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 (ArrayRef<Module::ModuleFlagEntry>::iterator
494          i = ModuleFlags.begin(), e = ModuleFlags.end(); i != e; ++i) {
495     const Module::ModuleFlagEntry &MFE = *i;
496 
497     // Ignore flags with 'Require' behavior.
498     if (MFE.Behavior == Module::Require)
499       continue;
500 
501     StringRef Key = MFE.Key->getString();
502     Metadata *Val = MFE.Val;
503 
504     if (Key == "Objective-C Image Info Version") {
505       VersionVal = mdconst::extract<ConstantInt>(Val)->getZExtValue();
506     } else if (Key == "Objective-C Garbage Collection" ||
507                Key == "Objective-C GC Only" ||
508                Key == "Objective-C Is Simulated" ||
509                Key == "Objective-C Class Properties" ||
510                Key == "Objective-C Image Swift Version") {
511       ImageInfoFlags |= mdconst::extract<ConstantInt>(Val)->getZExtValue();
512     } else if (Key == "Objective-C Image Info Section") {
513       SectionVal = cast<MDString>(Val)->getString();
514     } else if (Key == "Linker Options") {
515       LinkerOptions = cast<MDNode>(Val);
516     }
517   }
518 
519   // Emit the linker options if present.
520   if (LinkerOptions) {
521     for (unsigned i = 0, e = LinkerOptions->getNumOperands(); i != e; ++i) {
522       MDNode *MDOptions = cast<MDNode>(LinkerOptions->getOperand(i));
523       SmallVector<std::string, 4> StrOptions;
524 
525       // Convert to strings.
526       for (unsigned ii = 0, ie = MDOptions->getNumOperands(); ii != ie; ++ii) {
527         MDString *MDOption = cast<MDString>(MDOptions->getOperand(ii));
528         StrOptions.push_back(MDOption->getString());
529       }
530 
531       Streamer.EmitLinkerOptions(StrOptions);
532     }
533   }
534 
535   // The section is mandatory. If we don't have it, then we don't have GC info.
536   if (SectionVal.empty()) return;
537 
538   StringRef Segment, Section;
539   unsigned TAA = 0, StubSize = 0;
540   bool TAAParsed;
541   std::string ErrorCode =
542     MCSectionMachO::ParseSectionSpecifier(SectionVal, Segment, Section,
543                                           TAA, TAAParsed, StubSize);
544   if (!ErrorCode.empty())
545     // If invalid, report the error with report_fatal_error.
546     report_fatal_error("Invalid section specifier '" + Section + "': " +
547                        ErrorCode + ".");
548 
549   // Get the section.
550   MCSectionMachO *S = getContext().getMachOSection(
551       Segment, Section, TAA, StubSize, SectionKind::getData());
552   Streamer.SwitchSection(S);
553   Streamer.EmitLabel(getContext().
554                      getOrCreateSymbol(StringRef("L_OBJC_IMAGE_INFO")));
555   Streamer.EmitIntValue(VersionVal, 4);
556   Streamer.EmitIntValue(ImageInfoFlags, 4);
557   Streamer.AddBlankLine();
558 }
559 
560 static void checkMachOComdat(const GlobalValue *GV) {
561   const Comdat *C = GV->getComdat();
562   if (!C)
563     return;
564 
565   report_fatal_error("MachO doesn't support COMDATs, '" + C->getName() +
566                      "' cannot be lowered.");
567 }
568 
569 MCSection *TargetLoweringObjectFileMachO::getExplicitSectionGlobal(
570     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
571     const TargetMachine &TM) const {
572   // Parse the section specifier and create it if valid.
573   StringRef Segment, Section;
574   unsigned TAA = 0, StubSize = 0;
575   bool TAAParsed;
576 
577   checkMachOComdat(GV);
578 
579   std::string ErrorCode =
580     MCSectionMachO::ParseSectionSpecifier(GV->getSection(), Segment, Section,
581                                           TAA, TAAParsed, StubSize);
582   if (!ErrorCode.empty()) {
583     // If invalid, report the error with report_fatal_error.
584     report_fatal_error("Global variable '" + GV->getName() +
585                        "' has an invalid section specifier '" +
586                        GV->getSection() + "': " + ErrorCode + ".");
587   }
588 
589   // Get the section.
590   MCSectionMachO *S =
591       getContext().getMachOSection(Segment, Section, TAA, StubSize, Kind);
592 
593   // If TAA wasn't set by ParseSectionSpecifier() above,
594   // use the value returned by getMachOSection() as a default.
595   if (!TAAParsed)
596     TAA = S->getTypeAndAttributes();
597 
598   // Okay, now that we got the section, verify that the TAA & StubSize agree.
599   // If the user declared multiple globals with different section flags, we need
600   // to reject it here.
601   if (S->getTypeAndAttributes() != TAA || S->getStubSize() != StubSize) {
602     // If invalid, report the error with report_fatal_error.
603     report_fatal_error("Global variable '" + GV->getName() +
604                        "' section type or attributes does not match previous"
605                        " section specifier");
606   }
607 
608   return S;
609 }
610 
611 MCSection *TargetLoweringObjectFileMachO::SelectSectionForGlobal(
612     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
613     const TargetMachine &TM) const {
614   checkMachOComdat(GV);
615 
616   // Handle thread local data.
617   if (Kind.isThreadBSS()) return TLSBSSSection;
618   if (Kind.isThreadData()) return TLSDataSection;
619 
620   if (Kind.isText())
621     return GV->isWeakForLinker() ? TextCoalSection : TextSection;
622 
623   // If this is weak/linkonce, put this in a coalescable section, either in text
624   // or data depending on if it is writable.
625   if (GV->isWeakForLinker()) {
626     if (Kind.isReadOnly())
627       return ConstTextCoalSection;
628     return DataCoalSection;
629   }
630 
631   // FIXME: Alignment check should be handled by section classifier.
632   if (Kind.isMergeable1ByteCString() &&
633       GV->getParent()->getDataLayout().getPreferredAlignment(
634           cast<GlobalVariable>(GV)) < 32)
635     return CStringSection;
636 
637   // Do not put 16-bit arrays in the UString section if they have an
638   // externally visible label, this runs into issues with certain linker
639   // versions.
640   if (Kind.isMergeable2ByteCString() && !GV->hasExternalLinkage() &&
641       GV->getParent()->getDataLayout().getPreferredAlignment(
642           cast<GlobalVariable>(GV)) < 32)
643     return UStringSection;
644 
645   // With MachO only variables whose corresponding symbol starts with 'l' or
646   // 'L' can be merged, so we only try merging GVs with private linkage.
647   if (GV->hasPrivateLinkage() && Kind.isMergeableConst()) {
648     if (Kind.isMergeableConst4())
649       return FourByteConstantSection;
650     if (Kind.isMergeableConst8())
651       return EightByteConstantSection;
652     if (Kind.isMergeableConst16())
653       return SixteenByteConstantSection;
654   }
655 
656   // Otherwise, if it is readonly, but not something we can specially optimize,
657   // just drop it in .const.
658   if (Kind.isReadOnly())
659     return ReadOnlySection;
660 
661   // If this is marked const, put it into a const section.  But if the dynamic
662   // linker needs to write to it, put it in the data segment.
663   if (Kind.isReadOnlyWithRel())
664     return ConstDataSection;
665 
666   // Put zero initialized globals with strong external linkage in the
667   // DATA, __common section with the .zerofill directive.
668   if (Kind.isBSSExtern())
669     return DataCommonSection;
670 
671   // Put zero initialized globals with local linkage in __DATA,__bss directive
672   // with the .zerofill directive (aka .lcomm).
673   if (Kind.isBSSLocal())
674     return DataBSSSection;
675 
676   // Otherwise, just drop the variable in the normal data section.
677   return DataSection;
678 }
679 
680 MCSection *TargetLoweringObjectFileMachO::getSectionForConstant(
681     const DataLayout &DL, SectionKind Kind, const Constant *C,
682     unsigned &Align) const {
683   // If this constant requires a relocation, we have to put it in the data
684   // segment, not in the text segment.
685   if (Kind.isData() || Kind.isReadOnlyWithRel())
686     return ConstDataSection;
687 
688   if (Kind.isMergeableConst4())
689     return FourByteConstantSection;
690   if (Kind.isMergeableConst8())
691     return EightByteConstantSection;
692   if (Kind.isMergeableConst16())
693     return SixteenByteConstantSection;
694   return ReadOnlySection;  // .const
695 }
696 
697 const MCExpr *TargetLoweringObjectFileMachO::getTTypeGlobalReference(
698     const GlobalValue *GV, unsigned Encoding, Mangler &Mang,
699     const TargetMachine &TM, MachineModuleInfo *MMI,
700     MCStreamer &Streamer) const {
701   // The mach-o version of this method defaults to returning a stub reference.
702 
703   if (Encoding & DW_EH_PE_indirect) {
704     MachineModuleInfoMachO &MachOMMI =
705       MMI->getObjFileInfo<MachineModuleInfoMachO>();
706 
707     MCSymbol *SSym =
708         getSymbolWithGlobalValueBase(GV, "$non_lazy_ptr", Mang, TM);
709 
710     // Add information about the stub reference to MachOMMI so that the stub
711     // gets emitted by the asmprinter.
712     MachineModuleInfoImpl::StubValueTy &StubSym =
713       GV->hasHiddenVisibility() ? MachOMMI.getHiddenGVStubEntry(SSym) :
714                                   MachOMMI.getGVStubEntry(SSym);
715     if (!StubSym.getPointer()) {
716       MCSymbol *Sym = TM.getSymbol(GV, Mang);
717       StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
718     }
719 
720     return TargetLoweringObjectFile::
721       getTTypeReference(MCSymbolRefExpr::create(SSym, getContext()),
722                         Encoding & ~dwarf::DW_EH_PE_indirect, Streamer);
723   }
724 
725   return TargetLoweringObjectFile::getTTypeGlobalReference(GV, Encoding, Mang,
726                                                            TM, MMI, Streamer);
727 }
728 
729 MCSymbol *TargetLoweringObjectFileMachO::getCFIPersonalitySymbol(
730     const GlobalValue *GV, Mangler &Mang, const TargetMachine &TM,
731     MachineModuleInfo *MMI) const {
732   // The mach-o version of this method defaults to returning a stub reference.
733   MachineModuleInfoMachO &MachOMMI =
734     MMI->getObjFileInfo<MachineModuleInfoMachO>();
735 
736   MCSymbol *SSym = getSymbolWithGlobalValueBase(GV, "$non_lazy_ptr", Mang, TM);
737 
738   // Add information about the stub reference to MachOMMI so that the stub
739   // gets emitted by the asmprinter.
740   MachineModuleInfoImpl::StubValueTy &StubSym = MachOMMI.getGVStubEntry(SSym);
741   if (!StubSym.getPointer()) {
742     MCSymbol *Sym = TM.getSymbol(GV, Mang);
743     StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
744   }
745 
746   return SSym;
747 }
748 
749 const MCExpr *TargetLoweringObjectFileMachO::getIndirectSymViaGOTPCRel(
750     const MCSymbol *Sym, const MCValue &MV, int64_t Offset,
751     MachineModuleInfo *MMI, MCStreamer &Streamer) const {
752   // Although MachO 32-bit targets do not explicitly have a GOTPCREL relocation
753   // as 64-bit do, we replace the GOT equivalent by accessing the final symbol
754   // through a non_lazy_ptr stub instead. One advantage is that it allows the
755   // computation of deltas to final external symbols. Example:
756   //
757   //    _extgotequiv:
758   //       .long   _extfoo
759   //
760   //    _delta:
761   //       .long   _extgotequiv-_delta
762   //
763   // is transformed to:
764   //
765   //    _delta:
766   //       .long   L_extfoo$non_lazy_ptr-(_delta+0)
767   //
768   //       .section        __IMPORT,__pointers,non_lazy_symbol_pointers
769   //    L_extfoo$non_lazy_ptr:
770   //       .indirect_symbol        _extfoo
771   //       .long   0
772   //
773   MachineModuleInfoMachO &MachOMMI =
774     MMI->getObjFileInfo<MachineModuleInfoMachO>();
775   MCContext &Ctx = getContext();
776 
777   // The offset must consider the original displacement from the base symbol
778   // since 32-bit targets don't have a GOTPCREL to fold the PC displacement.
779   Offset = -MV.getConstant();
780   const MCSymbol *BaseSym = &MV.getSymB()->getSymbol();
781 
782   // Access the final symbol via sym$non_lazy_ptr and generate the appropriated
783   // non_lazy_ptr stubs.
784   SmallString<128> Name;
785   StringRef Suffix = "$non_lazy_ptr";
786   Name += MMI->getModule()->getDataLayout().getPrivateGlobalPrefix();
787   Name += Sym->getName();
788   Name += Suffix;
789   MCSymbol *Stub = Ctx.getOrCreateSymbol(Name);
790 
791   MachineModuleInfoImpl::StubValueTy &StubSym = MachOMMI.getGVStubEntry(Stub);
792   if (!StubSym.getPointer())
793     StubSym = MachineModuleInfoImpl::
794       StubValueTy(const_cast<MCSymbol *>(Sym), true /* access indirectly */);
795 
796   const MCExpr *BSymExpr =
797     MCSymbolRefExpr::create(BaseSym, MCSymbolRefExpr::VK_None, Ctx);
798   const MCExpr *LHS =
799     MCSymbolRefExpr::create(Stub, MCSymbolRefExpr::VK_None, Ctx);
800 
801   if (!Offset)
802     return MCBinaryExpr::createSub(LHS, BSymExpr, Ctx);
803 
804   const MCExpr *RHS =
805     MCBinaryExpr::createAdd(BSymExpr, MCConstantExpr::create(Offset, Ctx), Ctx);
806   return MCBinaryExpr::createSub(LHS, RHS, Ctx);
807 }
808 
809 static bool canUsePrivateLabel(const MCAsmInfo &AsmInfo,
810                                const MCSection &Section) {
811   if (!AsmInfo.isSectionAtomizableBySymbols(Section))
812     return true;
813 
814   // If it is not dead stripped, it is safe to use private labels.
815   const MCSectionMachO &SMO = cast<MCSectionMachO>(Section);
816   if (SMO.hasAttribute(MachO::S_ATTR_NO_DEAD_STRIP))
817     return true;
818 
819   return false;
820 }
821 
822 void TargetLoweringObjectFileMachO::getNameWithPrefix(
823     SmallVectorImpl<char> &OutName, const GlobalValue *GV, Mangler &Mang,
824     const TargetMachine &TM) const {
825   SectionKind GVKind = TargetLoweringObjectFile::getKindForGlobal(GV, TM);
826   const MCSection *TheSection = SectionForGlobal(GV, GVKind, Mang, TM);
827   bool CannotUsePrivateLabel =
828       !canUsePrivateLabel(*TM.getMCAsmInfo(), *TheSection);
829   Mang.getNameWithPrefix(OutName, GV, CannotUsePrivateLabel);
830 }
831 
832 //===----------------------------------------------------------------------===//
833 //                                  COFF
834 //===----------------------------------------------------------------------===//
835 
836 static unsigned
837 getCOFFSectionFlags(SectionKind K) {
838   unsigned Flags = 0;
839 
840   if (K.isMetadata())
841     Flags |=
842       COFF::IMAGE_SCN_MEM_DISCARDABLE;
843   else if (K.isText())
844     Flags |=
845       COFF::IMAGE_SCN_MEM_EXECUTE |
846       COFF::IMAGE_SCN_MEM_READ |
847       COFF::IMAGE_SCN_CNT_CODE;
848   else if (K.isBSS())
849     Flags |=
850       COFF::IMAGE_SCN_CNT_UNINITIALIZED_DATA |
851       COFF::IMAGE_SCN_MEM_READ |
852       COFF::IMAGE_SCN_MEM_WRITE;
853   else if (K.isThreadLocal())
854     Flags |=
855       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
856       COFF::IMAGE_SCN_MEM_READ |
857       COFF::IMAGE_SCN_MEM_WRITE;
858   else if (K.isReadOnly() || K.isReadOnlyWithRel())
859     Flags |=
860       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
861       COFF::IMAGE_SCN_MEM_READ;
862   else if (K.isWriteable())
863     Flags |=
864       COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
865       COFF::IMAGE_SCN_MEM_READ |
866       COFF::IMAGE_SCN_MEM_WRITE;
867 
868   return Flags;
869 }
870 
871 static const GlobalValue *getComdatGVForCOFF(const GlobalValue *GV) {
872   const Comdat *C = GV->getComdat();
873   assert(C && "expected GV to have a Comdat!");
874 
875   StringRef ComdatGVName = C->getName();
876   const GlobalValue *ComdatGV = GV->getParent()->getNamedValue(ComdatGVName);
877   if (!ComdatGV)
878     report_fatal_error("Associative COMDAT symbol '" + ComdatGVName +
879                        "' does not exist.");
880 
881   if (ComdatGV->getComdat() != C)
882     report_fatal_error("Associative COMDAT symbol '" + ComdatGVName +
883                        "' is not a key for its COMDAT.");
884 
885   return ComdatGV;
886 }
887 
888 static int getSelectionForCOFF(const GlobalValue *GV) {
889   if (const Comdat *C = GV->getComdat()) {
890     const GlobalValue *ComdatKey = getComdatGVForCOFF(GV);
891     if (const auto *GA = dyn_cast<GlobalAlias>(ComdatKey))
892       ComdatKey = GA->getBaseObject();
893     if (ComdatKey == GV) {
894       switch (C->getSelectionKind()) {
895       case Comdat::Any:
896         return COFF::IMAGE_COMDAT_SELECT_ANY;
897       case Comdat::ExactMatch:
898         return COFF::IMAGE_COMDAT_SELECT_EXACT_MATCH;
899       case Comdat::Largest:
900         return COFF::IMAGE_COMDAT_SELECT_LARGEST;
901       case Comdat::NoDuplicates:
902         return COFF::IMAGE_COMDAT_SELECT_NODUPLICATES;
903       case Comdat::SameSize:
904         return COFF::IMAGE_COMDAT_SELECT_SAME_SIZE;
905       }
906     } else {
907       return COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE;
908     }
909   }
910   return 0;
911 }
912 
913 MCSection *TargetLoweringObjectFileCOFF::getExplicitSectionGlobal(
914     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
915     const TargetMachine &TM) const {
916   int Selection = 0;
917   unsigned Characteristics = getCOFFSectionFlags(Kind);
918   StringRef Name = GV->getSection();
919   StringRef COMDATSymName = "";
920   if (GV->hasComdat()) {
921     Selection = getSelectionForCOFF(GV);
922     const GlobalValue *ComdatGV;
923     if (Selection == COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE)
924       ComdatGV = getComdatGVForCOFF(GV);
925     else
926       ComdatGV = GV;
927 
928     if (!ComdatGV->hasPrivateLinkage()) {
929       MCSymbol *Sym = TM.getSymbol(ComdatGV, Mang);
930       COMDATSymName = Sym->getName();
931       Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
932     } else {
933       Selection = 0;
934     }
935   }
936   return getContext().getCOFFSection(Name,
937                                      Characteristics,
938                                      Kind,
939                                      COMDATSymName,
940                                      Selection);
941 }
942 
943 static const char *getCOFFSectionNameForUniqueGlobal(SectionKind Kind) {
944   if (Kind.isText())
945     return ".text";
946   if (Kind.isBSS())
947     return ".bss";
948   if (Kind.isThreadLocal())
949     return ".tls$";
950   if (Kind.isReadOnly() || Kind.isReadOnlyWithRel())
951     return ".rdata";
952   return ".data";
953 }
954 
955 MCSection *TargetLoweringObjectFileCOFF::SelectSectionForGlobal(
956     const GlobalValue *GV, SectionKind Kind, Mangler &Mang,
957     const TargetMachine &TM) const {
958   // If we have -ffunction-sections then we should emit the global value to a
959   // uniqued section specifically for it.
960   bool EmitUniquedSection;
961   if (Kind.isText())
962     EmitUniquedSection = TM.getFunctionSections();
963   else
964     EmitUniquedSection = TM.getDataSections();
965 
966   if ((EmitUniquedSection && !Kind.isCommon()) || GV->hasComdat()) {
967     const char *Name = getCOFFSectionNameForUniqueGlobal(Kind);
968     unsigned Characteristics = getCOFFSectionFlags(Kind);
969 
970     Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
971     int Selection = getSelectionForCOFF(GV);
972     if (!Selection)
973       Selection = COFF::IMAGE_COMDAT_SELECT_NODUPLICATES;
974     const GlobalValue *ComdatGV;
975     if (GV->hasComdat())
976       ComdatGV = getComdatGVForCOFF(GV);
977     else
978       ComdatGV = GV;
979 
980     if (!ComdatGV->hasPrivateLinkage()) {
981       MCSymbol *Sym = TM.getSymbol(ComdatGV, Mang);
982       StringRef COMDATSymName = Sym->getName();
983       return getContext().getCOFFSection(Name, Characteristics, Kind,
984                                          COMDATSymName, Selection);
985     } else {
986       SmallString<256> TmpData;
987       Mang.getNameWithPrefix(TmpData, GV, /*CannotUsePrivateLabel=*/true);
988       return getContext().getCOFFSection(Name, Characteristics, Kind, TmpData,
989                                          Selection);
990     }
991   }
992 
993   if (Kind.isText())
994     return TextSection;
995 
996   if (Kind.isThreadLocal())
997     return TLSDataSection;
998 
999   if (Kind.isReadOnly() || Kind.isReadOnlyWithRel())
1000     return ReadOnlySection;
1001 
1002   // Note: we claim that common symbols are put in BSSSection, but they are
1003   // really emitted with the magic .comm directive, which creates a symbol table
1004   // entry but not a section.
1005   if (Kind.isBSS() || Kind.isCommon())
1006     return BSSSection;
1007 
1008   return DataSection;
1009 }
1010 
1011 void TargetLoweringObjectFileCOFF::getNameWithPrefix(
1012     SmallVectorImpl<char> &OutName, const GlobalValue *GV, Mangler &Mang,
1013     const TargetMachine &TM) const {
1014   bool CannotUsePrivateLabel = false;
1015   if (GV->hasPrivateLinkage() &&
1016       ((isa<Function>(GV) && TM.getFunctionSections()) ||
1017        (isa<GlobalVariable>(GV) && TM.getDataSections())))
1018     CannotUsePrivateLabel = true;
1019 
1020   Mang.getNameWithPrefix(OutName, GV, CannotUsePrivateLabel);
1021 }
1022 
1023 MCSection *TargetLoweringObjectFileCOFF::getSectionForJumpTable(
1024     const Function &F, Mangler &Mang, const TargetMachine &TM) const {
1025   // If the function can be removed, produce a unique section so that
1026   // the table doesn't prevent the removal.
1027   const Comdat *C = F.getComdat();
1028   bool EmitUniqueSection = TM.getFunctionSections() || C;
1029   if (!EmitUniqueSection)
1030     return ReadOnlySection;
1031 
1032   // FIXME: we should produce a symbol for F instead.
1033   if (F.hasPrivateLinkage())
1034     return ReadOnlySection;
1035 
1036   MCSymbol *Sym = TM.getSymbol(&F, Mang);
1037   StringRef COMDATSymName = Sym->getName();
1038 
1039   SectionKind Kind = SectionKind::getReadOnly();
1040   const char *Name = getCOFFSectionNameForUniqueGlobal(Kind);
1041   unsigned Characteristics = getCOFFSectionFlags(Kind);
1042   Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
1043 
1044   return getContext().getCOFFSection(Name, Characteristics, Kind, COMDATSymName,
1045                                      COFF::IMAGE_COMDAT_SELECT_ASSOCIATIVE);
1046 }
1047 
1048 void TargetLoweringObjectFileCOFF::
1049 emitModuleFlags(MCStreamer &Streamer,
1050                 ArrayRef<Module::ModuleFlagEntry> ModuleFlags,
1051                 Mangler &Mang, const TargetMachine &TM) const {
1052   MDNode *LinkerOptions = nullptr;
1053 
1054   // Look for the "Linker Options" flag, since it's the only one we support.
1055   for (ArrayRef<Module::ModuleFlagEntry>::iterator
1056        i = ModuleFlags.begin(), e = ModuleFlags.end(); i != e; ++i) {
1057     const Module::ModuleFlagEntry &MFE = *i;
1058     StringRef Key = MFE.Key->getString();
1059     Metadata *Val = MFE.Val;
1060     if (Key == "Linker Options") {
1061       LinkerOptions = cast<MDNode>(Val);
1062       break;
1063     }
1064   }
1065   if (!LinkerOptions)
1066     return;
1067 
1068   // Emit the linker options to the linker .drectve section.  According to the
1069   // spec, this section is a space-separated string containing flags for linker.
1070   MCSection *Sec = getDrectveSection();
1071   Streamer.SwitchSection(Sec);
1072   for (unsigned i = 0, e = LinkerOptions->getNumOperands(); i != e; ++i) {
1073     MDNode *MDOptions = cast<MDNode>(LinkerOptions->getOperand(i));
1074     for (unsigned ii = 0, ie = MDOptions->getNumOperands(); ii != ie; ++ii) {
1075       MDString *MDOption = cast<MDString>(MDOptions->getOperand(ii));
1076       // Lead with a space for consistency with our dllexport implementation.
1077       std::string Directive(" ");
1078       Directive.append(MDOption->getString());
1079       Streamer.EmitBytes(Directive);
1080     }
1081   }
1082 }
1083 
1084 MCSection *TargetLoweringObjectFileCOFF::getStaticCtorSection(
1085     unsigned Priority, const MCSymbol *KeySym) const {
1086   return getContext().getAssociativeCOFFSection(
1087       cast<MCSectionCOFF>(StaticCtorSection), KeySym);
1088 }
1089 
1090 MCSection *TargetLoweringObjectFileCOFF::getStaticDtorSection(
1091     unsigned Priority, const MCSymbol *KeySym) const {
1092   return getContext().getAssociativeCOFFSection(
1093       cast<MCSectionCOFF>(StaticDtorSection), KeySym);
1094 }
1095 
1096 void TargetLoweringObjectFileCOFF::emitLinkerFlagsForGlobal(
1097     raw_ostream &OS, const GlobalValue *GV, const Mangler &Mang) const {
1098   if (!GV->hasDLLExportStorageClass() || GV->isDeclaration())
1099     return;
1100 
1101   const Triple &TT = getTargetTriple();
1102 
1103   if (TT.isKnownWindowsMSVCEnvironment())
1104     OS << " /EXPORT:";
1105   else
1106     OS << " -export:";
1107 
1108   if (TT.isWindowsGNUEnvironment() || TT.isWindowsCygwinEnvironment()) {
1109     std::string Flag;
1110     raw_string_ostream FlagOS(Flag);
1111     Mang.getNameWithPrefix(FlagOS, GV, false);
1112     FlagOS.flush();
1113     if (Flag[0] == GV->getParent()->getDataLayout().getGlobalPrefix())
1114       OS << Flag.substr(1);
1115     else
1116       OS << Flag;
1117   } else {
1118     Mang.getNameWithPrefix(OS, GV, false);
1119   }
1120 
1121   if (!GV->getValueType()->isFunctionTy()) {
1122     if (TT.isKnownWindowsMSVCEnvironment())
1123       OS << ",DATA";
1124     else
1125       OS << ",data";
1126   }
1127 }
1128