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 SupportsCompactUnwindInfo = false; 65 } 66 67 TargetLoweringObjectFile::~TargetLoweringObjectFile() { 68 } 69 70 static bool isSuitableForBSS(const GlobalVariable *GV) { 71 const Constant *C = GV->getInitializer(); 72 73 // Must have zero initializer. 74 if (!C->isNullValue()) 75 return false; 76 77 // Leave constant zeros in readonly constant sections, so they can be shared. 78 if (GV->isConstant()) 79 return false; 80 81 // If the global has an explicit section specified, don't put it in BSS. 82 if (!GV->getSection().empty()) 83 return false; 84 85 // If -nozero-initialized-in-bss is specified, don't ever use BSS. 86 if (NoZerosInBSS) 87 return false; 88 89 // Otherwise, put it in BSS! 90 return true; 91 } 92 93 /// IsNullTerminatedString - Return true if the specified constant (which is 94 /// known to have a type that is an array of 1/2/4 byte elements) ends with a 95 /// nul value and contains no other nuls in it. 96 static bool IsNullTerminatedString(const Constant *C) { 97 const ArrayType *ATy = cast<ArrayType>(C->getType()); 98 99 // First check: is we have constant array of i8 terminated with zero 100 if (const ConstantArray *CVA = dyn_cast<ConstantArray>(C)) { 101 if (ATy->getNumElements() == 0) return false; 102 103 ConstantInt *Null = 104 dyn_cast<ConstantInt>(CVA->getOperand(ATy->getNumElements()-1)); 105 if (Null == 0 || !Null->isZero()) 106 return false; // Not null terminated. 107 108 // Verify that the null doesn't occur anywhere else in the string. 109 for (unsigned i = 0, e = ATy->getNumElements()-1; i != e; ++i) 110 // Reject constantexpr elements etc. 111 if (!isa<ConstantInt>(CVA->getOperand(i)) || 112 CVA->getOperand(i) == Null) 113 return false; 114 return true; 115 } 116 117 // Another possibility: [1 x i8] zeroinitializer 118 if (isa<ConstantAggregateZero>(C)) 119 return ATy->getNumElements() == 1; 120 121 return false; 122 } 123 124 MCSymbol *TargetLoweringObjectFile:: 125 getCFIPersonalitySymbol(const GlobalValue *GV, Mangler *Mang, 126 MachineModuleInfo *MMI) const { 127 return Mang->getSymbol(GV); 128 } 129 130 void TargetLoweringObjectFile::emitPersonalityValue(MCStreamer &Streamer, 131 const TargetMachine &TM, 132 const MCSymbol *Sym) const { 133 } 134 135 136 /// getKindForGlobal - This is a top-level target-independent classifier for 137 /// a global variable. Given an global variable and information from TM, it 138 /// classifies the global in a variety of ways that make various target 139 /// implementations simpler. The target implementation is free to ignore this 140 /// extra info of course. 141 SectionKind TargetLoweringObjectFile::getKindForGlobal(const GlobalValue *GV, 142 const TargetMachine &TM){ 143 assert(!GV->isDeclaration() && !GV->hasAvailableExternallyLinkage() && 144 "Can only be used for global definitions"); 145 146 Reloc::Model ReloModel = TM.getRelocationModel(); 147 148 // Early exit - functions should be always in text sections. 149 const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV); 150 if (GVar == 0) 151 return SectionKind::getText(); 152 153 // Handle thread-local data first. 154 if (GVar->isThreadLocal()) { 155 if (isSuitableForBSS(GVar)) 156 return SectionKind::getThreadBSS(); 157 return SectionKind::getThreadData(); 158 } 159 160 // Variables with common linkage always get classified as common. 161 if (GVar->hasCommonLinkage()) 162 return SectionKind::getCommon(); 163 164 // Variable can be easily put to BSS section. 165 if (isSuitableForBSS(GVar)) { 166 if (GVar->hasLocalLinkage()) 167 return SectionKind::getBSSLocal(); 168 else if (GVar->hasExternalLinkage()) 169 return SectionKind::getBSSExtern(); 170 return SectionKind::getBSS(); 171 } 172 173 const Constant *C = GVar->getInitializer(); 174 175 // If the global is marked constant, we can put it into a mergable section, 176 // a mergable string section, or general .data if it contains relocations. 177 if (GVar->isConstant()) { 178 // If the initializer for the global contains something that requires a 179 // relocation, then we may have to drop this into a wriable data section 180 // even though it is marked const. 181 switch (C->getRelocationInfo()) { 182 default: assert(0 && "unknown relocation info kind"); 183 case Constant::NoRelocation: 184 // If the global is required to have a unique address, it can't be put 185 // into a mergable section: just drop it into the general read-only 186 // section instead. 187 if (!GVar->hasUnnamedAddr()) 188 return SectionKind::getReadOnly(); 189 190 // If initializer is a null-terminated string, put it in a "cstring" 191 // section of the right width. 192 if (const ArrayType *ATy = dyn_cast<ArrayType>(C->getType())) { 193 if (const IntegerType *ITy = 194 dyn_cast<IntegerType>(ATy->getElementType())) { 195 if ((ITy->getBitWidth() == 8 || ITy->getBitWidth() == 16 || 196 ITy->getBitWidth() == 32) && 197 IsNullTerminatedString(C)) { 198 if (ITy->getBitWidth() == 8) 199 return SectionKind::getMergeable1ByteCString(); 200 if (ITy->getBitWidth() == 16) 201 return SectionKind::getMergeable2ByteCString(); 202 203 assert(ITy->getBitWidth() == 32 && "Unknown width"); 204 return SectionKind::getMergeable4ByteCString(); 205 } 206 } 207 } 208 209 // Otherwise, just drop it into a mergable constant section. If we have 210 // a section for this size, use it, otherwise use the arbitrary sized 211 // mergable section. 212 switch (TM.getTargetData()->getTypeAllocSize(C->getType())) { 213 case 4: return SectionKind::getMergeableConst4(); 214 case 8: return SectionKind::getMergeableConst8(); 215 case 16: return SectionKind::getMergeableConst16(); 216 default: return SectionKind::getMergeableConst(); 217 } 218 219 case Constant::LocalRelocation: 220 // In static relocation model, the linker will resolve all addresses, so 221 // the relocation entries will actually be constants by the time the app 222 // starts up. However, we can't put this into a mergable section, because 223 // the linker doesn't take relocations into consideration when it tries to 224 // merge entries in the section. 225 if (ReloModel == Reloc::Static) 226 return SectionKind::getReadOnly(); 227 228 // Otherwise, the dynamic linker needs to fix it up, put it in the 229 // writable data.rel.local section. 230 return SectionKind::getReadOnlyWithRelLocal(); 231 232 case Constant::GlobalRelocations: 233 // In static relocation model, the linker will resolve all addresses, so 234 // the relocation entries will actually be constants by the time the app 235 // starts up. However, we can't put this into a mergable section, because 236 // the linker doesn't take relocations into consideration when it tries to 237 // merge entries in the section. 238 if (ReloModel == Reloc::Static) 239 return SectionKind::getReadOnly(); 240 241 // Otherwise, the dynamic linker needs to fix it up, put it in the 242 // writable data.rel section. 243 return SectionKind::getReadOnlyWithRel(); 244 } 245 } 246 247 // Okay, this isn't a constant. If the initializer for the global is going 248 // to require a runtime relocation by the dynamic linker, put it into a more 249 // specific section to improve startup time of the app. This coalesces these 250 // globals together onto fewer pages, improving the locality of the dynamic 251 // linker. 252 if (ReloModel == Reloc::Static) 253 return SectionKind::getDataNoRel(); 254 255 switch (C->getRelocationInfo()) { 256 default: assert(0 && "unknown relocation info kind"); 257 case Constant::NoRelocation: 258 return SectionKind::getDataNoRel(); 259 case Constant::LocalRelocation: 260 return SectionKind::getDataRelLocal(); 261 case Constant::GlobalRelocations: 262 return SectionKind::getDataRel(); 263 } 264 } 265 266 /// SectionForGlobal - This method computes the appropriate section to emit 267 /// the specified global variable or function definition. This should not 268 /// be passed external (or available externally) globals. 269 const MCSection *TargetLoweringObjectFile:: 270 SectionForGlobal(const GlobalValue *GV, SectionKind Kind, Mangler *Mang, 271 const TargetMachine &TM) const { 272 // Select section name. 273 if (GV->hasSection()) 274 return getExplicitSectionGlobal(GV, Kind, Mang, TM); 275 276 277 // Use default section depending on the 'type' of global 278 return SelectSectionForGlobal(GV, Kind, Mang, TM); 279 } 280 281 282 // Lame default implementation. Calculate the section name for global. 283 const MCSection * 284 TargetLoweringObjectFile::SelectSectionForGlobal(const GlobalValue *GV, 285 SectionKind Kind, 286 Mangler *Mang, 287 const TargetMachine &TM) const{ 288 assert(!Kind.isThreadLocal() && "Doesn't support TLS"); 289 290 if (Kind.isText()) 291 return getTextSection(); 292 293 if (Kind.isBSS() && BSSSection != 0) 294 return BSSSection; 295 296 if (Kind.isReadOnly() && ReadOnlySection != 0) 297 return ReadOnlySection; 298 299 return getDataSection(); 300 } 301 302 /// getSectionForConstant - Given a mergable constant with the 303 /// specified size and relocation information, return a section that it 304 /// should be placed in. 305 const MCSection * 306 TargetLoweringObjectFile::getSectionForConstant(SectionKind Kind) const { 307 if (Kind.isReadOnly() && ReadOnlySection != 0) 308 return ReadOnlySection; 309 310 return DataSection; 311 } 312 313 /// getExprForDwarfGlobalReference - Return an MCExpr to use for a 314 /// reference to the specified global variable from exception 315 /// handling information. 316 const MCExpr *TargetLoweringObjectFile:: 317 getExprForDwarfGlobalReference(const GlobalValue *GV, Mangler *Mang, 318 MachineModuleInfo *MMI, unsigned Encoding, 319 MCStreamer &Streamer) const { 320 const MCSymbol *Sym = Mang->getSymbol(GV); 321 return getExprForDwarfReference(Sym, Encoding, Streamer); 322 } 323 324 const MCExpr *TargetLoweringObjectFile:: 325 getExprForDwarfReference(const MCSymbol *Sym, unsigned Encoding, 326 MCStreamer &Streamer) const { 327 const MCExpr *Res = MCSymbolRefExpr::Create(Sym, getContext()); 328 329 switch (Encoding & 0x70) { 330 default: 331 report_fatal_error("We do not support this DWARF encoding yet!"); 332 case dwarf::DW_EH_PE_absptr: 333 // Do nothing special 334 return Res; 335 case dwarf::DW_EH_PE_pcrel: { 336 // Emit a label to the streamer for the current position. This gives us 337 // .-foo addressing. 338 MCSymbol *PCSym = getContext().CreateTempSymbol(); 339 Streamer.EmitLabel(PCSym); 340 const MCExpr *PC = MCSymbolRefExpr::Create(PCSym, getContext()); 341 return MCBinaryExpr::CreateSub(Res, PC, getContext()); 342 } 343 } 344 } 345 346 unsigned TargetLoweringObjectFile::getPersonalityEncoding() const { 347 return dwarf::DW_EH_PE_absptr; 348 } 349 350 unsigned TargetLoweringObjectFile::getLSDAEncoding() const { 351 return dwarf::DW_EH_PE_absptr; 352 } 353 354 unsigned TargetLoweringObjectFile::getFDEEncoding(bool CFI) const { 355 return dwarf::DW_EH_PE_absptr; 356 } 357 358 unsigned TargetLoweringObjectFile::getTTypeEncoding() const { 359 return dwarf::DW_EH_PE_absptr; 360 } 361 362