lib/Target/TargetLoweringObjectFile.cpp

   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 }