TargetLoweringObjectFileImpl.cpp revision 671215464c8335e383fa2db90df2eab73ef83b10 
1//===-- llvm/CodeGen/TargetLoweringObjectFileImpl.cpp - Object File Info --===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements classes used to handle lowerings specific to common
11// object file formats.
12//
13//===----------------------------------------------------------------------===//
14
15#include "llvm/CodeGen/TargetLoweringObjectFileImpl.h"
16#include "llvm/Constants.h"
17#include "llvm/DerivedTypes.h"
18#include "llvm/Function.h"
19#include "llvm/GlobalVariable.h"
20#include "llvm/CodeGen/MachineModuleInfoImpls.h"
21#include "llvm/MC/MCContext.h"
22#include "llvm/MC/MCExpr.h"
23#include "llvm/MC/MCSectionMachO.h"
24#include "llvm/MC/MCSectionELF.h"
25#include "llvm/MC/MCSectionCOFF.h"
26#include "llvm/MC/MCStreamer.h"
27#include "llvm/MC/MCSymbol.h"
28#include "llvm/Target/Mangler.h"
29#include "llvm/Target/TargetData.h"
30#include "llvm/Target/TargetMachine.h"
31#include "llvm/Target/TargetOptions.h"
32#include "llvm/Support/Dwarf.h"
33#include "llvm/Support/ELF.h"
34#include "llvm/Support/ErrorHandling.h"
35#include "llvm/Support/raw_ostream.h"
36#include "llvm/ADT/SmallString.h"
37#include "llvm/ADT/StringExtras.h"
38#include "llvm/ADT/Triple.h"
39using namespace llvm;
40using namespace dwarf;
41
42//===----------------------------------------------------------------------===//
43//                                  ELF
44//===----------------------------------------------------------------------===//
45
46MCSymbol *
47TargetLoweringObjectFileELF::getCFIPersonalitySymbol(const GlobalValue *GV,
48                                                     Mangler *Mang,
49                                                MachineModuleInfo *MMI) const {
50  unsigned Encoding = getPersonalityEncoding();
51  switch (Encoding & 0x70) {
52  default:
53    report_fatal_error("We do not support this DWARF encoding yet!");
54  case dwarf::DW_EH_PE_absptr:
55    return  Mang->getSymbol(GV);
56    break;
57  case dwarf::DW_EH_PE_pcrel: {
58    return getContext().GetOrCreateSymbol(StringRef("DW.ref.") +
59                                          Mang->getSymbol(GV)->getName());
60    break;
61  }
62  }
63}
64
65void TargetLoweringObjectFileELF::emitPersonalityValue(MCStreamer &Streamer,
66                                                       const TargetMachine &TM,
67                                                       const MCSymbol *Sym) const {
68  SmallString<64> NameData("DW.ref.");
69  NameData += Sym->getName();
70  MCSymbol *Label = 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  const MCSection *Sec = getContext().getELFSection(NameData,
77                                                    ELF::SHT_PROGBITS,
78                                                    Flags,
79                                                    SectionKind::getDataRel(),
80                                                    0, Label->getName());
81  Streamer.SwitchSection(Sec);
82  Streamer.EmitValueToAlignment(8);
83  Streamer.EmitSymbolAttribute(Label, MCSA_ELF_TypeObject);
84  const MCExpr *E = MCConstantExpr::Create(8, getContext());
85  Streamer.EmitELFSize(Label, E);
86  Streamer.EmitLabel(Label);
87
88  unsigned Size = TM.getTargetData()->getPointerSize();
89  Streamer.EmitSymbolValue(Sym, Size);
90}
91
92static SectionKind
93getELFKindForNamedSection(StringRef Name, SectionKind K) {
94  // N.B.: The defaults used in here are no the same ones used in MC.
95  // We follow gcc, MC follows gas. For example, given ".section .eh_frame",
96  // both gas and MC will produce a section with no flags. Given
97  // section(".eh_frame") gcc will produce
98  // .section	.eh_frame,"a",@progbits
99  if (Name.empty() || Name[0] != '.') return K;
100
101  // Some lame default implementation based on some magic section names.
102  if (Name == ".bss" ||
103      Name.startswith(".bss.") ||
104      Name.startswith(".gnu.linkonce.b.") ||
105      Name.startswith(".llvm.linkonce.b.") ||
106      Name == ".sbss" ||
107      Name.startswith(".sbss.") ||
108      Name.startswith(".gnu.linkonce.sb.") ||
109      Name.startswith(".llvm.linkonce.sb."))
110    return SectionKind::getBSS();
111
112  if (Name == ".tdata" ||
113      Name.startswith(".tdata.") ||
114      Name.startswith(".gnu.linkonce.td.") ||
115      Name.startswith(".llvm.linkonce.td."))
116    return SectionKind::getThreadData();
117
118  if (Name == ".tbss" ||
119      Name.startswith(".tbss.") ||
120      Name.startswith(".gnu.linkonce.tb.") ||
121      Name.startswith(".llvm.linkonce.tb."))
122    return SectionKind::getThreadBSS();
123
124  return K;
125}
126
127
128static unsigned getELFSectionType(StringRef Name, SectionKind K) {
129
130  if (Name == ".init_array")
131    return ELF::SHT_INIT_ARRAY;
132
133  if (Name == ".fini_array")
134    return ELF::SHT_FINI_ARRAY;
135
136  if (Name == ".preinit_array")
137    return ELF::SHT_PREINIT_ARRAY;
138
139  if (K.isBSS() || K.isThreadBSS())
140    return ELF::SHT_NOBITS;
141
142  return ELF::SHT_PROGBITS;
143}
144
145
146static unsigned
147getELFSectionFlags(SectionKind K) {
148  unsigned Flags = 0;
149
150  if (!K.isMetadata())
151    Flags |= ELF::SHF_ALLOC;
152
153  if (K.isText())
154    Flags |= ELF::SHF_EXECINSTR;
155
156  if (K.isWriteable())
157    Flags |= ELF::SHF_WRITE;
158
159  if (K.isThreadLocal())
160    Flags |= ELF::SHF_TLS;
161
162  // K.isMergeableConst() is left out to honour PR4650
163  if (K.isMergeableCString() || K.isMergeableConst4() ||
164      K.isMergeableConst8() || K.isMergeableConst16())
165    Flags |= ELF::SHF_MERGE;
166
167  if (K.isMergeableCString())
168    Flags |= ELF::SHF_STRINGS;
169
170  return Flags;
171}
172
173
174const MCSection *TargetLoweringObjectFileELF::
175getExplicitSectionGlobal(const GlobalValue *GV, SectionKind Kind,
176                         Mangler *Mang, const TargetMachine &TM) const {
177  StringRef SectionName = GV->getSection();
178
179  // Infer section flags from the section name if we can.
180  Kind = getELFKindForNamedSection(SectionName, Kind);
181
182  return getContext().getELFSection(SectionName,
183                                    getELFSectionType(SectionName, Kind),
184                                    getELFSectionFlags(Kind), Kind);
185}
186
187/// getSectionPrefixForGlobal - Return the section prefix name used by options
188/// FunctionsSections and DataSections.
189static const char *getSectionPrefixForGlobal(SectionKind Kind) {
190  if (Kind.isText())                 return ".text.";
191  if (Kind.isReadOnly())             return ".rodata.";
192
193  if (Kind.isThreadData())           return ".tdata.";
194  if (Kind.isThreadBSS())            return ".tbss.";
195
196  if (Kind.isDataNoRel())            return ".data.";
197  if (Kind.isDataRelLocal())         return ".data.rel.local.";
198  if (Kind.isDataRel())              return ".data.rel.";
199  if (Kind.isReadOnlyWithRelLocal()) return ".data.rel.ro.local.";
200
201  assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
202  return ".data.rel.ro.";
203}
204
205
206const MCSection *TargetLoweringObjectFileELF::
207SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
208                       Mangler *Mang, const TargetMachine &TM) const {
209  // If we have -ffunction-section or -fdata-section then we should emit the
210  // global value to a uniqued section specifically for it.
211  bool EmitUniquedSection;
212  if (Kind.isText())
213    EmitUniquedSection = TM.getFunctionSections();
214  else
215    EmitUniquedSection = TM.getDataSections();
216
217  // If this global is linkonce/weak and the target handles this by emitting it
218  // into a 'uniqued' section name, create and return the section now.
219  if ((GV->isWeakForLinker() || EmitUniquedSection) &&
220      !Kind.isCommon() && !Kind.isBSS()) {
221    const char *Prefix;
222    Prefix = getSectionPrefixForGlobal(Kind);
223
224    SmallString<128> Name(Prefix, Prefix+strlen(Prefix));
225    MCSymbol *Sym = Mang->getSymbol(GV);
226    Name.append(Sym->getName().begin(), Sym->getName().end());
227    StringRef Group = "";
228    unsigned Flags = getELFSectionFlags(Kind);
229    if (GV->isWeakForLinker()) {
230      Group = Sym->getName();
231      Flags |= ELF::SHF_GROUP;
232    }
233
234    return getContext().getELFSection(Name.str(),
235                                      getELFSectionType(Name.str(), Kind),
236                                      Flags, Kind, 0, Group);
237  }
238
239  if (Kind.isText()) return TextSection;
240
241  if (Kind.isMergeable1ByteCString() ||
242      Kind.isMergeable2ByteCString() ||
243      Kind.isMergeable4ByteCString()) {
244
245    // We also need alignment here.
246    // FIXME: this is getting the alignment of the character, not the
247    // alignment of the global!
248    unsigned Align =
249      TM.getTargetData()->getPreferredAlignment(cast<GlobalVariable>(GV));
250
251    const char *SizeSpec = ".rodata.str1.";
252    if (Kind.isMergeable2ByteCString())
253      SizeSpec = ".rodata.str2.";
254    else if (Kind.isMergeable4ByteCString())
255      SizeSpec = ".rodata.str4.";
256    else
257      assert(Kind.isMergeable1ByteCString() && "unknown string width");
258
259
260    std::string Name = SizeSpec + utostr(Align);
261    return getContext().getELFSection(Name, ELF::SHT_PROGBITS,
262                                      ELF::SHF_ALLOC |
263                                      ELF::SHF_MERGE |
264                                      ELF::SHF_STRINGS,
265                                      Kind);
266  }
267
268  if (Kind.isMergeableConst()) {
269    if (Kind.isMergeableConst4() && MergeableConst4Section)
270      return MergeableConst4Section;
271    if (Kind.isMergeableConst8() && MergeableConst8Section)
272      return MergeableConst8Section;
273    if (Kind.isMergeableConst16() && MergeableConst16Section)
274      return MergeableConst16Section;
275    return ReadOnlySection;  // .const
276  }
277
278  if (Kind.isReadOnly())             return ReadOnlySection;
279
280  if (Kind.isThreadData())           return TLSDataSection;
281  if (Kind.isThreadBSS())            return TLSBSSSection;
282
283  // Note: we claim that common symbols are put in BSSSection, but they are
284  // really emitted with the magic .comm directive, which creates a symbol table
285  // entry but not a section.
286  if (Kind.isBSS() || Kind.isCommon()) return BSSSection;
287
288  if (Kind.isDataNoRel())            return DataSection;
289  if (Kind.isDataRelLocal())         return DataRelLocalSection;
290  if (Kind.isDataRel())              return DataRelSection;
291  if (Kind.isReadOnlyWithRelLocal()) return DataRelROLocalSection;
292
293  assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
294  return DataRelROSection;
295}
296
297/// getSectionForConstant - Given a mergeable constant with the
298/// specified size and relocation information, return a section that it
299/// should be placed in.
300const MCSection *TargetLoweringObjectFileELF::
301getSectionForConstant(SectionKind Kind) const {
302  if (Kind.isMergeableConst4() && MergeableConst4Section)
303    return MergeableConst4Section;
304  if (Kind.isMergeableConst8() && MergeableConst8Section)
305    return MergeableConst8Section;
306  if (Kind.isMergeableConst16() && MergeableConst16Section)
307    return MergeableConst16Section;
308  if (Kind.isReadOnly())
309    return ReadOnlySection;
310
311  if (Kind.isReadOnlyWithRelLocal()) return DataRelROLocalSection;
312  assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
313  return DataRelROSection;
314}
315
316const MCExpr *TargetLoweringObjectFileELF::
317getExprForDwarfGlobalReference(const GlobalValue *GV, Mangler *Mang,
318                               MachineModuleInfo *MMI,
319                               unsigned Encoding, MCStreamer &Streamer) const {
320
321  if (Encoding & dwarf::DW_EH_PE_indirect) {
322    MachineModuleInfoELF &ELFMMI = MMI->getObjFileInfo<MachineModuleInfoELF>();
323
324    SmallString<128> Name;
325    Mang->getNameWithPrefix(Name, GV, true);
326    Name += ".DW.stub";
327
328    // Add information about the stub reference to ELFMMI so that the stub
329    // gets emitted by the asmprinter.
330    MCSymbol *SSym = getContext().GetOrCreateSymbol(Name.str());
331    MachineModuleInfoImpl::StubValueTy &StubSym = ELFMMI.getGVStubEntry(SSym);
332    if (StubSym.getPointer() == 0) {
333      MCSymbol *Sym = Mang->getSymbol(GV);
334      StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
335    }
336
337    return TargetLoweringObjectFile::
338      getExprForDwarfReference(SSym, Encoding & ~dwarf::DW_EH_PE_indirect, Streamer);
339  }
340
341  return TargetLoweringObjectFile::
342    getExprForDwarfGlobalReference(GV, Mang, MMI, Encoding, Streamer);
343}
344
345//===----------------------------------------------------------------------===//
346//                                 MachO
347//===----------------------------------------------------------------------===//
348
349const MCSection *TargetLoweringObjectFileMachO::
350getExplicitSectionGlobal(const GlobalValue *GV, SectionKind Kind,
351                         Mangler *Mang, const TargetMachine &TM) const {
352  // Parse the section specifier and create it if valid.
353  StringRef Segment, Section;
354  unsigned TAA = 0, StubSize = 0;
355  bool TAAParsed;
356  std::string ErrorCode =
357    MCSectionMachO::ParseSectionSpecifier(GV->getSection(), Segment, Section,
358                                          TAA, TAAParsed, StubSize);
359  if (!ErrorCode.empty()) {
360    // If invalid, report the error with report_fatal_error.
361    report_fatal_error("Global variable '" + GV->getNameStr() +
362                      "' has an invalid section specifier '" + GV->getSection()+
363                      "': " + ErrorCode + ".");
364    // Fall back to dropping it into the data section.
365    return DataSection;
366  }
367
368  // Get the section.
369  const MCSectionMachO *S =
370    getContext().getMachOSection(Segment, Section, TAA, StubSize, Kind);
371
372  // If TAA wasn't set by ParseSectionSpecifier() above,
373  // use the value returned by getMachOSection() as a default.
374  if (!TAAParsed)
375    TAA = S->getTypeAndAttributes();
376
377  // Okay, now that we got the section, verify that the TAA & StubSize agree.
378  // If the user declared multiple globals with different section flags, we need
379  // to reject it here.
380  if (S->getTypeAndAttributes() != TAA || S->getStubSize() != StubSize) {
381    // If invalid, report the error with report_fatal_error.
382    report_fatal_error("Global variable '" + GV->getNameStr() +
383                      "' section type or attributes does not match previous"
384                      " section specifier");
385  }
386
387  return S;
388}
389
390const MCSection *TargetLoweringObjectFileMachO::
391SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
392                       Mangler *Mang, const TargetMachine &TM) const {
393
394  // Handle thread local data.
395  if (Kind.isThreadBSS()) return TLSBSSSection;
396  if (Kind.isThreadData()) return TLSDataSection;
397
398  if (Kind.isText())
399    return GV->isWeakForLinker() ? TextCoalSection : TextSection;
400
401  // If this is weak/linkonce, put this in a coalescable section, either in text
402  // or data depending on if it is writable.
403  if (GV->isWeakForLinker()) {
404    if (Kind.isReadOnly())
405      return ConstTextCoalSection;
406    return DataCoalSection;
407  }
408
409  // FIXME: Alignment check should be handled by section classifier.
410  if (Kind.isMergeable1ByteCString() &&
411      TM.getTargetData()->getPreferredAlignment(cast<GlobalVariable>(GV)) < 32)
412    return CStringSection;
413
414  // Do not put 16-bit arrays in the UString section if they have an
415  // externally visible label, this runs into issues with certain linker
416  // versions.
417  if (Kind.isMergeable2ByteCString() && !GV->hasExternalLinkage() &&
418      TM.getTargetData()->getPreferredAlignment(cast<GlobalVariable>(GV)) < 32)
419    return UStringSection;
420
421  if (Kind.isMergeableConst()) {
422    if (Kind.isMergeableConst4())
423      return FourByteConstantSection;
424    if (Kind.isMergeableConst8())
425      return EightByteConstantSection;
426    if (Kind.isMergeableConst16() && SixteenByteConstantSection)
427      return SixteenByteConstantSection;
428  }
429
430  // Otherwise, if it is readonly, but not something we can specially optimize,
431  // just drop it in .const.
432  if (Kind.isReadOnly())
433    return ReadOnlySection;
434
435  // If this is marked const, put it into a const section.  But if the dynamic
436  // linker needs to write to it, put it in the data segment.
437  if (Kind.isReadOnlyWithRel())
438    return ConstDataSection;
439
440  // Put zero initialized globals with strong external linkage in the
441  // DATA, __common section with the .zerofill directive.
442  if (Kind.isBSSExtern())
443    return DataCommonSection;
444
445  // Put zero initialized globals with local linkage in __DATA,__bss directive
446  // with the .zerofill directive (aka .lcomm).
447  if (Kind.isBSSLocal())
448    return DataBSSSection;
449
450  // Otherwise, just drop the variable in the normal data section.
451  return DataSection;
452}
453
454const MCSection *
455TargetLoweringObjectFileMachO::getSectionForConstant(SectionKind Kind) const {
456  // If this constant requires a relocation, we have to put it in the data
457  // segment, not in the text segment.
458  if (Kind.isDataRel() || Kind.isReadOnlyWithRel())
459    return ConstDataSection;
460
461  if (Kind.isMergeableConst4())
462    return FourByteConstantSection;
463  if (Kind.isMergeableConst8())
464    return EightByteConstantSection;
465  if (Kind.isMergeableConst16() && SixteenByteConstantSection)
466    return SixteenByteConstantSection;
467  return ReadOnlySection;  // .const
468}
469
470/// shouldEmitUsedDirectiveFor - This hook allows targets to selectively decide
471/// not to emit the UsedDirective for some symbols in llvm.used.
472// FIXME: REMOVE this (rdar://7071300)
473bool TargetLoweringObjectFileMachO::
474shouldEmitUsedDirectiveFor(const GlobalValue *GV, Mangler *Mang) const {
475  /// On Darwin, internally linked data beginning with "L" or "l" does not have
476  /// the directive emitted (this occurs in ObjC metadata).
477  if (!GV) return false;
478
479  // Check whether the mangled name has the "Private" or "LinkerPrivate" prefix.
480  if (GV->hasLocalLinkage() && !isa<Function>(GV)) {
481    // FIXME: ObjC metadata is currently emitted as internal symbols that have
482    // \1L and \0l prefixes on them.  Fix them to be Private/LinkerPrivate and
483    // this horrible hack can go away.
484    MCSymbol *Sym = Mang->getSymbol(GV);
485    if (Sym->getName()[0] == 'L' || Sym->getName()[0] == 'l')
486      return false;
487  }
488
489  return true;
490}
491
492const MCExpr *TargetLoweringObjectFileMachO::
493getExprForDwarfGlobalReference(const GlobalValue *GV, Mangler *Mang,
494                               MachineModuleInfo *MMI, unsigned Encoding,
495                               MCStreamer &Streamer) const {
496  // The mach-o version of this method defaults to returning a stub reference.
497
498  if (Encoding & DW_EH_PE_indirect) {
499    MachineModuleInfoMachO &MachOMMI =
500      MMI->getObjFileInfo<MachineModuleInfoMachO>();
501
502    SmallString<128> Name;
503    Mang->getNameWithPrefix(Name, GV, true);
504    Name += "$non_lazy_ptr";
505
506    // Add information about the stub reference to MachOMMI so that the stub
507    // gets emitted by the asmprinter.
508    MCSymbol *SSym = getContext().GetOrCreateSymbol(Name.str());
509    MachineModuleInfoImpl::StubValueTy &StubSym =
510      GV->hasHiddenVisibility() ? MachOMMI.getHiddenGVStubEntry(SSym) :
511                                  MachOMMI.getGVStubEntry(SSym);
512    if (StubSym.getPointer() == 0) {
513      MCSymbol *Sym = Mang->getSymbol(GV);
514      StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
515    }
516
517    return TargetLoweringObjectFile::
518      getExprForDwarfReference(SSym, Encoding & ~dwarf::DW_EH_PE_indirect, Streamer);
519  }
520
521  return TargetLoweringObjectFile::
522    getExprForDwarfGlobalReference(GV, Mang, MMI, Encoding, Streamer);
523}
524
525MCSymbol *TargetLoweringObjectFileMachO::
526getCFIPersonalitySymbol(const GlobalValue *GV, Mangler *Mang,
527                        MachineModuleInfo *MMI) const {
528  // The mach-o version of this method defaults to returning a stub reference.
529  MachineModuleInfoMachO &MachOMMI =
530    MMI->getObjFileInfo<MachineModuleInfoMachO>();
531
532  SmallString<128> Name;
533  Mang->getNameWithPrefix(Name, GV, true);
534  Name += "$non_lazy_ptr";
535
536  // Add information about the stub reference to MachOMMI so that the stub
537  // gets emitted by the asmprinter.
538  MCSymbol *SSym = getContext().GetOrCreateSymbol(Name.str());
539  MachineModuleInfoImpl::StubValueTy &StubSym =
540      GV->hasHiddenVisibility() ? MachOMMI.getHiddenGVStubEntry(SSym) :
541                                  MachOMMI.getGVStubEntry(SSym);
542  if (StubSym.getPointer() == 0) {
543    MCSymbol *Sym = Mang->getSymbol(GV);
544    StubSym = MachineModuleInfoImpl::StubValueTy(Sym, !GV->hasLocalLinkage());
545  }
546
547  return SSym;
548}
549
550//===----------------------------------------------------------------------===//
551//                                  COFF
552//===----------------------------------------------------------------------===//
553
554static unsigned
555getCOFFSectionFlags(SectionKind K) {
556  unsigned Flags = 0;
557
558  if (K.isMetadata())
559    Flags |=
560      COFF::IMAGE_SCN_MEM_DISCARDABLE;
561  else if (K.isText())
562    Flags |=
563      COFF::IMAGE_SCN_MEM_EXECUTE |
564      COFF::IMAGE_SCN_MEM_READ |
565      COFF::IMAGE_SCN_CNT_CODE;
566  else if (K.isBSS ())
567    Flags |=
568      COFF::IMAGE_SCN_CNT_UNINITIALIZED_DATA |
569      COFF::IMAGE_SCN_MEM_READ |
570      COFF::IMAGE_SCN_MEM_WRITE;
571  else if (K.isReadOnly())
572    Flags |=
573      COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
574      COFF::IMAGE_SCN_MEM_READ;
575  else if (K.isWriteable())
576    Flags |=
577      COFF::IMAGE_SCN_CNT_INITIALIZED_DATA |
578      COFF::IMAGE_SCN_MEM_READ |
579      COFF::IMAGE_SCN_MEM_WRITE;
580
581  return Flags;
582}
583
584const MCSection *TargetLoweringObjectFileCOFF::
585getExplicitSectionGlobal(const GlobalValue *GV, SectionKind Kind,
586                         Mangler *Mang, const TargetMachine &TM) const {
587  return getContext().getCOFFSection(GV->getSection(),
588                                     getCOFFSectionFlags(Kind),
589                                     Kind);
590}
591
592static const char *getCOFFSectionPrefixForUniqueGlobal(SectionKind Kind) {
593  if (Kind.isText())
594    return ".text$";
595  if (Kind.isBSS ())
596    return ".bss$";
597  if (Kind.isWriteable())
598    return ".data$";
599  return ".rdata$";
600}
601
602
603const MCSection *TargetLoweringObjectFileCOFF::
604SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
605                       Mangler *Mang, const TargetMachine &TM) const {
606  assert(!Kind.isThreadLocal() && "Doesn't support TLS");
607
608  // If this global is linkonce/weak and the target handles this by emitting it
609  // into a 'uniqued' section name, create and return the section now.
610  if (GV->isWeakForLinker()) {
611    const char *Prefix = getCOFFSectionPrefixForUniqueGlobal(Kind);
612    SmallString<128> Name(Prefix, Prefix+strlen(Prefix));
613    MCSymbol *Sym = Mang->getSymbol(GV);
614    Name.append(Sym->getName().begin() + 1, Sym->getName().end());
615
616    unsigned Characteristics = getCOFFSectionFlags(Kind);
617
618    Characteristics |= COFF::IMAGE_SCN_LNK_COMDAT;
619
620    return getContext().getCOFFSection(Name.str(), Characteristics,
621                          COFF::IMAGE_COMDAT_SELECT_ANY, Kind);
622  }
623
624  if (Kind.isText())
625    return getTextSection();
626
627  return getDataSection();
628}
629
630