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