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 EHFrameSection = 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 IsFunctionEHSymbolGlobal = false; 63 IsFunctionEHFrameSymbolPrivate = true; 64 SupportsWeakOmittedEHFrame = true; 65 } 66 67 TargetLoweringObjectFile::~TargetLoweringObjectFile() { 68 } 69 70 static bool isSuitableForBSS(const GlobalVariable *GV) { 71 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 /// getKindForGlobal - This is a top-level target-independent classifier for 125 /// a global variable. Given an global variable and information from TM, it 126 /// classifies the global in a variety of ways that make various target 127 /// implementations simpler. The target implementation is free to ignore this 128 /// extra info of course. 129 SectionKind TargetLoweringObjectFile::getKindForGlobal(const GlobalValue *GV, 130 const TargetMachine &TM){ 131 assert(!GV->isDeclaration() && !GV->hasAvailableExternallyLinkage() && 132 "Can only be used for global definitions"); 133 134 Reloc::Model ReloModel = TM.getRelocationModel(); 135 136 // Early exit - functions should be always in text sections. 137 const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV); 138 if (GVar == 0) 139 return SectionKind::getText(); 140 141 // Handle thread-local data first. 142 if (GVar->isThreadLocal()) { 143 if (isSuitableForBSS(GVar)) 144 return SectionKind::getThreadBSS(); 145 return SectionKind::getThreadData(); 146 } 147 148 // Variables with common linkage always get classified as common. 149 if (GVar->hasCommonLinkage()) 150 return SectionKind::getCommon(); 151 152 // Variable can be easily put to BSS section. 153 if (isSuitableForBSS(GVar)) { 154 if (GVar->hasLocalLinkage()) 155 return SectionKind::getBSSLocal(); 156 else if (GVar->hasExternalLinkage()) 157 return SectionKind::getBSSExtern(); 158 return SectionKind::getBSS(); 159 } 160 161 Constant *C = GVar->getInitializer(); 162 163 // If the global is marked constant, we can put it into a mergable section, 164 // a mergable string section, or general .data if it contains relocations. 165 if (GVar->isConstant()) { 166 // If the initializer for the global contains something that requires a 167 // relocation, then we may have to drop this into a wriable data section 168 // even though it is marked const. 169 switch (C->getRelocationInfo()) { 170 default: assert(0 && "unknown relocation info kind"); 171 case Constant::NoRelocation: 172 // If initializer is a null-terminated string, put it in a "cstring" 173 // section of the right width. 174 if (const ArrayType *ATy = dyn_cast<ArrayType>(C->getType())) { 175 if (const IntegerType *ITy = 176 dyn_cast<IntegerType>(ATy->getElementType())) { 177 if ((ITy->getBitWidth() == 8 || ITy->getBitWidth() == 16 || 178 ITy->getBitWidth() == 32) && 179 IsNullTerminatedString(C)) { 180 if (ITy->getBitWidth() == 8) 181 return SectionKind::getMergeable1ByteCString(); 182 if (ITy->getBitWidth() == 16) 183 return SectionKind::getMergeable2ByteCString(); 184 185 assert(ITy->getBitWidth() == 32 && "Unknown width"); 186 return SectionKind::getMergeable4ByteCString(); 187 } 188 } 189 } 190 191 // Otherwise, just drop it into a mergable constant section. If we have 192 // a section for this size, use it, otherwise use the arbitrary sized 193 // mergable section. 194 switch (TM.getTargetData()->getTypeAllocSize(C->getType())) { 195 case 4: return SectionKind::getMergeableConst4(); 196 case 8: return SectionKind::getMergeableConst8(); 197 case 16: return SectionKind::getMergeableConst16(); 198 default: return SectionKind::getMergeableConst(); 199 } 200 201 case Constant::LocalRelocation: 202 // In static relocation model, the linker will resolve all addresses, so 203 // the relocation entries will actually be constants by the time the app 204 // starts up. However, we can't put this into a mergable section, because 205 // the linker doesn't take relocations into consideration when it tries to 206 // merge entries in the section. 207 if (ReloModel == Reloc::Static) 208 return SectionKind::getReadOnly(); 209 210 // Otherwise, the dynamic linker needs to fix it up, put it in the 211 // writable data.rel.local section. 212 return SectionKind::getReadOnlyWithRelLocal(); 213 214 case Constant::GlobalRelocations: 215 // In static relocation model, the linker will resolve all addresses, so 216 // the relocation entries will actually be constants by the time the app 217 // starts up. However, we can't put this into a mergable section, because 218 // the linker doesn't take relocations into consideration when it tries to 219 // merge entries in the section. 220 if (ReloModel == Reloc::Static) 221 return SectionKind::getReadOnly(); 222 223 // Otherwise, the dynamic linker needs to fix it up, put it in the 224 // writable data.rel section. 225 return SectionKind::getReadOnlyWithRel(); 226 } 227 } 228 229 // Okay, this isn't a constant. If the initializer for the global is going 230 // to require a runtime relocation by the dynamic linker, put it into a more 231 // specific section to improve startup time of the app. This coalesces these 232 // globals together onto fewer pages, improving the locality of the dynamic 233 // linker. 234 if (ReloModel == Reloc::Static) 235 return SectionKind::getDataNoRel(); 236 237 switch (C->getRelocationInfo()) { 238 default: assert(0 && "unknown relocation info kind"); 239 case Constant::NoRelocation: 240 return SectionKind::getDataNoRel(); 241 case Constant::LocalRelocation: 242 return SectionKind::getDataRelLocal(); 243 case Constant::GlobalRelocations: 244 return SectionKind::getDataRel(); 245 } 246 } 247 248 /// SectionForGlobal - This method computes the appropriate section to emit 249 /// the specified global variable or function definition. This should not 250 /// be passed external (or available externally) globals. 251 const MCSection *TargetLoweringObjectFile:: 252 SectionForGlobal(const GlobalValue *GV, SectionKind Kind, Mangler *Mang, 253 const TargetMachine &TM) const { 254 // Select section name. 255 if (GV->hasSection()) 256 return getExplicitSectionGlobal(GV, Kind, Mang, TM); 257 258 259 // Use default section depending on the 'type' of global 260 return SelectSectionForGlobal(GV, Kind, Mang, TM); 261 } 262 263 264 // Lame default implementation. Calculate the section name for global. 265 const MCSection * 266 TargetLoweringObjectFile::SelectSectionForGlobal(const GlobalValue *GV, 267 SectionKind Kind, 268 Mangler *Mang, 269 const TargetMachine &TM) const{ 270 assert(!Kind.isThreadLocal() && "Doesn't support TLS"); 271 272 if (Kind.isText()) 273 return getTextSection(); 274 275 if (Kind.isBSS() && BSSSection != 0) 276 return BSSSection; 277 278 if (Kind.isReadOnly() && ReadOnlySection != 0) 279 return ReadOnlySection; 280 281 return getDataSection(); 282 } 283 284 /// getSectionForConstant - Given a mergable constant with the 285 /// specified size and relocation information, return a section that it 286 /// should be placed in. 287 const MCSection * 288 TargetLoweringObjectFile::getSectionForConstant(SectionKind Kind) const { 289 if (Kind.isReadOnly() && ReadOnlySection != 0) 290 return ReadOnlySection; 291 292 return DataSection; 293 } 294 295 /// getExprForDwarfGlobalReference - Return an MCExpr to use for a 296 /// reference to the specified global variable from exception 297 /// handling information. 298 const MCExpr *TargetLoweringObjectFile:: 299 getExprForDwarfGlobalReference(const GlobalValue *GV, Mangler *Mang, 300 MachineModuleInfo *MMI, unsigned Encoding, 301 MCStreamer &Streamer) const { 302 const MCSymbol *Sym = Mang->getSymbol(GV); 303 return getExprForDwarfReference(Sym, Mang, MMI, Encoding, Streamer); 304 } 305 306 const MCExpr *TargetLoweringObjectFile:: 307 getExprForDwarfReference(const MCSymbol *Sym, Mangler *Mang, 308 MachineModuleInfo *MMI, unsigned Encoding, 309 MCStreamer &Streamer) const { 310 const MCExpr *Res = MCSymbolRefExpr::Create(Sym, getContext()); 311 312 switch (Encoding & 0xF0) { 313 default: 314 report_fatal_error("We do not support this DWARF encoding yet!"); 315 case dwarf::DW_EH_PE_absptr: 316 // Do nothing special 317 return Res; 318 case dwarf::DW_EH_PE_pcrel: { 319 // Emit a label to the streamer for the current position. This gives us 320 // .-foo addressing. 321 MCSymbol *PCSym = getContext().CreateTempSymbol(); 322 Streamer.EmitLabel(PCSym); 323 const MCExpr *PC = MCSymbolRefExpr::Create(PCSym, getContext()); 324 return MCBinaryExpr::CreateSub(Res, PC, getContext()); 325 } 326 } 327 } 328 329 unsigned TargetLoweringObjectFile::getPersonalityEncoding() const { 330 return dwarf::DW_EH_PE_absptr; 331 } 332 333 unsigned TargetLoweringObjectFile::getLSDAEncoding() const { 334 return dwarf::DW_EH_PE_absptr; 335 } 336 337 unsigned TargetLoweringObjectFile::getFDEEncoding() const { 338 return dwarf::DW_EH_PE_absptr; 339 } 340 341 unsigned TargetLoweringObjectFile::getTTypeEncoding() const { 342 return dwarf::DW_EH_PE_absptr; 343 } 344 345