xref: /llvm-project/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp (revision 5bf8fef58013e2c97180236fa6973faa40435d5f) 
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                                                     SectionKind::getDataRel(),
75                                                     0, Label->getName());
76   unsigned Size = TM.getSubtargetImpl()->getDataLayout()->getPointerSize();
77   Streamer.SwitchSection(Sec);
78   Streamer.EmitValueToAlignment(
79       TM.getSubtargetImpl()->getDataLayout()->getPointerABIAlignment());
80   Streamer.EmitSymbolAttribute(Label, MCSA_ELF_TypeObject);
81   const MCExpr *E = MCConstantExpr::Create(Size, getContext());
82   Streamer.EmitELFSize(Label, E);
83   Streamer.EmitLabel(Label);
84 
85   Streamer.EmitSymbolValue(Sym, Size);
86 }
87 
88 const MCExpr *TargetLoweringObjectFileELF::getTTypeGlobalReference(
89     const GlobalValue *GV, unsigned Encoding, Mangler &Mang,
90     const TargetMachine &TM, MachineModuleInfo *MMI,
91     MCStreamer &Streamer) const {
92 
93   if (Encoding & dwarf::DW_EH_PE_indirect) {
94     MachineModuleInfoELF &ELFMMI = MMI->getObjFileInfo<MachineModuleInfoELF>();
95 
96     MCSymbol *SSym = getSymbolWithGlobalValueBase(GV, ".DW.stub", Mang, TM);
97 
98     // Add information about the stub reference to ELFMMI so that the stub
99     // gets emitted by the asmprinter.
100     MachineModuleInfoImpl::StubValueTy &StubSym = ELFMMI.getGVStubEntry(SSym);
101     if (!StubSym.getPointer()) {
102       MCSymbol *Sym = TM.getSymbol(GV, Mang);
103       StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
104     }
105 
106     return TargetLoweringObjectFile::
107       getTTypeReference(MCSymbolRefExpr::Create(SSym, getContext()),
108                         Encoding & ~dwarf::DW_EH_PE_indirect, Streamer);
109   }
110 
111   return TargetLoweringObjectFile::
112     getTTypeGlobalReference(GV, Encoding, Mang, TM, MMI, Streamer);
113 }
114 
115 static SectionKind
116 getELFKindForNamedSection(StringRef Name, SectionKind K) {
117   // N.B.: The defaults used in here are no the same ones used in MC.
118   // We follow gcc, MC follows gas. For example, given ".section .eh_frame",
119   // both gas and MC will produce a section with no flags. Given
120   // section(".eh_frame") gcc will produce:
121   //
122   //   .section   .eh_frame,"a",@progbits
123   if (Name.empty() || Name[0] != '.') return K;
124 
125   // Some lame default implementation based on some magic section names.
126   if (Name == ".bss" ||
127       Name.startswith(".bss.") ||
128       Name.startswith(".gnu.linkonce.b.") ||
129       Name.startswith(".llvm.linkonce.b.") ||
130       Name == ".sbss" ||
131       Name.startswith(".sbss.") ||
132       Name.startswith(".gnu.linkonce.sb.") ||
133       Name.startswith(".llvm.linkonce.sb."))
134     return SectionKind::getBSS();
135 
136   if (Name == ".tdata" ||
137       Name.startswith(".tdata.") ||
138       Name.startswith(".gnu.linkonce.td.") ||
139       Name.startswith(".llvm.linkonce.td."))
140     return SectionKind::getThreadData();
141 
142   if (Name == ".tbss" ||
143       Name.startswith(".tbss.") ||
144       Name.startswith(".gnu.linkonce.tb.") ||
145       Name.startswith(".llvm.linkonce.tb."))
146     return SectionKind::getThreadBSS();
147 
148   return K;
149 }
150 
151 
152 static unsigned getELFSectionType(StringRef Name, SectionKind K) {
153 
154   if (Name == ".init_array")
155     return ELF::SHT_INIT_ARRAY;
156 
157   if (Name == ".fini_array")
158     return ELF::SHT_FINI_ARRAY;
159 
160   if (Name == ".preinit_array")
161     return ELF::SHT_PREINIT_ARRAY;
162 
163   if (K.isBSS() || K.isThreadBSS())
164     return ELF::SHT_NOBITS;
165 
166   return ELF::SHT_PROGBITS;
167 }
168 
169 
170 static unsigned
171 getELFSectionFlags(SectionKind K) {
172   unsigned Flags = 0;
173 
174   if (!K.isMetadata())
175     Flags |= ELF::SHF_ALLOC;
176 
177   if (K.isText())
178     Flags |= ELF::SHF_EXECINSTR;
179 
180   if (K.isWriteable())
181     Flags |= ELF::SHF_WRITE;
182 
183   if (K.isThreadLocal())
184     Flags |= ELF::SHF_TLS;
185 
186   // K.isMergeableConst() is left out to honour PR4650
187   if (K.isMergeableCString() || K.isMergeableConst4() ||
188       K.isMergeableConst8() || K.isMergeableConst16())
189     Flags |= ELF::SHF_MERGE;
190 
191   if (K.isMergeableCString())
192     Flags |= ELF::SHF_STRINGS;
193 
194   return Flags;
195 }
196 
197 static const Comdat *getELFComdat(const GlobalValue *GV) {
198   const Comdat *C = GV->getComdat();
199   if (!C)
200     return nullptr;
201 
202   if (C->getSelectionKind() != Comdat::Any)
203     report_fatal_error("ELF COMDATs only support SelectionKind::Any, '" +
204                        C->getName() + "' cannot be lowered.");
205 
206   return C;
207 }
208 
209 const MCSection *TargetLoweringObjectFileELF::getExplicitSectionGlobal(
210     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
211     const TargetMachine &TM) const {
212   StringRef SectionName = GV->getSection();
213 
214   // Infer section flags from the section name if we can.
215   Kind = getELFKindForNamedSection(SectionName, Kind);
216 
217   StringRef Group = "";
218   unsigned Flags = getELFSectionFlags(Kind);
219   if (const Comdat *C = getELFComdat(GV)) {
220     Group = C->getName();
221     Flags |= ELF::SHF_GROUP;
222   }
223   return getContext().getELFSection(SectionName,
224                                     getELFSectionType(SectionName, Kind), Flags,
225                                     Kind, /*EntrySize=*/0, Group);
226 }
227 
228 /// getSectionPrefixForGlobal - Return the section prefix name used by options
229 /// FunctionsSections and DataSections.
230 static StringRef getSectionPrefixForGlobal(SectionKind Kind) {
231   if (Kind.isText())                 return ".text.";
232   if (Kind.isReadOnly())             return ".rodata.";
233   if (Kind.isBSS())                  return ".bss.";
234 
235   if (Kind.isThreadData())           return ".tdata.";
236   if (Kind.isThreadBSS())            return ".tbss.";
237 
238   if (Kind.isDataNoRel())            return ".data.";
239   if (Kind.isDataRelLocal())         return ".data.rel.local.";
240   if (Kind.isDataRel())              return ".data.rel.";
241   if (Kind.isReadOnlyWithRelLocal()) return ".data.rel.ro.local.";
242 
243   assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
244   return ".data.rel.ro.";
245 }
246 
247 const MCSection *TargetLoweringObjectFileELF::
248 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
249                        Mangler &Mang, const TargetMachine &TM) const {
250   // If we have -ffunction-section or -fdata-section then we should emit the
251   // global value to a uniqued section specifically for it.
252   bool EmitUniquedSection;
253   if (Kind.isText())
254     EmitUniquedSection = TM.getFunctionSections();
255   else
256     EmitUniquedSection = TM.getDataSections();
257 
258   // If this global is linkonce/weak and the target handles this by emitting it
259   // into a 'uniqued' section name, create and return the section now.
260   if ((GV->isWeakForLinker() || EmitUniquedSection || GV->hasComdat()) &&
261       !Kind.isCommon()) {
262     StringRef Prefix = getSectionPrefixForGlobal(Kind);
263 
264     SmallString<128> Name(Prefix);
265     TM.getNameWithPrefix(Name, GV, Mang, true);
266 
267     StringRef Group = "";
268     unsigned Flags = getELFSectionFlags(Kind);
269     if (GV->isWeakForLinker() || GV->hasComdat()) {
270       if (const Comdat *C = getELFComdat(GV))
271         Group = C->getName();
272       else
273         Group = Name.substr(Prefix.size());
274       Flags |= ELF::SHF_GROUP;
275     }
276 
277     return getContext().getELFSection(Name.str(),
278                                       getELFSectionType(Name.str(), Kind),
279                                       Flags, Kind, 0, Group);
280   }
281 
282   if (Kind.isText()) return TextSection;
283 
284   if (Kind.isMergeable1ByteCString() ||
285       Kind.isMergeable2ByteCString() ||
286       Kind.isMergeable4ByteCString()) {
287 
288     // We also need alignment here.
289     // FIXME: this is getting the alignment of the character, not the
290     // alignment of the global!
291     unsigned Align =
292         TM.getSubtargetImpl()->getDataLayout()->getPreferredAlignment(
293             cast<GlobalVariable>(GV));
294 
295     const char *SizeSpec = ".rodata.str1.";
296     if (Kind.isMergeable2ByteCString())
297       SizeSpec = ".rodata.str2.";
298     else if (Kind.isMergeable4ByteCString())
299       SizeSpec = ".rodata.str4.";
300     else
301       assert(Kind.isMergeable1ByteCString() && "unknown string width");
302 
303 
304     std::string Name = SizeSpec + utostr(Align);
305     return getContext().getELFSection(Name, ELF::SHT_PROGBITS,
306                                       ELF::SHF_ALLOC |
307                                       ELF::SHF_MERGE |
308                                       ELF::SHF_STRINGS,
309                                       Kind);
310   }
311 
312   if (Kind.isMergeableConst()) {
313     if (Kind.isMergeableConst4() && MergeableConst4Section)
314       return MergeableConst4Section;
315     if (Kind.isMergeableConst8() && MergeableConst8Section)
316       return MergeableConst8Section;
317     if (Kind.isMergeableConst16() && MergeableConst16Section)
318       return MergeableConst16Section;
319     return ReadOnlySection;  // .const
320   }
321 
322   if (Kind.isReadOnly())             return ReadOnlySection;
323 
324   if (Kind.isThreadData())           return TLSDataSection;
325   if (Kind.isThreadBSS())            return TLSBSSSection;
326 
327   // Note: we claim that common symbols are put in BSSSection, but they are
328   // really emitted with the magic .comm directive, which creates a symbol table
329   // entry but not a section.
330   if (Kind.isBSS() || Kind.isCommon()) return BSSSection;
331 
332   if (Kind.isDataNoRel())            return DataSection;
333   if (Kind.isDataRelLocal())         return DataRelLocalSection;
334   if (Kind.isDataRel())              return DataRelSection;
335   if (Kind.isReadOnlyWithRelLocal()) return DataRelROLocalSection;
336 
337   assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
338   return DataRelROSection;
339 }
340 
341 /// getSectionForConstant - Given a mergeable constant with the
342 /// specified size and relocation information, return a section that it
343 /// should be placed in.
344 const MCSection *
345 TargetLoweringObjectFileELF::getSectionForConstant(SectionKind Kind,
346                                                    const Constant *C) const {
347   if (Kind.isMergeableConst4() && MergeableConst4Section)
348     return MergeableConst4Section;
349   if (Kind.isMergeableConst8() && MergeableConst8Section)
350     return MergeableConst8Section;
351   if (Kind.isMergeableConst16() && MergeableConst16Section)
352     return MergeableConst16Section;
353   if (Kind.isReadOnly())
354     return ReadOnlySection;
355 
356   if (Kind.isReadOnlyWithRelLocal()) return DataRelROLocalSection;
357   assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
358   return DataRelROSection;
359 }
360 
361 static const MCSectionELF *getStaticStructorSection(MCContext &Ctx,
362                                                     bool UseInitArray,
363                                                     bool IsCtor,
364                                                     unsigned Priority,
365                                                     const MCSymbol *KeySym) {
366   std::string Name;
367   unsigned Type;
368   unsigned Flags = ELF::SHF_ALLOC | ELF::SHF_WRITE;
369   SectionKind Kind = SectionKind::getDataRel();
370   StringRef COMDAT = KeySym ? KeySym->getName() : "";
371 
372   if (KeySym)
373     Flags |= ELF::SHF_GROUP;
374 
375   if (UseInitArray) {
376     if (IsCtor) {
377       Type = ELF::SHT_INIT_ARRAY;
378       Name = ".init_array";
379     } else {
380       Type = ELF::SHT_FINI_ARRAY;
381       Name = ".fini_array";
382     }
383     if (Priority != 65535) {
384       Name += '.';
385       Name += utostr(Priority);
386     }
387   } else {
388     // The default scheme is .ctor / .dtor, so we have to invert the priority
389     // numbering.
390     if (IsCtor)
391       Name = ".ctors";
392     else
393       Name = ".dtors";
394     if (Priority != 65535) {
395       Name += '.';
396       Name += utostr(65535 - Priority);
397     }
398     Type = ELF::SHT_PROGBITS;
399   }
400 
401   return Ctx.getELFSection(Name, Type, Flags, Kind, 0, COMDAT);
402 }
403 
404 const MCSection *TargetLoweringObjectFileELF::getStaticCtorSection(
405     unsigned Priority, const MCSymbol *KeySym) const {
406   return getStaticStructorSection(getContext(), UseInitArray, true, Priority,
407                                   KeySym);
408 }
409 
410 const MCSection *TargetLoweringObjectFileELF::getStaticDtorSection(
411     unsigned Priority, const MCSymbol *KeySym) const {
412   return getStaticStructorSection(getContext(), UseInitArray, false, Priority,
413                                   KeySym);
414 }
415 
416 void
417 TargetLoweringObjectFileELF::InitializeELF(bool UseInitArray_) {
418   UseInitArray = UseInitArray_;
419   if (!UseInitArray)
420     return;
421 
422   StaticCtorSection =
423     getContext().getELFSection(".init_array", ELF::SHT_INIT_ARRAY,
424                                ELF::SHF_WRITE |
425                                ELF::SHF_ALLOC,
426                                SectionKind::getDataRel());
427   StaticDtorSection =
428     getContext().getELFSection(".fini_array", ELF::SHT_FINI_ARRAY,
429                                ELF::SHF_WRITE |
430                                ELF::SHF_ALLOC,
431                                SectionKind::getDataRel());
432 }
433 
434 //===----------------------------------------------------------------------===//
435 //                                 MachO
436 //===----------------------------------------------------------------------===//
437 
438 /// getDepLibFromLinkerOpt - Extract the dependent library name from a linker
439 /// option string. Returns StringRef() if the option does not specify a library.
440 StringRef TargetLoweringObjectFileMachO::
441 getDepLibFromLinkerOpt(StringRef LinkerOption) const {
442   const char *LibCmd = "-l";
443   if (LinkerOption.startswith(LibCmd))
444     return LinkerOption.substr(strlen(LibCmd));
445   return StringRef();
446 }
447 
448 /// emitModuleFlags - Perform code emission for module flags.
449 void TargetLoweringObjectFileMachO::
450 emitModuleFlags(MCStreamer &Streamer,
451                 ArrayRef<Module::ModuleFlagEntry> ModuleFlags,
452                 Mangler &Mang, const TargetMachine &TM) const {
453   unsigned VersionVal = 0;
454   unsigned ImageInfoFlags = 0;
455   MDNode *LinkerOptions = nullptr;
456   StringRef SectionVal;
457 
458   for (ArrayRef<Module::ModuleFlagEntry>::iterator
459          i = ModuleFlags.begin(), e = ModuleFlags.end(); i != e; ++i) {
460     const Module::ModuleFlagEntry &MFE = *i;
461 
462     // Ignore flags with 'Require' behavior.
463     if (MFE.Behavior == Module::Require)
464       continue;
465 
466     StringRef Key = MFE.Key->getString();
467     Metadata *Val = MFE.Val;
468 
469     if (Key == "Objective-C Image Info Version") {
470       VersionVal = mdconst::extract<ConstantInt>(Val)->getZExtValue();
471     } else if (Key == "Objective-C Garbage Collection" ||
472                Key == "Objective-C GC Only" ||
473                Key == "Objective-C Is Simulated" ||
474                Key == "Objective-C Image Swift Version") {
475       ImageInfoFlags |= mdconst::extract<ConstantInt>(Val)->getZExtValue();
476     } else if (Key == "Objective-C Image Info Section") {
477       SectionVal = cast<MDString>(Val)->getString();
478     } else if (Key == "Linker Options") {
479       LinkerOptions = cast<MDNode>(Val);
480     }
481   }
482 
483   // Emit the linker options if present.
484   if (LinkerOptions) {
485     for (unsigned i = 0, e = LinkerOptions->getNumOperands(); i != e; ++i) {
486       MDNode *MDOptions = cast<MDNode>(LinkerOptions->getOperand(i));
487       SmallVector<std::string, 4> StrOptions;
488 
489       // Convert to strings.
490       for (unsigned ii = 0, ie = MDOptions->getNumOperands(); ii != ie; ++ii) {
491         MDString *MDOption = cast<MDString>(MDOptions->getOperand(ii));
492         StrOptions.push_back(MDOption->getString());
493       }
494 
495       Streamer.EmitLinkerOptions(StrOptions);
496     }
497   }
498 
499   // The section is mandatory. If we don't have it, then we don't have GC info.
500   if (SectionVal.empty()) return;
501 
502   StringRef Segment, Section;
503   unsigned TAA = 0, StubSize = 0;
504   bool TAAParsed;
505   std::string ErrorCode =
506     MCSectionMachO::ParseSectionSpecifier(SectionVal, Segment, Section,
507                                           TAA, TAAParsed, StubSize);
508   if (!ErrorCode.empty())
509     // If invalid, report the error with report_fatal_error.
510     report_fatal_error("Invalid section specifier '" + Section + "': " +
511                        ErrorCode + ".");
512 
513   // Get the section.
514   const MCSectionMachO *S =
515     getContext().getMachOSection(Segment, Section, TAA, StubSize,
516                                  SectionKind::getDataNoRel());
517   Streamer.SwitchSection(S);
518   Streamer.EmitLabel(getContext().
519                      GetOrCreateSymbol(StringRef("L_OBJC_IMAGE_INFO")));
520   Streamer.EmitIntValue(VersionVal, 4);
521   Streamer.EmitIntValue(ImageInfoFlags, 4);
522   Streamer.AddBlankLine();
523 }
524 
525 static void checkMachOComdat(const GlobalValue *GV) {
526   const Comdat *C = GV->getComdat();
527   if (!C)
528     return;
529 
530   report_fatal_error("MachO doesn't support COMDATs, '" + C->getName() +
531                      "' cannot be lowered.");
532 }
533 
534 const MCSection *TargetLoweringObjectFileMachO::getExplicitSectionGlobal(
535     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
536     const TargetMachine &TM) const {
537   // Parse the section specifier and create it if valid.
538   StringRef Segment, Section;
539   unsigned TAA = 0, StubSize = 0;
540   bool TAAParsed;
541 
542   checkMachOComdat(GV);
543 
544   std::string ErrorCode =
545     MCSectionMachO::ParseSectionSpecifier(GV->getSection(), Segment, Section,
546                                           TAA, TAAParsed, StubSize);
547   if (!ErrorCode.empty()) {
548     // If invalid, report the error with report_fatal_error.
549     report_fatal_error("Global variable '" + GV->getName() +
550                        "' has an invalid section specifier '" +
551                        GV->getSection() + "': " + ErrorCode + ".");
552   }
553 
554   // Get the section.
555   const MCSectionMachO *S =
556     getContext().getMachOSection(Segment, Section, TAA, StubSize, Kind);
557 
558   // If TAA wasn't set by ParseSectionSpecifier() above,
559   // use the value returned by getMachOSection() as a default.
560   if (!TAAParsed)
561     TAA = S->getTypeAndAttributes();
562 
563   // Okay, now that we got the section, verify that the TAA & StubSize agree.
564   // If the user declared multiple globals with different section flags, we need
565   // to reject it here.
566   if (S->getTypeAndAttributes() != TAA || S->getStubSize() != StubSize) {
567     // If invalid, report the error with report_fatal_error.
568     report_fatal_error("Global variable '" + GV->getName() +
569                        "' section type or attributes does not match previous"
570                        " section specifier");
571   }
572 
573   return S;
574 }
575 
576 bool TargetLoweringObjectFileMachO::isSectionAtomizableBySymbols(
577     const MCSection &Section) const {
578     const MCSectionMachO &SMO = static_cast<const MCSectionMachO&>(Section);
579 
580     // Sections holding 1 byte strings are atomized based on the data
581     // they contain.
582     // Sections holding 2 byte strings require symbols in order to be
583     // atomized.
584     // There is no dedicated section for 4 byte strings.
585     if (SMO.getKind().isMergeable1ByteCString())
586       return false;
587 
588     if (SMO.getSegmentName() == "__TEXT" &&
589         SMO.getSectionName() == "__objc_classname" &&
590         SMO.getType() == MachO::S_CSTRING_LITERALS)
591       return false;
592 
593     if (SMO.getSegmentName() == "__TEXT" &&
594         SMO.getSectionName() == "__objc_methname" &&
595         SMO.getType() == MachO::S_CSTRING_LITERALS)
596       return false;
597 
598     if (SMO.getSegmentName() == "__TEXT" &&
599         SMO.getSectionName() == "__objc_methtype" &&
600         SMO.getType() == MachO::S_CSTRING_LITERALS)
601       return false;
602 
603     if (SMO.getSegmentName() == "__DATA" &&
604         SMO.getSectionName() == "__cfstring")
605       return false;
606 
607     // no_dead_strip sections are not atomized in practice.
608     if (SMO.hasAttribute(MachO::S_ATTR_NO_DEAD_STRIP))
609       return false;
610 
611     switch (SMO.getType()) {
612     default:
613       return true;
614 
615       // These sections are atomized at the element boundaries without using
616       // symbols.
617     case MachO::S_4BYTE_LITERALS:
618     case MachO::S_8BYTE_LITERALS:
619     case MachO::S_16BYTE_LITERALS:
620     case MachO::S_LITERAL_POINTERS:
621     case MachO::S_NON_LAZY_SYMBOL_POINTERS:
622     case MachO::S_LAZY_SYMBOL_POINTERS:
623     case MachO::S_MOD_INIT_FUNC_POINTERS:
624     case MachO::S_MOD_TERM_FUNC_POINTERS:
625     case MachO::S_INTERPOSING:
626       return false;
627     }
628 }
629 
630 const MCSection *TargetLoweringObjectFileMachO::
631 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
632                        Mangler &Mang, const TargetMachine &TM) const {
633   checkMachOComdat(GV);
634 
635   // Handle thread local data.
636   if (Kind.isThreadBSS()) return TLSBSSSection;
637   if (Kind.isThreadData()) return TLSDataSection;
638 
639   if (Kind.isText())
640     return GV->isWeakForLinker() ? TextCoalSection : TextSection;
641 
642   // If this is weak/linkonce, put this in a coalescable section, either in text
643   // or data depending on if it is writable.
644   if (GV->isWeakForLinker()) {
645     if (Kind.isReadOnly())
646       return ConstTextCoalSection;
647     return DataCoalSection;
648   }
649 
650   // FIXME: Alignment check should be handled by section classifier.
651   if (Kind.isMergeable1ByteCString() &&
652       TM.getSubtargetImpl()->getDataLayout()->getPreferredAlignment(
653           cast<GlobalVariable>(GV)) < 32)
654     return CStringSection;
655 
656   // Do not put 16-bit arrays in the UString section if they have an
657   // externally visible label, this runs into issues with certain linker
658   // versions.
659   if (Kind.isMergeable2ByteCString() && !GV->hasExternalLinkage() &&
660       TM.getSubtargetImpl()->getDataLayout()->getPreferredAlignment(
661           cast<GlobalVariable>(GV)) < 32)
662     return UStringSection;
663 
664   // With MachO only variables whose corresponding symbol starts with 'l' or
665   // 'L' can be merged, so we only try merging GVs with private linkage.
666   if (GV->hasPrivateLinkage() && Kind.isMergeableConst()) {
667     if (Kind.isMergeableConst4())
668       return FourByteConstantSection;
669     if (Kind.isMergeableConst8())
670       return EightByteConstantSection;
671     if (Kind.isMergeableConst16())
672       return SixteenByteConstantSection;
673   }
674 
675   // Otherwise, if it is readonly, but not something we can specially optimize,
676   // just drop it in .const.
677   if (Kind.isReadOnly())
678     return ReadOnlySection;
679 
680   // If this is marked const, put it into a const section.  But if the dynamic
681   // linker needs to write to it, put it in the data segment.
682   if (Kind.isReadOnlyWithRel())
683     return ConstDataSection;
684 
685   // Put zero initialized globals with strong external linkage in the
686   // DATA, __common section with the .zerofill directive.
687   if (Kind.isBSSExtern())
688     return DataCommonSection;
689 
690   // Put zero initialized globals with local linkage in __DATA,__bss directive
691   // with the .zerofill directive (aka .lcomm).
692   if (Kind.isBSSLocal())
693     return DataBSSSection;
694 
695   // Otherwise, just drop the variable in the normal data section.
696   return DataSection;
697 }
698 
699 const MCSection *
700 TargetLoweringObjectFileMachO::getSectionForConstant(SectionKind Kind,
701                                                      const Constant *C) const {
702   // If this constant requires a relocation, we have to put it in the data
703   // segment, not in the text segment.
704   if (Kind.isDataRel() || Kind.isReadOnlyWithRel())
705     return ConstDataSection;
706 
707   if (Kind.isMergeableConst4())
708     return FourByteConstantSection;
709   if (Kind.isMergeableConst8())
710     return EightByteConstantSection;
711   if (Kind.isMergeableConst16())
712     return SixteenByteConstantSection;
713   return ReadOnlySection;  // .const
714 }
715 
716 const MCExpr *TargetLoweringObjectFileMachO::getTTypeGlobalReference(
717     const GlobalValue *GV, unsigned Encoding, Mangler &Mang,
718     const TargetMachine &TM, MachineModuleInfo *MMI,
719     MCStreamer &Streamer) const {
720   // The mach-o version of this method defaults to returning a stub reference.
721 
722   if (Encoding & DW_EH_PE_indirect) {
723     MachineModuleInfoMachO &MachOMMI =
724       MMI->getObjFileInfo<MachineModuleInfoMachO>();
725 
726     MCSymbol *SSym =
727         getSymbolWithGlobalValueBase(GV, "$non_lazy_ptr", Mang, TM);
728 
729     // Add information about the stub reference to MachOMMI so that the stub
730     // gets emitted by the asmprinter.
731     MachineModuleInfoImpl::StubValueTy &StubSym =
732       GV->hasHiddenVisibility() ? MachOMMI.getHiddenGVStubEntry(SSym) :
733                                   MachOMMI.getGVStubEntry(SSym);
734     if (!StubSym.getPointer()) {
735       MCSymbol *Sym = TM.getSymbol(GV, Mang);
736       StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
737     }
738 
739     return TargetLoweringObjectFile::
740       getTTypeReference(MCSymbolRefExpr::Create(SSym, getContext()),
741                         Encoding & ~dwarf::DW_EH_PE_indirect, Streamer);
742   }
743 
744   return TargetLoweringObjectFile::getTTypeGlobalReference(GV, Encoding, Mang,
745                                                            TM, MMI, Streamer);
746 }
747 
748 MCSymbol *TargetLoweringObjectFileMachO::getCFIPersonalitySymbol(
749     const GlobalValue *GV, Mangler &Mang, const TargetMachine &TM,
750     MachineModuleInfo *MMI) const {
751   // The mach-o version of this method defaults to returning a stub reference.
752   MachineModuleInfoMachO &MachOMMI =
753     MMI->getObjFileInfo<MachineModuleInfoMachO>();
754 
755   MCSymbol *SSym = getSymbolWithGlobalValueBase(GV, "$non_lazy_ptr", Mang, TM);
756 
757   // Add information about the stub reference to MachOMMI so that the stub
758   // gets emitted by the asmprinter.
759   MachineModuleInfoImpl::StubValueTy &StubSym = MachOMMI.getGVStubEntry(SSym);
760   if (!StubSym.getPointer()) {
761     MCSymbol *Sym = TM.getSymbol(GV, Mang);
762     StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
763   }
764 
765   return SSym;
766 }
767 
768 //===----------------------------------------------------------------------===//
769 //                                  COFF
770 //===----------------------------------------------------------------------===//
771 
772 static unsigned
773 getCOFFSectionFlags(SectionKind K) {
774   unsigned Flags = 0;
775 
776   if (K.isMetadata())
777     Flags |=
778       COFF::IMAGE_SCN_MEM_DISCARDABLE;
779   else if (K.isText())
780     Flags |=
781       COFF::IMAGE_SCN_MEM_EXECUTE |
782       COFF::IMAGE_SCN_MEM_READ |
783       COFF::IMAGE_SCN_CNT_CODE;
784   else if (K.isBSS())
785     Flags |=
786       COFF::IMAGE_SCN_CNT_UNINITIALIZED_DATA |
787       COFF::IMAGE_SCN_MEM_READ |
788       COFF::IMAGE_SCN_MEM_WRITE;
789   else if (K.isThreadLocal())
790     Flags |=
791       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
792       COFF::IMAGE_SCN_MEM_READ |
793       COFF::IMAGE_SCN_MEM_WRITE;
794   else if (K.isReadOnly() || K.isReadOnlyWithRel())
795     Flags |=
796       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
797       COFF::IMAGE_SCN_MEM_READ;
798   else if (K.isWriteable())
799     Flags |=
800       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
801       COFF::IMAGE_SCN_MEM_READ |
802       COFF::IMAGE_SCN_MEM_WRITE;
803 
804   return Flags;
805 }
806 
807 static const GlobalValue *getComdatGVForCOFF(const GlobalValue *GV) {
808   const Comdat *C = GV->getComdat();
809   assert(C && "expected GV to have a Comdat!");
810 
811   StringRef ComdatGVName = C->getName();
812   const GlobalValue *ComdatGV = GV->getParent()->getNamedValue(ComdatGVName);
813   if (!ComdatGV)
814     report_fatal_error("Associative COMDAT symbol '" + ComdatGVName +
815                        "' does not exist.");
816 
817   if (ComdatGV->getComdat() != C)
818     report_fatal_error("Associative COMDAT symbol '" + ComdatGVName +
819                        "' is not a key for its COMDAT.");
820 
821   return ComdatGV;
822 }
823 
824 static int getSelectionForCOFF(const GlobalValue *GV) {
825   if (const Comdat *C = GV->getComdat()) {
826     const GlobalValue *ComdatKey = getComdatGVForCOFF(GV);
827     if (const auto *GA = dyn_cast<GlobalAlias>(ComdatKey))
828       ComdatKey = GA->getBaseObject();
829     if (ComdatKey == GV) {
830       switch (C->getSelectionKind()) {
831       case Comdat::Any:
832         return COFF::IMAGE_COMDAT_SELECT_ANY;
833       case Comdat::ExactMatch:
834         return COFF::IMAGE_COMDAT_SELECT_EXACT_MATCH;
835       case Comdat::Largest:
836         return COFF::IMAGE_COMDAT_SELECT_LARGEST;
837       case Comdat::NoDuplicates:
838         return COFF::IMAGE_COMDAT_SELECT_NODUPLICATES;
839       case Comdat::SameSize:
840         return COFF::IMAGE_COMDAT_SELECT_SAME_SIZE;
841       }
842     } else {
843       return COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE;
844     }
845   } else if (GV->isWeakForLinker()) {
846     return COFF::IMAGE_COMDAT_SELECT_ANY;
847   }
848   return 0;
849 }
850 
851 const MCSection *TargetLoweringObjectFileCOFF::getExplicitSectionGlobal(
852     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
853     const TargetMachine &TM) const {
854   int Selection = 0;
855   unsigned Characteristics = getCOFFSectionFlags(Kind);
856   StringRef Name = GV->getSection();
857   StringRef COMDATSymName = "";
858   if ((GV->isWeakForLinker() || GV->hasComdat()) && !Kind.isCommon()) {
859     Selection = getSelectionForCOFF(GV);
860     const GlobalValue *ComdatGV;
861     if (Selection == COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE)
862       ComdatGV = getComdatGVForCOFF(GV);
863     else
864       ComdatGV = GV;
865 
866     if (!ComdatGV->hasPrivateLinkage()) {
867       MCSymbol *Sym = TM.getSymbol(ComdatGV, Mang);
868       COMDATSymName = Sym->getName();
869       Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
870     } else {
871       Selection = 0;
872     }
873   }
874   return getContext().getCOFFSection(Name,
875                                      Characteristics,
876                                      Kind,
877                                      COMDATSymName,
878                                      Selection);
879 }
880 
881 static const char *getCOFFSectionNameForUniqueGlobal(SectionKind Kind) {
882   if (Kind.isText())
883     return ".text";
884   if (Kind.isBSS())
885     return ".bss";
886   if (Kind.isThreadLocal())
887     return ".tls$";
888   if (Kind.isReadOnly() || Kind.isReadOnlyWithRel())
889     return ".rdata";
890   return ".data";
891 }
892 
893 
894 const MCSection *TargetLoweringObjectFileCOFF::
895 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
896                        Mangler &Mang, const TargetMachine &TM) const {
897   // If we have -ffunction-sections then we should emit the global value to a
898   // uniqued section specifically for it.
899   bool EmitUniquedSection;
900   if (Kind.isText())
901     EmitUniquedSection = TM.getFunctionSections();
902   else
903     EmitUniquedSection = TM.getDataSections();
904 
905   // If this global is linkonce/weak and the target handles this by emitting it
906   // into a 'uniqued' section name, create and return the section now.
907   // Section names depend on the name of the symbol which is not feasible if the
908   // symbol has private linkage.
909   if ((GV->isWeakForLinker() || EmitUniquedSection || GV->hasComdat()) &&
910       !Kind.isCommon()) {
911     const char *Name = getCOFFSectionNameForUniqueGlobal(Kind);
912     unsigned Characteristics = getCOFFSectionFlags(Kind);
913 
914     Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
915     int Selection = getSelectionForCOFF(GV);
916     if (!Selection)
917       Selection = COFF::IMAGE_COMDAT_SELECT_NODUPLICATES;
918     const GlobalValue *ComdatGV;
919     if (GV->hasComdat())
920       ComdatGV = getComdatGVForCOFF(GV);
921     else
922       ComdatGV = GV;
923 
924     if (!ComdatGV->hasPrivateLinkage()) {
925       MCSymbol *Sym = TM.getSymbol(ComdatGV, Mang);
926       StringRef COMDATSymName = Sym->getName();
927       return getContext().getCOFFSection(Name, Characteristics, Kind,
928                                          COMDATSymName, Selection);
929     }
930   }
931 
932   if (Kind.isText())
933     return TextSection;
934 
935   if (Kind.isThreadLocal())
936     return TLSDataSection;
937 
938   if (Kind.isReadOnly() || Kind.isReadOnlyWithRel())
939     return ReadOnlySection;
940 
941   // Note: we claim that common symbols are put in BSSSection, but they are
942   // really emitted with the magic .comm directive, which creates a symbol table
943   // entry but not a section.
944   if (Kind.isBSS() || Kind.isCommon())
945     return BSSSection;
946 
947   return DataSection;
948 }
949 
950 StringRef TargetLoweringObjectFileCOFF::
951 getDepLibFromLinkerOpt(StringRef LinkerOption) const {
952   const char *LibCmd = "/DEFAULTLIB:";
953   if (LinkerOption.startswith(LibCmd))
954     return LinkerOption.substr(strlen(LibCmd));
955   return StringRef();
956 }
957 
958 void TargetLoweringObjectFileCOFF::
959 emitModuleFlags(MCStreamer &Streamer,
960                 ArrayRef<Module::ModuleFlagEntry> ModuleFlags,
961                 Mangler &Mang, const TargetMachine &TM) const {
962   MDNode *LinkerOptions = nullptr;
963 
964   // Look for the "Linker Options" flag, since it's the only one we support.
965   for (ArrayRef<Module::ModuleFlagEntry>::iterator
966        i = ModuleFlags.begin(), e = ModuleFlags.end(); i != e; ++i) {
967     const Module::ModuleFlagEntry &MFE = *i;
968     StringRef Key = MFE.Key->getString();
969     Metadata *Val = MFE.Val;
970     if (Key == "Linker Options") {
971       LinkerOptions = cast<MDNode>(Val);
972       break;
973     }
974   }
975   if (!LinkerOptions)
976     return;
977 
978   // Emit the linker options to the linker .drectve section.  According to the
979   // spec, this section is a space-separated string containing flags for linker.
980   const MCSection *Sec = getDrectveSection();
981   Streamer.SwitchSection(Sec);
982   for (unsigned i = 0, e = LinkerOptions->getNumOperands(); i != e; ++i) {
983     MDNode *MDOptions = cast<MDNode>(LinkerOptions->getOperand(i));
984     for (unsigned ii = 0, ie = MDOptions->getNumOperands(); ii != ie; ++ii) {
985       MDString *MDOption = cast<MDString>(MDOptions->getOperand(ii));
986       StringRef Op = MDOption->getString();
987       // Lead with a space for consistency with our dllexport implementation.
988       std::string Escaped(" ");
989       if (Op.find(" ") != StringRef::npos) {
990         // The PE-COFF spec says args with spaces must be quoted.  It doesn't say
991         // how to escape quotes, but it probably uses this algorithm:
992         // http://msdn.microsoft.com/en-us/library/17w5ykft(v=vs.85).aspx
993         // FIXME: Reuse escaping code from Support/Windows/Program.inc
994         Escaped.push_back('\"');
995         Escaped.append(Op);
996         Escaped.push_back('\"');
997       } else {
998         Escaped.append(Op);
999       }
1000       Streamer.EmitBytes(Escaped);
1001     }
1002   }
1003 }
1004 
1005 const MCSection *TargetLoweringObjectFileCOFF::getStaticCtorSection(
1006     unsigned Priority, const MCSymbol *KeySym) const {
1007   return getContext().getAssociativeCOFFSection(
1008       cast<MCSectionCOFF>(StaticCtorSection), KeySym);
1009 }
1010 
1011 const MCSection *TargetLoweringObjectFileCOFF::getStaticDtorSection(
1012     unsigned Priority, const MCSymbol *KeySym) const {
1013   return getContext().getAssociativeCOFFSection(
1014       cast<MCSectionCOFF>(StaticDtorSection), KeySym);
1015 }
1016