1 //===- lib/MC/ELFObjectWriter.cpp - ELF File Writer -----------------------===// 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 ELF object file writer information. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #include "llvm/MC/MCELFObjectWriter.h" 15 #include "llvm/ADT/OwningPtr.h" 16 #include "llvm/ADT/STLExtras.h" 17 #include "llvm/ADT/SmallPtrSet.h" 18 #include "llvm/ADT/SmallString.h" 19 #include "llvm/ADT/StringMap.h" 20 #include "llvm/MC/MCAsmBackend.h" 21 #include "llvm/MC/MCAsmLayout.h" 22 #include "llvm/MC/MCAssembler.h" 23 #include "llvm/MC/MCContext.h" 24 #include "llvm/MC/MCELF.h" 25 #include "llvm/MC/MCELFSymbolFlags.h" 26 #include "llvm/MC/MCExpr.h" 27 #include "llvm/MC/MCFixupKindInfo.h" 28 #include "llvm/MC/MCObjectWriter.h" 29 #include "llvm/MC/MCSectionELF.h" 30 #include "llvm/MC/MCValue.h" 31 #include "llvm/Support/Debug.h" 32 #include "llvm/Support/ELF.h" 33 #include "llvm/Support/ErrorHandling.h" 34 #include <vector> 35 using namespace llvm; 36 37 #undef DEBUG_TYPE 38 #define DEBUG_TYPE "reloc-info" 39 40 namespace { 41 class ELFObjectWriter : public MCObjectWriter { 42 protected: 43 44 static bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind); 45 static bool RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant); 46 static uint64_t SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout); 47 static bool isInSymtab(const MCAssembler &Asm, const MCSymbolData &Data, 48 bool Used, bool Renamed); 49 static bool isLocal(const MCSymbolData &Data, bool isSignature, 50 bool isUsedInReloc); 51 static bool IsELFMetaDataSection(const MCSectionData &SD); 52 static uint64_t DataSectionSize(const MCSectionData &SD); 53 static uint64_t GetSectionFileSize(const MCAsmLayout &Layout, 54 const MCSectionData &SD); 55 static uint64_t GetSectionAddressSize(const MCAsmLayout &Layout, 56 const MCSectionData &SD); 57 58 void WriteDataSectionData(MCAssembler &Asm, 59 const MCAsmLayout &Layout, 60 const MCSectionELF &Section); 61 62 /*static bool isFixupKindX86RIPRel(unsigned Kind) { 63 return Kind == X86::reloc_riprel_4byte || 64 Kind == X86::reloc_riprel_4byte_movq_load; 65 }*/ 66 67 /// ELFSymbolData - Helper struct for containing some precomputed 68 /// information on symbols. 69 struct ELFSymbolData { 70 MCSymbolData *SymbolData; 71 uint64_t StringIndex; 72 uint32_t SectionIndex; 73 74 // Support lexicographic sorting. 75 bool operator<(const ELFSymbolData &RHS) const { 76 return SymbolData->getSymbol().getName() < 77 RHS.SymbolData->getSymbol().getName(); 78 } 79 }; 80 81 /// The target specific ELF writer instance. 82 llvm::OwningPtr<MCELFObjectTargetWriter> TargetObjectWriter; 83 84 SmallPtrSet<const MCSymbol *, 16> UsedInReloc; 85 SmallPtrSet<const MCSymbol *, 16> WeakrefUsedInReloc; 86 DenseMap<const MCSymbol *, const MCSymbol *> Renames; 87 88 llvm::DenseMap<const MCSectionData*, 89 std::vector<ELFRelocationEntry> > Relocations; 90 DenseMap<const MCSection*, uint64_t> SectionStringTableIndex; 91 92 /// @} 93 /// @name Symbol Table Data 94 /// @{ 95 96 SmallString<256> StringTable; 97 std::vector<uint64_t> FileSymbolData; 98 std::vector<ELFSymbolData> LocalSymbolData; 99 std::vector<ELFSymbolData> ExternalSymbolData; 100 std::vector<ELFSymbolData> UndefinedSymbolData; 101 102 /// @} 103 104 bool NeedsGOT; 105 106 bool NeedsSymtabShndx; 107 108 // This holds the symbol table index of the last local symbol. 109 unsigned LastLocalSymbolIndex; 110 // This holds the .strtab section index. 111 unsigned StringTableIndex; 112 // This holds the .symtab section index. 113 unsigned SymbolTableIndex; 114 115 unsigned ShstrtabIndex; 116 117 118 const MCSymbol *SymbolToReloc(const MCAssembler &Asm, 119 const MCValue &Target, 120 const MCFragment &F, 121 const MCFixup &Fixup, 122 bool IsPCRel) const; 123 124 // TargetObjectWriter wrappers. 125 const MCSymbol *ExplicitRelSym(const MCAssembler &Asm, 126 const MCValue &Target, 127 const MCFragment &F, 128 const MCFixup &Fixup, 129 bool IsPCRel) const { 130 return TargetObjectWriter->ExplicitRelSym(Asm, Target, F, Fixup, IsPCRel); 131 } 132 const MCSymbol *undefinedExplicitRelSym(const MCValue &Target, 133 const MCFixup &Fixup, 134 bool IsPCRel) const { 135 return TargetObjectWriter->undefinedExplicitRelSym(Target, Fixup, 136 IsPCRel); 137 } 138 139 bool is64Bit() const { return TargetObjectWriter->is64Bit(); } 140 bool hasRelocationAddend() const { 141 return TargetObjectWriter->hasRelocationAddend(); 142 } 143 unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup, 144 bool IsPCRel, bool IsRelocWithSymbol, 145 int64_t Addend) const { 146 return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel, 147 IsRelocWithSymbol, Addend); 148 } 149 150 public: 151 ELFObjectWriter(MCELFObjectTargetWriter *MOTW, 152 raw_ostream &_OS, bool IsLittleEndian) 153 : MCObjectWriter(_OS, IsLittleEndian), 154 TargetObjectWriter(MOTW), 155 NeedsGOT(false), NeedsSymtabShndx(false) { 156 } 157 158 virtual ~ELFObjectWriter(); 159 160 void WriteWord(uint64_t W) { 161 if (is64Bit()) 162 Write64(W); 163 else 164 Write32(W); 165 } 166 167 void StringLE16(char *buf, uint16_t Value) { 168 buf[0] = char(Value >> 0); 169 buf[1] = char(Value >> 8); 170 } 171 172 void StringLE32(char *buf, uint32_t Value) { 173 StringLE16(buf, uint16_t(Value >> 0)); 174 StringLE16(buf + 2, uint16_t(Value >> 16)); 175 } 176 177 void StringLE64(char *buf, uint64_t Value) { 178 StringLE32(buf, uint32_t(Value >> 0)); 179 StringLE32(buf + 4, uint32_t(Value >> 32)); 180 } 181 182 void StringBE16(char *buf ,uint16_t Value) { 183 buf[0] = char(Value >> 8); 184 buf[1] = char(Value >> 0); 185 } 186 187 void StringBE32(char *buf, uint32_t Value) { 188 StringBE16(buf, uint16_t(Value >> 16)); 189 StringBE16(buf + 2, uint16_t(Value >> 0)); 190 } 191 192 void StringBE64(char *buf, uint64_t Value) { 193 StringBE32(buf, uint32_t(Value >> 32)); 194 StringBE32(buf + 4, uint32_t(Value >> 0)); 195 } 196 197 void String8(MCDataFragment &F, uint8_t Value) { 198 char buf[1]; 199 buf[0] = Value; 200 F.getContents().append(&buf[0], &buf[1]); 201 } 202 203 void String16(MCDataFragment &F, uint16_t Value) { 204 char buf[2]; 205 if (isLittleEndian()) 206 StringLE16(buf, Value); 207 else 208 StringBE16(buf, Value); 209 F.getContents().append(&buf[0], &buf[2]); 210 } 211 212 void String32(MCDataFragment &F, uint32_t Value) { 213 char buf[4]; 214 if (isLittleEndian()) 215 StringLE32(buf, Value); 216 else 217 StringBE32(buf, Value); 218 F.getContents().append(&buf[0], &buf[4]); 219 } 220 221 void String64(MCDataFragment &F, uint64_t Value) { 222 char buf[8]; 223 if (isLittleEndian()) 224 StringLE64(buf, Value); 225 else 226 StringBE64(buf, Value); 227 F.getContents().append(&buf[0], &buf[8]); 228 } 229 230 void WriteHeader(const MCAssembler &Asm, 231 uint64_t SectionDataSize, 232 unsigned NumberOfSections); 233 234 void WriteSymbolEntry(MCDataFragment *SymtabF, 235 MCDataFragment *ShndxF, 236 uint64_t name, uint8_t info, 237 uint64_t value, uint64_t size, 238 uint8_t other, uint32_t shndx, 239 bool Reserved); 240 241 void WriteSymbol(MCDataFragment *SymtabF, MCDataFragment *ShndxF, 242 ELFSymbolData &MSD, 243 const MCAsmLayout &Layout); 244 245 typedef DenseMap<const MCSectionELF*, uint32_t> SectionIndexMapTy; 246 void WriteSymbolTable(MCDataFragment *SymtabF, 247 MCDataFragment *ShndxF, 248 const MCAssembler &Asm, 249 const MCAsmLayout &Layout, 250 const SectionIndexMapTy &SectionIndexMap); 251 252 virtual void RecordRelocation(const MCAssembler &Asm, 253 const MCAsmLayout &Layout, 254 const MCFragment *Fragment, 255 const MCFixup &Fixup, 256 MCValue Target, uint64_t &FixedValue); 257 258 uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm, 259 const MCSymbol *S); 260 261 // Map from a group section to the signature symbol 262 typedef DenseMap<const MCSectionELF*, const MCSymbol*> GroupMapTy; 263 // Map from a signature symbol to the group section 264 typedef DenseMap<const MCSymbol*, const MCSectionELF*> RevGroupMapTy; 265 // Map from a section to the section with the relocations 266 typedef DenseMap<const MCSectionELF*, const MCSectionELF*> RelMapTy; 267 // Map from a section to its offset 268 typedef DenseMap<const MCSectionELF*, uint64_t> SectionOffsetMapTy; 269 270 /// ComputeSymbolTable - Compute the symbol table data 271 /// 272 /// \param Asm - The assembler. 273 /// \param SectionIndexMap - Maps a section to its index. 274 /// \param RevGroupMap - Maps a signature symbol to the group section. 275 /// \param NumRegularSections - Number of non-relocation sections. 276 void ComputeSymbolTable(MCAssembler &Asm, 277 const SectionIndexMapTy &SectionIndexMap, 278 RevGroupMapTy RevGroupMap, 279 unsigned NumRegularSections); 280 281 void ComputeIndexMap(MCAssembler &Asm, 282 SectionIndexMapTy &SectionIndexMap, 283 const RelMapTy &RelMap); 284 285 void CreateRelocationSections(MCAssembler &Asm, MCAsmLayout &Layout, 286 RelMapTy &RelMap); 287 288 void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout, 289 const RelMapTy &RelMap); 290 291 void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout, 292 SectionIndexMapTy &SectionIndexMap, 293 const RelMapTy &RelMap); 294 295 // Create the sections that show up in the symbol table. Currently 296 // those are the .note.GNU-stack section and the group sections. 297 void CreateIndexedSections(MCAssembler &Asm, MCAsmLayout &Layout, 298 GroupMapTy &GroupMap, 299 RevGroupMapTy &RevGroupMap, 300 SectionIndexMapTy &SectionIndexMap, 301 const RelMapTy &RelMap); 302 303 virtual void ExecutePostLayoutBinding(MCAssembler &Asm, 304 const MCAsmLayout &Layout); 305 306 void WriteSectionHeader(MCAssembler &Asm, const GroupMapTy &GroupMap, 307 const MCAsmLayout &Layout, 308 const SectionIndexMapTy &SectionIndexMap, 309 const SectionOffsetMapTy &SectionOffsetMap); 310 311 void ComputeSectionOrder(MCAssembler &Asm, 312 std::vector<const MCSectionELF*> &Sections); 313 314 void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags, 315 uint64_t Address, uint64_t Offset, 316 uint64_t Size, uint32_t Link, uint32_t Info, 317 uint64_t Alignment, uint64_t EntrySize); 318 319 void WriteRelocationsFragment(const MCAssembler &Asm, 320 MCDataFragment *F, 321 const MCSectionData *SD); 322 323 virtual bool 324 IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm, 325 const MCSymbolData &DataA, 326 const MCFragment &FB, 327 bool InSet, 328 bool IsPCRel) const; 329 330 virtual void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout); 331 void WriteSection(MCAssembler &Asm, 332 const SectionIndexMapTy &SectionIndexMap, 333 uint32_t GroupSymbolIndex, 334 uint64_t Offset, uint64_t Size, uint64_t Alignment, 335 const MCSectionELF &Section); 336 }; 337 } 338 339 bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) { 340 const MCFixupKindInfo &FKI = 341 Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind); 342 343 return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel; 344 } 345 346 bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) { 347 switch (Variant) { 348 default: 349 return false; 350 case MCSymbolRefExpr::VK_GOT: 351 case MCSymbolRefExpr::VK_PLT: 352 case MCSymbolRefExpr::VK_GOTPCREL: 353 case MCSymbolRefExpr::VK_GOTOFF: 354 case MCSymbolRefExpr::VK_TPOFF: 355 case MCSymbolRefExpr::VK_TLSGD: 356 case MCSymbolRefExpr::VK_GOTTPOFF: 357 case MCSymbolRefExpr::VK_INDNTPOFF: 358 case MCSymbolRefExpr::VK_NTPOFF: 359 case MCSymbolRefExpr::VK_GOTNTPOFF: 360 case MCSymbolRefExpr::VK_TLSLDM: 361 case MCSymbolRefExpr::VK_DTPOFF: 362 case MCSymbolRefExpr::VK_TLSLD: 363 return true; 364 } 365 } 366 367 ELFObjectWriter::~ELFObjectWriter() 368 {} 369 370 // Emit the ELF header. 371 void ELFObjectWriter::WriteHeader(const MCAssembler &Asm, 372 uint64_t SectionDataSize, 373 unsigned NumberOfSections) { 374 // ELF Header 375 // ---------- 376 // 377 // Note 378 // ---- 379 // emitWord method behaves differently for ELF32 and ELF64, writing 380 // 4 bytes in the former and 8 in the latter. 381 382 Write8(0x7f); // e_ident[EI_MAG0] 383 Write8('E'); // e_ident[EI_MAG1] 384 Write8('L'); // e_ident[EI_MAG2] 385 Write8('F'); // e_ident[EI_MAG3] 386 387 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS] 388 389 // e_ident[EI_DATA] 390 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB); 391 392 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION] 393 // e_ident[EI_OSABI] 394 Write8(TargetObjectWriter->getOSABI()); 395 Write8(0); // e_ident[EI_ABIVERSION] 396 397 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD); 398 399 Write16(ELF::ET_REL); // e_type 400 401 Write16(TargetObjectWriter->getEMachine()); // e_machine = target 402 403 Write32(ELF::EV_CURRENT); // e_version 404 WriteWord(0); // e_entry, no entry point in .o file 405 WriteWord(0); // e_phoff, no program header for .o 406 WriteWord(SectionDataSize + (is64Bit() ? sizeof(ELF::Elf64_Ehdr) : 407 sizeof(ELF::Elf32_Ehdr))); // e_shoff = sec hdr table off in bytes 408 409 // e_flags = whatever the target wants 410 Write32(Asm.getELFHeaderEFlags()); 411 412 // e_ehsize = ELF header size 413 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr)); 414 415 Write16(0); // e_phentsize = prog header entry size 416 Write16(0); // e_phnum = # prog header entries = 0 417 418 // e_shentsize = Section header entry size 419 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr)); 420 421 // e_shnum = # of section header ents 422 if (NumberOfSections >= ELF::SHN_LORESERVE) 423 Write16(ELF::SHN_UNDEF); 424 else 425 Write16(NumberOfSections); 426 427 // e_shstrndx = Section # of '.shstrtab' 428 if (ShstrtabIndex >= ELF::SHN_LORESERVE) 429 Write16(ELF::SHN_XINDEX); 430 else 431 Write16(ShstrtabIndex); 432 } 433 434 void ELFObjectWriter::WriteSymbolEntry(MCDataFragment *SymtabF, 435 MCDataFragment *ShndxF, 436 uint64_t name, 437 uint8_t info, uint64_t value, 438 uint64_t size, uint8_t other, 439 uint32_t shndx, 440 bool Reserved) { 441 if (ShndxF) { 442 if (shndx >= ELF::SHN_LORESERVE && !Reserved) 443 String32(*ShndxF, shndx); 444 else 445 String32(*ShndxF, 0); 446 } 447 448 uint16_t Index = (shndx >= ELF::SHN_LORESERVE && !Reserved) ? 449 uint16_t(ELF::SHN_XINDEX) : shndx; 450 451 if (is64Bit()) { 452 String32(*SymtabF, name); // st_name 453 String8(*SymtabF, info); // st_info 454 String8(*SymtabF, other); // st_other 455 String16(*SymtabF, Index); // st_shndx 456 String64(*SymtabF, value); // st_value 457 String64(*SymtabF, size); // st_size 458 } else { 459 String32(*SymtabF, name); // st_name 460 String32(*SymtabF, value); // st_value 461 String32(*SymtabF, size); // st_size 462 String8(*SymtabF, info); // st_info 463 String8(*SymtabF, other); // st_other 464 String16(*SymtabF, Index); // st_shndx 465 } 466 } 467 468 uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &Data, 469 const MCAsmLayout &Layout) { 470 if (Data.isCommon() && Data.isExternal()) 471 return Data.getCommonAlignment(); 472 473 const MCSymbol &Symbol = Data.getSymbol(); 474 475 if (Symbol.isAbsolute() && Symbol.isVariable()) { 476 if (const MCExpr *Value = Symbol.getVariableValue()) { 477 int64_t IntValue; 478 if (Value->EvaluateAsAbsolute(IntValue, Layout)) 479 return (uint64_t)IntValue; 480 } 481 } 482 483 if (!Symbol.isInSection()) 484 return 0; 485 486 487 if (Data.getFragment()) { 488 if (Data.getFlags() & ELF_Other_ThumbFunc) 489 return Layout.getSymbolOffset(&Data)+1; 490 else 491 return Layout.getSymbolOffset(&Data); 492 } 493 494 return 0; 495 } 496 497 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm, 498 const MCAsmLayout &Layout) { 499 // The presence of symbol versions causes undefined symbols and 500 // versions declared with @@@ to be renamed. 501 502 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(), 503 ie = Asm.symbol_end(); it != ie; ++it) { 504 const MCSymbol &Alias = it->getSymbol(); 505 const MCSymbol &Symbol = Alias.AliasedSymbol(); 506 MCSymbolData &SD = Asm.getSymbolData(Symbol); 507 508 // Not an alias. 509 if (&Symbol == &Alias) 510 continue; 511 512 StringRef AliasName = Alias.getName(); 513 size_t Pos = AliasName.find('@'); 514 if (Pos == StringRef::npos) 515 continue; 516 517 // Aliases defined with .symvar copy the binding from the symbol they alias. 518 // This is the first place we are able to copy this information. 519 it->setExternal(SD.isExternal()); 520 MCELF::SetBinding(*it, MCELF::GetBinding(SD)); 521 522 StringRef Rest = AliasName.substr(Pos); 523 if (!Symbol.isUndefined() && !Rest.startswith("@@@")) 524 continue; 525 526 // FIXME: produce a better error message. 527 if (Symbol.isUndefined() && Rest.startswith("@@") && 528 !Rest.startswith("@@@")) 529 report_fatal_error("A @@ version cannot be undefined"); 530 531 Renames.insert(std::make_pair(&Symbol, &Alias)); 532 } 533 } 534 535 static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) { 536 uint8_t Type = newType; 537 538 // Propagation rules: 539 // IFUNC > FUNC > OBJECT > NOTYPE 540 // TLS_OBJECT > OBJECT > NOTYPE 541 // 542 // dont let the new type degrade the old type 543 switch (origType) { 544 default: 545 break; 546 case ELF::STT_GNU_IFUNC: 547 if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT || 548 Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS) 549 Type = ELF::STT_GNU_IFUNC; 550 break; 551 case ELF::STT_FUNC: 552 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE || 553 Type == ELF::STT_TLS) 554 Type = ELF::STT_FUNC; 555 break; 556 case ELF::STT_OBJECT: 557 if (Type == ELF::STT_NOTYPE) 558 Type = ELF::STT_OBJECT; 559 break; 560 case ELF::STT_TLS: 561 if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE || 562 Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC) 563 Type = ELF::STT_TLS; 564 break; 565 } 566 567 return Type; 568 } 569 570 void ELFObjectWriter::WriteSymbol(MCDataFragment *SymtabF, 571 MCDataFragment *ShndxF, 572 ELFSymbolData &MSD, 573 const MCAsmLayout &Layout) { 574 MCSymbolData &OrigData = *MSD.SymbolData; 575 MCSymbolData &Data = 576 Layout.getAssembler().getSymbolData(OrigData.getSymbol().AliasedSymbol()); 577 578 bool IsReserved = Data.isCommon() || Data.getSymbol().isAbsolute() || 579 Data.getSymbol().isVariable(); 580 581 // Binding and Type share the same byte as upper and lower nibbles 582 uint8_t Binding = MCELF::GetBinding(OrigData); 583 uint8_t Type = mergeTypeForSet(MCELF::GetType(OrigData), MCELF::GetType(Data)); 584 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift); 585 586 // Other and Visibility share the same byte with Visibility using the lower 587 // 2 bits 588 uint8_t Visibility = MCELF::GetVisibility(OrigData); 589 uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift); 590 Other |= Visibility; 591 592 uint64_t Value = SymbolValue(Data, Layout); 593 uint64_t Size = 0; 594 595 assert(!(Data.isCommon() && !Data.isExternal())); 596 597 const MCExpr *ESize = Data.getSize(); 598 if (ESize) { 599 int64_t Res; 600 if (!ESize->EvaluateAsAbsolute(Res, Layout)) 601 report_fatal_error("Size expression must be absolute."); 602 Size = Res; 603 } 604 605 // Write out the symbol table entry 606 WriteSymbolEntry(SymtabF, ShndxF, MSD.StringIndex, Info, Value, 607 Size, Other, MSD.SectionIndex, IsReserved); 608 } 609 610 void ELFObjectWriter::WriteSymbolTable(MCDataFragment *SymtabF, 611 MCDataFragment *ShndxF, 612 const MCAssembler &Asm, 613 const MCAsmLayout &Layout, 614 const SectionIndexMapTy &SectionIndexMap) { 615 // The string table must be emitted first because we need the index 616 // into the string table for all the symbol names. 617 assert(StringTable.size() && "Missing string table"); 618 619 // FIXME: Make sure the start of the symbol table is aligned. 620 621 // The first entry is the undefined symbol entry. 622 WriteSymbolEntry(SymtabF, ShndxF, 0, 0, 0, 0, 0, 0, false); 623 624 for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) { 625 WriteSymbolEntry(SymtabF, ShndxF, FileSymbolData[i], 626 ELF::STT_FILE | ELF::STB_LOCAL, 0, 0, 627 ELF::STV_DEFAULT, ELF::SHN_ABS, true); 628 } 629 630 // Write the symbol table entries. 631 LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1; 632 633 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) { 634 ELFSymbolData &MSD = LocalSymbolData[i]; 635 WriteSymbol(SymtabF, ShndxF, MSD, Layout); 636 } 637 638 // Write out a symbol table entry for each regular section. 639 for (MCAssembler::const_iterator i = Asm.begin(), e = Asm.end(); i != e; 640 ++i) { 641 const MCSectionELF &Section = 642 static_cast<const MCSectionELF&>(i->getSection()); 643 if (Section.getType() == ELF::SHT_RELA || 644 Section.getType() == ELF::SHT_REL || 645 Section.getType() == ELF::SHT_STRTAB || 646 Section.getType() == ELF::SHT_SYMTAB || 647 Section.getType() == ELF::SHT_SYMTAB_SHNDX) 648 continue; 649 WriteSymbolEntry(SymtabF, ShndxF, 0, ELF::STT_SECTION, 0, 0, 650 ELF::STV_DEFAULT, SectionIndexMap.lookup(&Section), 651 false); 652 LastLocalSymbolIndex++; 653 } 654 655 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) { 656 ELFSymbolData &MSD = ExternalSymbolData[i]; 657 MCSymbolData &Data = *MSD.SymbolData; 658 assert(((Data.getFlags() & ELF_STB_Global) || 659 (Data.getFlags() & ELF_STB_Weak)) && 660 "External symbol requires STB_GLOBAL or STB_WEAK flag"); 661 WriteSymbol(SymtabF, ShndxF, MSD, Layout); 662 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL) 663 LastLocalSymbolIndex++; 664 } 665 666 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) { 667 ELFSymbolData &MSD = UndefinedSymbolData[i]; 668 MCSymbolData &Data = *MSD.SymbolData; 669 WriteSymbol(SymtabF, ShndxF, MSD, Layout); 670 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL) 671 LastLocalSymbolIndex++; 672 } 673 } 674 675 const MCSymbol *ELFObjectWriter::SymbolToReloc(const MCAssembler &Asm, 676 const MCValue &Target, 677 const MCFragment &F, 678 const MCFixup &Fixup, 679 bool IsPCRel) const { 680 const MCSymbol &Symbol = Target.getSymA()->getSymbol(); 681 const MCSymbol &ASymbol = Symbol.AliasedSymbol(); 682 const MCSymbol *Renamed = Renames.lookup(&Symbol); 683 const MCSymbolData &SD = Asm.getSymbolData(Symbol); 684 685 if (ASymbol.isUndefined()) { 686 if (Renamed) 687 return Renamed; 688 return undefinedExplicitRelSym(Target, Fixup, IsPCRel); 689 } 690 691 if (SD.isExternal()) { 692 if (Renamed) 693 return Renamed; 694 return &Symbol; 695 } 696 697 const MCSectionELF &Section = 698 static_cast<const MCSectionELF&>(ASymbol.getSection()); 699 const SectionKind secKind = Section.getKind(); 700 701 if (secKind.isBSS()) 702 return ExplicitRelSym(Asm, Target, F, Fixup, IsPCRel); 703 704 if (secKind.isThreadLocal()) { 705 if (Renamed) 706 return Renamed; 707 return &Symbol; 708 } 709 710 MCSymbolRefExpr::VariantKind Kind = Target.getSymA()->getKind(); 711 const MCSectionELF &Sec2 = 712 static_cast<const MCSectionELF&>(F.getParent()->getSection()); 713 714 if (&Sec2 != &Section && 715 (Kind == MCSymbolRefExpr::VK_PLT || 716 Kind == MCSymbolRefExpr::VK_GOTPCREL || 717 Kind == MCSymbolRefExpr::VK_GOTOFF)) { 718 if (Renamed) 719 return Renamed; 720 return &Symbol; 721 } 722 723 if (Section.getFlags() & ELF::SHF_MERGE) { 724 if (Target.getConstant() == 0) 725 return ExplicitRelSym(Asm, Target, F, Fixup, IsPCRel); 726 if (Renamed) 727 return Renamed; 728 return &Symbol; 729 } 730 731 return ExplicitRelSym(Asm, Target, F, Fixup, IsPCRel); 732 733 } 734 735 736 void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm, 737 const MCAsmLayout &Layout, 738 const MCFragment *Fragment, 739 const MCFixup &Fixup, 740 MCValue Target, 741 uint64_t &FixedValue) { 742 int64_t Addend = 0; 743 int Index = 0; 744 int64_t Value = Target.getConstant(); 745 const MCSymbol *RelocSymbol = NULL; 746 747 bool IsPCRel = isFixupKindPCRel(Asm, Fixup.getKind()); 748 if (!Target.isAbsolute()) { 749 const MCSymbol &Symbol = Target.getSymA()->getSymbol(); 750 const MCSymbol &ASymbol = Symbol.AliasedSymbol(); 751 RelocSymbol = SymbolToReloc(Asm, Target, *Fragment, Fixup, IsPCRel); 752 753 if (const MCSymbolRefExpr *RefB = Target.getSymB()) { 754 const MCSymbol &SymbolB = RefB->getSymbol(); 755 MCSymbolData &SDB = Asm.getSymbolData(SymbolB); 756 IsPCRel = true; 757 758 if (!SDB.getFragment()) 759 Asm.getContext().FatalError( 760 Fixup.getLoc(), 761 Twine("symbol '") + SymbolB.getName() + 762 "' can not be undefined in a subtraction expression"); 763 764 // Offset of the symbol in the section 765 int64_t a = Layout.getSymbolOffset(&SDB); 766 767 // Offset of the relocation in the section 768 int64_t b = Layout.getFragmentOffset(Fragment) + Fixup.getOffset(); 769 Value += b - a; 770 } 771 772 if (!RelocSymbol) { 773 MCSymbolData &SD = Asm.getSymbolData(ASymbol); 774 MCFragment *F = SD.getFragment(); 775 776 if (F) { 777 Index = F->getParent()->getOrdinal() + 1; 778 // Offset of the symbol in the section 779 Value += Layout.getSymbolOffset(&SD); 780 } else { 781 Index = 0; 782 } 783 } else { 784 if (Asm.getSymbolData(Symbol).getFlags() & ELF_Other_Weakref) 785 WeakrefUsedInReloc.insert(RelocSymbol); 786 else 787 UsedInReloc.insert(RelocSymbol); 788 Index = -1; 789 } 790 Addend = Value; 791 if (hasRelocationAddend()) 792 Value = 0; 793 } 794 795 FixedValue = Value; 796 unsigned Type = GetRelocType(Target, Fixup, IsPCRel, 797 (RelocSymbol != 0), Addend); 798 MCSymbolRefExpr::VariantKind Modifier = Target.isAbsolute() ? 799 MCSymbolRefExpr::VK_None : Target.getSymA()->getKind(); 800 if (RelocNeedsGOT(Modifier)) 801 NeedsGOT = true; 802 803 uint64_t RelocOffset = Layout.getFragmentOffset(Fragment) + 804 Fixup.getOffset(); 805 806 if (!hasRelocationAddend()) 807 Addend = 0; 808 809 if (is64Bit()) 810 assert(isInt<64>(Addend)); 811 else 812 assert(isInt<32>(Addend)); 813 814 ELFRelocationEntry ERE(RelocOffset, Index, Type, RelocSymbol, Addend, Fixup); 815 Relocations[Fragment->getParent()].push_back(ERE); 816 } 817 818 819 uint64_t 820 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm, 821 const MCSymbol *S) { 822 MCSymbolData &SD = Asm.getSymbolData(*S); 823 return SD.getIndex(); 824 } 825 826 bool ELFObjectWriter::isInSymtab(const MCAssembler &Asm, 827 const MCSymbolData &Data, 828 bool Used, bool Renamed) { 829 if (Data.getFlags() & ELF_Other_Weakref) 830 return false; 831 832 if (Used) 833 return true; 834 835 if (Renamed) 836 return false; 837 838 const MCSymbol &Symbol = Data.getSymbol(); 839 840 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_") 841 return true; 842 843 const MCSymbol &A = Symbol.AliasedSymbol(); 844 if (Symbol.isVariable() && !A.isVariable() && A.isUndefined()) 845 return false; 846 847 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL; 848 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal) 849 return false; 850 851 if (Symbol.isTemporary()) 852 return false; 853 854 return true; 855 } 856 857 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isSignature, 858 bool isUsedInReloc) { 859 if (Data.isExternal()) 860 return false; 861 862 const MCSymbol &Symbol = Data.getSymbol(); 863 const MCSymbol &RefSymbol = Symbol.AliasedSymbol(); 864 865 if (RefSymbol.isUndefined() && !RefSymbol.isVariable()) { 866 if (isSignature && !isUsedInReloc) 867 return true; 868 869 return false; 870 } 871 872 return true; 873 } 874 875 void ELFObjectWriter::ComputeIndexMap(MCAssembler &Asm, 876 SectionIndexMapTy &SectionIndexMap, 877 const RelMapTy &RelMap) { 878 unsigned Index = 1; 879 for (MCAssembler::iterator it = Asm.begin(), 880 ie = Asm.end(); it != ie; ++it) { 881 const MCSectionELF &Section = 882 static_cast<const MCSectionELF &>(it->getSection()); 883 if (Section.getType() != ELF::SHT_GROUP) 884 continue; 885 SectionIndexMap[&Section] = Index++; 886 } 887 888 for (MCAssembler::iterator it = Asm.begin(), 889 ie = Asm.end(); it != ie; ++it) { 890 const MCSectionELF &Section = 891 static_cast<const MCSectionELF &>(it->getSection()); 892 if (Section.getType() == ELF::SHT_GROUP || 893 Section.getType() == ELF::SHT_REL || 894 Section.getType() == ELF::SHT_RELA) 895 continue; 896 SectionIndexMap[&Section] = Index++; 897 const MCSectionELF *RelSection = RelMap.lookup(&Section); 898 if (RelSection) 899 SectionIndexMap[RelSection] = Index++; 900 } 901 } 902 903 void ELFObjectWriter::ComputeSymbolTable(MCAssembler &Asm, 904 const SectionIndexMapTy &SectionIndexMap, 905 RevGroupMapTy RevGroupMap, 906 unsigned NumRegularSections) { 907 // FIXME: Is this the correct place to do this? 908 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed? 909 if (NeedsGOT) { 910 StringRef Name = "_GLOBAL_OFFSET_TABLE_"; 911 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name); 912 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym); 913 Data.setExternal(true); 914 MCELF::SetBinding(Data, ELF::STB_GLOBAL); 915 } 916 917 // Index 0 is always the empty string. 918 StringMap<uint64_t> StringIndexMap; 919 StringTable += '\x00'; 920 921 // FIXME: We could optimize suffixes in strtab in the same way we 922 // optimize them in shstrtab. 923 924 for (MCAssembler::const_file_name_iterator it = Asm.file_names_begin(), 925 ie = Asm.file_names_end(); 926 it != ie; 927 ++it) { 928 StringRef Name = *it; 929 uint64_t &Entry = StringIndexMap[Name]; 930 if (!Entry) { 931 Entry = StringTable.size(); 932 StringTable += Name; 933 StringTable += '\x00'; 934 } 935 FileSymbolData.push_back(Entry); 936 } 937 938 // Add the data for the symbols. 939 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(), 940 ie = Asm.symbol_end(); it != ie; ++it) { 941 const MCSymbol &Symbol = it->getSymbol(); 942 943 bool Used = UsedInReloc.count(&Symbol); 944 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol); 945 bool isSignature = RevGroupMap.count(&Symbol); 946 947 if (!isInSymtab(Asm, *it, 948 Used || WeakrefUsed || isSignature, 949 Renames.count(&Symbol))) 950 continue; 951 952 ELFSymbolData MSD; 953 MSD.SymbolData = it; 954 const MCSymbol &RefSymbol = Symbol.AliasedSymbol(); 955 956 // Undefined symbols are global, but this is the first place we 957 // are able to set it. 958 bool Local = isLocal(*it, isSignature, Used); 959 if (!Local && MCELF::GetBinding(*it) == ELF::STB_LOCAL) { 960 MCSymbolData &SD = Asm.getSymbolData(RefSymbol); 961 MCELF::SetBinding(*it, ELF::STB_GLOBAL); 962 MCELF::SetBinding(SD, ELF::STB_GLOBAL); 963 } 964 965 if (RefSymbol.isUndefined() && !Used && WeakrefUsed) 966 MCELF::SetBinding(*it, ELF::STB_WEAK); 967 968 if (it->isCommon()) { 969 assert(!Local); 970 MSD.SectionIndex = ELF::SHN_COMMON; 971 } else if (Symbol.isAbsolute() || RefSymbol.isVariable()) { 972 MSD.SectionIndex = ELF::SHN_ABS; 973 } else if (RefSymbol.isUndefined()) { 974 if (isSignature && !Used) 975 MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap[&Symbol]); 976 else 977 MSD.SectionIndex = ELF::SHN_UNDEF; 978 } else { 979 const MCSectionELF &Section = 980 static_cast<const MCSectionELF&>(RefSymbol.getSection()); 981 MSD.SectionIndex = SectionIndexMap.lookup(&Section); 982 if (MSD.SectionIndex >= ELF::SHN_LORESERVE) 983 NeedsSymtabShndx = true; 984 assert(MSD.SectionIndex && "Invalid section index!"); 985 } 986 987 // The @@@ in symbol version is replaced with @ in undefined symbols and 988 // @@ in defined ones. 989 StringRef Name = Symbol.getName(); 990 SmallString<32> Buf; 991 992 size_t Pos = Name.find("@@@"); 993 if (Pos != StringRef::npos) { 994 Buf += Name.substr(0, Pos); 995 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1; 996 Buf += Name.substr(Pos + Skip); 997 Name = Buf; 998 } 999 1000 uint64_t &Entry = StringIndexMap[Name]; 1001 if (!Entry) { 1002 Entry = StringTable.size(); 1003 StringTable += Name; 1004 StringTable += '\x00'; 1005 } 1006 MSD.StringIndex = Entry; 1007 if (MSD.SectionIndex == ELF::SHN_UNDEF) 1008 UndefinedSymbolData.push_back(MSD); 1009 else if (Local) 1010 LocalSymbolData.push_back(MSD); 1011 else 1012 ExternalSymbolData.push_back(MSD); 1013 } 1014 1015 // Symbols are required to be in lexicographic order. 1016 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end()); 1017 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end()); 1018 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end()); 1019 1020 // Set the symbol indices. Local symbols must come before all other 1021 // symbols with non-local bindings. 1022 unsigned Index = FileSymbolData.size() + 1; 1023 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) 1024 LocalSymbolData[i].SymbolData->setIndex(Index++); 1025 1026 Index += NumRegularSections; 1027 1028 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) 1029 ExternalSymbolData[i].SymbolData->setIndex(Index++); 1030 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) 1031 UndefinedSymbolData[i].SymbolData->setIndex(Index++); 1032 1033 if (Index >= ELF::SHN_LORESERVE) 1034 NeedsSymtabShndx = true; 1035 } 1036 1037 void ELFObjectWriter::CreateRelocationSections(MCAssembler &Asm, 1038 MCAsmLayout &Layout, 1039 RelMapTy &RelMap) { 1040 for (MCAssembler::const_iterator it = Asm.begin(), 1041 ie = Asm.end(); it != ie; ++it) { 1042 const MCSectionData &SD = *it; 1043 if (Relocations[&SD].empty()) 1044 continue; 1045 1046 MCContext &Ctx = Asm.getContext(); 1047 const MCSectionELF &Section = 1048 static_cast<const MCSectionELF&>(SD.getSection()); 1049 1050 const StringRef SectionName = Section.getSectionName(); 1051 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel"; 1052 RelaSectionName += SectionName; 1053 1054 unsigned EntrySize; 1055 if (hasRelocationAddend()) 1056 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela); 1057 else 1058 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel); 1059 1060 unsigned Flags = 0; 1061 StringRef Group = ""; 1062 if (Section.getFlags() & ELF::SHF_GROUP) { 1063 Flags = ELF::SHF_GROUP; 1064 Group = Section.getGroup()->getName(); 1065 } 1066 1067 const MCSectionELF *RelaSection = 1068 Ctx.getELFSection(RelaSectionName, hasRelocationAddend() ? 1069 ELF::SHT_RELA : ELF::SHT_REL, Flags, 1070 SectionKind::getReadOnly(), 1071 EntrySize, Group); 1072 RelMap[&Section] = RelaSection; 1073 Asm.getOrCreateSectionData(*RelaSection); 1074 } 1075 } 1076 1077 void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout, 1078 const RelMapTy &RelMap) { 1079 for (MCAssembler::const_iterator it = Asm.begin(), 1080 ie = Asm.end(); it != ie; ++it) { 1081 const MCSectionData &SD = *it; 1082 const MCSectionELF &Section = 1083 static_cast<const MCSectionELF&>(SD.getSection()); 1084 1085 const MCSectionELF *RelaSection = RelMap.lookup(&Section); 1086 if (!RelaSection) 1087 continue; 1088 MCSectionData &RelaSD = Asm.getOrCreateSectionData(*RelaSection); 1089 RelaSD.setAlignment(is64Bit() ? 8 : 4); 1090 1091 MCDataFragment *F = new MCDataFragment(&RelaSD); 1092 WriteRelocationsFragment(Asm, F, &*it); 1093 } 1094 } 1095 1096 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type, 1097 uint64_t Flags, uint64_t Address, 1098 uint64_t Offset, uint64_t Size, 1099 uint32_t Link, uint32_t Info, 1100 uint64_t Alignment, 1101 uint64_t EntrySize) { 1102 Write32(Name); // sh_name: index into string table 1103 Write32(Type); // sh_type 1104 WriteWord(Flags); // sh_flags 1105 WriteWord(Address); // sh_addr 1106 WriteWord(Offset); // sh_offset 1107 WriteWord(Size); // sh_size 1108 Write32(Link); // sh_link 1109 Write32(Info); // sh_info 1110 WriteWord(Alignment); // sh_addralign 1111 WriteWord(EntrySize); // sh_entsize 1112 } 1113 1114 void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm, 1115 MCDataFragment *F, 1116 const MCSectionData *SD) { 1117 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD]; 1118 1119 // Sort the relocation entries. Most targets just sort by r_offset, but some 1120 // (e.g., MIPS) have additional constraints. 1121 TargetObjectWriter->sortRelocs(Asm, Relocs); 1122 1123 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) { 1124 ELFRelocationEntry entry = Relocs[e - i - 1]; 1125 1126 if (!entry.Index) 1127 ; 1128 else if (entry.Index < 0) 1129 entry.Index = getSymbolIndexInSymbolTable(Asm, entry.Symbol); 1130 else 1131 entry.Index += FileSymbolData.size() + LocalSymbolData.size(); 1132 if (is64Bit()) { 1133 String64(*F, entry.r_offset); 1134 if (TargetObjectWriter->isN64()) { 1135 String32(*F, entry.Index); 1136 1137 String8(*F, TargetObjectWriter->getRSsym(entry.Type)); 1138 String8(*F, TargetObjectWriter->getRType3(entry.Type)); 1139 String8(*F, TargetObjectWriter->getRType2(entry.Type)); 1140 String8(*F, TargetObjectWriter->getRType(entry.Type)); 1141 } 1142 else { 1143 struct ELF::Elf64_Rela ERE64; 1144 ERE64.setSymbolAndType(entry.Index, entry.Type); 1145 String64(*F, ERE64.r_info); 1146 } 1147 if (hasRelocationAddend()) 1148 String64(*F, entry.r_addend); 1149 } else { 1150 String32(*F, entry.r_offset); 1151 1152 struct ELF::Elf32_Rela ERE32; 1153 ERE32.setSymbolAndType(entry.Index, entry.Type); 1154 String32(*F, ERE32.r_info); 1155 1156 if (hasRelocationAddend()) 1157 String32(*F, entry.r_addend); 1158 } 1159 } 1160 } 1161 1162 static int compareBySuffix(const MCSectionELF *const *a, 1163 const MCSectionELF *const *b) { 1164 const StringRef &NameA = (*a)->getSectionName(); 1165 const StringRef &NameB = (*b)->getSectionName(); 1166 const unsigned sizeA = NameA.size(); 1167 const unsigned sizeB = NameB.size(); 1168 const unsigned len = std::min(sizeA, sizeB); 1169 for (unsigned int i = 0; i < len; ++i) { 1170 char ca = NameA[sizeA - i - 1]; 1171 char cb = NameB[sizeB - i - 1]; 1172 if (ca != cb) 1173 return cb - ca; 1174 } 1175 1176 return sizeB - sizeA; 1177 } 1178 1179 void ELFObjectWriter::CreateMetadataSections(MCAssembler &Asm, 1180 MCAsmLayout &Layout, 1181 SectionIndexMapTy &SectionIndexMap, 1182 const RelMapTy &RelMap) { 1183 MCContext &Ctx = Asm.getContext(); 1184 MCDataFragment *F; 1185 1186 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32; 1187 1188 // We construct .shstrtab, .symtab and .strtab in this order to match gnu as. 1189 const MCSectionELF *ShstrtabSection = 1190 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0, 1191 SectionKind::getReadOnly()); 1192 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection); 1193 ShstrtabSD.setAlignment(1); 1194 1195 const MCSectionELF *SymtabSection = 1196 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, 1197 SectionKind::getReadOnly(), 1198 EntrySize, ""); 1199 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection); 1200 SymtabSD.setAlignment(is64Bit() ? 8 : 4); 1201 1202 MCSectionData *SymtabShndxSD = NULL; 1203 1204 if (NeedsSymtabShndx) { 1205 const MCSectionELF *SymtabShndxSection = 1206 Ctx.getELFSection(".symtab_shndx", ELF::SHT_SYMTAB_SHNDX, 0, 1207 SectionKind::getReadOnly(), 4, ""); 1208 SymtabShndxSD = &Asm.getOrCreateSectionData(*SymtabShndxSection); 1209 SymtabShndxSD->setAlignment(4); 1210 } 1211 1212 const MCSectionELF *StrtabSection; 1213 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0, 1214 SectionKind::getReadOnly()); 1215 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection); 1216 StrtabSD.setAlignment(1); 1217 1218 ComputeIndexMap(Asm, SectionIndexMap, RelMap); 1219 1220 ShstrtabIndex = SectionIndexMap.lookup(ShstrtabSection); 1221 SymbolTableIndex = SectionIndexMap.lookup(SymtabSection); 1222 StringTableIndex = SectionIndexMap.lookup(StrtabSection); 1223 1224 // Symbol table 1225 F = new MCDataFragment(&SymtabSD); 1226 MCDataFragment *ShndxF = NULL; 1227 if (NeedsSymtabShndx) { 1228 ShndxF = new MCDataFragment(SymtabShndxSD); 1229 } 1230 WriteSymbolTable(F, ShndxF, Asm, Layout, SectionIndexMap); 1231 1232 F = new MCDataFragment(&StrtabSD); 1233 F->getContents().append(StringTable.begin(), StringTable.end()); 1234 1235 F = new MCDataFragment(&ShstrtabSD); 1236 1237 std::vector<const MCSectionELF*> Sections; 1238 for (MCAssembler::const_iterator it = Asm.begin(), 1239 ie = Asm.end(); it != ie; ++it) { 1240 const MCSectionELF &Section = 1241 static_cast<const MCSectionELF&>(it->getSection()); 1242 Sections.push_back(&Section); 1243 } 1244 array_pod_sort(Sections.begin(), Sections.end(), compareBySuffix); 1245 1246 // Section header string table. 1247 // 1248 // The first entry of a string table holds a null character so skip 1249 // section 0. 1250 uint64_t Index = 1; 1251 F->getContents().push_back('\x00'); 1252 1253 for (unsigned int I = 0, E = Sections.size(); I != E; ++I) { 1254 const MCSectionELF &Section = *Sections[I]; 1255 1256 StringRef Name = Section.getSectionName(); 1257 if (I != 0) { 1258 StringRef PreviousName = Sections[I - 1]->getSectionName(); 1259 if (PreviousName.endswith(Name)) { 1260 SectionStringTableIndex[&Section] = Index - Name.size() - 1; 1261 continue; 1262 } 1263 } 1264 // Remember the index into the string table so we can write it 1265 // into the sh_name field of the section header table. 1266 SectionStringTableIndex[&Section] = Index; 1267 1268 Index += Name.size() + 1; 1269 F->getContents().append(Name.begin(), Name.end()); 1270 F->getContents().push_back('\x00'); 1271 } 1272 } 1273 1274 void ELFObjectWriter::CreateIndexedSections(MCAssembler &Asm, 1275 MCAsmLayout &Layout, 1276 GroupMapTy &GroupMap, 1277 RevGroupMapTy &RevGroupMap, 1278 SectionIndexMapTy &SectionIndexMap, 1279 const RelMapTy &RelMap) { 1280 // Create the .note.GNU-stack section if needed. 1281 MCContext &Ctx = Asm.getContext(); 1282 if (Asm.getNoExecStack()) { 1283 const MCSectionELF *GnuStackSection = 1284 Ctx.getELFSection(".note.GNU-stack", ELF::SHT_PROGBITS, 0, 1285 SectionKind::getReadOnly()); 1286 Asm.getOrCreateSectionData(*GnuStackSection); 1287 } 1288 1289 // Build the groups 1290 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end(); 1291 it != ie; ++it) { 1292 const MCSectionELF &Section = 1293 static_cast<const MCSectionELF&>(it->getSection()); 1294 if (!(Section.getFlags() & ELF::SHF_GROUP)) 1295 continue; 1296 1297 const MCSymbol *SignatureSymbol = Section.getGroup(); 1298 Asm.getOrCreateSymbolData(*SignatureSymbol); 1299 const MCSectionELF *&Group = RevGroupMap[SignatureSymbol]; 1300 if (!Group) { 1301 Group = Ctx.CreateELFGroupSection(); 1302 MCSectionData &Data = Asm.getOrCreateSectionData(*Group); 1303 Data.setAlignment(4); 1304 MCDataFragment *F = new MCDataFragment(&Data); 1305 String32(*F, ELF::GRP_COMDAT); 1306 } 1307 GroupMap[Group] = SignatureSymbol; 1308 } 1309 1310 ComputeIndexMap(Asm, SectionIndexMap, RelMap); 1311 1312 // Add sections to the groups 1313 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end(); 1314 it != ie; ++it) { 1315 const MCSectionELF &Section = 1316 static_cast<const MCSectionELF&>(it->getSection()); 1317 if (!(Section.getFlags() & ELF::SHF_GROUP)) 1318 continue; 1319 const MCSectionELF *Group = RevGroupMap[Section.getGroup()]; 1320 MCSectionData &Data = Asm.getOrCreateSectionData(*Group); 1321 // FIXME: we could use the previous fragment 1322 MCDataFragment *F = new MCDataFragment(&Data); 1323 unsigned Index = SectionIndexMap.lookup(&Section); 1324 String32(*F, Index); 1325 } 1326 } 1327 1328 void ELFObjectWriter::WriteSection(MCAssembler &Asm, 1329 const SectionIndexMapTy &SectionIndexMap, 1330 uint32_t GroupSymbolIndex, 1331 uint64_t Offset, uint64_t Size, 1332 uint64_t Alignment, 1333 const MCSectionELF &Section) { 1334 uint64_t sh_link = 0; 1335 uint64_t sh_info = 0; 1336 1337 switch(Section.getType()) { 1338 case ELF::SHT_DYNAMIC: 1339 sh_link = SectionStringTableIndex[&Section]; 1340 sh_info = 0; 1341 break; 1342 1343 case ELF::SHT_REL: 1344 case ELF::SHT_RELA: { 1345 const MCSectionELF *SymtabSection; 1346 const MCSectionELF *InfoSection; 1347 SymtabSection = Asm.getContext().getELFSection(".symtab", ELF::SHT_SYMTAB, 1348 0, 1349 SectionKind::getReadOnly()); 1350 sh_link = SectionIndexMap.lookup(SymtabSection); 1351 assert(sh_link && ".symtab not found"); 1352 1353 // Remove ".rel" and ".rela" prefixes. 1354 unsigned SecNameLen = (Section.getType() == ELF::SHT_REL) ? 4 : 5; 1355 StringRef SectionName = Section.getSectionName().substr(SecNameLen); 1356 StringRef GroupName = 1357 Section.getGroup() ? Section.getGroup()->getName() : ""; 1358 1359 InfoSection = Asm.getContext().getELFSection(SectionName, ELF::SHT_PROGBITS, 1360 0, SectionKind::getReadOnly(), 1361 0, GroupName); 1362 sh_info = SectionIndexMap.lookup(InfoSection); 1363 break; 1364 } 1365 1366 case ELF::SHT_SYMTAB: 1367 case ELF::SHT_DYNSYM: 1368 sh_link = StringTableIndex; 1369 sh_info = LastLocalSymbolIndex; 1370 break; 1371 1372 case ELF::SHT_SYMTAB_SHNDX: 1373 sh_link = SymbolTableIndex; 1374 break; 1375 1376 case ELF::SHT_PROGBITS: 1377 case ELF::SHT_STRTAB: 1378 case ELF::SHT_NOBITS: 1379 case ELF::SHT_NOTE: 1380 case ELF::SHT_NULL: 1381 case ELF::SHT_ARM_ATTRIBUTES: 1382 case ELF::SHT_INIT_ARRAY: 1383 case ELF::SHT_FINI_ARRAY: 1384 case ELF::SHT_PREINIT_ARRAY: 1385 case ELF::SHT_X86_64_UNWIND: 1386 case ELF::SHT_MIPS_REGINFO: 1387 case ELF::SHT_MIPS_OPTIONS: 1388 // Nothing to do. 1389 break; 1390 1391 case ELF::SHT_GROUP: 1392 sh_link = SymbolTableIndex; 1393 sh_info = GroupSymbolIndex; 1394 break; 1395 1396 default: 1397 assert(0 && "FIXME: sh_type value not supported!"); 1398 break; 1399 } 1400 1401 if (TargetObjectWriter->getEMachine() == ELF::EM_ARM && 1402 Section.getType() == ELF::SHT_ARM_EXIDX) { 1403 StringRef SecName(Section.getSectionName()); 1404 if (SecName == ".ARM.exidx") { 1405 sh_link = SectionIndexMap.lookup( 1406 Asm.getContext().getELFSection(".text", 1407 ELF::SHT_PROGBITS, 1408 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC, 1409 SectionKind::getText())); 1410 } else if (SecName.startswith(".ARM.exidx")) { 1411 StringRef GroupName = 1412 Section.getGroup() ? Section.getGroup()->getName() : ""; 1413 sh_link = SectionIndexMap.lookup(Asm.getContext().getELFSection( 1414 SecName.substr(sizeof(".ARM.exidx") - 1), ELF::SHT_PROGBITS, 1415 ELF::SHF_EXECINSTR | ELF::SHF_ALLOC, SectionKind::getText(), 0, 1416 GroupName)); 1417 } 1418 } 1419 1420 WriteSecHdrEntry(SectionStringTableIndex[&Section], Section.getType(), 1421 Section.getFlags(), 0, Offset, Size, sh_link, sh_info, 1422 Alignment, Section.getEntrySize()); 1423 } 1424 1425 bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) { 1426 return SD.getOrdinal() == ~UINT32_C(0) && 1427 !SD.getSection().isVirtualSection(); 1428 } 1429 1430 uint64_t ELFObjectWriter::DataSectionSize(const MCSectionData &SD) { 1431 uint64_t Ret = 0; 1432 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e; 1433 ++i) { 1434 const MCFragment &F = *i; 1435 assert(F.getKind() == MCFragment::FT_Data); 1436 Ret += cast<MCDataFragment>(F).getContents().size(); 1437 } 1438 return Ret; 1439 } 1440 1441 uint64_t ELFObjectWriter::GetSectionFileSize(const MCAsmLayout &Layout, 1442 const MCSectionData &SD) { 1443 if (IsELFMetaDataSection(SD)) 1444 return DataSectionSize(SD); 1445 return Layout.getSectionFileSize(&SD); 1446 } 1447 1448 uint64_t ELFObjectWriter::GetSectionAddressSize(const MCAsmLayout &Layout, 1449 const MCSectionData &SD) { 1450 if (IsELFMetaDataSection(SD)) 1451 return DataSectionSize(SD); 1452 return Layout.getSectionAddressSize(&SD); 1453 } 1454 1455 void ELFObjectWriter::WriteDataSectionData(MCAssembler &Asm, 1456 const MCAsmLayout &Layout, 1457 const MCSectionELF &Section) { 1458 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1459 1460 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment()); 1461 WriteZeros(Padding); 1462 1463 if (IsELFMetaDataSection(SD)) { 1464 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e; 1465 ++i) { 1466 const MCFragment &F = *i; 1467 assert(F.getKind() == MCFragment::FT_Data); 1468 WriteBytes(cast<MCDataFragment>(F).getContents()); 1469 } 1470 } else { 1471 Asm.writeSectionData(&SD, Layout); 1472 } 1473 } 1474 1475 void ELFObjectWriter::WriteSectionHeader(MCAssembler &Asm, 1476 const GroupMapTy &GroupMap, 1477 const MCAsmLayout &Layout, 1478 const SectionIndexMapTy &SectionIndexMap, 1479 const SectionOffsetMapTy &SectionOffsetMap) { 1480 const unsigned NumSections = Asm.size() + 1; 1481 1482 std::vector<const MCSectionELF*> Sections; 1483 Sections.resize(NumSections - 1); 1484 1485 for (SectionIndexMapTy::const_iterator i= 1486 SectionIndexMap.begin(), e = SectionIndexMap.end(); i != e; ++i) { 1487 const std::pair<const MCSectionELF*, uint32_t> &p = *i; 1488 Sections[p.second - 1] = p.first; 1489 } 1490 1491 // Null section first. 1492 uint64_t FirstSectionSize = 1493 NumSections >= ELF::SHN_LORESERVE ? NumSections : 0; 1494 uint32_t FirstSectionLink = 1495 ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0; 1496 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0); 1497 1498 for (unsigned i = 0; i < NumSections - 1; ++i) { 1499 const MCSectionELF &Section = *Sections[i]; 1500 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1501 uint32_t GroupSymbolIndex; 1502 if (Section.getType() != ELF::SHT_GROUP) 1503 GroupSymbolIndex = 0; 1504 else 1505 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm, 1506 GroupMap.lookup(&Section)); 1507 1508 uint64_t Size = GetSectionAddressSize(Layout, SD); 1509 1510 WriteSection(Asm, SectionIndexMap, GroupSymbolIndex, 1511 SectionOffsetMap.lookup(&Section), Size, 1512 SD.getAlignment(), Section); 1513 } 1514 } 1515 1516 void ELFObjectWriter::ComputeSectionOrder(MCAssembler &Asm, 1517 std::vector<const MCSectionELF*> &Sections) { 1518 for (MCAssembler::iterator it = Asm.begin(), 1519 ie = Asm.end(); it != ie; ++it) { 1520 const MCSectionELF &Section = 1521 static_cast<const MCSectionELF &>(it->getSection()); 1522 if (Section.getType() == ELF::SHT_GROUP) 1523 Sections.push_back(&Section); 1524 } 1525 1526 for (MCAssembler::iterator it = Asm.begin(), 1527 ie = Asm.end(); it != ie; ++it) { 1528 const MCSectionELF &Section = 1529 static_cast<const MCSectionELF &>(it->getSection()); 1530 if (Section.getType() != ELF::SHT_GROUP && 1531 Section.getType() != ELF::SHT_REL && 1532 Section.getType() != ELF::SHT_RELA) 1533 Sections.push_back(&Section); 1534 } 1535 1536 for (MCAssembler::iterator it = Asm.begin(), 1537 ie = Asm.end(); it != ie; ++it) { 1538 const MCSectionELF &Section = 1539 static_cast<const MCSectionELF &>(it->getSection()); 1540 if (Section.getType() == ELF::SHT_REL || 1541 Section.getType() == ELF::SHT_RELA) 1542 Sections.push_back(&Section); 1543 } 1544 } 1545 1546 void ELFObjectWriter::WriteObject(MCAssembler &Asm, 1547 const MCAsmLayout &Layout) { 1548 GroupMapTy GroupMap; 1549 RevGroupMapTy RevGroupMap; 1550 SectionIndexMapTy SectionIndexMap; 1551 1552 unsigned NumUserSections = Asm.size(); 1553 1554 DenseMap<const MCSectionELF*, const MCSectionELF*> RelMap; 1555 CreateRelocationSections(Asm, const_cast<MCAsmLayout&>(Layout), RelMap); 1556 1557 const unsigned NumUserAndRelocSections = Asm.size(); 1558 CreateIndexedSections(Asm, const_cast<MCAsmLayout&>(Layout), GroupMap, 1559 RevGroupMap, SectionIndexMap, RelMap); 1560 const unsigned AllSections = Asm.size(); 1561 const unsigned NumIndexedSections = AllSections - NumUserAndRelocSections; 1562 1563 unsigned NumRegularSections = NumUserSections + NumIndexedSections; 1564 1565 // Compute symbol table information. 1566 ComputeSymbolTable(Asm, SectionIndexMap, RevGroupMap, NumRegularSections); 1567 1568 1569 WriteRelocations(Asm, const_cast<MCAsmLayout&>(Layout), RelMap); 1570 1571 CreateMetadataSections(const_cast<MCAssembler&>(Asm), 1572 const_cast<MCAsmLayout&>(Layout), 1573 SectionIndexMap, 1574 RelMap); 1575 1576 uint64_t NaturalAlignment = is64Bit() ? 8 : 4; 1577 uint64_t HeaderSize = is64Bit() ? sizeof(ELF::Elf64_Ehdr) : 1578 sizeof(ELF::Elf32_Ehdr); 1579 uint64_t FileOff = HeaderSize; 1580 1581 std::vector<const MCSectionELF*> Sections; 1582 ComputeSectionOrder(Asm, Sections); 1583 unsigned NumSections = Sections.size(); 1584 SectionOffsetMapTy SectionOffsetMap; 1585 for (unsigned i = 0; i < NumRegularSections + 1; ++i) { 1586 const MCSectionELF &Section = *Sections[i]; 1587 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1588 1589 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment()); 1590 1591 // Remember the offset into the file for this section. 1592 SectionOffsetMap[&Section] = FileOff; 1593 1594 // Get the size of the section in the output file (including padding). 1595 FileOff += GetSectionFileSize(Layout, SD); 1596 } 1597 1598 FileOff = RoundUpToAlignment(FileOff, NaturalAlignment); 1599 1600 const unsigned SectionHeaderOffset = FileOff - HeaderSize; 1601 1602 uint64_t SectionHeaderEntrySize = is64Bit() ? 1603 sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr); 1604 FileOff += (NumSections + 1) * SectionHeaderEntrySize; 1605 1606 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) { 1607 const MCSectionELF &Section = *Sections[i]; 1608 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1609 1610 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment()); 1611 1612 // Remember the offset into the file for this section. 1613 SectionOffsetMap[&Section] = FileOff; 1614 1615 // Get the size of the section in the output file (including padding). 1616 FileOff += GetSectionFileSize(Layout, SD); 1617 } 1618 1619 // Write out the ELF header ... 1620 WriteHeader(Asm, SectionHeaderOffset, NumSections + 1); 1621 1622 // ... then the regular sections ... 1623 // + because of .shstrtab 1624 for (unsigned i = 0; i < NumRegularSections + 1; ++i) 1625 WriteDataSectionData(Asm, Layout, *Sections[i]); 1626 1627 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment); 1628 WriteZeros(Padding); 1629 1630 // ... then the section header table ... 1631 WriteSectionHeader(Asm, GroupMap, Layout, SectionIndexMap, 1632 SectionOffsetMap); 1633 1634 // ... and then the remaining sections ... 1635 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) 1636 WriteDataSectionData(Asm, Layout, *Sections[i]); 1637 } 1638 1639 bool 1640 ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm, 1641 const MCSymbolData &DataA, 1642 const MCFragment &FB, 1643 bool InSet, 1644 bool IsPCRel) const { 1645 if (DataA.getFlags() & ELF_STB_Weak || MCELF::GetType(DataA) == ELF::STT_GNU_IFUNC) 1646 return false; 1647 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl( 1648 Asm, DataA, FB,InSet, IsPCRel); 1649 } 1650 1651 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW, 1652 raw_ostream &OS, 1653 bool IsLittleEndian) { 1654 return new ELFObjectWriter(MOTW, OS, IsLittleEndian); 1655 } 1656