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/MCExpr.h"
  22 #include "llvm/MC/MCStreamer.h"
  23 #include "llvm/MC/MCSymbol.h"
  24 #include "llvm/Target/Mangler.h"
  25 #include "llvm/Target/TargetData.h"
  26 #include "llvm/Target/TargetMachine.h"
  27 #include "llvm/Target/TargetOptions.h"
  28 #include "llvm/Support/Dwarf.h"
  29 #include "llvm/Support/ErrorHandling.h"
  30 #include "llvm/Support/raw_ostream.h"
  31 #include "llvm/ADT/SmallString.h"
  32 using namespace llvm;
  33
  34 //===----------------------------------------------------------------------===//
  35 //                              Generic Code
  36 //===----------------------------------------------------------------------===//
  37
  38 TargetLoweringObjectFile::TargetLoweringObjectFile() : Ctx(0) {
  39   TextSection = 0;
  40   DataSection = 0;
  41   BSSSection = 0;
  42   ReadOnlySection = 0;
  43   StaticCtorSection = 0;
  44   StaticDtorSection = 0;
  45   LSDASection = 0;
  46   CompactUnwindSection = 0;
  47
  48   CommDirectiveSupportsAlignment = true;
  49   DwarfAbbrevSection = 0;
  50   DwarfInfoSection = 0;
  51   DwarfLineSection = 0;
  52   DwarfFrameSection = 0;
  53   DwarfPubNamesSection = 0;
  54   DwarfPubTypesSection = 0;
  55   DwarfDebugInlineSection = 0;
  56   DwarfStrSection = 0;
  57   DwarfLocSection = 0;
  58   DwarfARangesSection = 0;
  59   DwarfRangesSection = 0;
  60   DwarfMacroInfoSection = 0;
  61
  62   IsFunctionEHFrameSymbolPrivate = true;
  63   SupportsWeakOmittedEHFrame = true;
  64 }
  65
  66 TargetLoweringObjectFile::~TargetLoweringObjectFile() {
  67 }
  68
  69 static bool isSuitableForBSS(const GlobalVariable *GV) {
  70   const Constant *C = GV->getInitializer();
  71
  72   // Must have zero initializer.
  73   if (!C->isNullValue())
  74     return false;
  75
  76   // Leave constant zeros in readonly constant sections, so they can be shared.
  77   if (GV->isConstant())
  78     return false;
  79
  80   // If the global has an explicit section specified, don't put it in BSS.
  81   if (!GV->getSection().empty())
  82     return false;
  83
  84   // If -nozero-initialized-in-bss is specified, don't ever use BSS.
  85   if (NoZerosInBSS)
  86     return false;
  87
  88   // Otherwise, put it in BSS!
  89   return true;
  90 }
  91
  92 /// IsNullTerminatedString - Return true if the specified constant (which is
  93 /// known to have a type that is an array of 1/2/4 byte elements) ends with a
  94 /// nul value and contains no other nuls in it.
  95 static bool IsNullTerminatedString(const Constant *C) {
  96   const ArrayType *ATy = cast<ArrayType>(C->getType());
  97
  98   // First check: is we have constant array of i8 terminated with zero
  99   if (const ConstantArray *CVA = dyn_cast<ConstantArray>(C)) {
 100     if (ATy->getNumElements() == 0) return false;
 101
 102     ConstantInt *Null =
 103       dyn_cast<ConstantInt>(CVA->getOperand(ATy->getNumElements()-1));
 104     if (Null == 0 || !Null->isZero())
 105       return false; // Not null terminated.
 106
 107     // Verify that the null doesn't occur anywhere else in the string.
 108     for (unsigned i = 0, e = ATy->getNumElements()-1; i != e; ++i)
 109       // Reject constantexpr elements etc.
 110       if (!isa<ConstantInt>(CVA->getOperand(i)) ||
 111           CVA->getOperand(i) == Null)
 112         return false;
 113     return true;
 114   }
 115
 116   // Another possibility: [1 x i8] zeroinitializer
 117   if (isa<ConstantAggregateZero>(C))
 118     return ATy->getNumElements() == 1;
 119
 120   return false;
 121 }
 122
 123 MCSymbol *TargetLoweringObjectFile::
 124 getCFIPersonalitySymbol(const GlobalValue *GV, Mangler *Mang,
 125                         MachineModuleInfo *MMI) const {
 126   return Mang->getSymbol(GV);
 127 }
 128
 129 void TargetLoweringObjectFile::emitPersonalityValue(MCStreamer &Streamer,
 130                                                     const TargetMachine &TM,
 131                                                     const MCSymbol *Sym) const {
 132 }
 133
 134
 135 /// getKindForGlobal - This is a top-level target-independent classifier for
 136 /// a global variable.  Given an global variable and information from TM, it
 137 /// classifies the global in a variety of ways that make various target
 138 /// implementations simpler.  The target implementation is free to ignore this
 139 /// extra info of course.
 140 SectionKind TargetLoweringObjectFile::getKindForGlobal(const GlobalValue *GV,
 141                                                        const TargetMachine &TM){
 142   assert(!GV->isDeclaration() && !GV->hasAvailableExternallyLinkage() &&
 143          "Can only be used for global definitions");
 144
 145   Reloc::Model ReloModel = TM.getRelocationModel();
 146
 147   // Early exit - functions should be always in text sections.
 148   const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV);
 149   if (GVar == 0)
 150     return SectionKind::getText();
 151
 152   // Handle thread-local data first.
 153   if (GVar->isThreadLocal()) {
 154     if (isSuitableForBSS(GVar))
 155       return SectionKind::getThreadBSS();
 156     return SectionKind::getThreadData();
 157   }
 158
 159   // Variables with common linkage always get classified as common.
 160   if (GVar->hasCommonLinkage())
 161     return SectionKind::getCommon();
 162
 163   // Variable can be easily put to BSS section.
 164   if (isSuitableForBSS(GVar)) {
 165     if (GVar->hasLocalLinkage())
 166       return SectionKind::getBSSLocal();
 167     else if (GVar->hasExternalLinkage())
 168       return SectionKind::getBSSExtern();
 169     return SectionKind::getBSS();
 170   }
 171
 172   const Constant *C = GVar->getInitializer();
 173
 174   // If the global is marked constant, we can put it into a mergable section,
 175   // a mergable string section, or general .data if it contains relocations.
 176   if (GVar->isConstant()) {
 177     // If the initializer for the global contains something that requires a
 178     // relocation, then we may have to drop this into a wriable data section
 179     // even though it is marked const.
 180     switch (C->getRelocationInfo()) {
 181     default: assert(0 && "unknown relocation info kind");
 182     case Constant::NoRelocation:
 183       // If the global is required to have a unique address, it can't be put
 184       // into a mergable section: just drop it into the general read-only
 185       // section instead.
 186       if (!GVar->hasUnnamedAddr())
 187         return SectionKind::getReadOnly();
 188
 189       // If initializer is a null-terminated string, put it in a "cstring"
 190       // section of the right width.
 191       if (const ArrayType *ATy = dyn_cast<ArrayType>(C->getType())) {
 192         if (const IntegerType *ITy =
 193               dyn_cast<IntegerType>(ATy->getElementType())) {
 194           if ((ITy->getBitWidth() == 8 || ITy->getBitWidth() == 16 ||
 195                ITy->getBitWidth() == 32) &&
 196               IsNullTerminatedString(C)) {
 197             if (ITy->getBitWidth() == 8)
 198               return SectionKind::getMergeable1ByteCString();
 199             if (ITy->getBitWidth() == 16)
 200               return SectionKind::getMergeable2ByteCString();
 201
 202             assert(ITy->getBitWidth() == 32 && "Unknown width");
 203             return SectionKind::getMergeable4ByteCString();
 204           }
 205         }
 206       }
 207
 208       // Otherwise, just drop it into a mergable constant section.  If we have
 209       // a section for this size, use it, otherwise use the arbitrary sized
 210       // mergable section.
 211       switch (TM.getTargetData()->getTypeAllocSize(C->getType())) {
 212       case 4:  return SectionKind::getMergeableConst4();
 213       case 8:  return SectionKind::getMergeableConst8();
 214       case 16: return SectionKind::getMergeableConst16();
 215       default: return SectionKind::getMergeableConst();
 216       }
 217
 218     case Constant::LocalRelocation:
 219       // In static relocation model, the linker will resolve all addresses, so
 220       // the relocation entries will actually be constants by the time the app
 221       // starts up.  However, we can't put this into a mergable section, because
 222       // the linker doesn't take relocations into consideration when it tries to
 223       // merge entries in the section.
 224       if (ReloModel == Reloc::Static)
 225         return SectionKind::getReadOnly();
 226
 227       // Otherwise, the dynamic linker needs to fix it up, put it in the
 228       // writable data.rel.local section.
 229       return SectionKind::getReadOnlyWithRelLocal();
 230
 231     case Constant::GlobalRelocations:
 232       // In static relocation model, the linker will resolve all addresses, so
 233       // the relocation entries will actually be constants by the time the app
 234       // starts up.  However, we can't put this into a mergable section, because
 235       // the linker doesn't take relocations into consideration when it tries to
 236       // merge entries in the section.
 237       if (ReloModel == Reloc::Static)
 238         return SectionKind::getReadOnly();
 239
 240       // Otherwise, the dynamic linker needs to fix it up, put it in the
 241       // writable data.rel section.
 242       return SectionKind::getReadOnlyWithRel();
 243     }
 244   }
 245
 246   // Okay, this isn't a constant.  If the initializer for the global is going
 247   // to require a runtime relocation by the dynamic linker, put it into a more
 248   // specific section to improve startup time of the app.  This coalesces these
 249   // globals together onto fewer pages, improving the locality of the dynamic
 250   // linker.
 251   if (ReloModel == Reloc::Static)
 252     return SectionKind::getDataNoRel();
 253
 254   switch (C->getRelocationInfo()) {
 255   default: assert(0 && "unknown relocation info kind");
 256   case Constant::NoRelocation:
 257     return SectionKind::getDataNoRel();
 258   case Constant::LocalRelocation:
 259     return SectionKind::getDataRelLocal();
 260   case Constant::GlobalRelocations:
 261     return SectionKind::getDataRel();
 262   }
 263 }
 264
 265 /// SectionForGlobal - This method computes the appropriate section to emit
 266 /// the specified global variable or function definition.  This should not
 267 /// be passed external (or available externally) globals.
 268 const MCSection *TargetLoweringObjectFile::
 269 SectionForGlobal(const GlobalValue *GV, SectionKind Kind, Mangler *Mang,
 270                  const TargetMachine &TM) const {
 271   // Select section name.
 272   if (GV->hasSection())
 273     return getExplicitSectionGlobal(GV, Kind, Mang, TM);
 274
 275
 276   // Use default section depending on the 'type' of global
 277   return SelectSectionForGlobal(GV, Kind, Mang, TM);
 278 }
 279
 280
 281 // Lame default implementation. Calculate the section name for global.
 282 const MCSection *
 283 TargetLoweringObjectFile::SelectSectionForGlobal(const GlobalValue *GV,
 284                                                  SectionKind Kind,
 285                                                  Mangler *Mang,
 286                                                  const TargetMachine &TM) const{
 287   assert(!Kind.isThreadLocal() && "Doesn't support TLS");
 288
 289   if (Kind.isText())
 290     return getTextSection();
 291
 292   if (Kind.isBSS() && BSSSection != 0)
 293     return BSSSection;
 294
 295   if (Kind.isReadOnly() && ReadOnlySection != 0)
 296     return ReadOnlySection;
 297
 298   return getDataSection();
 299 }
 300
 301 /// getSectionForConstant - Given a mergable constant with the
 302 /// specified size and relocation information, return a section that it
 303 /// should be placed in.
 304 const MCSection *
 305 TargetLoweringObjectFile::getSectionForConstant(SectionKind Kind) const {
 306   if (Kind.isReadOnly() && ReadOnlySection != 0)
 307     return ReadOnlySection;
 308
 309   return DataSection;
 310 }
 311
 312 /// getExprForDwarfGlobalReference - Return an MCExpr to use for a
 313 /// reference to the specified global variable from exception
 314 /// handling information.
 315 const MCExpr *TargetLoweringObjectFile::
 316 getExprForDwarfGlobalReference(const GlobalValue *GV, Mangler *Mang,
 317                                MachineModuleInfo *MMI, unsigned Encoding,
 318                                MCStreamer &Streamer) const {
 319   const MCSymbol *Sym = Mang->getSymbol(GV);
 320   return getExprForDwarfReference(Sym, Encoding, Streamer);
 321 }
 322
 323 const MCExpr *TargetLoweringObjectFile::
 324 getExprForDwarfReference(const MCSymbol *Sym, unsigned Encoding,
 325                          MCStreamer &Streamer) const {
 326   const MCExpr *Res = MCSymbolRefExpr::Create(Sym, getContext());
 327
 328   switch (Encoding & 0x70) {
 329   default:
 330     report_fatal_error("We do not support this DWARF encoding yet!");
 331   case dwarf::DW_EH_PE_absptr:
 332     // Do nothing special
 333     return Res;
 334   case dwarf::DW_EH_PE_pcrel: {
 335     // Emit a label to the streamer for the current position.  This gives us
 336     // .-foo addressing.
 337     MCSymbol *PCSym = getContext().CreateTempSymbol();
 338     Streamer.EmitLabel(PCSym);
 339     const MCExpr *PC = MCSymbolRefExpr::Create(PCSym, getContext());
 340     return MCBinaryExpr::CreateSub(Res, PC, getContext());
 341   }
 342   }
 343 }
 344
 345 unsigned TargetLoweringObjectFile::getPersonalityEncoding() const {
 346   return dwarf::DW_EH_PE_absptr;
 347 }
 348
 349 unsigned TargetLoweringObjectFile::getLSDAEncoding() const {
 350   return dwarf::DW_EH_PE_absptr;
 351 }
 352
 353 unsigned TargetLoweringObjectFile::getFDEEncoding(bool CFI) const {
 354   return dwarf::DW_EH_PE_absptr;
 355 }
 356
 357 unsigned TargetLoweringObjectFile::getTTypeEncoding() const {
 358   return dwarf::DW_EH_PE_absptr;
 359 }
 360