->getStubSize() != StubSize) {
547     // If invalid, report the error with report_fatal_error.
548     report_fatal_error("Global variable '" + GV->getName() +
549                        "' section type or attributes does not match previous"
550                        " section specifier");
551   }
552 
553   return S;
554 }
555 
556 const MCSection *TargetLoweringObjectFileMachO::
557 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
558                        Mangler &Mang, const TargetMachine &TM) const {
559   checkMachOComdat(GV);
560 
561   // Handle thread local data.
562   if (Kind.isThreadBSS()) return TLSBSSSection;
563   if (Kind.isThreadData()) return TLSDataSection;
564 
565   if (Kind.isText())
566     return GV->isWeakForLinker() ? TextCoalSection : TextSection;
567 
568   // If this is weak/linkonce, put this in a coalescable section, either in text
569   // or data depending on if it is writable.
570   if (GV->isWeakForLinker()) {
571     if (Kind.isReadOnly())
572       return ConstTextCoalSection;
573     return DataCoalSection;
574   }
575 
576   // FIXME: Alignment check should be handled by section classifier.
577   if (Kind.isMergeable1ByteCString() &&
578       TM.getDataLayout()->getPreferredAlignment(cast<GlobalVariable>(GV)) < 32)
579     return CStringSection;
580 
581   // Do not put 16-bit arrays in the UString section if they have an
582   // externally visible label, this runs into issues with certain linker
583   // versions.
584   if (Kind.isMergeable2ByteCString() && !GV->hasExternalLinkage() &&
585       TM.getDataLayout()->getPreferredAlignment(cast<GlobalVariable>(GV)) < 32)
586     return UStringSection;
587 
588   // With MachO only variables whose corresponding symbol starts with 'l' or
589   // 'L' can be merged, so we only try merging GVs with private linkage.
590   if (GV->hasPrivateLinkage() && Kind.isMergeableConst()) {
591     if (Kind.isMergeableConst4())
592       return FourByteConstantSection;
593     if (Kind.isMergeableConst8())
594       return EightByteConstantSection;
595     if (Kind.isMergeableConst16())
596       return SixteenByteConstantSection;
597   }
598 
599   // Otherwise, if it is readonly, but not something we can specially optimize,
600   // just drop it in .const.
601   if (Kind.isReadOnly())
602     return ReadOnlySection;
603 
604   // If this is marked const, put it into a const section.  But if the dynamic
605   // linker needs to write to it, put it in the data segment.
606   if (Kind.isReadOnlyWithRel())
607     return ConstDataSection;
608 
609   // Put zero initialized globals with strong external linkage in the
610   // DATA, __common section with the .zerofill directive.
611   if (Kind.isBSSExtern())
612     return DataCommonSection;
613 
614   // Put zero initialized globals with local linkage in __DATA,__bss directive
615   // with the .zerofill directive (aka .lcomm).
616   if (Kind.isBSSLocal())
617     return DataBSSSection;
618 
619   // Otherwise, just drop the variable in the normal data section.
620   return DataSection;
621 }
622 
623 const MCSection *
624 TargetLoweringObjectFileMachO::getSectionForConstant(SectionKind Kind,
625                                                      const Constant *C) const {
626   // If this constant requires a relocation, we have to put it in the data
627   // segment, not in the text segment.
628   if (Kind.isDataRel() || Kind.isReadOnlyWithRel())
629     return ConstDataSection;
630 
631   if (Kind.isMergeableConst4())
632     return FourByteConstantSection;
633   if (Kind.isMergeableConst8())
634     return EightByteConstantSection;
635   if (Kind.isMergeableConst16())
636     return SixteenByteConstantSection;
637   return ReadOnlySection;  // .const
638 }
639 
640 const MCExpr *TargetLoweringObjectFileMachO::getTTypeGlobalReference(
641     const GlobalValue *GV, unsigned Encoding, Mangler &Mang,
642     const TargetMachine &TM, MachineModuleInfo *MMI,
643     MCStreamer &Streamer) const {
644   // The mach-o version of this method defaults to returning a stub reference.
645 
646   if (Encoding & DW_EH_PE_indirect) {
647     MachineModuleInfoMachO &MachOMMI =
648       MMI->getObjFileInfo<MachineModuleInfoMachO>();
649 
650     MCSymbol *SSym =
651         getSymbolWithGlobalValueBase(GV, "$non_lazy_ptr", Mang, TM);
652 
653     // Add information about the stub reference to MachOMMI so that the stub
654     // gets emitted by the asmprinter.
655     MachineModuleInfoImpl::StubValueTy &StubSym =
656       GV->hasHiddenVisibility() ? MachOMMI.getHiddenGVStubEntry(SSym) :
657                                   MachOMMI.getGVStubEntry(SSym);
658     if (!StubSym.getPointer()) {
659       MCSymbol *Sym = TM.getSymbol(GV, Mang);
660       StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
661     }
662 
663     return TargetLoweringObjectFile::
664       getTTypeReference(MCSymbolRefExpr::Create(SSym, getContext()),
665                         Encoding & ~dwarf::DW_EH_PE_indirect, Streamer);
666   }
667 
668   return TargetLoweringObjectFile::getTTypeGlobalReference(GV, Encoding, Mang,
669                                                            TM, MMI, Streamer);
670 }
671 
672 MCSymbol *TargetLoweringObjectFileMachO::getCFIPersonalitySymbol(
673     const GlobalValue *GV, Mangler &Mang, const TargetMachine &TM,
674     MachineModuleInfo *MMI) const {
675   // The mach-o version of this method defaults to returning a stub reference.
676   MachineModuleInfoMachO &MachOMMI =
677     MMI->getObjFileInfo<MachineModuleInfoMachO>();
678 
679   MCSymbol *SSym = getSymbolWithGlobalValueBase(GV, "$non_lazy_ptr", Mang, TM);
680 
681   // Add information about the stub reference to MachOMMI so that the stub
682   // gets emitted by the asmprinter.
683   MachineModuleInfoImpl::StubValueTy &StubSym = MachOMMI.getGVStubEntry(SSym);
684   if (!StubSym.getPointer()) {
685     MCSymbol *Sym = TM.getSymbol(GV, Mang);
686     StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
687   }
688 
689   return SSym;
690 }
691 
692 //===----------------------------------------------------------------------===//
693 //                                  COFF
694 //===----------------------------------------------------------------------===//
695 
696 static unsigned
697 getCOFFSectionFlags(SectionKind K) {
698   unsigned Flags = 0;
699 
700   if (K.isMetadata())
701     Flags |=
702       COFF::IMAGE_SCN_MEM_DISCARDABLE;
703   else if (K.isText())
704     Flags |=
705       COFF::IMAGE_SCN_MEM_EXECUTE |
706       COFF::IMAGE_SCN_MEM_READ |
707       COFF::IMAGE_SCN_CNT_CODE;
708   else if (K.isBSS())
709     Flags |=
710       COFF::IMAGE_SCN_CNT_UNINITIALIZED_DATA |
711       COFF::IMAGE_SCN_MEM_READ |
712       COFF::IMAGE_SCN_MEM_WRITE;
713   else if (K.isThreadLocal())
714     Flags |=
715       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
716       COFF::IMAGE_SCN_MEM_READ |
717       COFF::IMAGE_SCN_MEM_WRITE;
718   else if (K.isReadOnly() || K.isReadOnlyWithRel())
719     Flags |=
720       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
721       COFF::IMAGE_SCN_MEM_READ;
722   else if (K.isWriteable())
723     Flags |=
724       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
725       COFF::IMAGE_SCN_MEM_READ |
726       COFF::IMAGE_SCN_MEM_WRITE;
727 
728   return Flags;
729 }
730 
731 static const GlobalValue *getComdatGVForCOFF(const GlobalValue *GV) {
732   const Comdat *C = GV->getComdat();
733   assert(C && "expected GV to have a Comdat!");
734 
735   StringRef ComdatGVName = C->getName();
736   const GlobalValue *ComdatGV = GV->getParent()->getNamedValue(ComdatGVName);
737   if (!ComdatGV)
738     report_fatal_error("Associative COMDAT symbol '" + ComdatGVName +
739                        "' does not exist.");
740 
741   if (ComdatGV->getComdat() != C)
742     report_fatal_error("Associative COMDAT symbol '" + ComdatGVName +
743                        "' is not a key for its COMDAT.");
744 
745   return ComdatGV;
746 }
747 
748 static int getSelectionForCOFF(const GlobalValue *GV) {
749   if (const Comdat *C = GV->getComdat()) {
750     const GlobalValue *ComdatKey = getComdatGVForCOFF(GV);
751     if (const auto *GA = dyn_cast<GlobalAlias>(ComdatKey))
752       ComdatKey = GA->getBaseObject();
753     if (ComdatKey == GV) {
754       switch (C->getSelectionKind()) {
755       case Comdat::Any:
756         return COFF::IMAGE_COMDAT_SELECT_ANY;
757       case Comdat::ExactMatch:
758         return COFF::IMAGE_COMDAT_SELECT_EXACT_MATCH;
759       case Comdat::Largest:
760         return COFF::IMAGE_COMDAT_SELECT_LARGEST;
761       case Comdat::NoDuplicates:
762         return COFF::IMAGE_COMDAT_SELECT_NODUPLICATES;
763       case Comdat::SameSize:
764         return COFF::IMAGE_COMDAT_SELECT_SAME_SIZE;
765       }
766     } else {
767       return COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE;
768     }
769   } else if (GV->isWeakForLinker()) {
770     return COFF::IMAGE_COMDAT_SELECT_ANY;
771   }
772   return 0;
773 }
774 
775 const MCSection *TargetLoweringObjectFileCOFF::getExplicitSectionGlobal(
776     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
777     const TargetMachine &TM) const {
778   int Selection = 0;
779   unsigned Characteristics = getCOFFSectionFlags(Kind);
780   StringRef Name = GV->getSection();
781   StringRef COMDATSymName = "";
782   if (GV->hasComdat()) {
783     Selection = getSelectionForCOFF(GV);
784     const GlobalValue *ComdatGV;
785     if (Selection == COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE)
786       ComdatGV = getComdatGVForCOFF(GV);
787     else
788       ComdatGV = GV;
789 
790     if (!ComdatGV->hasPrivateLinkage()) {
791       MCSymbol *Sym = TM.getSymbol(ComdatGV, Mang);
792       COMDATSymName = Sym->getName();
793       Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
794     } else {
795       Selection = 0;
796     }
797   }
798   return getContext().getCOFFSection(Name,
799                                      Characteristics,
800                                      Kind,
801                                      COMDATSymName,
802                                      Selection);
803 }
804 
805 static const char *getCOFFSectionNameForUniqueGlobal(SectionKind Kind) {
806   if (Kind.isText())
807     return ".text";
808   if (Kind.isBSS())
809     return ".bss";
810   if (Kind.isThreadLocal())
811     return ".tls$";
812   if (Kind.isReadOnly() || Kind.isReadOnlyWithRel())
813     return ".rdata";
814   return ".data";
815 }
816 
817 
818 const MCSection *TargetLoweringObjectFileCOFF::
819 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
820                        Mangler &Mang, const TargetMachine &TM) const {
821   // If we have -ffunction-sections then we should emit the global value to a
822   // uniqued section specifically for it.
823   bool EmitUniquedSection;
824   if (Kind.isText())
825     EmitUniquedSection = TM.getFunctionSections();
826   else
827     EmitUniquedSection = TM.getDataSections();
828 
829   if ((EmitUniquedSection && !Kind.isCommon()) || GV->hasComdat()) {
830     const char *Name = getCOFFSectionNameForUniqueGlobal(Kind);
831     unsigned Characteristics = getCOFFSectionFlags(Kind);
832 
833     Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
834     int Selection = getSelectionForCOFF(GV);
835     if (!Selection)
836       Selection = COFF::IMAGE_COMDAT_SELECT_NODUPLICATES;
837     const GlobalValue *ComdatGV;
838     if (GV->hasComdat())
839       ComdatGV = getComdatGVForCOFF(GV);
840     else
841       ComdatGV = GV;
842 
843     if (!ComdatGV->hasPrivateLinkage()) {
844       MCSymbol *Sym = TM.getSymbol(ComdatGV, Mang);
845       StringRef COMDATSymName = Sym->getName();
846       return getContext().getCOFFSection(Name, Characteristics, Kind,
847                                          COMDATSymName, Selection);
848     }
849   }
850 
851   if (Kind.isText())
852     return TextSection;
853 
854   if (Kind.isThreadLocal())
855     return TLSDataSection;
856 
857   if (Kind.isReadOnly() || Kind.isReadOnlyWithRel())
858     return ReadOnlySection;
859 
860   // Note: we claim that common symbols are put in BSSSection, but they are
861   // really emitted with the magic .comm directive, which creates a symbol table
862   // entry but not a section.
863   if (Kind.isBSS() || Kind.isCommon())
864     return BSSSection;
865 
866   return DataSection;
867 }
868 
869 StringRef TargetLoweringObjectFileCOFF::
870 getDepLibFromLinkerOpt(StringRef LinkerOption) const {
871   const char *LibCmd = "/DEFAULTLIB:";
872   if (LinkerOption.startswith(LibCmd))
873     return LinkerOption.substr(strlen(LibCmd));
874   return StringRef();
875 }
876 
877 void TargetLoweringObjectFileCOFF::
878 emitModuleFlags(MCStreamer &Streamer,
879                 ArrayRef<Module::ModuleFlagEntry> ModuleFlags,
880                 Mangler &Mang, const TargetMachine &TM) const {
881   MDNode *LinkerOptions = nullptr;
882 
883   // Look for the "Linker Options" flag, since it's the only one we support.
884   for (ArrayRef<Module::ModuleFlagEntry>::iterator
885        i = ModuleFlags.begin(), e = ModuleFlags.end(); i != e; ++i) {
886     const Module::ModuleFlagEntry &MFE = *i;
887     StringRef Key = MFE.Key->getString();
888     Metadata *Val = MFE.Val;
889     if (Key == "Linker Options") {
890       LinkerOptions = cast<MDNode>(Val);
891       break;
892     }
893   }
894   if (!LinkerOptions)
895     return;
896 
897   // Emit the linker options to the linker .drectve section.  According to the
898   // spec, this section is a space-separated string containing flags for linker.
899   const MCSection *Sec = getDrectveSection();
900   Streamer.SwitchSection(Sec);
901   for (unsigned i = 0, e = LinkerOptions->getNumOperands(); i != e; ++i) {
902     MDNode *MDOptions = cast<MDNode>(LinkerOptions->getOperand(i));
903     for (unsigned ii = 0, ie = MDOptions->getNumOperands(); ii != ie; ++ii) {
904       MDString *MDOption = cast<MDString>(MDOptions->getOperand(ii));
905       StringRef Op = MDOption->getString();
906       // Lead with a space for consistency with our dllexport implementation.
907       std::string Escaped(" ");
908       if (!Op.startswith("\"") && (Op.find(" ") != StringRef::npos)) {
909         // The PE-COFF spec says args with spaces must be quoted.  It doesn't say
910         // how to escape quotes, but it probably uses this algorithm:
911         // http://msdn.microsoft.com/en-us/library/17w5ykft(v=vs.85).aspx
912         // FIXME: Reuse escaping code from Support/Windows/Program.inc
913         Escaped.push_back('\"');
914         Escaped.append(Op);
915         Escaped.push_back('\"');
916       } else {
917         Escaped.append(Op);
918       }
919       Streamer.EmitBytes(Escaped);
920     }
921   }
922 }
923 
924 const MCSection *TargetLoweringObjectFileCOFF::getStaticCtorSection(
925     unsigned Priority, const MCSymbol *KeySym) const {
926   return getContext().getAssociativeCOFFSection(
927       cast<MCSectionCOFF>(StaticCtorSection), KeySym);
928 }
929 
930 const MCSection *TargetLoweringObjectFileCOFF::getStaticDtorSection(
931     unsigned Priority, const MCSymbol *KeySym) const {
932   return getContext().getAssociativeCOFFSection(
933       cast<MCSectionCOFF>(StaticDtorSection), KeySym);
934 }
935