1 //===-- llvm/Target/TargetLoweringObjectFile.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/Target/TargetLoweringObjectFile.h"
16 #include "llvm/Constants.h"
17 #include "llvm/DerivedTypes.h"
18 #include "llvm/Function.h"
19 #include "llvm/GlobalVariable.h"
20 #include "llvm/MC/MCContext.h"
21 #include "llvm/MC/MCExpr.h"
22 #include "llvm/MC/MCSectionMachO.h"
23 #include "llvm/MC/MCSectionELF.h"
24 #include "llvm/Target/TargetData.h"
25 #include "llvm/Target/TargetMachine.h"
26 #include "llvm/Target/TargetOptions.h"
27 #include "llvm/Support/Mangler.h"
28 #include "llvm/ADT/SmallString.h"
29 #include "llvm/ADT/StringExtras.h"
30 using namespace llvm;
31 
32 //===----------------------------------------------------------------------===//
33 //                              Generic Code
34 //===----------------------------------------------------------------------===//
35 
36 TargetLoweringObjectFile::TargetLoweringObjectFile() : Ctx(0) {
37   TextSection = 0;
38   DataSection = 0;
39   BSSSection = 0;
40   ReadOnlySection = 0;
41   StaticCtorSection = 0;
42   StaticDtorSection = 0;
43   LSDASection = 0;
44   EHFrameSection = 0;
45 
46   DwarfAbbrevSection = 0;
47   DwarfInfoSection = 0;
48   DwarfLineSection = 0;
49   DwarfFrameSection = 0;
50   DwarfPubNamesSection = 0;
51   DwarfPubTypesSection = 0;
52   DwarfDebugInlineSection = 0;
53   DwarfStrSection = 0;
54   DwarfLocSection = 0;
55   DwarfARangesSection = 0;
56   DwarfRangesSection = 0;
57   DwarfMacroInfoSection = 0;
58 }
59 
60 TargetLoweringObjectFile::~TargetLoweringObjectFile() {
61 }
62 
63 static bool isSuitableForBSS(const GlobalVariable *GV) {
64   Constant *C = GV->getInitializer();
65 
66   // Must have zero initializer.
67   if (!C->isNullValue())
68     return false;
69 
70   // Leave constant zeros in readonly constant sections, so they can be shared.
71   if (GV->isConstant())
72     return false;
73 
74   // If the global has an explicit section specified, don't put it in BSS.
75   if (!GV->getSection().empty())
76     return false;
77 
78   // If -nozero-initialized-in-bss is specified, don't ever use BSS.
79   if (NoZerosInBSS)
80     return false;
81 
82   // Otherwise, put it in BSS!
83   return true;
84 }
85 
86 /// IsNullTerminatedString - Return true if the specified constant (which is
87 /// known to have a type that is an array of 1/2/4 byte elements) ends with a
88 /// nul value and contains no other nuls in it.
89 static bool IsNullTerminatedString(const Constant *C) {
90   const ArrayType *ATy = cast<ArrayType>(C->getType());
91 
92   // First check: is we have constant array of i8 terminated with zero
93   if (const ConstantArray *CVA = dyn_cast<ConstantArray>(C)) {
94     if (ATy->getNumElements() == 0) return false;
95 
96     ConstantInt *Null =
97       dyn_cast<ConstantInt>(CVA->getOperand(ATy->getNumElements()-1));
98     if (Null == 0 || Null->getZExtValue() != 0)
99       return false; // Not null terminated.
100 
101     // Verify that the null doesn't occur anywhere else in the string.
102     for (unsigned i = 0, e = ATy->getNumElements()-1; i != e; ++i)
103       // Reject constantexpr elements etc.
104       if (!isa<ConstantInt>(CVA->getOperand(i)) ||
105           CVA->getOperand(i) == Null)
106         return false;
107     return true;
108   }
109 
110   // Another possibility: [1 x i8] zeroinitializer
111   if (isa<ConstantAggregateZero>(C))
112     return ATy->getNumElements() == 1;
113 
114   return false;
115 }
116 
117 /// getKindForGlobal - This is a top-level target-independent classifier for
118 /// a global variable.  Given an global variable and information from TM, it
119 /// classifies the global in a variety of ways that make various target
120 /// implementations simpler.  The target implementation is free to ignore this
121 /// extra info of course.
122 SectionKind TargetLoweringObjectFile::getKindForGlobal(const GlobalValue *GV,
123                                                        const TargetMachine &TM){
124   assert(!GV->isDeclaration() && !GV->hasAvailableExternallyLinkage() &&
125          "Can only be used for global definitions");
126 
127   Reloc::Model ReloModel = TM.getRelocationModel();
128 
129   // Early exit - functions should be always in text sections.
130   const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV);
131   if (GVar == 0)
132     return SectionKind::getText();
133 
134   // Handle thread-local data first.
135   if (GVar->isThreadLocal()) {
136     if (isSuitableForBSS(GVar))
137       return SectionKind::getThreadBSS();
138     return SectionKind::getThreadData();
139   }
140 
141   // Variable can be easily put to BSS section.
142   if (isSuitableForBSS(GVar))
143     return SectionKind::getBSS();
144 
145   Constant *C = GVar->getInitializer();
146 
147   // If the global is marked constant, we can put it into a mergable section,
148   // a mergable string section, or general .data if it contains relocations.
149   if (GVar->isConstant()) {
150     // If the initializer for the global contains something that requires a
151     // relocation, then we may have to drop this into a wriable data section
152     // even though it is marked const.
153     switch (C->getRelocationInfo()) {
154     default: llvm_unreachable("unknown relocation info kind");
155     case Constant::NoRelocation:
156       // If initializer is a null-terminated string, put it in a "cstring"
157       // section of the right width.
158       if (const ArrayType *ATy = dyn_cast<ArrayType>(C->getType())) {
159         if (const IntegerType *ITy =
160               dyn_cast<IntegerType>(ATy->getElementType())) {
161           if ((ITy->getBitWidth() == 8 || ITy->getBitWidth() == 16 ||
162                ITy->getBitWidth() == 32) &&
163               IsNullTerminatedString(C)) {
164             if (ITy->getBitWidth() == 8)
165               return SectionKind::getMergeable1ByteCString();
166             if (ITy->getBitWidth() == 16)
167               return SectionKind::getMergeable2ByteCString();
168 
169             assert(ITy->getBitWidth() == 32 && "Unknown width");
170             return SectionKind::getMergeable4ByteCString();
171           }
172         }
173       }
174 
175       // Otherwise, just drop it into a mergable constant section.  If we have
176       // a section for this size, use it, otherwise use the arbitrary sized
177       // mergable section.
178       switch (TM.getTargetData()->getTypeAllocSize(C->getType())) {
179       case 4:  return SectionKind::getMergeableConst4();
180       case 8:  return SectionKind::getMergeableConst8();
181       case 16: return SectionKind::getMergeableConst16();
182       default: return SectionKind::getMergeableConst();
183       }
184 
185     case Constant::LocalRelocation:
186       // In static relocation model, the linker will resolve all addresses, so
187       // the relocation entries will actually be constants by the time the app
188       // starts up.  However, we can't put this into a mergable section, because
189       // the linker doesn't take relocations into consideration when it tries to
190       // merge entries in the section.
191       if (ReloModel == Reloc::Static)
192         return SectionKind::getReadOnly();
193 
194       // Otherwise, the dynamic linker needs to fix it up, put it in the
195       // writable data.rel.local section.
196       return SectionKind::getReadOnlyWithRelLocal();
197 
198     case Constant::GlobalRelocations:
199       // In static relocation model, the linker will resolve all addresses, so
200       // the relocation entries will actually be constants by the time the app
201       // starts up.  However, we can't put this into a mergable section, because
202       // the linker doesn't take relocations into consideration when it tries to
203       // merge entries in the section.
204       if (ReloModel == Reloc::Static)
205         return SectionKind::getReadOnly();
206 
207       // Otherwise, the dynamic linker needs to fix it up, put it in the
208       // writable data.rel section.
209       return SectionKind::getReadOnlyWithRel();
210     }
211   }
212 
213   // Okay, this isn't a constant.  If the initializer for the global is going
214   // to require a runtime relocation by the dynamic linker, put it into a more
215   // specific section to improve startup time of the app.  This coalesces these
216   // globals together onto fewer pages, improving the locality of the dynamic
217   // linker.
218   if (ReloModel == Reloc::Static)
219     return SectionKind::getDataNoRel();
220 
221   switch (C->getRelocationInfo()) {
222   default: llvm_unreachable("unknown relocation info kind");
223   case Constant::NoRelocation:
224     return SectionKind::getDataNoRel();
225   case Constant::LocalRelocation:
226     return SectionKind::getDataRelLocal();
227   case Constant::GlobalRelocations:
228     return SectionKind::getDataRel();
229   }
230 }
231 
232 /// SectionForGlobal - This method computes the appropriate section to emit
233 /// the specified global variable or function definition.  This should not
234 /// be passed external (or available externally) globals.
235 const MCSection *TargetLoweringObjectFile::
236 SectionForGlobal(const GlobalValue *GV, SectionKind Kind, Mangler *Mang,
237                  const TargetMachine &TM) const {
238   // Select section name.
239   if (GV->hasSection())
240     return getExplicitSectionGlobal(GV, Kind, Mang, TM);
241 
242 
243   // Use default section depending on the 'type' of global
244   return SelectSectionForGlobal(GV, Kind, Mang, TM);
245 }
246 
247 
248 // Lame default implementation. Calculate the section name for global.
249 const MCSection *
250 TargetLoweringObjectFile::SelectSectionForGlobal(const GlobalValue *GV,
251                                                  SectionKind Kind,
252                                                  Mangler *Mang,
253                                                  const TargetMachine &TM) const{
254   assert(!Kind.isThreadLocal() && "Doesn't support TLS");
255 
256   if (Kind.isText())
257     return getTextSection();
258 
259   if (Kind.isBSS() && BSSSection != 0)
260     return BSSSection;
261 
262   if (Kind.isReadOnly() && ReadOnlySection != 0)
263     return ReadOnlySection;
264 
265   return getDataSection();
266 }
267 
268 /// getSectionForConstant - Given a mergable constant with the
269 /// specified size and relocation information, return a section that it
270 /// should be placed in.
271 const MCSection *
272 TargetLoweringObjectFile::getSectionForConstant(SectionKind Kind) const {
273   if (Kind.isReadOnly() && ReadOnlySection != 0)
274     return ReadOnlySection;
275 
276   return DataSection;
277 }
278 
279 /// getSymbolForDwarfGlobalReference - Return an MCExpr to use for a
280 /// pc-relative reference to the specified global variable from exception
281 /// handling information.  In addition to the symbol, this returns
282 /// by-reference:
283 ///
284 /// IsIndirect - True if the returned symbol is actually a stub that contains
285 ///    the address of the symbol, false if the symbol is the global itself.
286 ///
287 /// IsPCRel - True if the symbol reference is already pc-relative, false if
288 ///    the caller needs to subtract off the address of the reference from the
289 ///    symbol.
290 ///
291 const MCExpr *TargetLoweringObjectFile::
292 getSymbolForDwarfGlobalReference(const GlobalValue *GV, Mangler *Mang,
293                                  bool &IsIndirect, bool &IsPCRel) const {
294   // The generic implementation of this just returns a direct reference to the
295   // symbol.
296   IsIndirect = false;
297   IsPCRel    = false;
298 
299   SmallString<128> Name;
300   Mang->getNameWithPrefix(Name, GV, false);
301   return MCSymbolRefExpr::Create(Name.str(), getContext());
302 }
303 
304 
305 //===----------------------------------------------------------------------===//
306 //                                  ELF
307 //===----------------------------------------------------------------------===//
308 typedef StringMap<const MCSectionELF*> ELFUniqueMapTy;
309 
310 TargetLoweringObjectFileELF::~TargetLoweringObjectFileELF() {
311   // If we have the section uniquing map, free it.
312   delete (ELFUniqueMapTy*)UniquingMap;
313 }
314 
315 const MCSection *TargetLoweringObjectFileELF::
316 getELFSection(StringRef Section, unsigned Type, unsigned Flags,
317               SectionKind Kind, bool IsExplicit) const {
318   if (UniquingMap == 0)
319     UniquingMap = new ELFUniqueMapTy();
320   ELFUniqueMapTy &Map = *(ELFUniqueMapTy*)UniquingMap;
321 
322   // Do the lookup, if we have a hit, return it.
323   const MCSectionELF *&Entry = Map[Section];
324   if (Entry) return Entry;
325 
326   return Entry = MCSectionELF::Create(Section, Type, Flags, Kind, IsExplicit,
327                                       getContext());
328 }
329 
330 void TargetLoweringObjectFileELF::Initialize(MCContext &Ctx,
331                                              const TargetMachine &TM) {
332   if (UniquingMap != 0)
333     ((ELFUniqueMapTy*)UniquingMap)->clear();
334   TargetLoweringObjectFile::Initialize(Ctx, TM);
335 
336   BSSSection =
337     getELFSection(".bss", MCSectionELF::SHT_NOBITS,
338                   MCSectionELF::SHF_WRITE | MCSectionELF::SHF_ALLOC,
339                   SectionKind::getBSS());
340 
341   TextSection =
342     getELFSection(".text", MCSectionELF::SHT_PROGBITS,
343                   MCSectionELF::SHF_EXECINSTR | MCSectionELF::SHF_ALLOC,
344                   SectionKind::getText());
345 
346   DataSection =
347     getELFSection(".data", MCSectionELF::SHT_PROGBITS,
348                   MCSectionELF::SHF_WRITE | MCSectionELF::SHF_ALLOC,
349                   SectionKind::getDataRel());
350 
351   ReadOnlySection =
352     getELFSection(".rodata", MCSectionELF::SHT_PROGBITS,
353                   MCSectionELF::SHF_ALLOC,
354                   SectionKind::getReadOnly());
355 
356   TLSDataSection =
357     getELFSection(".tdata", MCSectionELF::SHT_PROGBITS,
358                   MCSectionELF::SHF_ALLOC | MCSectionELF::SHF_TLS |
359                   MCSectionELF::SHF_WRITE, SectionKind::getThreadData());
360 
361   TLSBSSSection =
362     getELFSection(".tbss", MCSectionELF::SHT_NOBITS,
363                   MCSectionELF::SHF_ALLOC | MCSectionELF::SHF_TLS |
364                   MCSectionELF::SHF_WRITE, SectionKind::getThreadBSS());
365 
366   DataRelSection =
367     getELFSection(".data.rel", MCSectionELF::SHT_PROGBITS,
368                   MCSectionELF::SHF_ALLOC | MCSectionELF::SHF_WRITE,
369                   SectionKind::getDataRel());
370 
371   DataRelLocalSection =
372     getELFSection(".data.rel.local", MCSectionELF::SHT_PROGBITS,
373                   MCSectionELF::SHF_ALLOC | MCSectionELF::SHF_WRITE,
374                   SectionKind::getDataRelLocal());
375 
376   DataRelROSection =
377     getELFSection(".data.rel.ro", MCSectionELF::SHT_PROGBITS,
378                   MCSectionELF::SHF_ALLOC | MCSectionELF::SHF_WRITE,
379                   SectionKind::getReadOnlyWithRel());
380 
381   DataRelROLocalSection =
382     getELFSection(".data.rel.ro.local", MCSectionELF::SHT_PROGBITS,
383                   MCSectionELF::SHF_ALLOC | MCSectionELF::SHF_WRITE,
384                   SectionKind::getReadOnlyWithRelLocal());
385 
386   MergeableConst4Section =
387     getELFSection(".rodata.cst4", MCSectionELF::SHT_PROGBITS,
388                   MCSectionELF::SHF_ALLOC | MCSectionELF::SHF_MERGE,
389                   SectionKind::getMergeableConst4());
390 
391   MergeableConst8Section =
392     getELFSection(".rodata.cst8", MCSectionELF::SHT_PROGBITS,
393                   MCSectionELF::SHF_ALLOC | MCSectionELF::SHF_MERGE,
394                   SectionKind::getMergeableConst8());
395 
396   MergeableConst16Section =
397     getELFSection(".rodata.cst16", MCSectionELF::SHT_PROGBITS,
398                   MCSectionELF::SHF_ALLOC | MCSectionELF::SHF_MERGE,
399                   SectionKind::getMergeableConst16());
400 
401   StaticCtorSection =
402     getELFSection(".ctors", MCSectionELF::SHT_PROGBITS,
403                   MCSectionELF::SHF_ALLOC | MCSectionELF::SHF_WRITE,
404                   SectionKind::getDataRel());
405 
406   StaticDtorSection =
407     getELFSection(".dtors", MCSectionELF::SHT_PROGBITS,
408                   MCSectionELF::SHF_ALLOC | MCSectionELF::SHF_WRITE,
409                   SectionKind::getDataRel());
410 
411   // Exception Handling Sections.
412 
413   // FIXME: We're emitting LSDA info into a readonly section on ELF, even though
414   // it contains relocatable pointers.  In PIC mode, this is probably a big
415   // runtime hit for C++ apps.  Either the contents of the LSDA need to be
416   // adjusted or this should be a data section.
417   LSDASection =
418     getELFSection(".gcc_except_table", MCSectionELF::SHT_PROGBITS,
419                   MCSectionELF::SHF_ALLOC, SectionKind::getReadOnly());
420   EHFrameSection =
421     getELFSection(".eh_frame", MCSectionELF::SHT_PROGBITS,
422                   MCSectionELF::SHF_ALLOC | MCSectionELF::SHF_WRITE,
423                   SectionKind::getDataRel());
424 
425   // Debug Info Sections.
426   DwarfAbbrevSection =
427     getELFSection(".debug_abbrev", MCSectionELF::SHT_PROGBITS, 0,
428                   SectionKind::getMetadata());
429   DwarfInfoSection =
430     getELFSection(".debug_info", MCSectionELF::SHT_PROGBITS, 0,
431                   SectionKind::getMetadata());
432   DwarfLineSection =
433     getELFSection(".debug_line", MCSectionELF::SHT_PROGBITS, 0,
434                   SectionKind::getMetadata());
435   DwarfFrameSection =
436     getELFSection(".debug_frame", MCSectionELF::SHT_PROGBITS, 0,
437                   SectionKind::getMetadata());
438   DwarfPubNamesSection =
439     getELFSection(".debug_pubnames", MCSectionELF::SHT_PROGBITS, 0,
440                   SectionKind::getMetadata());
441   DwarfPubTypesSection =
442     getELFSection(".debug_pubtypes", MCSectionELF::SHT_PROGBITS, 0,
443                   SectionKind::getMetadata());
444   DwarfStrSection =
445     getELFSection(".debug_str", MCSectionELF::SHT_PROGBITS, 0,
446                   SectionKind::getMetadata());
447   DwarfLocSection =
448     getELFSection(".debug_loc", MCSectionELF::SHT_PROGBITS, 0,
449                   SectionKind::getMetadata());
450   DwarfARangesSection =
451     getELFSection(".debug_aranges", MCSectionELF::SHT_PROGBITS, 0,
452                   SectionKind::getMetadata());
453   DwarfRangesSection =
454     getELFSection(".debug_ranges", MCSectionELF::SHT_PROGBITS, 0,
455                   SectionKind::getMetadata());
456   DwarfMacroInfoSection =
457     getELFSection(".debug_macinfo", MCSectionELF::SHT_PROGBITS, 0,
458                   SectionKind::getMetadata());
459 }
460 
461 
462 static SectionKind
463 getELFKindForNamedSection(const char *Name, SectionKind K) {
464   if (Name[0] != '.') return K;
465 
466   // Some lame default implementation based on some magic section names.
467   if (strcmp(Name, ".bss") == 0 ||
468       strncmp(Name, ".bss.", 5) == 0 ||
469       strncmp(Name, ".gnu.linkonce.b.", 16) == 0 ||
470       strncmp(Name, ".llvm.linkonce.b.", 17) == 0 ||
471       strcmp(Name, ".sbss") == 0 ||
472       strncmp(Name, ".sbss.", 6) == 0 ||
473       strncmp(Name, ".gnu.linkonce.sb.", 17) == 0 ||
474       strncmp(Name, ".llvm.linkonce.sb.", 18) == 0)
475     return SectionKind::getBSS();
476 
477   if (strcmp(Name, ".tdata") == 0 ||
478       strncmp(Name, ".tdata.", 7) == 0 ||
479       strncmp(Name, ".gnu.linkonce.td.", 17) == 0 ||
480       strncmp(Name, ".llvm.linkonce.td.", 18) == 0)
481     return SectionKind::getThreadData();
482 
483   if (strcmp(Name, ".tbss") == 0 ||
484       strncmp(Name, ".tbss.", 6) == 0 ||
485       strncmp(Name, ".gnu.linkonce.tb.", 17) == 0 ||
486       strncmp(Name, ".llvm.linkonce.tb.", 18) == 0)
487     return SectionKind::getThreadBSS();
488 
489   return K;
490 }
491 
492 
493 static unsigned
494 getELFSectionType(const char *Name, SectionKind K) {
495 
496   if (strcmp(Name, ".init_array") == 0)
497     return MCSectionELF::SHT_INIT_ARRAY;
498 
499   if (strcmp(Name, ".fini_array") == 0)
500     return MCSectionELF::SHT_FINI_ARRAY;
501 
502   if (strcmp(Name, ".preinit_array") == 0)
503     return MCSectionELF::SHT_PREINIT_ARRAY;
504 
505   if (K.isBSS() || K.isThreadBSS())
506     return MCSectionELF::SHT_NOBITS;
507 
508   return MCSectionELF::SHT_PROGBITS;
509 }
510 
511 
512 static unsigned
513 getELFSectionFlags(SectionKind K) {
514   unsigned Flags = 0;
515 
516   if (!K.isMetadata())
517     Flags |= MCSectionELF::SHF_ALLOC;
518 
519   if (K.isText())
520     Flags |= MCSectionELF::SHF_EXECINSTR;
521 
522   if (K.isWriteable())
523     Flags |= MCSectionELF::SHF_WRITE;
524 
525   if (K.isThreadLocal())
526     Flags |= MCSectionELF::SHF_TLS;
527 
528   // K.isMergeableConst() is left out to honour PR4650
529   if (K.isMergeableCString() || K.isMergeableConst4() ||
530       K.isMergeableConst8() || K.isMergeableConst16())
531     Flags |= MCSectionELF::SHF_MERGE;
532 
533   if (K.isMergeableCString())
534     Flags |= MCSectionELF::SHF_STRINGS;
535 
536   return Flags;
537 }
538 
539 
540 const MCSection *TargetLoweringObjectFileELF::
541 getExplicitSectionGlobal(const GlobalValue *GV, SectionKind Kind,
542                          Mangler *Mang, const TargetMachine &TM) const {
543   const char *SectionName = GV->getSection().c_str();
544 
545   // Infer section flags from the section name if we can.
546   Kind = getELFKindForNamedSection(SectionName, Kind);
547 
548   return getELFSection(SectionName,
549                        getELFSectionType(SectionName, Kind),
550                        getELFSectionFlags(Kind), Kind, true);
551 }
552 
553 static const char *getSectionPrefixForUniqueGlobal(SectionKind Kind) {
554   if (Kind.isText())                 return ".gnu.linkonce.t.";
555   if (Kind.isReadOnly())             return ".gnu.linkonce.r.";
556 
557   if (Kind.isThreadData())           return ".gnu.linkonce.td.";
558   if (Kind.isThreadBSS())            return ".gnu.linkonce.tb.";
559 
560   if (Kind.isBSS())                  return ".gnu.linkonce.b.";
561   if (Kind.isDataNoRel())            return ".gnu.linkonce.d.";
562   if (Kind.isDataRelLocal())         return ".gnu.linkonce.d.rel.local.";
563   if (Kind.isDataRel())              return ".gnu.linkonce.d.rel.";
564   if (Kind.isReadOnlyWithRelLocal()) return ".gnu.linkonce.d.rel.ro.local.";
565 
566   assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
567   return ".gnu.linkonce.d.rel.ro.";
568 }
569 
570 const MCSection *TargetLoweringObjectFileELF::
571 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
572                        Mangler *Mang, const TargetMachine &TM) const {
573 
574   // If this global is linkonce/weak and the target handles this by emitting it
575   // into a 'uniqued' section name, create and return the section now.
576   if (GV->isWeakForLinker()) {
577     const char *Prefix = getSectionPrefixForUniqueGlobal(Kind);
578     std::string Name = Mang->makeNameProper(GV->getNameStr());
579 
580     return getELFSection((Prefix+Name).c_str(),
581                          getELFSectionType((Prefix+Name).c_str(), Kind),
582                          getELFSectionFlags(Kind),
583                          Kind);
584   }
585 
586   if (Kind.isText()) return TextSection;
587 
588   if (Kind.isMergeable1ByteCString() ||
589       Kind.isMergeable2ByteCString() ||
590       Kind.isMergeable4ByteCString()) {
591 
592     // We also need alignment here.
593     // FIXME: this is getting the alignment of the character, not the
594     // alignment of the global!
595     unsigned Align =
596       TM.getTargetData()->getPreferredAlignment(cast<GlobalVariable>(GV));
597 
598     const char *SizeSpec = ".rodata.str1.";
599     if (Kind.isMergeable2ByteCString())
600       SizeSpec = ".rodata.str2.";
601     else if (Kind.isMergeable4ByteCString())
602       SizeSpec = ".rodata.str4.";
603     else
604       assert(Kind.isMergeable1ByteCString() && "unknown string width");
605 
606 
607     std::string Name = SizeSpec + utostr(Align);
608     return getELFSection(Name.c_str(), MCSectionELF::SHT_PROGBITS,
609                          MCSectionELF::SHF_ALLOC |
610                          MCSectionELF::SHF_MERGE |
611                          MCSectionELF::SHF_STRINGS,
612                          Kind);
613   }
614 
615   if (Kind.isMergeableConst()) {
616     if (Kind.isMergeableConst4() && MergeableConst4Section)
617       return MergeableConst4Section;
618     if (Kind.isMergeableConst8() && MergeableConst8Section)
619       return MergeableConst8Section;
620     if (Kind.isMergeableConst16() && MergeableConst16Section)
621       return MergeableConst16Section;
622     return ReadOnlySection;  // .const
623   }
624 
625   if (Kind.isReadOnly())             return ReadOnlySection;
626 
627   if (Kind.isThreadData())           return TLSDataSection;
628   if (Kind.isThreadBSS())            return TLSBSSSection;
629 
630   if (Kind.isBSS())                  return BSSSection;
631 
632   if (Kind.isDataNoRel())            return DataSection;
633   if (Kind.isDataRelLocal())         return DataRelLocalSection;
634   if (Kind.isDataRel())              return DataRelSection;
635   if (Kind.isReadOnlyWithRelLocal()) return DataRelROLocalSection;
636 
637   assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
638   return DataRelROSection;
639 }
640 
641 /// getSectionForConstant - Given a mergeable constant with the
642 /// specified size and relocation information, return a section that it
643 /// should be placed in.
644 const MCSection *TargetLoweringObjectFileELF::
645 getSectionForConstant(SectionKind Kind) const {
646   if (Kind.isMergeableConst4() && MergeableConst4Section)
647     return MergeableConst4Section;
648   if (Kind.isMergeableConst8() && MergeableConst8Section)
649     return MergeableConst8Section;
650   if (Kind.isMergeableConst16() && MergeableConst16Section)
651     return MergeableConst16Section;
652   if (Kind.isReadOnly())
653     return ReadOnlySection;
654 
655   if (Kind.isReadOnlyWithRelLocal()) return DataRelROLocalSection;
656   assert(Kind.isReadOnlyWithRel() && "Unknown section kind");
657   return DataRelROSection;
658 }
659 
660 //===----------------------------------------------------------------------===//
661 //                                 MachO
662 //===----------------------------------------------------------------------===//
663 
664 typedef StringMap<const MCSectionMachO*> MachOUniqueMapTy;
665 
666 TargetLoweringObjectFileMachO::~TargetLoweringObjectFileMachO() {
667   // If we have the MachO uniquing map, free it.
668   delete (MachOUniqueMapTy*)UniquingMap;
669 }
670 
671 
672 const MCSectionMachO *TargetLoweringObjectFileMachO::
673 getMachOSection(const StringRef &Segment, const StringRef &Section,
674                 unsigned TypeAndAttributes,
675                 unsigned Reserved2, SectionKind Kind) const {
676   // We unique sections by their segment/section pair.  The returned section
677   // may not have the same flags as the requested section, if so this should be
678   // diagnosed by the client as an error.
679 
680   // Create the map if it doesn't already exist.
681   if (UniquingMap == 0)
682     UniquingMap = new MachOUniqueMapTy();
683   MachOUniqueMapTy &Map = *(MachOUniqueMapTy*)UniquingMap;
684 
685   // Form the name to look up.
686   SmallString<64> Name;
687   Name += Segment;
688   Name.push_back(',');
689   Name += Section;
690 
691   // Do the lookup, if we have a hit, return it.
692   const MCSectionMachO *&Entry = Map[Name.str()];
693   if (Entry) return Entry;
694 
695   // Otherwise, return a new section.
696   return Entry = MCSectionMachO::Create(Segment, Section, TypeAndAttributes,
697                                         Reserved2, Kind, getContext());
698 }
699 
700 
701 void TargetLoweringObjectFileMachO::Initialize(MCContext &Ctx,
702                                                const TargetMachine &TM) {
703   if (UniquingMap != 0)
704     ((MachOUniqueMapTy*)UniquingMap)->clear();
705   TargetLoweringObjectFile::Initialize(Ctx, TM);
706 
707   TextSection // .text
708     = getMachOSection("__TEXT", "__text",
709                       MCSectionMachO::S_ATTR_PURE_INSTRUCTIONS,
710                       SectionKind::getText());
711   DataSection // .data
712     = getMachOSection("__DATA", "__data", 0, SectionKind::getDataRel());
713 
714   CStringSection // .cstring
715     = getMachOSection("__TEXT", "__cstring", MCSectionMachO::S_CSTRING_LITERALS,
716                       SectionKind::getMergeable1ByteCString());
717   UStringSection
718     = getMachOSection("__TEXT","__ustring", 0,
719                       SectionKind::getMergeable2ByteCString());
720   FourByteConstantSection // .literal4
721     = getMachOSection("__TEXT", "__literal4", MCSectionMachO::S_4BYTE_LITERALS,
722                       SectionKind::getMergeableConst4());
723   EightByteConstantSection // .literal8
724     = getMachOSection("__TEXT", "__literal8", MCSectionMachO::S_8BYTE_LITERALS,
725                       SectionKind::getMergeableConst8());
726 
727   // ld_classic doesn't support .literal16 in 32-bit mode, and ld64 falls back
728   // to using it in -static mode.
729   SixteenByteConstantSection = 0;
730   if (TM.getRelocationModel() != Reloc::Static &&
731       TM.getTargetData()->getPointerSize() == 32)
732     SixteenByteConstantSection =   // .literal16
733       getMachOSection("__TEXT", "__literal16",MCSectionMachO::S_16BYTE_LITERALS,
734                       SectionKind::getMergeableConst16());
735 
736   ReadOnlySection  // .const
737     = getMachOSection("__TEXT", "__const", 0, SectionKind::getReadOnly());
738 
739   TextCoalSection
740     = getMachOSection("__TEXT", "__textcoal_nt",
741                       MCSectionMachO::S_COALESCED |
742                       MCSectionMachO::S_ATTR_PURE_INSTRUCTIONS,
743                       SectionKind::getText());
744   ConstTextCoalSection
745     = getMachOSection("__TEXT", "__const_coal", MCSectionMachO::S_COALESCED,
746                       SectionKind::getText());
747   ConstDataCoalSection
748     = getMachOSection("__DATA","__const_coal", MCSectionMachO::S_COALESCED,
749                       SectionKind::getText());
750   ConstDataSection  // .const_data
751     = getMachOSection("__DATA", "__const", 0,
752                       SectionKind::getReadOnlyWithRel());
753   DataCoalSection
754     = getMachOSection("__DATA","__datacoal_nt", MCSectionMachO::S_COALESCED,
755                       SectionKind::getDataRel());
756 
757 
758   LazySymbolPointerSection
759     = getMachOSection("__DATA", "__la_symbol_ptr",
760                       MCSectionMachO::S_LAZY_SYMBOL_POINTERS,
761                       SectionKind::getMetadata());
762   NonLazySymbolPointerSection
763     = getMachOSection("__DATA", "__nl_symbol_ptr",
764                       MCSectionMachO::S_NON_LAZY_SYMBOL_POINTERS,
765                       SectionKind::getMetadata());
766 
767   if (TM.getRelocationModel() == Reloc::Static) {
768     StaticCtorSection
769       = getMachOSection("__TEXT", "__constructor", 0,SectionKind::getDataRel());
770     StaticDtorSection
771       = getMachOSection("__TEXT", "__destructor", 0, SectionKind::getDataRel());
772   } else {
773     StaticCtorSection
774       = getMachOSection("__DATA", "__mod_init_func",
775                         MCSectionMachO::S_MOD_INIT_FUNC_POINTERS,
776                         SectionKind::getDataRel());
777     StaticDtorSection
778       = getMachOSection("__DATA", "__mod_term_func",
779                         MCSectionMachO::S_MOD_TERM_FUNC_POINTERS,
780                         SectionKind::getDataRel());
781   }
782 
783   // Exception Handling.
784   LSDASection = getMachOSection("__DATA", "__gcc_except_tab", 0,
785                                 SectionKind::getDataRel());
786   EHFrameSection =
787     getMachOSection("__TEXT", "__eh_frame",
788                     MCSectionMachO::S_COALESCED |
789                     MCSectionMachO::S_ATTR_NO_TOC |
790                     MCSectionMachO::S_ATTR_STRIP_STATIC_SYMS |
791                     MCSectionMachO::S_ATTR_LIVE_SUPPORT,
792                     SectionKind::getReadOnly());
793 
794   // Debug Information.
795   DwarfAbbrevSection =
796     getMachOSection("__DWARF", "__debug_abbrev", MCSectionMachO::S_ATTR_DEBUG,
797                     SectionKind::getMetadata());
798   DwarfInfoSection =
799     getMachOSection("__DWARF", "__debug_info", MCSectionMachO::S_ATTR_DEBUG,
800                     SectionKind::getMetadata());
801   DwarfLineSection =
802     getMachOSection("__DWARF", "__debug_line", MCSectionMachO::S_ATTR_DEBUG,
803                     SectionKind::getMetadata());
804   DwarfFrameSection =
805     getMachOSection("__DWARF", "__debug_frame", MCSectionMachO::S_ATTR_DEBUG,
806                     SectionKind::getMetadata());
807   DwarfPubNamesSection =
808     getMachOSection("__DWARF", "__debug_pubnames", MCSectionMachO::S_ATTR_DEBUG,
809                     SectionKind::getMetadata());
810   DwarfPubTypesSection =
811     getMachOSection("__DWARF", "__debug_pubtypes", MCSectionMachO::S_ATTR_DEBUG,
812                     SectionKind::getMetadata());
813   DwarfStrSection =
814     getMachOSection("__DWARF", "__debug_str", MCSectionMachO::S_ATTR_DEBUG,
815                     SectionKind::getMetadata());
816   DwarfLocSection =
817     getMachOSection("__DWARF", "__debug_loc", MCSectionMachO::S_ATTR_DEBUG,
818                     SectionKind::getMetadata());
819   DwarfARangesSection =
820     getMachOSection("__DWARF", "__debug_aranges", MCSectionMachO::S_ATTR_DEBUG,
821                     SectionKind::getMetadata());
822   DwarfRangesSection =
823     getMachOSection("__DWARF", "__debug_ranges", MCSectionMachO::S_ATTR_DEBUG,
824                     SectionKind::getMetadata());
825   DwarfMacroInfoSection =
826     getMachOSection("__DWARF", "__debug_macinfo", MCSectionMachO::S_ATTR_DEBUG,
827                     SectionKind::getMetadata());
828   DwarfDebugInlineSection =
829     getMachOSection("__DWARF", "__debug_inlined", MCSectionMachO::S_ATTR_DEBUG,
830                     SectionKind::getMetadata());
831 }
832 
833 const MCSection *TargetLoweringObjectFileMachO::
834 getExplicitSectionGlobal(const GlobalValue *GV, SectionKind Kind,
835                          Mangler *Mang, const TargetMachine &TM) const {
836   // Parse the section specifier and create it if valid.
837   StringRef Segment, Section;
838   unsigned TAA, StubSize;
839   std::string ErrorCode =
840     MCSectionMachO::ParseSectionSpecifier(GV->getSection(), Segment, Section,
841                                           TAA, StubSize);
842   if (!ErrorCode.empty()) {
843     // If invalid, report the error with llvm_report_error.
844     llvm_report_error("Global variable '" + GV->getNameStr() +
845                       "' has an invalid section specifier '" + GV->getSection()+
846                       "': " + ErrorCode + ".");
847     // Fall back to dropping it into the data section.
848     return DataSection;
849   }
850 
851   // Get the section.
852   const MCSectionMachO *S =
853     getMachOSection(Segment, Section, TAA, StubSize, Kind);
854 
855   // Okay, now that we got the section, verify that the TAA & StubSize agree.
856   // If the user declared multiple globals with different section flags, we need
857   // to reject it here.
858   if (S->getTypeAndAttributes() != TAA || S->getStubSize() != StubSize) {
859     // If invalid, report the error with llvm_report_error.
860     llvm_report_error("Global variable '" + GV->getNameStr() +
861                       "' section type or attributes does not match previous"
862                       " section specifier");
863   }
864 
865   return S;
866 }
867 
868 const MCSection *TargetLoweringObjectFileMachO::
869 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
870                        Mangler *Mang, const TargetMachine &TM) const {
871   assert(!Kind.isThreadLocal() && "Darwin doesn't support TLS");
872 
873   if (Kind.isText())
874     return GV->isWeakForLinker() ? TextCoalSection : TextSection;
875 
876   // If this is weak/linkonce, put this in a coalescable section, either in text
877   // or data depending on if it is writable.
878   if (GV->isWeakForLinker()) {
879     if (Kind.isReadOnly())
880       return ConstTextCoalSection;
881     return DataCoalSection;
882   }
883 
884   // FIXME: Alignment check should be handled by section classifier.
885   if (Kind.isMergeable1ByteCString() ||
886       Kind.isMergeable2ByteCString()) {
887     if (TM.getTargetData()->getPreferredAlignment(
888                                               cast<GlobalVariable>(GV)) < 32) {
889       if (Kind.isMergeable1ByteCString())
890         return CStringSection;
891       assert(Kind.isMergeable2ByteCString());
892       return UStringSection;
893     }
894   }
895 
896   if (Kind.isMergeableConst()) {
897     if (Kind.isMergeableConst4())
898       return FourByteConstantSection;
899     if (Kind.isMergeableConst8())
900       return EightByteConstantSection;
901     if (Kind.isMergeableConst16() && SixteenByteConstantSection)
902       return SixteenByteConstantSection;
903   }
904 
905   // Otherwise, if it is readonly, but not something we can specially optimize,
906   // just drop it in .const.
907   if (Kind.isReadOnly())
908     return ReadOnlySection;
909 
910   // If this is marked const, put it into a const section.  But if the dynamic
911   // linker needs to write to it, put it in the data segment.
912   if (Kind.isReadOnlyWithRel())
913     return ConstDataSection;
914 
915   // Otherwise, just drop the variable in the normal data section.
916   return DataSection;
917 }
918 
919 const MCSection *
920 TargetLoweringObjectFileMachO::getSectionForConstant(SectionKind Kind) const {
921   // If this constant requires a relocation, we have to put it in the data
922   // segment, not in the text segment.
923   if (Kind.isDataRel())
924     return ConstDataSection;
925 
926   if (Kind.isMergeableConst4())
927     return FourByteConstantSection;
928   if (Kind.isMergeableConst8())
929     return EightByteConstantSection;
930   if (Kind.isMergeableConst16() && SixteenByteConstantSection)
931     return SixteenByteConstantSection;
932   return ReadOnlySection;  // .const
933 }
934 
935 /// shouldEmitUsedDirectiveFor - This hook allows targets to selectively decide
936 /// not to emit the UsedDirective for some symbols in llvm.used.
937 // FIXME: REMOVE this (rdar://7071300)
938 bool TargetLoweringObjectFileMachO::
939 shouldEmitUsedDirectiveFor(const GlobalValue *GV, Mangler *Mang) const {
940   /// On Darwin, internally linked data beginning with "L" or "l" does not have
941   /// the directive emitted (this occurs in ObjC metadata).
942   if (!GV) return false;
943 
944   // Check whether the mangled name has the "Private" or "LinkerPrivate" prefix.
945   if (GV->hasLocalLinkage() && !isa<Function>(GV)) {
946     // FIXME: ObjC metadata is currently emitted as internal symbols that have
947     // \1L and \0l prefixes on them.  Fix them to be Private/LinkerPrivate and
948     // this horrible hack can go away.
949     const std::string &Name = Mang->getMangledName(GV);
950     if (Name[0] == 'L' || Name[0] == 'l')
951       return false;
952   }
953 
954   return true;
955 }
956 
957 const MCExpr *TargetLoweringObjectFileMachO::
958 getSymbolForDwarfGlobalReference(const GlobalValue *GV, Mangler *Mang,
959                                  bool &IsIndirect, bool &IsPCRel) const {
960   // The mach-o version of this method defaults to returning a stub reference.
961   IsIndirect = true;
962   IsPCRel    = false;
963 
964   SmallString<128> Name;
965   Mang->getNameWithPrefix(Name, GV, true);
966   Name += "$non_lazy_ptr";
967   return MCSymbolRefExpr::Create(Name.str(), getContext());
968 }
969 
970 
971 //===----------------------------------------------------------------------===//
972 //                                  COFF
973 //===----------------------------------------------------------------------===//
974 
975 typedef StringMap<const MCSectionCOFF*> COFFUniqueMapTy;
976 
977 TargetLoweringObjectFileCOFF::~TargetLoweringObjectFileCOFF() {
978   delete (COFFUniqueMapTy*)UniquingMap;
979 }
980 
981 
982 const MCSection *TargetLoweringObjectFileCOFF::
983 getCOFFSection(const char *Name, bool isDirective, SectionKind Kind) const {
984   // Create the map if it doesn't already exist.
985   if (UniquingMap == 0)
986     UniquingMap = new MachOUniqueMapTy();
987   COFFUniqueMapTy &Map = *(COFFUniqueMapTy*)UniquingMap;
988 
989   // Do the lookup, if we have a hit, return it.
990   const MCSectionCOFF *&Entry = Map[Name];
991   if (Entry) return Entry;
992 
993   return Entry = MCSectionCOFF::Create(Name, isDirective, Kind, getContext());
994 }
995 
996 void TargetLoweringObjectFileCOFF::Initialize(MCContext &Ctx,
997                                               const TargetMachine &TM) {
998   if (UniquingMap != 0)
999     ((COFFUniqueMapTy*)UniquingMap)->clear();
1000   TargetLoweringObjectFile::Initialize(Ctx, TM);
1001   TextSection = getCOFFSection("\t.text", true, SectionKind::getText());
1002   DataSection = getCOFFSection("\t.data", true, SectionKind::getDataRel());
1003   StaticCtorSection =
1004     getCOFFSection(".ctors", false, SectionKind::getDataRel());
1005   StaticDtorSection =
1006     getCOFFSection(".dtors", false, SectionKind::getDataRel());
1007 
1008   // FIXME: We're emitting LSDA info into a readonly section on COFF, even
1009   // though it contains relocatable pointers.  In PIC mode, this is probably a
1010   // big runtime hit for C++ apps.  Either the contents of the LSDA need to be
1011   // adjusted or this should be a data section.
1012   LSDASection =
1013     getCOFFSection(".gcc_except_table", false, SectionKind::getReadOnly());
1014   EHFrameSection =
1015     getCOFFSection(".eh_frame", false, SectionKind::getDataRel());
1016 
1017   // Debug info.
1018   // FIXME: Don't use 'directive' mode here.
1019   DwarfAbbrevSection =
1020     getCOFFSection("\t.section\t.debug_abbrev,\"dr\"",
1021                    true, SectionKind::getMetadata());
1022   DwarfInfoSection =
1023     getCOFFSection("\t.section\t.debug_info,\"dr\"",
1024                    true, SectionKind::getMetadata());
1025   DwarfLineSection =
1026     getCOFFSection("\t.section\t.debug_line,\"dr\"",
1027                    true, SectionKind::getMetadata());
1028   DwarfFrameSection =
1029     getCOFFSection("\t.section\t.debug_frame,\"dr\"",
1030                    true, SectionKind::getMetadata());
1031   DwarfPubNamesSection =
1032     getCOFFSection("\t.section\t.debug_pubnames,\"dr\"",
1033                    true, SectionKind::getMetadata());
1034   DwarfPubTypesSection =
1035     getCOFFSection("\t.section\t.debug_pubtypes,\"dr\"",
1036                    true, SectionKind::getMetadata());
1037   DwarfStrSection =
1038     getCOFFSection("\t.section\t.debug_str,\"dr\"",
1039                    true, SectionKind::getMetadata());
1040   DwarfLocSection =
1041     getCOFFSection("\t.section\t.debug_loc,\"dr\"",
1042                    true, SectionKind::getMetadata());
1043   DwarfARangesSection =
1044     getCOFFSection("\t.section\t.debug_aranges,\"dr\"",
1045                    true, SectionKind::getMetadata());
1046   DwarfRangesSection =
1047     getCOFFSection("\t.section\t.debug_ranges,\"dr\"",
1048                    true, SectionKind::getMetadata());
1049   DwarfMacroInfoSection =
1050     getCOFFSection("\t.section\t.debug_macinfo,\"dr\"",
1051                    true, SectionKind::getMetadata());
1052 }
1053 
1054 const MCSection *TargetLoweringObjectFileCOFF::
1055 getExplicitSectionGlobal(const GlobalValue *GV, SectionKind Kind,
1056                          Mangler *Mang, const TargetMachine &TM) const {
1057   return getCOFFSection(GV->getSection().c_str(), false, Kind);
1058 }
1059 
1060 static const char *getCOFFSectionPrefixForUniqueGlobal(SectionKind Kind) {
1061   if (Kind.isText())
1062     return ".text$linkonce";
1063   if (Kind.isWriteable())
1064     return ".data$linkonce";
1065   return ".rdata$linkonce";
1066 }
1067 
1068 
1069 const MCSection *TargetLoweringObjectFileCOFF::
1070 SelectSectionForGlobal(const GlobalValue *GV, SectionKind Kind,
1071                        Mangler *Mang, const TargetMachine &TM) const {
1072   assert(!Kind.isThreadLocal() && "Doesn't support TLS");
1073 
1074   // If this global is linkonce/weak and the target handles this by emitting it
1075   // into a 'uniqued' section name, create and return the section now.
1076   if (GV->isWeakForLinker()) {
1077     const char *Prefix = getCOFFSectionPrefixForUniqueGlobal(Kind);
1078     std::string Name = Mang->makeNameProper(GV->getNameStr());
1079     return getCOFFSection((Prefix+Name).c_str(), false, Kind);
1080   }
1081 
1082   if (Kind.isText())
1083     return getTextSection();
1084 
1085   return getDataSection();
1086 }
1087 
1088