xref: /llvm-project/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp (revision ca3e0ee8b3843c1c558e3ae824570d1b623fda9d) 
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/Constants.h"
17 #include "llvm/DerivedTypes.h"
18 #include "llvm/Function.h"
19 #include "llvm/GlobalVariable.h"
20 #include "llvm/Module.h"
21 #include "llvm/CodeGen/MachineModuleInfoImpls.h"
22 #include "llvm/MC/MCContext.h"
23 #include "llvm/MC/MCExpr.h"
24 #include "llvm/MC/MCSectionMachO.h"
25 #include "llvm/MC/MCSectionELF.h"
26 #include "llvm/MC/MCSectionCOFF.h"
27 #include "llvm/MC/MCStreamer.h"
28 #include "llvm/MC/MCSymbol.h"
29 #include "llvm/Target/Mangler.h"
30 #include "llvm/Target/TargetData.h"
31 #include "llvm/Target/TargetMachine.h"
32 #include "llvm/Target/TargetOptions.h"
33 #include "llvm/Support/Dwarf.h"
34 #include "llvm/Support/ELF.h"
35 #include "llvm/Support/ErrorHandling.h"
36 #include "llvm/Support/raw_ostream.h"
37 #include "llvm/ADT/SmallString.h"
38 #include "llvm/ADT/StringExtras.h"
39 #include "llvm/ADT/Triple.h"
40 using namespace llvm;
41 using namespace dwarf;
42 
43 //===----------------------------------------------------------------------===//
44 //                                  ELF
45 //===----------------------------------------------------------------------===//
46 
47 MCSymbol *
48 TargetLoweringObjectFileELF::getCFIPersonalitySymbol(const GlobalValue *GV,
49                                                      Mangler *Mang,
50                                                 MachineModuleInfo *MMI) const {
51   unsigned Encoding = getPersonalityEncoding();
52   switch (Encoding & 0x70) {
53   default:
54     report_fatal_error("We do not support this DWARF encoding yet!");
55   case dwarf::DW_EH_PE_absptr:
56     return  Mang->getSymbol(GV);
57   case dwarf::DW_EH_PE_pcrel: {
58     return getContext().GetOrCreateSymbol(StringRef("DW.ref.") +
59                                           Mang->getSymbol(GV)->getName());
60   }
61   }
62 }
63 
64 void TargetLoweringObjectFileELF::emitPersonalityValue(MCStreamer &Streamer,
65                                                        const TargetMachine &TM,
66                                                        const MCSymbol *Sym) const {
67   SmallString<64> NameData("DW.ref.");
68   NameData += Sym->getName();
69   MCSymbol *Label = getContext().GetOrCreateSymbol(NameData);
70   Streamer.EmitSymbolAttribute(Label, MCSA_Hidden);
71   Streamer.EmitSymbolAttribute(Label, MCSA_Weak);
72   StringRef Prefix = ".data.";
73   NameData.insert(NameData.begin(), Prefix.begin(), Prefix.end());
74   unsigned Flags = ELF::SHF_ALLOC | ELF::SHF_WRITE | ELF::SHF_GROUP;
75   const MCSection *Sec = getContext().getELFSection(NameData,
76                                                     ELF::SHT_PROGBITS,
77                                                     Flags,
78                                                     SectionKind::getDataRel(),
79                                                     0, Label->getName());
80   unsigned Size = TM.getTargetData()->getPointerSize();
81   Streamer.SwitchSection(Sec);
82   Streamer.EmitValueToAlignment(TM.getTargetData()->getPointerABIAlignment());
83   Streamer.EmitSymbolAttribute(Label, MCSA_ELF_TypeObject);
84   const MCExpr *E = MCConstantExpr::Create(Size, getContext());
85   Streamer.EmitELFSize(Label, E);
86   Streamer.EmitLabel(Label);
87 
88   Streamer.EmitSymbolValue(Sym, Size);
89 }
90 
91 static SectionKind
92 getELFKindForNamedSection(StringRef Name, SectionKind K) {
93   // N.B.: The defaults used in here are no the same ones used in MC.
94   // We follow gcc, MC follows gas. For example, given ".section .eh_frame",
95   // both gas and MC will produce a section with no flags. Given
96   // section(".eh_frame") gcc will produce
97   // .section	.eh_frame,"a",@progbits
98   if (Name.empty() || Name[0] != '.') return K;
99 
100   // Some lame default implementation based on some magic section names.
101   if (Name == ".bss" ||
102       Name.startswith(".bss.") ||
103       Name.startswith(".gnu.linkonce.b.") ||
104       Name.startswith(".llvm.linkonce.b.") ||
105       Name == ".sbss" ||
106       Name.startswith(".sbss.") ||
107       Name.startswith(".gnu.linkonce.sb.") ||
108       Name.startswith(".llvm.linkonce.sb."))
109     return SectionKind::getBSS();
110 
111   if (Name == ".tdata" ||
112       Name.startswith(".tdata.") ||
113       Name.startswith(".gnu.linkonce.td.") ||
114       Name.startswith(".llvm.linkonce.td."))
115     return SectionKind::getThreadData();
116 
117   if (Name == ".tbss" ||
118       Name.startswith(".tbss.") ||
119       Name.startswith(".gnu.linkonce.tb.") ||
120       Name.startswith(".llvm.linkonce.tb."))
121     return SectionKind::getThreadBSS();
122 
123   return K;
124 }
125 
126 
127 static unsigned getELFSectionType(StringRef Name, SectionKind K) {
128 
129   if (Name == ".init_array")
130     return ELF::SHT_INIT_ARRAY;
131 
132   if (Name == ".fini_array")
133     return ELF::SHT_FINI_ARRAY;
134 
135   if (Name == ".preinit_array")
136     return ELF::SHT_PREINIT_ARRAY;
137 
138   if (K.isBSS() || K.isThreadBSS())
139     return ELF::SHT_NOBITS;
140 
141   return ELF::SHT_PROGBITS;
142 }
143 
144 
145 static unsigned
146 getELFSectionFlags(SectionKind K) {
147   unsigned Flags = 0;
148 
149   if (!K.isMetadata())
150     Flags |= ELF::SHF_ALLOC;
151 
152   if (K.isText())
153     Flags |= ELF::SHF_EXECINSTR;
154 
155   if (K.isWriteable())
156     Flags |= ELF::SHF_WRITE;
157 
158   if (K.isThreadLocal())
159     Flags |= ELF::SHF_TLS;
160 
161   // K.isMergeableConst() is left out to honour PR4650
162   if (K.isMergeableCString() || K.isMergeableConst4() ||
163       K.isMergeableConst8() || K.isMergeableConst16())
164     Flags |= ELF::SHF_MERGE;
165 
166   if (K.isMergeableCString())
167     Flags |= ELF::SHF_STRINGS;
168 
169   return Flags;
170 }
171 
172 
173 const MCSection *TargetLoweringObjectFileELF::
174 getExplicitSectionGlobal(const GlobalValue *GV, SectionKind Kind,
175                          Mangler *Mang, const TargetMachine &TM) const {
176   StringRef SectionName = GV->getSection();
177 
178   // Infer section flags from the section name if we can.
179   Kind = getELFKindForNamedSection(SectionName, Kind);
180 
181   return getContext().getELFSection(SectionName,
182                                     getELFSectionType(SectionName, Kind),
183                                     getELFSectionFlags(Kind), Kind);
184 }
185 
186 /// getSectionPrefixForGlobal - Return the section prefix name used by options
187 /// FunctionsSections and DataSections.
188 static const char *getSectionPrefixForGlobal(SectionKind Kind) {
189   if (Kind.isText())                 return ".text.";
190   if (Kind.isReadOnly())             return ".rodata.";
191   if (Kind.isBSS())                  return ".bss.";
192 
193   if (Kind.isThreadData())           return ".tdata.";
194   if (Kind.isThreadBSS())            return ".tbss.";
195 
196   if (Kind.isDataNoRel())            return ".data.";
197   if (Kind.isDataRelLocal())         return ".data.rel.local.";
198   if (Kind.isDataRel())              return ".data.rel.";
199   if (Kind.isReadOnlyWithRelLocal()) return ".data.rel.ro.local.";
200 
201   assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
202   return ".data.rel.ro.";
203 }
204 
205 
206 const MCSection *TargetLoweringObjectFileELF::
207 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
208                        Mangler *Mang, const TargetMachine &TM) const {
209   // If we have -ffunction-section or -fdata-section then we should emit the
210   // global value to a uniqued section specifically for it.
211   bool EmitUniquedSection;
212   if (Kind.isText())
213     EmitUniquedSection = TM.getFunctionSections();
214   else
215     EmitUniquedSection = TM.getDataSections();
216 
217   // If this global is linkonce/weak and the target handles this by emitting it
218   // into a 'uniqued' section name, create and return the section now.
219   if ((GV->isWeakForLinker() || EmitUniquedSection) &&
220       !Kind.isCommon()) {
221     const char *Prefix;
222     Prefix = getSectionPrefixForGlobal(Kind);
223 
224     SmallString<128> Name(Prefix, Prefix+strlen(Prefix));
225     MCSymbol *Sym = Mang->getSymbol(GV);
226     Name.append(Sym->getName().begin(), Sym->getName().end());
227     StringRef Group = "";
228     unsigned Flags = getELFSectionFlags(Kind);
229     if (GV->isWeakForLinker()) {
230       Group = Sym->getName();
231       Flags |= ELF::SHF_GROUP;
232     }
233 
234     return getContext().getELFSection(Name.str(),
235                                       getELFSectionType(Name.str(), Kind),
236                                       Flags, Kind, 0, Group);
237   }
238 
239   if (Kind.isText()) return TextSection;
240 
241   if (Kind.isMergeable1ByteCString() ||
242       Kind.isMergeable2ByteCString() ||
243       Kind.isMergeable4ByteCString()) {
244 
245     // We also need alignment here.
246     // FIXME: this is getting the alignment of the character, not the
247     // alignment of the global!
248     unsigned Align =
249       TM.getTargetData()->getPreferredAlignment(cast<GlobalVariable>(GV));
250 
251     const char *SizeSpec = ".rodata.str1.";
252     if (Kind.isMergeable2ByteCString())
253       SizeSpec = ".rodata.str2.";
254     else if (Kind.isMergeable4ByteCString())
255       SizeSpec = ".rodata.str4.";
256     else
257       assert(Kind.isMergeable1ByteCString() && "unknown string width");
258 
259 
260     std::string Name = SizeSpec + utostr(Align);
261     return getContext().getELFSection(Name, ELF::SHT_PROGBITS,
262                                       ELF::SHF_ALLOC |
263                                       ELF::SHF_MERGE |
264                                       ELF::SHF_STRINGS,
265                                       Kind);
266   }
267 
268   if (Kind.isMergeableConst()) {
269     if (Kind.isMergeableConst4() && MergeableConst4Section)
270       return MergeableConst4Section;
271     if (Kind.isMergeableConst8() && MergeableConst8Section)
272       return MergeableConst8Section;
273     if (Kind.isMergeableConst16() && MergeableConst16Section)
274       return MergeableConst16Section;
275     return ReadOnlySection;  // .const
276   }
277 
278   if (Kind.isReadOnly())             return ReadOnlySection;
279 
280   if (Kind.isThreadData())           return TLSDataSection;
281   if (Kind.isThreadBSS())            return TLSBSSSection;
282 
283   // Note: we claim that common symbols are put in BSSSection, but they are
284   // really emitted with the magic .comm directive, which creates a symbol table
285   // entry but not a section.
286   if (Kind.isBSS() || Kind.isCommon()) return BSSSection;
287 
288   if (Kind.isDataNoRel())            return DataSection;
289   if (Kind.isDataRelLocal())         return DataRelLocalSection;
290   if (Kind.isDataRel())              return DataRelSection;
291   if (Kind.isReadOnlyWithRelLocal()) return DataRelROLocalSection;
292 
293   assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
294   return DataRelROSection;
295 }
296 
297 /// getSectionForConstant - Given a mergeable constant with the
298 /// specified size and relocation information, return a section that it
299 /// should be placed in.
300 const MCSection *TargetLoweringObjectFileELF::
301 getSectionForConstant(SectionKind Kind) const {
302   if (Kind.isMergeableConst4() && MergeableConst4Section)
303     return MergeableConst4Section;
304   if (Kind.isMergeableConst8() && MergeableConst8Section)
305     return MergeableConst8Section;
306   if (Kind.isMergeableConst16() && MergeableConst16Section)
307     return MergeableConst16Section;
308   if (Kind.isReadOnly())
309     return ReadOnlySection;
310 
311   if (Kind.isReadOnlyWithRelLocal()) return DataRelROLocalSection;
312   assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
313   return DataRelROSection;
314 }
315 
316 const MCExpr *TargetLoweringObjectFileELF::
317 getExprForDwarfGlobalReference(const GlobalValue *GV, Mangler *Mang,
318                                MachineModuleInfo *MMI,
319                                unsigned Encoding, MCStreamer &Streamer) const {
320 
321   if (Encoding & dwarf::DW_EH_PE_indirect) {
322     MachineModuleInfoELF &ELFMMI = MMI->getObjFileInfo<MachineModuleInfoELF>();
323 
324     SmallString<128> Name;
325     Mang->getNameWithPrefix(Name, GV, true);
326     Name += ".DW.stub";
327 
328     // Add information about the stub reference to ELFMMI so that the stub
329     // gets emitted by the asmprinter.
330     MCSymbol *SSym = getContext().GetOrCreateSymbol(Name.str());
331     MachineModuleInfoImpl::StubValueTy &StubSym = ELFMMI.getGVStubEntry(SSym);
332     if (StubSym.getPointer() == 0) {
333       MCSymbol *Sym = Mang->getSymbol(GV);
334       StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
335     }
336 
337     return TargetLoweringObjectFile::
338       getExprForDwarfReference(SSym, Encoding & ~dwarf::DW_EH_PE_indirect, Streamer);
339   }
340 
341   return TargetLoweringObjectFile::
342     getExprForDwarfGlobalReference(GV, Mang, MMI, Encoding, Streamer);
343 }
344 
345 const MCSection *
346 TargetLoweringObjectFileELF::getStaticCtorSection(unsigned Priority) const {
347   // The default scheme is .ctor / .dtor, so we have to invert the priority
348   // numbering.
349   if (Priority == 65535)
350     return StaticCtorSection;
351 
352   if (UseInitArray) {
353     std::string Name = std::string(".init_array.") + utostr(Priority);
354     return getContext().getELFSection(Name, ELF::SHT_INIT_ARRAY,
355                                       ELF::SHF_ALLOC | ELF::SHF_WRITE,
356                                       SectionKind::getDataRel());
357   } else {
358     std::string Name = std::string(".ctors.") + utostr(65535 - Priority);
359     return getContext().getELFSection(Name, ELF::SHT_PROGBITS,
360                                       ELF::SHF_ALLOC |ELF::SHF_WRITE,
361                                       SectionKind::getDataRel());
362   }
363 }
364 
365 const MCSection *
366 TargetLoweringObjectFileELF::getStaticDtorSection(unsigned Priority) const {
367   // The default scheme is .ctor / .dtor, so we have to invert the priority
368   // numbering.
369   if (Priority == 65535)
370     return StaticDtorSection;
371 
372   if (UseInitArray) {
373     std::string Name = std::string(".fini_array.") + utostr(Priority);
374     return getContext().getELFSection(Name, ELF::SHT_FINI_ARRAY,
375                                       ELF::SHF_ALLOC | ELF::SHF_WRITE,
376                                       SectionKind::getDataRel());
377   } else {
378     std::string Name = std::string(".dtors.") + utostr(65535 - Priority);
379     return getContext().getELFSection(Name, ELF::SHT_PROGBITS,
380                                       ELF::SHF_ALLOC |ELF::SHF_WRITE,
381                                       SectionKind::getDataRel());
382   }
383 }
384 
385 void
386 TargetLoweringObjectFileELF::InitializeELF(bool UseInitArray_) {
387   UseInitArray = UseInitArray_;
388   if (!UseInitArray)
389     return;
390 
391   StaticCtorSection =
392     getContext().getELFSection(".init_array", ELF::SHT_INIT_ARRAY,
393                                ELF::SHF_WRITE |
394                                ELF::SHF_ALLOC,
395                                SectionKind::getDataRel());
396   StaticDtorSection =
397     getContext().getELFSection(".fini_array", ELF::SHT_FINI_ARRAY,
398                                ELF::SHF_WRITE |
399                                ELF::SHF_ALLOC,
400                                SectionKind::getDataRel());
401 }
402 
403 //===----------------------------------------------------------------------===//
404 //                                 MachO
405 //===----------------------------------------------------------------------===//
406 
407 /// emitModuleFlags - Emit the module flags that specify the garbage collection
408 /// information.
409 void TargetLoweringObjectFileMachO::
410 emitModuleFlags(MCStreamer &Streamer,
411                 ArrayRef<Module::ModuleFlagEntry> ModuleFlags,
412                 Mangler *Mang, const TargetMachine &TM) const {
413   unsigned VersionVal = 0;
414   unsigned ImageInfoFlags = 0;
415   StringRef SectionVal;
416 
417   for (ArrayRef<Module::ModuleFlagEntry>::iterator
418          i = ModuleFlags.begin(), e = ModuleFlags.end(); i != e; ++i) {
419     const Module::ModuleFlagEntry &MFE = *i;
420 
421     // Ignore flags with 'Require' behavior.
422     if (MFE.Behavior == Module::Require)
423       continue;
424 
425     StringRef Key = MFE.Key->getString();
426     Value *Val = MFE.Val;
427 
428     if (Key == "Objective-C Image Info Version")
429       VersionVal = cast<ConstantInt>(Val)->getZExtValue();
430     else if (Key == "Objective-C Garbage Collection" ||
431              Key == "Objective-C GC Only" ||
432              Key == "Objective-C Is Simulated")
433       ImageInfoFlags |= cast<ConstantInt>(Val)->getZExtValue();
434     else if (Key == "Objective-C Image Info Section")
435       SectionVal = cast<MDString>(Val)->getString();
436   }
437 
438   // The section is mandatory. If we don't have it, then we don't have GC info.
439   if (SectionVal.empty()) return;
440 
441   StringRef Segment, Section;
442   unsigned TAA = 0, StubSize = 0;
443   bool TAAParsed;
444   std::string ErrorCode =
445     MCSectionMachO::ParseSectionSpecifier(SectionVal, Segment, Section,
446                                           TAA, TAAParsed, StubSize);
447   if (!ErrorCode.empty())
448     // If invalid, report the error with report_fatal_error.
449     report_fatal_error("Invalid section specifier '" + Section + "': " +
450                        ErrorCode + ".");
451 
452   // Get the section.
453   const MCSectionMachO *S =
454     getContext().getMachOSection(Segment, Section, TAA, StubSize,
455                                  SectionKind::getDataNoRel());
456   Streamer.SwitchSection(S);
457   Streamer.EmitLabel(getContext().
458                      GetOrCreateSymbol(StringRef("L_OBJC_IMAGE_INFO")));
459   Streamer.EmitIntValue(VersionVal, 4);
460   Streamer.EmitIntValue(ImageInfoFlags, 4);
461   Streamer.AddBlankLine();
462 }
463 
464 const MCSection *TargetLoweringObjectFileMachO::
465 getExplicitSectionGlobal(const GlobalValue *GV, SectionKind Kind,
466                          Mangler *Mang, const TargetMachine &TM) const {
467   // Parse the section specifier and create it if valid.
468   StringRef Segment, Section;
469   unsigned TAA = 0, StubSize = 0;
470   bool TAAParsed;
471   std::string ErrorCode =
472     MCSectionMachO::ParseSectionSpecifier(GV->getSection(), Segment, Section,
473                                           TAA, TAAParsed, StubSize);
474   if (!ErrorCode.empty()) {
475     // If invalid, report the error with report_fatal_error.
476     report_fatal_error("Global variable '" + GV->getName() +
477                        "' has an invalid section specifier '" +
478                        GV->getSection() + "': " + ErrorCode + ".");
479   }
480 
481   // Get the section.
482   const MCSectionMachO *S =
483     getContext().getMachOSection(Segment, Section, TAA, StubSize, Kind);
484 
485   // If TAA wasn't set by ParseSectionSpecifier() above,
486   // use the value returned by getMachOSection() as a default.
487   if (!TAAParsed)
488     TAA = S->getTypeAndAttributes();
489 
490   // Okay, now that we got the section, verify that the TAA & StubSize agree.
491   // If the user declared multiple globals with different section flags, we need
492   // to reject it here.
493   if (S->getTypeAndAttributes() != TAA || S->getStubSize() != StubSize) {
494     // If invalid, report the error with report_fatal_error.
495     report_fatal_error("Global variable '" + GV->getName() +
496                        "' section type or attributes does not match previous"
497                        " section specifier");
498   }
499 
500   return S;
501 }
502 
503 const MCSection *TargetLoweringObjectFileMachO::
504 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
505                        Mangler *Mang, const TargetMachine &TM) const {
506 
507   // Handle thread local data.
508   if (Kind.isThreadBSS()) return TLSBSSSection;
509   if (Kind.isThreadData()) return TLSDataSection;
510 
511   if (Kind.isText())
512     return GV->isWeakForLinker() ? TextCoalSection : TextSection;
513 
514   // If this is weak/linkonce, put this in a coalescable section, either in text
515   // or data depending on if it is writable.
516   if (GV->isWeakForLinker()) {
517     if (Kind.isReadOnly())
518       return ConstTextCoalSection;
519     return DataCoalSection;
520   }
521 
522   // FIXME: Alignment check should be handled by section classifier.
523   if (Kind.isMergeable1ByteCString() &&
524       TM.getTargetData()->getPreferredAlignment(cast<GlobalVariable>(GV)) < 32)
525     return CStringSection;
526 
527   // Do not put 16-bit arrays in the UString section if they have an
528   // externally visible label, this runs into issues with certain linker
529   // versions.
530   if (Kind.isMergeable2ByteCString() && !GV->hasExternalLinkage() &&
531       TM.getTargetData()->getPreferredAlignment(cast<GlobalVariable>(GV)) < 32)
532     return UStringSection;
533 
534   if (Kind.isMergeableConst()) {
535     if (Kind.isMergeableConst4())
536       return FourByteConstantSection;
537     if (Kind.isMergeableConst8())
538       return EightByteConstantSection;
539     if (Kind.isMergeableConst16() && SixteenByteConstantSection)
540       return SixteenByteConstantSection;
541   }
542 
543   // Otherwise, if it is readonly, but not something we can specially optimize,
544   // just drop it in .const.
545   if (Kind.isReadOnly())
546     return ReadOnlySection;
547 
548   // If this is marked const, put it into a const section.  But if the dynamic
549   // linker needs to write to it, put it in the data segment.
550   if (Kind.isReadOnlyWithRel())
551     return ConstDataSection;
552 
553   // Put zero initialized globals with strong external linkage in the
554   // DATA, __common section with the .zerofill directive.
555   if (Kind.isBSSExtern())
556     return DataCommonSection;
557 
558   // Put zero initialized globals with local linkage in __DATA,__bss directive
559   // with the .zerofill directive (aka .lcomm).
560   if (Kind.isBSSLocal())
561     return DataBSSSection;
562 
563   // Otherwise, just drop the variable in the normal data section.
564   return DataSection;
565 }
566 
567 const MCSection *
568 TargetLoweringObjectFileMachO::getSectionForConstant(SectionKind Kind) const {
569   // If this constant requires a relocation, we have to put it in the data
570   // segment, not in the text segment.
571   if (Kind.isDataRel() || Kind.isReadOnlyWithRel())
572     return ConstDataSection;
573 
574   if (Kind.isMergeableConst4())
575     return FourByteConstantSection;
576   if (Kind.isMergeableConst8())
577     return EightByteConstantSection;
578   if (Kind.isMergeableConst16() && SixteenByteConstantSection)
579     return SixteenByteConstantSection;
580   return ReadOnlySection;  // .const
581 }
582 
583 /// shouldEmitUsedDirectiveFor - This hook allows targets to selectively decide
584 /// not to emit the UsedDirective for some symbols in llvm.used.
585 // FIXME: REMOVE this (rdar://7071300)
586 bool TargetLoweringObjectFileMachO::
587 shouldEmitUsedDirectiveFor(const GlobalValue *GV, Mangler *Mang) const {
588   /// On Darwin, internally linked data beginning with "L" or "l" does not have
589   /// the directive emitted (this occurs in ObjC metadata).
590   if (!GV) return false;
591 
592   // Check whether the mangled name has the "Private" or "LinkerPrivate" prefix.
593   if (GV->hasLocalLinkage() && !isa<Function>(GV)) {
594     // FIXME: ObjC metadata is currently emitted as internal symbols that have
595     // \1L and \0l prefixes on them.  Fix them to be Private/LinkerPrivate and
596     // this horrible hack can go away.
597     MCSymbol *Sym = Mang->getSymbol(GV);
598     if (Sym->getName()[0] == 'L' || Sym->getName()[0] == 'l')
599       return false;
600   }
601 
602   return true;
603 }
604 
605 const MCExpr *TargetLoweringObjectFileMachO::
606 getExprForDwarfGlobalReference(const GlobalValue *GV, Mangler *Mang,
607                                MachineModuleInfo *MMI, unsigned Encoding,
608                                MCStreamer &Streamer) const {
609   // The mach-o version of this method defaults to returning a stub reference.
610 
611   if (Encoding & DW_EH_PE_indirect) {
612     MachineModuleInfoMachO &MachOMMI =
613       MMI->getObjFileInfo<MachineModuleInfoMachO>();
614 
615     SmallString<128> Name;
616     Mang->getNameWithPrefix(Name, GV, true);
617     Name += "$non_lazy_ptr";
618 
619     // Add information about the stub reference to MachOMMI so that the stub
620     // gets emitted by the asmprinter.
621     MCSymbol *SSym = getContext().GetOrCreateSymbol(Name.str());
622     MachineModuleInfoImpl::StubValueTy &StubSym =
623       GV->hasHiddenVisibility() ? MachOMMI.getHiddenGVStubEntry(SSym) :
624                                   MachOMMI.getGVStubEntry(SSym);
625     if (StubSym.getPointer() == 0) {
626       MCSymbol *Sym = Mang->getSymbol(GV);
627       StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
628     }
629 
630     return TargetLoweringObjectFile::
631       getExprForDwarfReference(SSym, Encoding & ~dwarf::DW_EH_PE_indirect, Streamer);
632   }
633 
634   return TargetLoweringObjectFile::
635     getExprForDwarfGlobalReference(GV, Mang, MMI, Encoding, Streamer);
636 }
637 
638 MCSymbol *TargetLoweringObjectFileMachO::
639 getCFIPersonalitySymbol(const GlobalValue *GV, Mangler *Mang,
640                         MachineModuleInfo *MMI) const {
641   // The mach-o version of this method defaults to returning a stub reference.
642   MachineModuleInfoMachO &MachOMMI =
643     MMI->getObjFileInfo<MachineModuleInfoMachO>();
644 
645   SmallString<128> Name;
646   Mang->getNameWithPrefix(Name, GV, true);
647   Name += "$non_lazy_ptr";
648 
649   // Add information about the stub reference to MachOMMI so that the stub
650   // gets emitted by the asmprinter.
651   MCSymbol *SSym = getContext().GetOrCreateSymbol(Name.str());
652   MachineModuleInfoImpl::StubValueTy &StubSym = MachOMMI.getGVStubEntry(SSym);
653   if (StubSym.getPointer() == 0) {
654     MCSymbol *Sym = Mang->getSymbol(GV);
655     StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
656   }
657 
658   return SSym;
659 }
660 
661 //===----------------------------------------------------------------------===//
662 //                                  COFF
663 //===----------------------------------------------------------------------===//
664 
665 static unsigned
666 getCOFFSectionFlags(SectionKind K) {
667   unsigned Flags = 0;
668 
669   if (K.isMetadata())
670     Flags |=
671       COFF::IMAGE_SCN_MEM_DISCARDABLE;
672   else if (K.isText())
673     Flags |=
674       COFF::IMAGE_SCN_MEM_EXECUTE |
675       COFF::IMAGE_SCN_MEM_READ |
676       COFF::IMAGE_SCN_CNT_CODE;
677   else if (K.isBSS ())
678     Flags |=
679       COFF::IMAGE_SCN_CNT_UNINITIALIZED_DATA |
680       COFF::IMAGE_SCN_MEM_READ |
681       COFF::IMAGE_SCN_MEM_WRITE;
682   else if (K.isThreadLocal())
683     Flags |=
684       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
685       COFF::IMAGE_SCN_MEM_READ |
686       COFF::IMAGE_SCN_MEM_WRITE;
687   else if (K.isReadOnly())
688     Flags |=
689       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
690       COFF::IMAGE_SCN_MEM_READ;
691   else if (K.isWriteable())
692     Flags |=
693       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
694       COFF::IMAGE_SCN_MEM_READ |
695       COFF::IMAGE_SCN_MEM_WRITE;
696 
697   return Flags;
698 }
699 
700 const MCSection *TargetLoweringObjectFileCOFF::
701 getExplicitSectionGlobal(const GlobalValue *GV, SectionKind Kind,
702                          Mangler *Mang, const TargetMachine &TM) const {
703   return getContext().getCOFFSection(GV->getSection(),
704                                      getCOFFSectionFlags(Kind),
705                                      Kind);
706 }
707 
708 static const char *getCOFFSectionPrefixForUniqueGlobal(SectionKind Kind) {
709   if (Kind.isText())
710     return ".text$";
711   if (Kind.isBSS ())
712     return ".bss$";
713   if (Kind.isThreadLocal())
714     return ".tls$";
715   if (Kind.isWriteable())
716     return ".data$";
717   return ".rdata$";
718 }
719 
720 
721 const MCSection *TargetLoweringObjectFileCOFF::
722 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
723                        Mangler *Mang, const TargetMachine &TM) const {
724 
725   // If this global is linkonce/weak and the target handles this by emitting it
726   // into a 'uniqued' section name, create and return the section now.
727   if (GV->isWeakForLinker()) {
728     const char *Prefix = getCOFFSectionPrefixForUniqueGlobal(Kind);
729     SmallString<128> Name(Prefix, Prefix+strlen(Prefix));
730     MCSymbol *Sym = Mang->getSymbol(GV);
731     Name.append(Sym->getName().begin() + 1, Sym->getName().end());
732 
733     unsigned Characteristics = getCOFFSectionFlags(Kind);
734 
735     Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
736 
737     return getContext().getCOFFSection(Name.str(), Characteristics,
738                           COFF::IMAGE_COMDAT_SELECT_ANY, Kind);
739   }
740 
741   if (Kind.isText())
742     return getTextSection();
743 
744   if (Kind.isThreadLocal())
745     return getTLSDataSection();
746 
747   return getDataSection();
748 }
749 
750