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