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 IsFunctionEHSymbolGlobal = false; 62 IsFunctionEHFrameSymbolPrivate = true; 63 SupportsWeakOmittedEHFrame = true; 64 } 65 66 TargetLoweringObjectFile::~TargetLoweringObjectFile() { 67 } 68 69 static bool isSuitableForBSS(const GlobalVariable *GV) { 70 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 /// getKindForGlobal - This is a top-level target-independent classifier for 124 /// a global variable. Given an global variable and information from TM, it 125 /// classifies the global in a variety of ways that make various target 126 /// implementations simpler. The target implementation is free to ignore this 127 /// extra info of course. 128 SectionKind TargetLoweringObjectFile::getKindForGlobal(const GlobalValue *GV, 129 const TargetMachine &TM){ 130 assert(!GV->isDeclaration() && !GV->hasAvailableExternallyLinkage() && 131 "Can only be used for global definitions"); 132 133 Reloc::Model ReloModel = TM.getRelocationModel(); 134 135 // Early exit - functions should be always in text sections. 136 const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV); 137 if (GVar == 0) 138 return SectionKind::getText(); 139 140 // Handle thread-local data first. 141 if (GVar->isThreadLocal()) { 142 if (isSuitableForBSS(GVar)) 143 return SectionKind::getThreadBSS(); 144 return SectionKind::getThreadData(); 145 } 146 147 // Variables with common linkage always get classified as common. 148 if (GVar->hasCommonLinkage()) 149 return SectionKind::getCommon(); 150 151 // Variable can be easily put to BSS section. 152 if (isSuitableForBSS(GVar)) { 153 if (GVar->hasLocalLinkage()) 154 return SectionKind::getBSSLocal(); 155 else if (GVar->hasExternalLinkage()) 156 return SectionKind::getBSSExtern(); 157 return SectionKind::getBSS(); 158 } 159 160 Constant *C = GVar->getInitializer(); 161 162 // If the global is marked constant, we can put it into a mergable section, 163 // a mergable string section, or general .data if it contains relocations. 164 if (GVar->isConstant()) { 165 // If the initializer for the global contains something that requires a 166 // relocation, then we may have to drop this into a wriable data section 167 // even though it is marked const. 168 switch (C->getRelocationInfo()) { 169 default: assert(0 && "unknown relocation info kind"); 170 case Constant::NoRelocation: 171 // If the global is required to have a unique address, it can't be put 172 // into a mergable section: just drop it into the general read-only 173 // section instead. 174 if (!GVar->hasUnnamedAddr()) 175 return SectionKind::getReadOnly(); 176 177 // If initializer is a null-terminated string, put it in a "cstring" 178 // section of the right width. 179 if (const ArrayType *ATy = dyn_cast<ArrayType>(C->getType())) { 180 if (const IntegerType *ITy = 181 dyn_cast<IntegerType>(ATy->getElementType())) { 182 if ((ITy->getBitWidth() == 8 || ITy->getBitWidth() == 16 || 183 ITy->getBitWidth() == 32) && 184 IsNullTerminatedString(C)) { 185 if (ITy->getBitWidth() == 8) 186 return SectionKind::getMergeable1ByteCString(); 187 if (ITy->getBitWidth() == 16) 188 return SectionKind::getMergeable2ByteCString(); 189 190 assert(ITy->getBitWidth() == 32 && "Unknown width"); 191 return SectionKind::getMergeable4ByteCString(); 192 } 193 } 194 } 195 196 // Otherwise, just drop it into a mergable constant section. If we have 197 // a section for this size, use it, otherwise use the arbitrary sized 198 // mergable section. 199 switch (TM.getTargetData()->getTypeAllocSize(C->getType())) { 200 case 4: return SectionKind::getMergeableConst4(); 201 case 8: return SectionKind::getMergeableConst8(); 202 case 16: return SectionKind::getMergeableConst16(); 203 default: return SectionKind::getMergeableConst(); 204 } 205 206 case Constant::LocalRelocation: 207 // In static relocation model, the linker will resolve all addresses, so 208 // the relocation entries will actually be constants by the time the app 209 // starts up. However, we can't put this into a mergable section, because 210 // the linker doesn't take relocations into consideration when it tries to 211 // merge entries in the section. 212 if (ReloModel == Reloc::Static) 213 return SectionKind::getReadOnly(); 214 215 // Otherwise, the dynamic linker needs to fix it up, put it in the 216 // writable data.rel.local section. 217 return SectionKind::getReadOnlyWithRelLocal(); 218 219 case Constant::GlobalRelocations: 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 section. 230 return SectionKind::getReadOnlyWithRel(); 231 } 232 } 233 234 // Okay, this isn't a constant. If the initializer for the global is going 235 // to require a runtime relocation by the dynamic linker, put it into a more 236 // specific section to improve startup time of the app. This coalesces these 237 // globals together onto fewer pages, improving the locality of the dynamic 238 // linker. 239 if (ReloModel == Reloc::Static) 240 return SectionKind::getDataNoRel(); 241 242 switch (C->getRelocationInfo()) { 243 default: assert(0 && "unknown relocation info kind"); 244 case Constant::NoRelocation: 245 return SectionKind::getDataNoRel(); 246 case Constant::LocalRelocation: 247 return SectionKind::getDataRelLocal(); 248 case Constant::GlobalRelocations: 249 return SectionKind::getDataRel(); 250 } 251 } 252 253 /// SectionForGlobal - This method computes the appropriate section to emit 254 /// the specified global variable or function definition. This should not 255 /// be passed external (or available externally) globals. 256 const MCSection *TargetLoweringObjectFile:: 257 SectionForGlobal(const GlobalValue *GV, SectionKind Kind, Mangler *Mang, 258 const TargetMachine &TM) const { 259 // Select section name. 260 if (GV->hasSection()) 261 return getExplicitSectionGlobal(GV, Kind, Mang, TM); 262 263 264 // Use default section depending on the 'type' of global 265 return SelectSectionForGlobal(GV, Kind, Mang, TM); 266 } 267 268 269 // Lame default implementation. Calculate the section name for global. 270 const MCSection * 271 TargetLoweringObjectFile::SelectSectionForGlobal(const GlobalValue *GV, 272 SectionKind Kind, 273 Mangler *Mang, 274 const TargetMachine &TM) const{ 275 assert(!Kind.isThreadLocal() && "Doesn't support TLS"); 276 277 if (Kind.isText()) 278 return getTextSection(); 279 280 if (Kind.isBSS() && BSSSection != 0) 281 return BSSSection; 282 283 if (Kind.isReadOnly() && ReadOnlySection != 0) 284 return ReadOnlySection; 285 286 return getDataSection(); 287 } 288 289 /// getSectionForConstant - Given a mergable constant with the 290 /// specified size and relocation information, return a section that it 291 /// should be placed in. 292 const MCSection * 293 TargetLoweringObjectFile::getSectionForConstant(SectionKind Kind) const { 294 if (Kind.isReadOnly() && ReadOnlySection != 0) 295 return ReadOnlySection; 296 297 return DataSection; 298 } 299 300 /// getExprForDwarfGlobalReference - Return an MCExpr to use for a 301 /// reference to the specified global variable from exception 302 /// handling information. 303 const MCExpr *TargetLoweringObjectFile:: 304 getExprForDwarfGlobalReference(const GlobalValue *GV, Mangler *Mang, 305 MachineModuleInfo *MMI, unsigned Encoding, 306 MCStreamer &Streamer) const { 307 const MCSymbol *Sym = Mang->getSymbol(GV); 308 return getExprForDwarfReference(Sym, Mang, MMI, Encoding, Streamer); 309 } 310 311 const MCExpr *TargetLoweringObjectFile:: 312 getExprForDwarfReference(const MCSymbol *Sym, Mangler *Mang, 313 MachineModuleInfo *MMI, unsigned Encoding, 314 MCStreamer &Streamer) const { 315 const MCExpr *Res = MCSymbolRefExpr::Create(Sym, getContext()); 316 317 switch (Encoding & 0xF0) { 318 default: 319 report_fatal_error("We do not support this DWARF encoding yet!"); 320 case dwarf::DW_EH_PE_absptr: 321 // Do nothing special 322 return Res; 323 case dwarf::DW_EH_PE_pcrel: { 324 // Emit a label to the streamer for the current position. This gives us 325 // .-foo addressing. 326 MCSymbol *PCSym = getContext().CreateTempSymbol(); 327 Streamer.EmitLabel(PCSym); 328 const MCExpr *PC = MCSymbolRefExpr::Create(PCSym, getContext()); 329 return MCBinaryExpr::CreateSub(Res, PC, getContext()); 330 } 331 } 332 } 333 334 unsigned TargetLoweringObjectFile::getPersonalityEncoding() const { 335 return dwarf::DW_EH_PE_absptr; 336 } 337 338 unsigned TargetLoweringObjectFile::getLSDAEncoding() const { 339 return dwarf::DW_EH_PE_absptr; 340 } 341 342 unsigned TargetLoweringObjectFile::getFDEEncoding() const { 343 return dwarf::DW_EH_PE_absptr; 344 } 345 346 unsigned TargetLoweringObjectFile::getTTypeEncoding() const { 347 return dwarf::DW_EH_PE_absptr; 348 } 349 350