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 } 360 361