xref: /llvm-project/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp (revision e0f0c0e247b29b9ec57dbd710608fa7132f5b504) 
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/MCAsmInfo.h"
28 #include "llvm/MC/MCContext.h"
29 #include "llvm/MC/MCExpr.h"
30 #include "llvm/MC/MCSectionCOFF.h"
31 #include "llvm/MC/MCSectionELF.h"
32 #include "llvm/MC/MCSectionMachO.h"
33 #include "llvm/MC/MCStreamer.h"
34 #include "llvm/MC/MCSymbolELF.h"
35 #include "llvm/MC/MCValue.h"
36 #include "llvm/ProfileData/InstrProf.h"
37 #include "llvm/ProfileData/ProfileCommon.h"
38 #include "llvm/Support/COFF.h"
39 #include "llvm/Support/Dwarf.h"
40 #include "llvm/Support/ELF.h"
41 #include "llvm/Support/ErrorHandling.h"
42 #include "llvm/Support/raw_ostream.h"
43 #include "llvm/Target/TargetLowering.h"
44 #include "llvm/Target/TargetMachine.h"
45 #include "llvm/Target/TargetSubtargetInfo.h"
46 using namespace llvm;
47 using namespace dwarf;
48 
49 //===----------------------------------------------------------------------===//
50 //                                  ELF
51 //===----------------------------------------------------------------------===//
52 
53 MCSymbol *TargetLoweringObjectFileELF::getCFIPersonalitySymbol(
54     const GlobalValue *GV, Mangler &Mang, const TargetMachine &TM,
55     MachineModuleInfo *MMI) const {
56   unsigned Encoding = getPersonalityEncoding();
57   if ((Encoding & 0x80) == dwarf::DW_EH_PE_indirect)
58     return getContext().getOrCreateSymbol(StringRef("DW.ref.") +
59                                           TM.getSymbol(GV, Mang)->getName());
60   if ((Encoding & 0x70) == dwarf::DW_EH_PE_absptr)
61     return TM.getSymbol(GV, Mang);
62   report_fatal_error("We do not support this DWARF encoding yet!");
63 }
64 
65 void TargetLoweringObjectFileELF::emitPersonalityValue(
66     MCStreamer &Streamer, const DataLayout &DL, const MCSymbol *Sym) const {
67   SmallString<64> NameData("DW.ref.");
68   NameData += Sym->getName();
69   MCSymbolELF *Label =
70       cast<MCSymbolELF>(getContext().getOrCreateSymbol(NameData));
71   Streamer.EmitSymbolAttribute(Label, MCSA_Hidden);
72   Streamer.EmitSymbolAttribute(Label, MCSA_Weak);
73   StringRef Prefix = ".data.";
74   NameData.insert(NameData.begin(), Prefix.begin(), Prefix.end());
75   unsigned Flags = ELF::SHF_ALLOC | ELF::SHF_WRITE | ELF::SHF_GROUP;
76   MCSection *Sec = getContext().getELFSection(NameData, ELF::SHT_PROGBITS,
77                                               Flags, 0, Label->getName());
78   unsigned Size = DL.getPointerSize();
79   Streamer.SwitchSection(Sec);
80   Streamer.EmitValueToAlignment(DL.getPointerABIAlignment());
81   Streamer.EmitSymbolAttribute(Label, MCSA_ELF_TypeObject);
82   const MCExpr *E = MCConstantExpr::create(Size, getContext());
83   Streamer.emitELFSize(Label, E);
84   Streamer.EmitLabel(Label);
85 
86   Streamer.EmitSymbolValue(Sym, Size);
87 }
88 
89 const MCExpr *TargetLoweringObjectFileELF::getTTypeGlobalReference(
90     const GlobalValue *GV, unsigned Encoding, Mangler &Mang,
91     const TargetMachine &TM, MachineModuleInfo *MMI,
92     MCStreamer &Streamer) const {
93 
94   if (Encoding & dwarf::DW_EH_PE_indirect) {
95     MachineModuleInfoELF &ELFMMI = MMI->getObjFileInfo<MachineModuleInfoELF>();
96 
97     MCSymbol *SSym = getSymbolWithGlobalValueBase(GV, ".DW.stub", Mang, TM);
98 
99     // Add information about the stub reference to ELFMMI so that the stub
100     // gets emitted by the asmprinter.
101     MachineModuleInfoImpl::StubValueTy &StubSym = ELFMMI.getGVStubEntry(SSym);
102     if (!StubSym.getPointer()) {
103       MCSymbol *Sym = TM.getSymbol(GV, Mang);
104       StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
105     }
106 
107     return TargetLoweringObjectFile::
108       getTTypeReference(MCSymbolRefExpr::create(SSym, getContext()),
109                         Encoding & ~dwarf::DW_EH_PE_indirect, Streamer);
110   }
111 
112   return TargetLoweringObjectFile::
113     getTTypeGlobalReference(GV, Encoding, Mang, TM, MMI, Streamer);
114 }
115 
116 static SectionKind
117 getELFKindForNamedSection(StringRef Name, SectionKind K) {
118   // N.B.: The defaults used in here are no the same ones used in MC.
119   // We follow gcc, MC follows gas. For example, given ".section .eh_frame",
120   // both gas and MC will produce a section with no flags. Given
121   // section(".eh_frame") gcc will produce:
122   //
123   //   .section   .eh_frame,"a",@progbits
124 
125   if (Name == getInstrProfCoverageSectionName(false))
126     return SectionKind::getMetadata();
127 
128   if (Name.empty() || Name[0] != '.') return K;
129 
130   // Some lame default implementation based on some magic section names.
131   if (Name == ".bss" ||
132       Name.startswith(".bss.") ||
133       Name.startswith(".gnu.linkonce.b.") ||
134       Name.startswith(".llvm.linkonce.b.") ||
135       Name == ".sbss" ||
136       Name.startswith(".sbss.") ||
137       Name.startswith(".gnu.linkonce.sb.") ||
138       Name.startswith(".llvm.linkonce.sb."))
139     return SectionKind::getBSS();
140 
141   if (Name == ".tdata" ||
142       Name.startswith(".tdata.") ||
143       Name.startswith(".gnu.linkonce.td.") ||
144       Name.startswith(".llvm.linkonce.td."))
145     return SectionKind::getThreadData();
146 
147   if (Name == ".tbss" ||
148       Name.startswith(".tbss.") ||
149       Name.startswith(".gnu.linkonce.tb.") ||
150       Name.startswith(".llvm.linkonce.tb."))
151     return SectionKind::getThreadBSS();
152 
153   return K;
154 }
155 
156 
157 static unsigned getELFSectionType(StringRef Name, SectionKind K) {
158 
159   if (Name == ".init_array")
160     return ELF::SHT_INIT_ARRAY;
161 
162   if (Name == ".fini_array")
163     return ELF::SHT_FINI_ARRAY;
164 
165   if (Name == ".preinit_array")
166     return ELF::SHT_PREINIT_ARRAY;
167 
168   if (K.isBSS() || K.isThreadBSS())
169     return ELF::SHT_NOBITS;
170 
171   return ELF::SHT_PROGBITS;
172 }
173 
174 static unsigned getELFSectionFlags(SectionKind K) {
175   unsigned Flags = 0;
176 
177   if (!K.isMetadata())
178     Flags |= ELF::SHF_ALLOC;
179 
180   if (K.isText())
181     Flags |= ELF::SHF_EXECINSTR;
182 
183   if (K.isWriteable())
184     Flags |= ELF::SHF_WRITE;
185 
186   if (K.isThreadLocal())
187     Flags |= ELF::SHF_TLS;
188 
189   if (K.isMergeableCString() || K.isMergeableConst())
190     Flags |= ELF::SHF_MERGE;
191 
192   if (K.isMergeableCString())
193     Flags |= ELF::SHF_STRINGS;
194 
195   return Flags;
196 }
197 
198 static const Comdat *getELFComdat(const GlobalValue *GV) {
199   const Comdat *C = GV->getComdat();
200   if (!C)
201     return nullptr;
202 
203   if (C->getSelectionKind() != Comdat::Any)
204     report_fatal_error("ELF COMDATs only support SelectionKind::Any, '" +
205                        C->getName() + "' cannot be lowered.");
206 
207   return C;
208 }
209 
210 MCSection *TargetLoweringObjectFileELF::getExplicitSectionGlobal(
211     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
212     const TargetMachine &TM) const {
213   StringRef SectionName = GV->getSection();
214 
215   // Infer section flags from the section name if we can.
216   Kind = getELFKindForNamedSection(SectionName, Kind);
217 
218   StringRef Group = "";
219   unsigned Flags = getELFSectionFlags(Kind);
220   if (const Comdat *C = getELFComdat(GV)) {
221     Group = C->getName();
222     Flags |= ELF::SHF_GROUP;
223   }
224   return getContext().getELFSection(SectionName,
225                                     getELFSectionType(SectionName, Kind), Flags,
226                                     /*EntrySize=*/0, Group);
227 }
228 
229 /// Return the section prefix name used by options FunctionsSections and
230 /// DataSections.
231 static StringRef getSectionPrefixForGlobal(SectionKind Kind) {
232   if (Kind.isText())
233     return ".text";
234   if (Kind.isReadOnly())
235     return ".rodata";
236   if (Kind.isBSS())
237     return ".bss";
238   if (Kind.isThreadData())
239     return ".tdata";
240   if (Kind.isThreadBSS())
241     return ".tbss";
242   if (Kind.isData())
243     return ".data";
244   assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
245   return ".data.rel.ro";
246 }
247 
248 static cl::opt<bool> GroupFunctionsByHotness(
249     "group-functions-by-hotness",
250     llvm::cl::desc("Partition hot/cold functions by sections prefix"),
251     cl::init(false));
252 
253 static MCSectionELF *
254 selectELFSectionForGlobal(MCContext &Ctx, const GlobalValue *GV,
255                           SectionKind Kind, Mangler &Mang,
256                           const TargetMachine &TM, bool EmitUniqueSection,
257                           unsigned Flags, unsigned *NextUniqueID) {
258   unsigned EntrySize = 0;
259   if (Kind.isMergeableCString()) {
260     if (Kind.isMergeable2ByteCString()) {
261       EntrySize = 2;
262     } else if (Kind.isMergeable4ByteCString()) {
263       EntrySize = 4;
264     } else {
265       EntrySize = 1;
266       assert(Kind.isMergeable1ByteCString() && "unknown string width");
267     }
268   } else if (Kind.isMergeableConst()) {
269     if (Kind.isMergeableConst4()) {
270       EntrySize = 4;
271     } else if (Kind.isMergeableConst8()) {
272       EntrySize = 8;
273     } else if (Kind.isMergeableConst16()) {
274       EntrySize = 16;
275     } else {
276       assert(Kind.isMergeableConst32() && "unknown data width");
277       EntrySize = 32;
278     }
279   }
280 
281   StringRef Group = "";
282   if (const Comdat *C = getELFComdat(GV)) {
283     Flags |= ELF::SHF_GROUP;
284     Group = C->getName();
285   }
286 
287   bool UniqueSectionNames = TM.getUniqueSectionNames();
288   SmallString<128> Name;
289   if (Kind.isMergeableCString()) {
290     // We also need alignment here.
291     // FIXME: this is getting the alignment of the character, not the
292     // alignment of the global!
293     unsigned Align = GV->getParent()->getDataLayout().getPreferredAlignment(
294         cast<GlobalVariable>(GV));
295 
296     std::string SizeSpec = ".rodata.str" + utostr(EntrySize) + ".";
297     Name = SizeSpec + utostr(Align);
298   } else if (Kind.isMergeableConst()) {
299     Name = ".rodata.cst";
300     Name += utostr(EntrySize);
301   } else {
302     Name = getSectionPrefixForGlobal(Kind);
303   }
304 
305   if (GroupFunctionsByHotness) {
306     if (const Function *F = dyn_cast<Function>(GV)) {
307       if (ProfileSummary::isFunctionHot(F)) {
308         Name += getHotSectionPrefix();
309       } else if (ProfileSummary::isFunctionUnlikely(F)) {
310         Name += getUnlikelySectionPrefix();
311       }
312     }
313   }
314 
315   if (EmitUniqueSection && UniqueSectionNames) {
316     Name.push_back('.');
317     TM.getNameWithPrefix(Name, GV, Mang, true);
318   }
319   unsigned UniqueID = ~0;
320   if (EmitUniqueSection && !UniqueSectionNames) {
321     UniqueID = *NextUniqueID;
322     (*NextUniqueID)++;
323   }
324   return Ctx.getELFSection(Name, getELFSectionType(Name, Kind), Flags,
325                            EntrySize, Group, UniqueID);
326 }
327 
328 MCSection *TargetLoweringObjectFileELF::SelectSectionForGlobal(
329     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
330     const TargetMachine &TM) const {
331   unsigned Flags = getELFSectionFlags(Kind);
332 
333   // If we have -ffunction-section or -fdata-section then we should emit the
334   // global value to a uniqued section specifically for it.
335   bool EmitUniqueSection = false;
336   if (!(Flags & ELF::SHF_MERGE) && !Kind.isCommon()) {
337     if (Kind.isText())
338       EmitUniqueSection = TM.getFunctionSections();
339     else
340       EmitUniqueSection = TM.getDataSections();
341   }
342   EmitUniqueSection |= GV->hasComdat();
343 
344   return selectELFSectionForGlobal(getContext(), GV, Kind, Mang, TM,
345                                    EmitUniqueSection, Flags, &NextUniqueID);
346 }
347 
348 MCSection *TargetLoweringObjectFileELF::getSectionForJumpTable(
349     const Function &F, Mangler &Mang, const TargetMachine &TM) const {
350   // If the function can be removed, produce a unique section so that
351   // the table doesn't prevent the removal.
352   const Comdat *C = F.getComdat();
353   bool EmitUniqueSection = TM.getFunctionSections() || C;
354   if (!EmitUniqueSection)
355     return ReadOnlySection;
356 
357   return selectELFSectionForGlobal(getContext(), &F, SectionKind::getReadOnly(),
358                                    Mang, TM, EmitUniqueSection, ELF::SHF_ALLOC,
359                                    &NextUniqueID);
360 }
361 
362 bool TargetLoweringObjectFileELF::shouldPutJumpTableInFunctionSection(
363     bool UsesLabelDifference, const Function &F) const {
364   // We can always create relative relocations, so use another section
365   // that can be marked non-executable.
366   return false;
367 }
368 
369 /// Given a mergeable constant with the specified size and relocation
370 /// information, return a section that it should be placed in.
371 MCSection *TargetLoweringObjectFileELF::getSectionForConstant(
372     const DataLayout &DL, SectionKind Kind, const Constant *C,
373     unsigned &Align) const {
374   if (Kind.isMergeableConst4() && MergeableConst4Section)
375     return MergeableConst4Section;
376   if (Kind.isMergeableConst8() && MergeableConst8Section)
377     return MergeableConst8Section;
378   if (Kind.isMergeableConst16() && MergeableConst16Section)
379     return MergeableConst16Section;
380   if (Kind.isMergeableConst32() && MergeableConst32Section)
381     return MergeableConst32Section;
382   if (Kind.isReadOnly())
383     return ReadOnlySection;
384 
385   assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
386   return DataRelROSection;
387 }
388 
389 static MCSectionELF *getStaticStructorSection(MCContext &Ctx, bool UseInitArray,
390                                               bool IsCtor, unsigned Priority,
391                                               const MCSymbol *KeySym) {
392   std::string Name;
393   unsigned Type;
394   unsigned Flags = ELF::SHF_ALLOC | ELF::SHF_WRITE;
395   StringRef COMDAT = KeySym ? KeySym->getName() : "";
396 
397   if (KeySym)
398     Flags |= ELF::SHF_GROUP;
399 
400   if (UseInitArray) {
401     if (IsCtor) {
402       Type = ELF::SHT_INIT_ARRAY;
403       Name = ".init_array";
404     } else {
405       Type = ELF::SHT_FINI_ARRAY;
406       Name = ".fini_array";
407     }
408     if (Priority != 65535) {
409       Name += '.';
410       Name += utostr(Priority);
411     }
412   } else {
413     // The default scheme is .ctor / .dtor, so we have to invert the priority
414     // numbering.
415     if (IsCtor)
416       Name = ".ctors";
417     else
418       Name = ".dtors";
419     if (Priority != 65535) {
420       Name += '.';
421       Name += utostr(65535 - Priority);
422     }
423     Type = ELF::SHT_PROGBITS;
424   }
425 
426   return Ctx.getELFSection(Name, Type, Flags, 0, COMDAT);
427 }
428 
429 MCSection *TargetLoweringObjectFileELF::getStaticCtorSection(
430     unsigned Priority, const MCSymbol *KeySym) const {
431   return getStaticStructorSection(getContext(), UseInitArray, true, Priority,
432                                   KeySym);
433 }
434 
435 MCSection *TargetLoweringObjectFileELF::getStaticDtorSection(
436     unsigned Priority, const MCSymbol *KeySym) const {
437   return getStaticStructorSection(getContext(), UseInitArray, false, Priority,
438                                   KeySym);
439 }
440 
441 const MCExpr *TargetLoweringObjectFileELF::lowerRelativeReference(
442     const GlobalValue *LHS, const GlobalValue *RHS, Mangler &Mang,
443     const TargetMachine &TM) const {
444   // We may only use a PLT-relative relocation to refer to unnamed_addr
445   // functions.
446   if (!LHS->hasUnnamedAddr() || !LHS->getValueType()->isFunctionTy())
447     return nullptr;
448 
449   // Basic sanity checks.
450   if (LHS->getType()->getPointerAddressSpace() != 0 ||
451       RHS->getType()->getPointerAddressSpace() != 0 || LHS->isThreadLocal() ||
452       RHS->isThreadLocal())
453     return nullptr;
454 
455   return MCBinaryExpr::createSub(
456       MCSymbolRefExpr::create(TM.getSymbol(LHS, Mang), PLTRelativeVariantKind,
457                               getContext()),
458       MCSymbolRefExpr::create(TM.getSymbol(RHS, Mang), getContext()),
459       getContext());
460 }
461 
462 void
463 TargetLoweringObjectFileELF::InitializeELF(bool UseInitArray_) {
464   UseInitArray = UseInitArray_;
465   if (!UseInitArray)
466     return;
467 
468   StaticCtorSection = getContext().getELFSection(
469       ".init_array", ELF::SHT_INIT_ARRAY, ELF::SHF_WRITE | ELF::SHF_ALLOC);
470   StaticDtorSection = getContext().getELFSection(
471       ".fini_array", ELF::SHT_FINI_ARRAY, ELF::SHF_WRITE | ELF::SHF_ALLOC);
472 }
473 
474 //===----------------------------------------------------------------------===//
475 //                                 MachO
476 //===----------------------------------------------------------------------===//
477 
478 TargetLoweringObjectFileMachO::TargetLoweringObjectFileMachO()
479   : TargetLoweringObjectFile() {
480   SupportIndirectSymViaGOTPCRel = true;
481 }
482 
483 /// emitModuleFlags - Perform code emission for module flags.
484 void TargetLoweringObjectFileMachO::
485 emitModuleFlags(MCStreamer &Streamer,
486                 ArrayRef<Module::ModuleFlagEntry> ModuleFlags,
487                 Mangler &Mang, const TargetMachine &TM) const {
488   unsigned VersionVal = 0;
489   unsigned ImageInfoFlags = 0;
490   MDNode *LinkerOptions = nullptr;
491   StringRef SectionVal;
492 
493   for (const auto &MFE : ModuleFlags) {
494     // Ignore flags with 'Require' behavior.
495     if (MFE.Behavior == Module::Require)
496       continue;
497 
498     StringRef Key = MFE.Key->getString();
499     Metadata *Val = MFE.Val;
500 
501     if (Key == "Objective-C Image Info Version") {
502       VersionVal = mdconst::extract<ConstantInt>(Val)->getZExtValue();
503     } else if (Key == "Objective-C Garbage Collection" ||
504                Key == "Objective-C GC Only" ||
505                Key == "Objective-C Is Simulated" ||
506                Key == "Objective-C Class Properties" ||
507                Key == "Objective-C Image Swift Version") {
508       ImageInfoFlags |= mdconst::extract<ConstantInt>(Val)->getZExtValue();
509     } else if (Key == "Objective-C Image Info Section") {
510       SectionVal = cast<MDString>(Val)->getString();
511     } else if (Key == "Linker Options") {
512       LinkerOptions = cast<MDNode>(Val);
513     }
514   }
515 
516   // Emit the linker options if present.
517   if (LinkerOptions) {
518     for (const auto &Option : LinkerOptions->operands()) {
519       SmallVector<std::string, 4> StrOptions;
520       for (const auto &Piece : cast<MDNode>(Option)->operands())
521         StrOptions.push_back(cast<MDString>(Piece)->getString());
522       Streamer.EmitLinkerOptions(StrOptions);
523     }
524   }
525 
526   // The section is mandatory. If we don't have it, then we don't have GC info.
527   if (SectionVal.empty()) return;
528 
529   StringRef Segment, Section;
530   unsigned TAA = 0, StubSize = 0;
531   bool TAAParsed;
532   std::string ErrorCode =
533     MCSectionMachO::ParseSectionSpecifier(SectionVal, Segment, Section,
534                                           TAA, TAAParsed, StubSize);
535   if (!ErrorCode.empty())
536     // If invalid, report the error with report_fatal_error.
537     report_fatal_error("Invalid section specifier '" + Section + "': " +
538                        ErrorCode + ".");
539 
540   // Get the section.
541   MCSectionMachO *S = getContext().getMachOSection(
542       Segment, Section, TAA, StubSize, SectionKind::getData());
543   Streamer.SwitchSection(S);
544   Streamer.EmitLabel(getContext().
545                      getOrCreateSymbol(StringRef("L_OBJC_IMAGE_INFO")));
546   Streamer.EmitIntValue(VersionVal, 4);
547   Streamer.EmitIntValue(ImageInfoFlags, 4);
548   Streamer.AddBlankLine();
549 }
550 
551 static void checkMachOComdat(const GlobalValue *GV) {
552   const Comdat *C = GV->getComdat();
553   if (!C)
554     return;
555 
556   report_fatal_error("MachO doesn't support COMDATs, '" + C->getName() +
557                      "' cannot be lowered.");
558 }
559 
560 MCSection *TargetLoweringObjectFileMachO::getExplicitSectionGlobal(
561     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
562     const TargetMachine &TM) const {
563   // Parse the section specifier and create it if valid.
564   StringRef Segment, Section;
565   unsigned TAA = 0, StubSize = 0;
566   bool TAAParsed;
567 
568   checkMachOComdat(GV);
569 
570   std::string ErrorCode =
571     MCSectionMachO::ParseSectionSpecifier(GV->getSection(), Segment, Section,
572                                           TAA, TAAParsed, StubSize);
573   if (!ErrorCode.empty()) {
574     // If invalid, report the error with report_fatal_error.
575     report_fatal_error("Global variable '" + GV->getName() +
576                        "' has an invalid section specifier '" +
577                        GV->getSection() + "': " + ErrorCode + ".");
578   }
579 
580   // Get the section.
581   MCSectionMachO *S =
582       getContext().getMachOSection(Segment, Section, TAA, StubSize, Kind);
583 
584   // If TAA wasn't set by ParseSectionSpecifier() above,
585   // use the value returned by getMachOSection() as a default.
586   if (!TAAParsed)
587     TAA = S->getTypeAndAttributes();
588 
589   // Okay, now that we got the section, verify that the TAA & StubSize agree.
590   // If the user declared multiple globals with different section flags, we need
591   // to reject it here.
592   if (S->getTypeAndAttributes() != TAA || S->getStubSize() != StubSize) {
593     // If invalid, report the error with report_fatal_error.
594     report_fatal_error("Global variable '" + GV->getName() +
595                        "' section type or attributes does not match previous"
596                        " section specifier");
597   }
598 
599   return S;
600 }
601 
602 MCSection *TargetLoweringObjectFileMachO::SelectSectionForGlobal(
603     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
604     const TargetMachine &TM) const {
605   checkMachOComdat(GV);
606 
607   // Handle thread local data.
608   if (Kind.isThreadBSS()) return TLSBSSSection;
609   if (Kind.isThreadData()) return TLSDataSection;
610 
611   if (Kind.isText())
612     return GV->isWeakForLinker() ? TextCoalSection : TextSection;
613 
614   // If this is weak/linkonce, put this in a coalescable section, either in text
615   // or data depending on if it is writable.
616   if (GV->isWeakForLinker()) {
617     if (Kind.isReadOnly())
618       return ConstTextCoalSection;
619     return DataCoalSection;
620   }
621 
622   // FIXME: Alignment check should be handled by section classifier.
623   if (Kind.isMergeable1ByteCString() &&
624       GV->getParent()->getDataLayout().getPreferredAlignment(
625           cast<GlobalVariable>(GV)) < 32)
626     return CStringSection;
627 
628   // Do not put 16-bit arrays in the UString section if they have an
629   // externally visible label, this runs into issues with certain linker
630   // versions.
631   if (Kind.isMergeable2ByteCString() && !GV->hasExternalLinkage() &&
632       GV->getParent()->getDataLayout().getPreferredAlignment(
633           cast<GlobalVariable>(GV)) < 32)
634     return UStringSection;
635 
636   // With MachO only variables whose corresponding symbol starts with 'l' or
637   // 'L' can be merged, so we only try merging GVs with private linkage.
638   if (GV->hasPrivateLinkage() && Kind.isMergeableConst()) {
639     if (Kind.isMergeableConst4())
640       return FourByteConstantSection;
641     if (Kind.isMergeableConst8())
642       return EightByteConstantSection;
643     if (Kind.isMergeableConst16())
644       return SixteenByteConstantSection;
645   }
646 
647   // Otherwise, if it is readonly, but not something we can specially optimize,
648   // just drop it in .const.
649   if (Kind.isReadOnly())
650     return ReadOnlySection;
651 
652   // If this is marked const, put it into a const section.  But if the dynamic
653   // linker needs to write to it, put it in the data segment.
654   if (Kind.isReadOnlyWithRel())
655     return ConstDataSection;
656 
657   // Put zero initialized globals with strong external linkage in the
658   // DATA, __common section with the .zerofill directive.
659   if (Kind.isBSSExtern())
660     return DataCommonSection;
661 
662   // Put zero initialized globals with local linkage in __DATA,__bss directive
663   // with the .zerofill directive (aka .lcomm).
664   if (Kind.isBSSLocal())
665     return DataBSSSection;
666 
667   // Otherwise, just drop the variable in the normal data section.
668   return DataSection;
669 }
670 
671 MCSection *TargetLoweringObjectFileMachO::getSectionForConstant(
672     const DataLayout &DL, SectionKind Kind, const Constant *C,
673     unsigned &Align) const {
674   // If this constant requires a relocation, we have to put it in the data
675   // segment, not in the text segment.
676   if (Kind.isData() || Kind.isReadOnlyWithRel())
677     return ConstDataSection;
678 
679   if (Kind.isMergeableConst4())
680     return FourByteConstantSection;
681   if (Kind.isMergeableConst8())
682     return EightByteConstantSection;
683   if (Kind.isMergeableConst16())
684     return SixteenByteConstantSection;
685   return ReadOnlySection;  // .const
686 }
687 
688 const MCExpr *TargetLoweringObjectFileMachO::getTTypeGlobalReference(
689     const GlobalValue *GV, unsigned Encoding, Mangler &Mang,
690     const TargetMachine &TM, MachineModuleInfo *MMI,
691     MCStreamer &Streamer) const {
692   // The mach-o version of this method defaults to returning a stub reference.
693 
694   if (Encoding & DW_EH_PE_indirect) {
695     MachineModuleInfoMachO &MachOMMI =
696       MMI->getObjFileInfo<MachineModuleInfoMachO>();
697 
698     MCSymbol *SSym =
699         getSymbolWithGlobalValueBase(GV, "$non_lazy_ptr", Mang, TM);
700 
701     // Add information about the stub reference to MachOMMI so that the stub
702     // gets emitted by the asmprinter.
703     MachineModuleInfoImpl::StubValueTy &StubSym =
704       GV->hasHiddenVisibility() ? MachOMMI.getHiddenGVStubEntry(SSym) :
705                                   MachOMMI.getGVStubEntry(SSym);
706     if (!StubSym.getPointer()) {
707       MCSymbol *Sym = TM.getSymbol(GV, Mang);
708       StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
709     }
710 
711     return TargetLoweringObjectFile::
712       getTTypeReference(MCSymbolRefExpr::create(SSym, getContext()),
713                         Encoding & ~dwarf::DW_EH_PE_indirect, Streamer);
714   }
715 
716   return TargetLoweringObjectFile::getTTypeGlobalReference(GV, Encoding, Mang,
717                                                            TM, MMI, Streamer);
718 }
719 
720 MCSymbol *TargetLoweringObjectFileMachO::getCFIPersonalitySymbol(
721     const GlobalValue *GV, Mangler &Mang, const TargetMachine &TM,
722     MachineModuleInfo *MMI) const {
723   // The mach-o version of this method defaults to returning a stub reference.
724   MachineModuleInfoMachO &MachOMMI =
725     MMI->getObjFileInfo<MachineModuleInfoMachO>();
726 
727   MCSymbol *SSym = getSymbolWithGlobalValueBase(GV, "$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 = MachOMMI.getGVStubEntry(SSym);
732   if (!StubSym.getPointer()) {
733     MCSymbol *Sym = TM.getSymbol(GV, Mang);
734     StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
735   }
736 
737   return SSym;
738 }
739 
740 const MCExpr *TargetLoweringObjectFileMachO::getIndirectSymViaGOTPCRel(
741     const MCSymbol *Sym, const MCValue &MV, int64_t Offset,
742     MachineModuleInfo *MMI, MCStreamer &Streamer) const {
743   // Although MachO 32-bit targets do not explicitly have a GOTPCREL relocation
744   // as 64-bit do, we replace the GOT equivalent by accessing the final symbol
745   // through a non_lazy_ptr stub instead. One advantage is that it allows the
746   // computation of deltas to final external symbols. Example:
747   //
748   //    _extgotequiv:
749   //       .long   _extfoo
750   //
751   //    _delta:
752   //       .long   _extgotequiv-_delta
753   //
754   // is transformed to:
755   //
756   //    _delta:
757   //       .long   L_extfoo$non_lazy_ptr-(_delta+0)
758   //
759   //       .section        __IMPORT,__pointers,non_lazy_symbol_pointers
760   //    L_extfoo$non_lazy_ptr:
761   //       .indirect_symbol        _extfoo
762   //       .long   0
763   //
764   MachineModuleInfoMachO &MachOMMI =
765     MMI->getObjFileInfo<MachineModuleInfoMachO>();
766   MCContext &Ctx = getContext();
767 
768   // The offset must consider the original displacement from the base symbol
769   // since 32-bit targets don't have a GOTPCREL to fold the PC displacement.
770   Offset = -MV.getConstant();
771   const MCSymbol *BaseSym = &MV.getSymB()->getSymbol();
772 
773   // Access the final symbol via sym$non_lazy_ptr and generate the appropriated
774   // non_lazy_ptr stubs.
775   SmallString<128> Name;
776   StringRef Suffix = "$non_lazy_ptr";
777   Name += MMI->getModule()->getDataLayout().getPrivateGlobalPrefix();
778   Name += Sym->getName();
779   Name += Suffix;
780   MCSymbol *Stub = Ctx.getOrCreateSymbol(Name);
781 
782   MachineModuleInfoImpl::StubValueTy &StubSym = MachOMMI.getGVStubEntry(Stub);
783   if (!StubSym.getPointer())
784     StubSym = MachineModuleInfoImpl::
785       StubValueTy(const_cast<MCSymbol *>(Sym), true /* access indirectly */);
786 
787   const MCExpr *BSymExpr =
788     MCSymbolRefExpr::create(BaseSym, MCSymbolRefExpr::VK_None, Ctx);
789   const MCExpr *LHS =
790     MCSymbolRefExpr::create(Stub, MCSymbolRefExpr::VK_None, Ctx);
791 
792   if (!Offset)
793     return MCBinaryExpr::createSub(LHS, BSymExpr, Ctx);
794 
795   const MCExpr *RHS =
796     MCBinaryExpr::createAdd(BSymExpr, MCConstantExpr::create(Offset, Ctx), Ctx);
797   return MCBinaryExpr::createSub(LHS, RHS, Ctx);
798 }
799 
800 static bool canUsePrivateLabel(const MCAsmInfo &AsmInfo,
801                                const MCSection &Section) {
802   if (!AsmInfo.isSectionAtomizableBySymbols(Section))
803     return true;
804 
805   // If it is not dead stripped, it is safe to use private labels.
806   const MCSectionMachO &SMO = cast<MCSectionMachO>(Section);
807   if (SMO.hasAttribute(MachO::S_ATTR_NO_DEAD_STRIP))
808     return true;
809 
810   return false;
811 }
812 
813 void TargetLoweringObjectFileMachO::getNameWithPrefix(
814     SmallVectorImpl<char> &OutName, const GlobalValue *GV, Mangler &Mang,
815     const TargetMachine &TM) const {
816   SectionKind GVKind = TargetLoweringObjectFile::getKindForGlobal(GV, TM);
817   const MCSection *TheSection = SectionForGlobal(GV, GVKind, Mang, TM);
818   bool CannotUsePrivateLabel =
819       !canUsePrivateLabel(*TM.getMCAsmInfo(), *TheSection);
820   Mang.getNameWithPrefix(OutName, GV, CannotUsePrivateLabel);
821 }
822 
823 //===----------------------------------------------------------------------===//
824 //                                  COFF
825 //===----------------------------------------------------------------------===//
826 
827 static unsigned
828 getCOFFSectionFlags(SectionKind K) {
829   unsigned Flags = 0;
830 
831   if (K.isMetadata())
832     Flags |=
833       COFF::IMAGE_SCN_MEM_DISCARDABLE;
834   else if (K.isText())
835     Flags |=
836       COFF::IMAGE_SCN_MEM_EXECUTE |
837       COFF::IMAGE_SCN_MEM_READ |
838       COFF::IMAGE_SCN_CNT_CODE;
839   else if (K.isBSS())
840     Flags |=
841       COFF::IMAGE_SCN_CNT_UNINITIALIZED_DATA |
842       COFF::IMAGE_SCN_MEM_READ |
843       COFF::IMAGE_SCN_MEM_WRITE;
844   else if (K.isThreadLocal())
845     Flags |=
846       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
847       COFF::IMAGE_SCN_MEM_READ |
848       COFF::IMAGE_SCN_MEM_WRITE;
849   else if (K.isReadOnly() || K.isReadOnlyWithRel())
850     Flags |=
851       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
852       COFF::IMAGE_SCN_MEM_READ;
853   else if (K.isWriteable())
854     Flags |=
855       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
856       COFF::IMAGE_SCN_MEM_READ |
857       COFF::IMAGE_SCN_MEM_WRITE;
858 
859   return Flags;
860 }
861 
862 static const GlobalValue *getComdatGVForCOFF(const GlobalValue *GV) {
863   const Comdat *C = GV->getComdat();
864   assert(C && "expected GV to have a Comdat!");
865 
866   StringRef ComdatGVName = C->getName();
867   const GlobalValue *ComdatGV = GV->getParent()->getNamedValue(ComdatGVName);
868   if (!ComdatGV)
869     report_fatal_error("Associative COMDAT symbol '" + ComdatGVName +
870                        "' does not exist.");
871 
872   if (ComdatGV->getComdat() != C)
873     report_fatal_error("Associative COMDAT symbol '" + ComdatGVName +
874                        "' is not a key for its COMDAT.");
875 
876   return ComdatGV;
877 }
878 
879 static int getSelectionForCOFF(const GlobalValue *GV) {
880   if (const Comdat *C = GV->getComdat()) {
881     const GlobalValue *ComdatKey = getComdatGVForCOFF(GV);
882     if (const auto *GA = dyn_cast<GlobalAlias>(ComdatKey))
883       ComdatKey = GA->getBaseObject();
884     if (ComdatKey == GV) {
885       switch (C->getSelectionKind()) {
886       case Comdat::Any:
887         return COFF::IMAGE_COMDAT_SELECT_ANY;
888       case Comdat::ExactMatch:
889         return COFF::IMAGE_COMDAT_SELECT_EXACT_MATCH;
890       case Comdat::Largest:
891         return COFF::IMAGE_COMDAT_SELECT_LARGEST;
892       case Comdat::NoDuplicates:
893         return COFF::IMAGE_COMDAT_SELECT_NODUPLICATES;
894       case Comdat::SameSize:
895         return COFF::IMAGE_COMDAT_SELECT_SAME_SIZE;
896       }
897     } else {
898       return COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE;
899     }
900   }
901   return 0;
902 }
903 
904 MCSection *TargetLoweringObjectFileCOFF::getExplicitSectionGlobal(
905     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
906     const TargetMachine &TM) const {
907   int Selection = 0;
908   unsigned Characteristics = getCOFFSectionFlags(Kind);
909   StringRef Name = GV->getSection();
910   StringRef COMDATSymName = "";
911   if (GV->hasComdat()) {
912     Selection = getSelectionForCOFF(GV);
913     const GlobalValue *ComdatGV;
914     if (Selection == COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE)
915       ComdatGV = getComdatGVForCOFF(GV);
916     else
917       ComdatGV = GV;
918 
919     if (!ComdatGV->hasPrivateLinkage()) {
920       MCSymbol *Sym = TM.getSymbol(ComdatGV, Mang);
921       COMDATSymName = Sym->getName();
922       Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
923     } else {
924       Selection = 0;
925     }
926   }
927   return getContext().getCOFFSection(Name,
928                                      Characteristics,
929                                      Kind,
930                                      COMDATSymName,
931                                      Selection);
932 }
933 
934 static const char *getCOFFSectionNameForUniqueGlobal(SectionKind Kind) {
935   if (Kind.isText())
936     return ".text";
937   if (Kind.isBSS())
938     return ".bss";
939   if (Kind.isThreadLocal())
940     return ".tls$";
941   if (Kind.isReadOnly() || Kind.isReadOnlyWithRel())
942     return ".rdata";
943   return ".data";
944 }
945 
946 MCSection *TargetLoweringObjectFileCOFF::SelectSectionForGlobal(
947     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
948     const TargetMachine &TM) const {
949   // If we have -ffunction-sections then we should emit the global value to a
950   // uniqued section specifically for it.
951   bool EmitUniquedSection;
952   if (Kind.isText())
953     EmitUniquedSection = TM.getFunctionSections();
954   else
955     EmitUniquedSection = TM.getDataSections();
956 
957   if ((EmitUniquedSection && !Kind.isCommon()) || GV->hasComdat()) {
958     const char *Name = getCOFFSectionNameForUniqueGlobal(Kind);
959     unsigned Characteristics = getCOFFSectionFlags(Kind);
960 
961     Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
962     int Selection = getSelectionForCOFF(GV);
963     if (!Selection)
964       Selection = COFF::IMAGE_COMDAT_SELECT_NODUPLICATES;
965     const GlobalValue *ComdatGV;
966     if (GV->hasComdat())
967       ComdatGV = getComdatGVForCOFF(GV);
968     else
969       ComdatGV = GV;
970 
971     if (!ComdatGV->hasPrivateLinkage()) {
972       MCSymbol *Sym = TM.getSymbol(ComdatGV, Mang);
973       StringRef COMDATSymName = Sym->getName();
974       return getContext().getCOFFSection(Name, Characteristics, Kind,
975                                          COMDATSymName, Selection);
976     } else {
977       SmallString<256> TmpData;
978       Mang.getNameWithPrefix(TmpData, GV, /*CannotUsePrivateLabel=*/true);
979       return getContext().getCOFFSection(Name, Characteristics, Kind, TmpData,
980                                          Selection);
981     }
982   }
983 
984   if (Kind.isText())
985     return TextSection;
986 
987   if (Kind.isThreadLocal())
988     return TLSDataSection;
989 
990   if (Kind.isReadOnly() || Kind.isReadOnlyWithRel())
991     return ReadOnlySection;
992 
993   // Note: we claim that common symbols are put in BSSSection, but they are
994   // really emitted with the magic .comm directive, which creates a symbol table
995   // entry but not a section.
996   if (Kind.isBSS() || Kind.isCommon())
997     return BSSSection;
998 
999   return DataSection;
1000 }
1001 
1002 void TargetLoweringObjectFileCOFF::getNameWithPrefix(
1003     SmallVectorImpl<char> &OutName, const GlobalValue *GV, Mangler &Mang,
1004     const TargetMachine &TM) const {
1005   bool CannotUsePrivateLabel = false;
1006   if (GV->hasPrivateLinkage() &&
1007       ((isa<Function>(GV) && TM.getFunctionSections()) ||
1008        (isa<GlobalVariable>(GV) && TM.getDataSections())))
1009     CannotUsePrivateLabel = true;
1010 
1011   Mang.getNameWithPrefix(OutName, GV, CannotUsePrivateLabel);
1012 }
1013 
1014 MCSection *TargetLoweringObjectFileCOFF::getSectionForJumpTable(
1015     const Function &F, Mangler &Mang, const TargetMachine &TM) const {
1016   // If the function can be removed, produce a unique section so that
1017   // the table doesn't prevent the removal.
1018   const Comdat *C = F.getComdat();
1019   bool EmitUniqueSection = TM.getFunctionSections() || C;
1020   if (!EmitUniqueSection)
1021     return ReadOnlySection;
1022 
1023   // FIXME: we should produce a symbol for F instead.
1024   if (F.hasPrivateLinkage())
1025     return ReadOnlySection;
1026 
1027   MCSymbol *Sym = TM.getSymbol(&F, Mang);
1028   StringRef COMDATSymName = Sym->getName();
1029 
1030   SectionKind Kind = SectionKind::getReadOnly();
1031   const char *Name = getCOFFSectionNameForUniqueGlobal(Kind);
1032   unsigned Characteristics = getCOFFSectionFlags(Kind);
1033   Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
1034 
1035   return getContext().getCOFFSection(Name, Characteristics, Kind, COMDATSymName,
1036                                      COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE);
1037 }
1038 
1039 void TargetLoweringObjectFileCOFF::
1040 emitModuleFlags(MCStreamer &Streamer,
1041                 ArrayRef<Module::ModuleFlagEntry> ModuleFlags,
1042                 Mangler &Mang, const TargetMachine &TM) const {
1043   MDNode *LinkerOptions = nullptr;
1044 
1045   for (const auto &MFE : ModuleFlags) {
1046     StringRef Key = MFE.Key->getString();
1047     if (Key == "Linker Options")
1048       LinkerOptions = cast<MDNode>(MFE.Val);
1049   }
1050 
1051   if (LinkerOptions) {
1052     // Emit the linker options to the linker .drectve section.  According to the
1053     // spec, this section is a space-separated string containing flags for
1054     // linker.
1055     MCSection *Sec = getDrectveSection();
1056     Streamer.SwitchSection(Sec);
1057     for (const auto &Option : LinkerOptions->operands()) {
1058       for (const auto &Piece : cast<MDNode>(Option)->operands()) {
1059         // Lead with a space for consistency with our dllexport implementation.
1060         std::string Directive(" ");
1061         Directive.append(cast<MDString>(Piece)->getString());
1062         Streamer.EmitBytes(Directive);
1063       }
1064     }
1065   }
1066 }
1067 
1068 MCSection *TargetLoweringObjectFileCOFF::getStaticCtorSection(
1069     unsigned Priority, const MCSymbol *KeySym) const {
1070   return getContext().getAssociativeCOFFSection(
1071       cast<MCSectionCOFF>(StaticCtorSection), KeySym);
1072 }
1073 
1074 MCSection *TargetLoweringObjectFileCOFF::getStaticDtorSection(
1075     unsigned Priority, const MCSymbol *KeySym) const {
1076   return getContext().getAssociativeCOFFSection(
1077       cast<MCSectionCOFF>(StaticDtorSection), KeySym);
1078 }
1079 
1080 void TargetLoweringObjectFileCOFF::emitLinkerFlagsForGlobal(
1081     raw_ostream &OS, const GlobalValue *GV, const Mangler &Mang) const {
1082   if (!GV->hasDLLExportStorageClass() || GV->isDeclaration())
1083     return;
1084 
1085   const Triple &TT = getTargetTriple();
1086 
1087   if (TT.isKnownWindowsMSVCEnvironment())
1088     OS << " /EXPORT:";
1089   else
1090     OS << " -export:";
1091 
1092   if (TT.isWindowsGNUEnvironment() || TT.isWindowsCygwinEnvironment()) {
1093     std::string Flag;
1094     raw_string_ostream FlagOS(Flag);
1095     Mang.getNameWithPrefix(FlagOS, GV, false);
1096     FlagOS.flush();
1097     if (Flag[0] == GV->getParent()->getDataLayout().getGlobalPrefix())
1098       OS << Flag.substr(1);
1099     else
1100       OS << Flag;
1101   } else {
1102     Mang.getNameWithPrefix(OS, GV, false);
1103   }
1104 
1105   if (!GV->getValueType()->isFunctionTy()) {
1106     if (TT.isKnownWindowsMSVCEnvironment())
1107       OS << ",DATA";
1108     else
1109       OS << ",data";
1110   }
1111 }
1112