xref: /llvm-project/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp (revision 01d98ba0b22bfb152a3db85cac7fcb23d9cb5c85) 
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/Support/COFF.h"
38 #include "llvm/Support/Dwarf.h"
39 #include "llvm/Support/ELF.h"
40 #include "llvm/Support/ErrorHandling.h"
41 #include "llvm/Support/raw_ostream.h"
42 #include "llvm/Target/TargetLowering.h"
43 #include "llvm/Target/TargetMachine.h"
44 #include "llvm/Target/TargetSubtargetInfo.h"
45 using namespace llvm;
46 using namespace dwarf;
47 
48 //===----------------------------------------------------------------------===//
49 //                                  ELF
50 //===----------------------------------------------------------------------===//
51 
52 MCSymbol *TargetLoweringObjectFileELF::getCFIPersonalitySymbol(
53     const GlobalValue *GV, Mangler &Mang, const TargetMachine &TM,
54     MachineModuleInfo *MMI) const {
55   unsigned Encoding = getPersonalityEncoding();
56   if ((Encoding & 0x80) == dwarf::DW_EH_PE_indirect)
57     return getContext().getOrCreateSymbol(StringRef("DW.ref.") +
58                                           TM.getSymbol(GV, Mang)->getName());
59   if ((Encoding & 0x70) == dwarf::DW_EH_PE_absptr)
60     return TM.getSymbol(GV, Mang);
61   report_fatal_error("We do not support this DWARF encoding yet!");
62 }
63 
64 void TargetLoweringObjectFileELF::emitPersonalityValue(
65     MCStreamer &Streamer, const DataLayout &DL, const MCSymbol *Sym) const {
66   SmallString<64> NameData("DW.ref.");
67   NameData += Sym->getName();
68   MCSymbolELF *Label =
69       cast<MCSymbolELF>(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   MCSection *Sec = getContext().getELFSection(NameData, ELF::SHT_PROGBITS,
76                                               Flags, 0, Label->getName());
77   unsigned Size = DL.getPointerSize();
78   Streamer.SwitchSection(Sec);
79   Streamer.EmitValueToAlignment(DL.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 
124   if (Name == getInstrProfCoverageSectionName(false))
125     return SectionKind::getMetadata();
126 
127   if (Name.empty() || Name[0] != '.') return K;
128 
129   // Some lame default implementation based on some magic section names.
130   if (Name == ".bss" ||
131       Name.startswith(".bss.") ||
132       Name.startswith(".gnu.linkonce.b.") ||
133       Name.startswith(".llvm.linkonce.b.") ||
134       Name == ".sbss" ||
135       Name.startswith(".sbss.") ||
136       Name.startswith(".gnu.linkonce.sb.") ||
137       Name.startswith(".llvm.linkonce.sb."))
138     return SectionKind::getBSS();
139 
140   if (Name == ".tdata" ||
141       Name.startswith(".tdata.") ||
142       Name.startswith(".gnu.linkonce.td.") ||
143       Name.startswith(".llvm.linkonce.td."))
144     return SectionKind::getThreadData();
145 
146   if (Name == ".tbss" ||
147       Name.startswith(".tbss.") ||
148       Name.startswith(".gnu.linkonce.tb.") ||
149       Name.startswith(".llvm.linkonce.tb."))
150     return SectionKind::getThreadBSS();
151 
152   return K;
153 }
154 
155 
156 static unsigned getELFSectionType(StringRef Name, SectionKind K) {
157 
158   if (Name == ".init_array")
159     return ELF::SHT_INIT_ARRAY;
160 
161   if (Name == ".fini_array")
162     return ELF::SHT_FINI_ARRAY;
163 
164   if (Name == ".preinit_array")
165     return ELF::SHT_PREINIT_ARRAY;
166 
167   if (K.isBSS() || K.isThreadBSS())
168     return ELF::SHT_NOBITS;
169 
170   return ELF::SHT_PROGBITS;
171 }
172 
173 static unsigned getELFSectionFlags(SectionKind K) {
174   unsigned Flags = 0;
175 
176   if (!K.isMetadata())
177     Flags |= ELF::SHF_ALLOC;
178 
179   if (K.isText())
180     Flags |= ELF::SHF_EXECINSTR;
181 
182   if (K.isWriteable())
183     Flags |= ELF::SHF_WRITE;
184 
185   if (K.isThreadLocal())
186     Flags |= ELF::SHF_TLS;
187 
188   if (K.isMergeableCString() || K.isMergeableConst())
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 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                                     /*EntrySize=*/0, Group);
226 }
227 
228 /// Return the section prefix name used by options FunctionsSections and
229 /// DataSections.
230 static StringRef getSectionPrefixForGlobal(SectionKind Kind) {
231   if (Kind.isText())
232     return ".text";
233   if (Kind.isReadOnly())
234     return ".rodata";
235   if (Kind.isBSS())
236     return ".bss";
237   if (Kind.isThreadData())
238     return ".tdata";
239   if (Kind.isThreadBSS())
240     return ".tbss";
241   if (Kind.isData())
242     return ".data";
243   assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
244   return ".data.rel.ro";
245 }
246 
247 static MCSectionELF *
248 selectELFSectionForGlobal(MCContext &Ctx, const GlobalValue *GV,
249                           SectionKind Kind, Mangler &Mang,
250                           const TargetMachine &TM, bool EmitUniqueSection,
251                           unsigned Flags, unsigned *NextUniqueID) {
252   unsigned EntrySize = 0;
253   if (Kind.isMergeableCString()) {
254     if (Kind.isMergeable2ByteCString()) {
255       EntrySize = 2;
256     } else if (Kind.isMergeable4ByteCString()) {
257       EntrySize = 4;
258     } else {
259       EntrySize = 1;
260       assert(Kind.isMergeable1ByteCString() && "unknown string width");
261     }
262   } else if (Kind.isMergeableConst()) {
263     if (Kind.isMergeableConst4()) {
264       EntrySize = 4;
265     } else if (Kind.isMergeableConst8()) {
266       EntrySize = 8;
267     } else if (Kind.isMergeableConst16()) {
268       EntrySize = 16;
269     } else {
270       assert(Kind.isMergeableConst32() && "unknown data width");
271       EntrySize = 32;
272     }
273   }
274 
275   StringRef Group = "";
276   if (const Comdat *C = getELFComdat(GV)) {
277     Flags |= ELF::SHF_GROUP;
278     Group = C->getName();
279   }
280 
281   bool UniqueSectionNames = TM.getUniqueSectionNames();
282   SmallString<128> Name;
283   if (Kind.isMergeableCString()) {
284     // We also need alignment here.
285     // FIXME: this is getting the alignment of the character, not the
286     // alignment of the global!
287     unsigned Align = GV->getParent()->getDataLayout().getPreferredAlignment(
288         cast<GlobalVariable>(GV));
289 
290     std::string SizeSpec = ".rodata.str" + utostr(EntrySize) + ".";
291     Name = SizeSpec + utostr(Align);
292   } else if (Kind.isMergeableConst()) {
293     Name = ".rodata.cst";
294     Name += utostr(EntrySize);
295   } else {
296     Name = getSectionPrefixForGlobal(Kind);
297   }
298   // FIXME: Extend the section prefix to include hotness catagories such as .hot
299   //  or .unlikely for functions.
300 
301   if (EmitUniqueSection && UniqueSectionNames) {
302     Name.push_back('.');
303     TM.getNameWithPrefix(Name, GV, Mang, true);
304   }
305   unsigned UniqueID = MCContext::GenericSectionID;
306   if (EmitUniqueSection && !UniqueSectionNames) {
307     UniqueID = *NextUniqueID;
308     (*NextUniqueID)++;
309   }
310   return Ctx.getELFSection(Name, getELFSectionType(Name, Kind), Flags,
311                            EntrySize, Group, UniqueID);
312 }
313 
314 MCSection *TargetLoweringObjectFileELF::SelectSectionForGlobal(
315     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
316     const TargetMachine &TM) const {
317   unsigned Flags = getELFSectionFlags(Kind);
318 
319   // If we have -ffunction-section or -fdata-section then we should emit the
320   // global value to a uniqued section specifically for it.
321   bool EmitUniqueSection = false;
322   if (!(Flags & ELF::SHF_MERGE) && !Kind.isCommon()) {
323     if (Kind.isText())
324       EmitUniqueSection = TM.getFunctionSections();
325     else
326       EmitUniqueSection = TM.getDataSections();
327   }
328   EmitUniqueSection |= GV->hasComdat();
329 
330   return selectELFSectionForGlobal(getContext(), GV, Kind, Mang, TM,
331                                    EmitUniqueSection, Flags, &NextUniqueID);
332 }
333 
334 MCSection *TargetLoweringObjectFileELF::getSectionForJumpTable(
335     const Function &F, Mangler &Mang, const TargetMachine &TM) const {
336   // If the function can be removed, produce a unique section so that
337   // the table doesn't prevent the removal.
338   const Comdat *C = F.getComdat();
339   bool EmitUniqueSection = TM.getFunctionSections() || C;
340   if (!EmitUniqueSection)
341     return ReadOnlySection;
342 
343   return selectELFSectionForGlobal(getContext(), &F, SectionKind::getReadOnly(),
344                                    Mang, TM, EmitUniqueSection, ELF::SHF_ALLOC,
345                                    &NextUniqueID);
346 }
347 
348 bool TargetLoweringObjectFileELF::shouldPutJumpTableInFunctionSection(
349     bool UsesLabelDifference, const Function &F) const {
350   // We can always create relative relocations, so use another section
351   // that can be marked non-executable.
352   return false;
353 }
354 
355 /// Given a mergeable constant with the specified size and relocation
356 /// information, return a section that it should be placed in.
357 MCSection *TargetLoweringObjectFileELF::getSectionForConstant(
358     const DataLayout &DL, SectionKind Kind, const Constant *C,
359     unsigned &Align) const {
360   if (Kind.isMergeableConst4() && MergeableConst4Section)
361     return MergeableConst4Section;
362   if (Kind.isMergeableConst8() && MergeableConst8Section)
363     return MergeableConst8Section;
364   if (Kind.isMergeableConst16() && MergeableConst16Section)
365     return MergeableConst16Section;
366   if (Kind.isMergeableConst32() && MergeableConst32Section)
367     return MergeableConst32Section;
368   if (Kind.isReadOnly())
369     return ReadOnlySection;
370 
371   assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
372   return DataRelROSection;
373 }
374 
375 static MCSectionELF *getStaticStructorSection(MCContext &Ctx, bool UseInitArray,
376                                               bool IsCtor, unsigned Priority,
377                                               const MCSymbol *KeySym) {
378   std::string Name;
379   unsigned Type;
380   unsigned Flags = ELF::SHF_ALLOC | ELF::SHF_WRITE;
381   StringRef COMDAT = KeySym ? KeySym->getName() : "";
382 
383   if (KeySym)
384     Flags |= ELF::SHF_GROUP;
385 
386   if (UseInitArray) {
387     if (IsCtor) {
388       Type = ELF::SHT_INIT_ARRAY;
389       Name = ".init_array";
390     } else {
391       Type = ELF::SHT_FINI_ARRAY;
392       Name = ".fini_array";
393     }
394     if (Priority != 65535) {
395       Name += '.';
396       Name += utostr(Priority);
397     }
398   } else {
399     // The default scheme is .ctor / .dtor, so we have to invert the priority
400     // numbering.
401     if (IsCtor)
402       Name = ".ctors";
403     else
404       Name = ".dtors";
405     if (Priority != 65535) {
406       Name += '.';
407       Name += utostr(65535 - Priority);
408     }
409     Type = ELF::SHT_PROGBITS;
410   }
411 
412   return Ctx.getELFSection(Name, Type, Flags, 0, COMDAT);
413 }
414 
415 MCSection *TargetLoweringObjectFileELF::getStaticCtorSection(
416     unsigned Priority, const MCSymbol *KeySym) const {
417   return getStaticStructorSection(getContext(), UseInitArray, true, Priority,
418                                   KeySym);
419 }
420 
421 MCSection *TargetLoweringObjectFileELF::getStaticDtorSection(
422     unsigned Priority, const MCSymbol *KeySym) const {
423   return getStaticStructorSection(getContext(), UseInitArray, false, Priority,
424                                   KeySym);
425 }
426 
427 const MCExpr *TargetLoweringObjectFileELF::lowerRelativeReference(
428     const GlobalValue *LHS, const GlobalValue *RHS, Mangler &Mang,
429     const TargetMachine &TM) const {
430   // We may only use a PLT-relative relocation to refer to unnamed_addr
431   // functions.
432   if (!LHS->hasUnnamedAddr() || !LHS->getValueType()->isFunctionTy())
433     return nullptr;
434 
435   // Basic sanity checks.
436   if (LHS->getType()->getPointerAddressSpace() != 0 ||
437       RHS->getType()->getPointerAddressSpace() != 0 || LHS->isThreadLocal() ||
438       RHS->isThreadLocal())
439     return nullptr;
440 
441   return MCBinaryExpr::createSub(
442       MCSymbolRefExpr::create(TM.getSymbol(LHS, Mang), PLTRelativeVariantKind,
443                               getContext()),
444       MCSymbolRefExpr::create(TM.getSymbol(RHS, Mang), getContext()),
445       getContext());
446 }
447 
448 void
449 TargetLoweringObjectFileELF::InitializeELF(bool UseInitArray_) {
450   UseInitArray = UseInitArray_;
451   if (!UseInitArray)
452     return;
453 
454   StaticCtorSection = getContext().getELFSection(
455       ".init_array", ELF::SHT_INIT_ARRAY, ELF::SHF_WRITE | ELF::SHF_ALLOC);
456   StaticDtorSection = getContext().getELFSection(
457       ".fini_array", ELF::SHT_FINI_ARRAY, ELF::SHF_WRITE | ELF::SHF_ALLOC);
458 }
459 
460 //===----------------------------------------------------------------------===//
461 //                                 MachO
462 //===----------------------------------------------------------------------===//
463 
464 TargetLoweringObjectFileMachO::TargetLoweringObjectFileMachO()
465   : TargetLoweringObjectFile() {
466   SupportIndirectSymViaGOTPCRel = true;
467 }
468 
469 /// emitModuleFlags - Perform code emission for module flags.
470 void TargetLoweringObjectFileMachO::
471 emitModuleFlags(MCStreamer &Streamer,
472                 ArrayRef<Module::ModuleFlagEntry> ModuleFlags,
473                 Mangler &Mang, const TargetMachine &TM) const {
474   unsigned VersionVal = 0;
475   unsigned ImageInfoFlags = 0;
476   MDNode *LinkerOptions = nullptr;
477   StringRef SectionVal;
478 
479   for (const auto &MFE : ModuleFlags) {
480     // Ignore flags with 'Require' behavior.
481     if (MFE.Behavior == Module::Require)
482       continue;
483 
484     StringRef Key = MFE.Key->getString();
485     Metadata *Val = MFE.Val;
486 
487     if (Key == "Objective-C Image Info Version") {
488       VersionVal = mdconst::extract<ConstantInt>(Val)->getZExtValue();
489     } else if (Key == "Objective-C Garbage Collection" ||
490                Key == "Objective-C GC Only" ||
491                Key == "Objective-C Is Simulated" ||
492                Key == "Objective-C Class Properties" ||
493                Key == "Objective-C Image Swift Version") {
494       ImageInfoFlags |= mdconst::extract<ConstantInt>(Val)->getZExtValue();
495     } else if (Key == "Objective-C Image Info Section") {
496       SectionVal = cast<MDString>(Val)->getString();
497     } else if (Key == "Linker Options") {
498       LinkerOptions = cast<MDNode>(Val);
499     }
500   }
501 
502   // Emit the linker options if present.
503   if (LinkerOptions) {
504     for (const auto &Option : LinkerOptions->operands()) {
505       SmallVector<std::string, 4> StrOptions;
506       for (const auto &Piece : cast<MDNode>(Option)->operands())
507         StrOptions.push_back(cast<MDString>(Piece)->getString());
508       Streamer.EmitLinkerOptions(StrOptions);
509     }
510   }
511 
512   // The section is mandatory. If we don't have it, then we don't have GC info.
513   if (SectionVal.empty()) return;
514 
515   StringRef Segment, Section;
516   unsigned TAA = 0, StubSize = 0;
517   bool TAAParsed;
518   std::string ErrorCode =
519     MCSectionMachO::ParseSectionSpecifier(SectionVal, Segment, Section,
520                                           TAA, TAAParsed, StubSize);
521   if (!ErrorCode.empty())
522     // If invalid, report the error with report_fatal_error.
523     report_fatal_error("Invalid section specifier '" + Section + "': " +
524                        ErrorCode + ".");
525 
526   // Get the section.
527   MCSectionMachO *S = getContext().getMachOSection(
528       Segment, Section, TAA, StubSize, SectionKind::getData());
529   Streamer.SwitchSection(S);
530   Streamer.EmitLabel(getContext().
531                      getOrCreateSymbol(StringRef("L_OBJC_IMAGE_INFO")));
532   Streamer.EmitIntValue(VersionVal, 4);
533   Streamer.EmitIntValue(ImageInfoFlags, 4);
534   Streamer.AddBlankLine();
535 }
536 
537 static void checkMachOComdat(const GlobalValue *GV) {
538   const Comdat *C = GV->getComdat();
539   if (!C)
540     return;
541 
542   report_fatal_error("MachO doesn't support COMDATs, '" + C->getName() +
543                      "' cannot be lowered.");
544 }
545 
546 MCSection *TargetLoweringObjectFileMachO::getExplicitSectionGlobal(
547     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
548     const TargetMachine &TM) const {
549   // Parse the section specifier and create it if valid.
550   StringRef Segment, Section;
551   unsigned TAA = 0, StubSize = 0;
552   bool TAAParsed;
553 
554   checkMachOComdat(GV);
555 
556   std::string ErrorCode =
557     MCSectionMachO::ParseSectionSpecifier(GV->getSection(), Segment, Section,
558                                           TAA, TAAParsed, StubSize);
559   if (!ErrorCode.empty()) {
560     // If invalid, report the error with report_fatal_error.
561     report_fatal_error("Global variable '" + GV->getName() +
562                        "' has an invalid section specifier '" +
563                        GV->getSection() + "': " + ErrorCode + ".");
564   }
565 
566   // Get the section.
567   MCSectionMachO *S =
568       getContext().getMachOSection(Segment, Section, TAA, StubSize, Kind);
569 
570   // If TAA wasn't set by ParseSectionSpecifier() above,
571   // use the value returned by getMachOSection() as a default.
572   if (!TAAParsed)
573     TAA = S->getTypeAndAttributes();
574 
575   // Okay, now that we got the section, verify that the TAA & StubSize agree.
576   // If the user declared multiple globals with different section flags, we need
577   // to reject it here.
578   if (S->getTypeAndAttributes() != TAA || S->getStubSize() != StubSize) {
579     // If invalid, report the error with report_fatal_error.
580     report_fatal_error("Global variable '" + GV->getName() +
581                        "' section type or attributes does not match previous"
582                        " section specifier");
583   }
584 
585   return S;
586 }
587 
588 MCSection *TargetLoweringObjectFileMachO::SelectSectionForGlobal(
589     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
590     const TargetMachine &TM) const {
591   checkMachOComdat(GV);
592 
593   // Handle thread local data.
594   if (Kind.isThreadBSS()) return TLSBSSSection;
595   if (Kind.isThreadData()) return TLSDataSection;
596 
597   if (Kind.isText())
598     return GV->isWeakForLinker() ? TextCoalSection : TextSection;
599 
600   // If this is weak/linkonce, put this in a coalescable section, either in text
601   // or data depending on if it is writable.
602   if (GV->isWeakForLinker()) {
603     if (Kind.isReadOnly())
604       return ConstTextCoalSection;
605     return DataCoalSection;
606   }
607 
608   // FIXME: Alignment check should be handled by section classifier.
609   if (Kind.isMergeable1ByteCString() &&
610       GV->getParent()->getDataLayout().getPreferredAlignment(
611           cast<GlobalVariable>(GV)) < 32)
612     return CStringSection;
613 
614   // Do not put 16-bit arrays in the UString section if they have an
615   // externally visible label, this runs into issues with certain linker
616   // versions.
617   if (Kind.isMergeable2ByteCString() && !GV->hasExternalLinkage() &&
618       GV->getParent()->getDataLayout().getPreferredAlignment(
619           cast<GlobalVariable>(GV)) < 32)
620     return UStringSection;
621 
622   // With MachO only variables whose corresponding symbol starts with 'l' or
623   // 'L' can be merged, so we only try merging GVs with private linkage.
624   if (GV->hasPrivateLinkage() && Kind.isMergeableConst()) {
625     if (Kind.isMergeableConst4())
626       return FourByteConstantSection;
627     if (Kind.isMergeableConst8())
628       return EightByteConstantSection;
629     if (Kind.isMergeableConst16())
630       return SixteenByteConstantSection;
631   }
632 
633   // Otherwise, if it is readonly, but not something we can specially optimize,
634   // just drop it in .const.
635   if (Kind.isReadOnly())
636     return ReadOnlySection;
637 
638   // If this is marked const, put it into a const section.  But if the dynamic
639   // linker needs to write to it, put it in the data segment.
640   if (Kind.isReadOnlyWithRel())
641     return ConstDataSection;
642 
643   // Put zero initialized globals with strong external linkage in the
644   // DATA, __common section with the .zerofill directive.
645   if (Kind.isBSSExtern())
646     return DataCommonSection;
647 
648   // Put zero initialized globals with local linkage in __DATA,__bss directive
649   // with the .zerofill directive (aka .lcomm).
650   if (Kind.isBSSLocal())
651     return DataBSSSection;
652 
653   // Otherwise, just drop the variable in the normal data section.
654   return DataSection;
655 }
656 
657 MCSection *TargetLoweringObjectFileMachO::getSectionForConstant(
658     const DataLayout &DL, SectionKind Kind, const Constant *C,
659     unsigned &Align) const {
660   // If this constant requires a relocation, we have to put it in the data
661   // segment, not in the text segment.
662   if (Kind.isData() || Kind.isReadOnlyWithRel())
663     return ConstDataSection;
664 
665   if (Kind.isMergeableConst4())
666     return FourByteConstantSection;
667   if (Kind.isMergeableConst8())
668     return EightByteConstantSection;
669   if (Kind.isMergeableConst16())
670     return SixteenByteConstantSection;
671   return ReadOnlySection;  // .const
672 }
673 
674 const MCExpr *TargetLoweringObjectFileMachO::getTTypeGlobalReference(
675     const GlobalValue *GV, unsigned Encoding, Mangler &Mang,
676     const TargetMachine &TM, MachineModuleInfo *MMI,
677     MCStreamer &Streamer) const {
678   // The mach-o version of this method defaults to returning a stub reference.
679 
680   if (Encoding & DW_EH_PE_indirect) {
681     MachineModuleInfoMachO &MachOMMI =
682       MMI->getObjFileInfo<MachineModuleInfoMachO>();
683 
684     MCSymbol *SSym =
685         getSymbolWithGlobalValueBase(GV, "$non_lazy_ptr", Mang, TM);
686 
687     // Add information about the stub reference to MachOMMI so that the stub
688     // gets emitted by the asmprinter.
689     MachineModuleInfoImpl::StubValueTy &StubSym =
690       GV->hasHiddenVisibility() ? MachOMMI.getHiddenGVStubEntry(SSym) :
691                                   MachOMMI.getGVStubEntry(SSym);
692     if (!StubSym.getPointer()) {
693       MCSymbol *Sym = TM.getSymbol(GV, Mang);
694       StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
695     }
696 
697     return TargetLoweringObjectFile::
698       getTTypeReference(MCSymbolRefExpr::create(SSym, getContext()),
699                         Encoding & ~dwarf::DW_EH_PE_indirect, Streamer);
700   }
701 
702   return TargetLoweringObjectFile::getTTypeGlobalReference(GV, Encoding, Mang,
703                                                            TM, MMI, Streamer);
704 }
705 
706 MCSymbol *TargetLoweringObjectFileMachO::getCFIPersonalitySymbol(
707     const GlobalValue *GV, Mangler &Mang, const TargetMachine &TM,
708     MachineModuleInfo *MMI) const {
709   // The mach-o version of this method defaults to returning a stub reference.
710   MachineModuleInfoMachO &MachOMMI =
711     MMI->getObjFileInfo<MachineModuleInfoMachO>();
712 
713   MCSymbol *SSym = getSymbolWithGlobalValueBase(GV, "$non_lazy_ptr", Mang, TM);
714 
715   // Add information about the stub reference to MachOMMI so that the stub
716   // gets emitted by the asmprinter.
717   MachineModuleInfoImpl::StubValueTy &StubSym = MachOMMI.getGVStubEntry(SSym);
718   if (!StubSym.getPointer()) {
719     MCSymbol *Sym = TM.getSymbol(GV, Mang);
720     StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
721   }
722 
723   return SSym;
724 }
725 
726 const MCExpr *TargetLoweringObjectFileMachO::getIndirectSymViaGOTPCRel(
727     const MCSymbol *Sym, const MCValue &MV, int64_t Offset,
728     MachineModuleInfo *MMI, MCStreamer &Streamer) const {
729   // Although MachO 32-bit targets do not explicitly have a GOTPCREL relocation
730   // as 64-bit do, we replace the GOT equivalent by accessing the final symbol
731   // through a non_lazy_ptr stub instead. One advantage is that it allows the
732   // computation of deltas to final external symbols. Example:
733   //
734   //    _extgotequiv:
735   //       .long   _extfoo
736   //
737   //    _delta:
738   //       .long   _extgotequiv-_delta
739   //
740   // is transformed to:
741   //
742   //    _delta:
743   //       .long   L_extfoo$non_lazy_ptr-(_delta+0)
744   //
745   //       .section        __IMPORT,__pointers,non_lazy_symbol_pointers
746   //    L_extfoo$non_lazy_ptr:
747   //       .indirect_symbol        _extfoo
748   //       .long   0
749   //
750   MachineModuleInfoMachO &MachOMMI =
751     MMI->getObjFileInfo<MachineModuleInfoMachO>();
752   MCContext &Ctx = getContext();
753 
754   // The offset must consider the original displacement from the base symbol
755   // since 32-bit targets don't have a GOTPCREL to fold the PC displacement.
756   Offset = -MV.getConstant();
757   const MCSymbol *BaseSym = &MV.getSymB()->getSymbol();
758 
759   // Access the final symbol via sym$non_lazy_ptr and generate the appropriated
760   // non_lazy_ptr stubs.
761   SmallString<128> Name;
762   StringRef Suffix = "$non_lazy_ptr";
763   Name += MMI->getModule()->getDataLayout().getPrivateGlobalPrefix();
764   Name += Sym->getName();
765   Name += Suffix;
766   MCSymbol *Stub = Ctx.getOrCreateSymbol(Name);
767 
768   MachineModuleInfoImpl::StubValueTy &StubSym = MachOMMI.getGVStubEntry(Stub);
769   if (!StubSym.getPointer())
770     StubSym = MachineModuleInfoImpl::
771       StubValueTy(const_cast<MCSymbol *>(Sym), true /* access indirectly */);
772 
773   const MCExpr *BSymExpr =
774     MCSymbolRefExpr::create(BaseSym, MCSymbolRefExpr::VK_None, Ctx);
775   const MCExpr *LHS =
776     MCSymbolRefExpr::create(Stub, MCSymbolRefExpr::VK_None, Ctx);
777 
778   if (!Offset)
779     return MCBinaryExpr::createSub(LHS, BSymExpr, Ctx);
780 
781   const MCExpr *RHS =
782     MCBinaryExpr::createAdd(BSymExpr, MCConstantExpr::create(Offset, Ctx), Ctx);
783   return MCBinaryExpr::createSub(LHS, RHS, Ctx);
784 }
785 
786 static bool canUsePrivateLabel(const MCAsmInfo &AsmInfo,
787                                const MCSection &Section) {
788   if (!AsmInfo.isSectionAtomizableBySymbols(Section))
789     return true;
790 
791   // If it is not dead stripped, it is safe to use private labels.
792   const MCSectionMachO &SMO = cast<MCSectionMachO>(Section);
793   if (SMO.hasAttribute(MachO::S_ATTR_NO_DEAD_STRIP))
794     return true;
795 
796   return false;
797 }
798 
799 void TargetLoweringObjectFileMachO::getNameWithPrefix(
800     SmallVectorImpl<char> &OutName, const GlobalValue *GV, Mangler &Mang,
801     const TargetMachine &TM) const {
802   SectionKind GVKind = TargetLoweringObjectFile::getKindForGlobal(GV, TM);
803   const MCSection *TheSection = SectionForGlobal(GV, GVKind, Mang, TM);
804   bool CannotUsePrivateLabel =
805       !canUsePrivateLabel(*TM.getMCAsmInfo(), *TheSection);
806   Mang.getNameWithPrefix(OutName, GV, CannotUsePrivateLabel);
807 }
808 
809 //===----------------------------------------------------------------------===//
810 //                                  COFF
811 //===----------------------------------------------------------------------===//
812 
813 static unsigned
814 getCOFFSectionFlags(SectionKind K) {
815   unsigned Flags = 0;
816 
817   if (K.isMetadata())
818     Flags |=
819       COFF::IMAGE_SCN_MEM_DISCARDABLE;
820   else if (K.isText())
821     Flags |=
822       COFF::IMAGE_SCN_MEM_EXECUTE |
823       COFF::IMAGE_SCN_MEM_READ |
824       COFF::IMAGE_SCN_CNT_CODE;
825   else if (K.isBSS())
826     Flags |=
827       COFF::IMAGE_SCN_CNT_UNINITIALIZED_DATA |
828       COFF::IMAGE_SCN_MEM_READ |
829       COFF::IMAGE_SCN_MEM_WRITE;
830   else if (K.isThreadLocal())
831     Flags |=
832       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
833       COFF::IMAGE_SCN_MEM_READ |
834       COFF::IMAGE_SCN_MEM_WRITE;
835   else if (K.isReadOnly() || K.isReadOnlyWithRel())
836     Flags |=
837       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
838       COFF::IMAGE_SCN_MEM_READ;
839   else if (K.isWriteable())
840     Flags |=
841       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
842       COFF::IMAGE_SCN_MEM_READ |
843       COFF::IMAGE_SCN_MEM_WRITE;
844 
845   return Flags;
846 }
847 
848 static const GlobalValue *getComdatGVForCOFF(const GlobalValue *GV) {
849   const Comdat *C = GV->getComdat();
850   assert(C && "expected GV to have a Comdat!");
851 
852   StringRef ComdatGVName = C->getName();
853   const GlobalValue *ComdatGV = GV->getParent()->getNamedValue(ComdatGVName);
854   if (!ComdatGV)
855     report_fatal_error("Associative COMDAT symbol '" + ComdatGVName +
856                        "' does not exist.");
857 
858   if (ComdatGV->getComdat() != C)
859     report_fatal_error("Associative COMDAT symbol '" + ComdatGVName +
860                        "' is not a key for its COMDAT.");
861 
862   return ComdatGV;
863 }
864 
865 static int getSelectionForCOFF(const GlobalValue *GV) {
866   if (const Comdat *C = GV->getComdat()) {
867     const GlobalValue *ComdatKey = getComdatGVForCOFF(GV);
868     if (const auto *GA = dyn_cast<GlobalAlias>(ComdatKey))
869       ComdatKey = GA->getBaseObject();
870     if (ComdatKey == GV) {
871       switch (C->getSelectionKind()) {
872       case Comdat::Any:
873         return COFF::IMAGE_COMDAT_SELECT_ANY;
874       case Comdat::ExactMatch:
875         return COFF::IMAGE_COMDAT_SELECT_EXACT_MATCH;
876       case Comdat::Largest:
877         return COFF::IMAGE_COMDAT_SELECT_LARGEST;
878       case Comdat::NoDuplicates:
879         return COFF::IMAGE_COMDAT_SELECT_NODUPLICATES;
880       case Comdat::SameSize:
881         return COFF::IMAGE_COMDAT_SELECT_SAME_SIZE;
882       }
883     } else {
884       return COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE;
885     }
886   }
887   return 0;
888 }
889 
890 MCSection *TargetLoweringObjectFileCOFF::getExplicitSectionGlobal(
891     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
892     const TargetMachine &TM) const {
893   int Selection = 0;
894   unsigned Characteristics = getCOFFSectionFlags(Kind);
895   StringRef Name = GV->getSection();
896   StringRef COMDATSymName = "";
897   if (GV->hasComdat()) {
898     Selection = getSelectionForCOFF(GV);
899     const GlobalValue *ComdatGV;
900     if (Selection == COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE)
901       ComdatGV = getComdatGVForCOFF(GV);
902     else
903       ComdatGV = GV;
904 
905     if (!ComdatGV->hasPrivateLinkage()) {
906       MCSymbol *Sym = TM.getSymbol(ComdatGV, Mang);
907       COMDATSymName = Sym->getName();
908       Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
909     } else {
910       Selection = 0;
911     }
912   }
913 
914   return getContext().getCOFFSection(Name, Characteristics, Kind, COMDATSymName,
915                                      Selection);
916 }
917 
918 static const char *getCOFFSectionNameForUniqueGlobal(SectionKind Kind) {
919   if (Kind.isText())
920     return ".text";
921   if (Kind.isBSS())
922     return ".bss";
923   if (Kind.isThreadLocal())
924     return ".tls$";
925   if (Kind.isReadOnly() || Kind.isReadOnlyWithRel())
926     return ".rdata";
927   return ".data";
928 }
929 
930 MCSection *TargetLoweringObjectFileCOFF::SelectSectionForGlobal(
931     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
932     const TargetMachine &TM) const {
933   // If we have -ffunction-sections then we should emit the global value to a
934   // uniqued section specifically for it.
935   bool EmitUniquedSection;
936   if (Kind.isText())
937     EmitUniquedSection = TM.getFunctionSections();
938   else
939     EmitUniquedSection = TM.getDataSections();
940 
941   if ((EmitUniquedSection && !Kind.isCommon()) || GV->hasComdat()) {
942     const char *Name = getCOFFSectionNameForUniqueGlobal(Kind);
943     unsigned Characteristics = getCOFFSectionFlags(Kind);
944 
945     Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
946     int Selection = getSelectionForCOFF(GV);
947     if (!Selection)
948       Selection = COFF::IMAGE_COMDAT_SELECT_NODUPLICATES;
949     const GlobalValue *ComdatGV;
950     if (GV->hasComdat())
951       ComdatGV = getComdatGVForCOFF(GV);
952     else
953       ComdatGV = GV;
954 
955     unsigned UniqueID = MCContext::GenericSectionID;
956     if (EmitUniquedSection)
957       UniqueID = NextUniqueID++;
958 
959     if (!ComdatGV->hasPrivateLinkage()) {
960       MCSymbol *Sym = TM.getSymbol(ComdatGV, Mang);
961       StringRef COMDATSymName = Sym->getName();
962       return getContext().getCOFFSection(Name, Characteristics, Kind,
963                                          COMDATSymName, Selection, UniqueID);
964     } else {
965       SmallString<256> TmpData;
966       Mang.getNameWithPrefix(TmpData, GV, /*CannotUsePrivateLabel=*/true);
967       return getContext().getCOFFSection(Name, Characteristics, Kind, TmpData,
968                                          Selection, UniqueID);
969     }
970   }
971 
972   if (Kind.isText())
973     return TextSection;
974 
975   if (Kind.isThreadLocal())
976     return TLSDataSection;
977 
978   if (Kind.isReadOnly() || Kind.isReadOnlyWithRel())
979     return ReadOnlySection;
980 
981   // Note: we claim that common symbols are put in BSSSection, but they are
982   // really emitted with the magic .comm directive, which creates a symbol table
983   // entry but not a section.
984   if (Kind.isBSS() || Kind.isCommon())
985     return BSSSection;
986 
987   return DataSection;
988 }
989 
990 void TargetLoweringObjectFileCOFF::getNameWithPrefix(
991     SmallVectorImpl<char> &OutName, const GlobalValue *GV, Mangler &Mang,
992     const TargetMachine &TM) const {
993   bool CannotUsePrivateLabel = false;
994   if (GV->hasPrivateLinkage() &&
995       ((isa<Function>(GV) && TM.getFunctionSections()) ||
996        (isa<GlobalVariable>(GV) && TM.getDataSections())))
997     CannotUsePrivateLabel = true;
998 
999   Mang.getNameWithPrefix(OutName, GV, CannotUsePrivateLabel);
1000 }
1001 
1002 MCSection *TargetLoweringObjectFileCOFF::getSectionForJumpTable(
1003     const Function &F, Mangler &Mang, const TargetMachine &TM) const {
1004   // If the function can be removed, produce a unique section so that
1005   // the table doesn't prevent the removal.
1006   const Comdat *C = F.getComdat();
1007   bool EmitUniqueSection = TM.getFunctionSections() || C;
1008   if (!EmitUniqueSection)
1009     return ReadOnlySection;
1010 
1011   // FIXME: we should produce a symbol for F instead.
1012   if (F.hasPrivateLinkage())
1013     return ReadOnlySection;
1014 
1015   MCSymbol *Sym = TM.getSymbol(&F, Mang);
1016   StringRef COMDATSymName = Sym->getName();
1017 
1018   SectionKind Kind = SectionKind::getReadOnly();
1019   const char *Name = getCOFFSectionNameForUniqueGlobal(Kind);
1020   unsigned Characteristics = getCOFFSectionFlags(Kind);
1021   Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
1022   unsigned UniqueID = NextUniqueID++;
1023 
1024   return getContext().getCOFFSection(Name, Characteristics, Kind, COMDATSymName,
1025                                      COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE, UniqueID);
1026 }
1027 
1028 void TargetLoweringObjectFileCOFF::
1029 emitModuleFlags(MCStreamer &Streamer,
1030                 ArrayRef<Module::ModuleFlagEntry> ModuleFlags,
1031                 Mangler &Mang, const TargetMachine &TM) const {
1032   MDNode *LinkerOptions = nullptr;
1033 
1034   for (const auto &MFE : ModuleFlags) {
1035     StringRef Key = MFE.Key->getString();
1036     if (Key == "Linker Options")
1037       LinkerOptions = cast<MDNode>(MFE.Val);
1038   }
1039 
1040   if (LinkerOptions) {
1041     // Emit the linker options to the linker .drectve section.  According to the
1042     // spec, this section is a space-separated string containing flags for
1043     // linker.
1044     MCSection *Sec = getDrectveSection();
1045     Streamer.SwitchSection(Sec);
1046     for (const auto &Option : LinkerOptions->operands()) {
1047       for (const auto &Piece : cast<MDNode>(Option)->operands()) {
1048         // Lead with a space for consistency with our dllexport implementation.
1049         std::string Directive(" ");
1050         Directive.append(cast<MDString>(Piece)->getString());
1051         Streamer.EmitBytes(Directive);
1052       }
1053     }
1054   }
1055 }
1056 
1057 MCSection *TargetLoweringObjectFileCOFF::getStaticCtorSection(
1058     unsigned Priority, const MCSymbol *KeySym) const {
1059   return getContext().getAssociativeCOFFSection(
1060       cast<MCSectionCOFF>(StaticCtorSection), KeySym, 0);
1061 }
1062 
1063 MCSection *TargetLoweringObjectFileCOFF::getStaticDtorSection(
1064     unsigned Priority, const MCSymbol *KeySym) const {
1065   return getContext().getAssociativeCOFFSection(
1066       cast<MCSectionCOFF>(StaticDtorSection), KeySym, 0);
1067 }
1068 
1069 void TargetLoweringObjectFileCOFF::emitLinkerFlagsForGlobal(
1070     raw_ostream &OS, const GlobalValue *GV, const Mangler &Mang) const {
1071   if (!GV->hasDLLExportStorageClass() || GV->isDeclaration())
1072     return;
1073 
1074   const Triple &TT = getTargetTriple();
1075 
1076   if (TT.isKnownWindowsMSVCEnvironment())
1077     OS << " /EXPORT:";
1078   else
1079     OS << " -export:";
1080 
1081   if (TT.isWindowsGNUEnvironment() || TT.isWindowsCygwinEnvironment()) {
1082     std::string Flag;
1083     raw_string_ostream FlagOS(Flag);
1084     Mang.getNameWithPrefix(FlagOS, GV, false);
1085     FlagOS.flush();
1086     if (Flag[0] == GV->getParent()->getDataLayout().getGlobalPrefix())
1087       OS << Flag.substr(1);
1088     else
1089       OS << Flag;
1090   } else {
1091     Mang.getNameWithPrefix(OS, GV, false);
1092   }
1093 
1094   if (!GV->getValueType()->isFunctionTy()) {
1095     if (TT.isKnownWindowsMSVCEnvironment())
1096       OS << ",DATA";
1097     else
1098       OS << ",data";
1099   }
1100 }
1101