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 "MCELF.h" 15 #include "llvm/ADT/OwningPtr.h" 16 #include "llvm/ADT/SmallPtrSet.h" 17 #include "llvm/ADT/SmallString.h" 18 #include "llvm/ADT/STLExtras.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/MCELFObjectWriter.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/ErrorHandling.h" 33 #include "llvm/Support/ELF.h" 34 35 #include <vector> 36 using namespace llvm; 37 38 #undef DEBUG_TYPE 39 #define DEBUG_TYPE "reloc-info" 40 41 namespace { 42 class ELFObjectWriter : public MCObjectWriter { 43 protected: 44 45 static bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind); 46 static bool RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant); 47 static uint64_t SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout); 48 static bool isInSymtab(const MCAssembler &Asm, const MCSymbolData &Data, 49 bool Used, bool Renamed); 50 static bool isLocal(const MCSymbolData &Data, bool isSignature, 51 bool isUsedInReloc); 52 static bool IsELFMetaDataSection(const MCSectionData &SD); 53 static uint64_t DataSectionSize(const MCSectionData &SD); 54 static uint64_t GetSectionFileSize(const MCAsmLayout &Layout, 55 const MCSectionData &SD); 56 static uint64_t GetSectionAddressSize(const MCAsmLayout &Layout, 57 const MCSectionData &SD); 58 59 void WriteDataSectionData(MCAssembler &Asm, 60 const MCAsmLayout &Layout, 61 const MCSectionELF &Section); 62 63 /*static bool isFixupKindX86RIPRel(unsigned Kind) { 64 return Kind == X86::reloc_riprel_4byte || 65 Kind == X86::reloc_riprel_4byte_movq_load; 66 }*/ 67 68 /// ELFSymbolData - Helper struct for containing some precomputed 69 /// information on symbols. 70 struct ELFSymbolData { 71 MCSymbolData *SymbolData; 72 uint64_t StringIndex; 73 uint32_t SectionIndex; 74 75 // Support lexicographic sorting. 76 bool operator<(const ELFSymbolData &RHS) const { 77 if (MCELF::GetType(*SymbolData) == ELF::STT_FILE) 78 return true; 79 if (MCELF::GetType(*RHS.SymbolData) == ELF::STT_FILE) 80 return false; 81 return SymbolData->getSymbol().getName() < 82 RHS.SymbolData->getSymbol().getName(); 83 } 84 }; 85 86 /// The target specific ELF writer instance. 87 llvm::OwningPtr<MCELFObjectTargetWriter> TargetObjectWriter; 88 89 SmallPtrSet<const MCSymbol *, 16> UsedInReloc; 90 SmallPtrSet<const MCSymbol *, 16> WeakrefUsedInReloc; 91 DenseMap<const MCSymbol *, const MCSymbol *> Renames; 92 93 llvm::DenseMap<const MCSectionData*, 94 std::vector<ELFRelocationEntry> > Relocations; 95 DenseMap<const MCSection*, uint64_t> SectionStringTableIndex; 96 97 /// @} 98 /// @name Symbol Table Data 99 /// @{ 100 101 SmallString<256> StringTable; 102 std::vector<ELFSymbolData> LocalSymbolData; 103 std::vector<ELFSymbolData> ExternalSymbolData; 104 std::vector<ELFSymbolData> UndefinedSymbolData; 105 106 /// @} 107 108 bool NeedsGOT; 109 110 bool NeedsSymtabShndx; 111 112 // This holds the symbol table index of the last local symbol. 113 unsigned LastLocalSymbolIndex; 114 // This holds the .strtab section index. 115 unsigned StringTableIndex; 116 // This holds the .symtab section index. 117 unsigned SymbolTableIndex; 118 119 unsigned ShstrtabIndex; 120 121 122 const MCSymbol *SymbolToReloc(const MCAssembler &Asm, 123 const MCValue &Target, 124 const MCFragment &F, 125 const MCFixup &Fixup, 126 bool IsPCRel) const; 127 128 // TargetObjectWriter wrappers. 129 const MCSymbol *ExplicitRelSym(const MCAssembler &Asm, 130 const MCValue &Target, 131 const MCFragment &F, 132 const MCFixup &Fixup, 133 bool IsPCRel) const { 134 return TargetObjectWriter->ExplicitRelSym(Asm, Target, F, Fixup, IsPCRel); 135 } 136 137 bool is64Bit() const { return TargetObjectWriter->is64Bit(); } 138 bool hasRelocationAddend() const { 139 return TargetObjectWriter->hasRelocationAddend(); 140 } 141 unsigned getEFlags() const { 142 return TargetObjectWriter->getEFlags(); 143 } 144 unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup, 145 bool IsPCRel, bool IsRelocWithSymbol, 146 int64_t Addend) const { 147 return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel, 148 IsRelocWithSymbol, Addend); 149 } 150 151 152 public: 153 ELFObjectWriter(MCELFObjectTargetWriter *MOTW, 154 raw_ostream &_OS, bool IsLittleEndian) 155 : MCObjectWriter(_OS, IsLittleEndian), 156 TargetObjectWriter(MOTW), 157 NeedsGOT(false), NeedsSymtabShndx(false){ 158 } 159 160 virtual ~ELFObjectWriter(); 161 162 void WriteWord(uint64_t W) { 163 if (is64Bit()) 164 Write64(W); 165 else 166 Write32(W); 167 } 168 169 void StringLE16(char *buf, uint16_t Value) { 170 buf[0] = char(Value >> 0); 171 buf[1] = char(Value >> 8); 172 } 173 174 void StringLE32(char *buf, uint32_t Value) { 175 StringLE16(buf, uint16_t(Value >> 0)); 176 StringLE16(buf + 2, uint16_t(Value >> 16)); 177 } 178 179 void StringLE64(char *buf, uint64_t Value) { 180 StringLE32(buf, uint32_t(Value >> 0)); 181 StringLE32(buf + 4, uint32_t(Value >> 32)); 182 } 183 184 void StringBE16(char *buf ,uint16_t Value) { 185 buf[0] = char(Value >> 8); 186 buf[1] = char(Value >> 0); 187 } 188 189 void StringBE32(char *buf, uint32_t Value) { 190 StringBE16(buf, uint16_t(Value >> 16)); 191 StringBE16(buf + 2, uint16_t(Value >> 0)); 192 } 193 194 void StringBE64(char *buf, uint64_t Value) { 195 StringBE32(buf, uint32_t(Value >> 32)); 196 StringBE32(buf + 4, uint32_t(Value >> 0)); 197 } 198 199 void String8(MCDataFragment &F, uint8_t Value) { 200 char buf[1]; 201 buf[0] = Value; 202 F.getContents() += StringRef(buf, 1); 203 } 204 205 void String16(MCDataFragment &F, uint16_t Value) { 206 char buf[2]; 207 if (isLittleEndian()) 208 StringLE16(buf, Value); 209 else 210 StringBE16(buf, Value); 211 F.getContents() += StringRef(buf, 2); 212 } 213 214 void String32(MCDataFragment &F, uint32_t Value) { 215 char buf[4]; 216 if (isLittleEndian()) 217 StringLE32(buf, Value); 218 else 219 StringBE32(buf, Value); 220 F.getContents() += StringRef(buf, 4); 221 } 222 223 void String64(MCDataFragment &F, uint64_t Value) { 224 char buf[8]; 225 if (isLittleEndian()) 226 StringLE64(buf, Value); 227 else 228 StringBE64(buf, Value); 229 F.getContents() += StringRef(buf, 8); 230 } 231 232 void WriteHeader(uint64_t SectionDataSize, 233 unsigned NumberOfSections); 234 235 void WriteSymbolEntry(MCDataFragment *SymtabF, 236 MCDataFragment *ShndxF, 237 uint64_t name, uint8_t info, 238 uint64_t value, uint64_t size, 239 uint8_t other, uint32_t shndx, 240 bool Reserved); 241 242 void WriteSymbol(MCDataFragment *SymtabF, MCDataFragment *ShndxF, 243 ELFSymbolData &MSD, 244 const MCAsmLayout &Layout); 245 246 typedef DenseMap<const MCSectionELF*, uint32_t> SectionIndexMapTy; 247 void WriteSymbolTable(MCDataFragment *SymtabF, 248 MCDataFragment *ShndxF, 249 const MCAssembler &Asm, 250 const MCAsmLayout &Layout, 251 const SectionIndexMapTy &SectionIndexMap); 252 253 virtual void RecordRelocation(const MCAssembler &Asm, 254 const MCAsmLayout &Layout, 255 const MCFragment *Fragment, 256 const MCFixup &Fixup, 257 MCValue Target, uint64_t &FixedValue); 258 259 uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm, 260 const MCSymbol *S); 261 262 // Map from a group section to the signature symbol 263 typedef DenseMap<const MCSectionELF*, const MCSymbol*> GroupMapTy; 264 // Map from a signature symbol to the group section 265 typedef DenseMap<const MCSymbol*, const MCSectionELF*> RevGroupMapTy; 266 // Map from a section to the section with the relocations 267 typedef DenseMap<const MCSectionELF*, const MCSectionELF*> RelMapTy; 268 // Map from a section to its offset 269 typedef DenseMap<const MCSectionELF*, uint64_t> SectionOffsetMapTy; 270 271 /// ComputeSymbolTable - Compute the symbol table data 272 /// 273 /// \param StringTable [out] - The string table data. 274 /// \param StringIndexMap [out] - Map from symbol names to offsets in the 275 /// string table. 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(uint64_t SectionDataSize, 372 unsigned NumberOfSections) { 373 // ELF Header 374 // ---------- 375 // 376 // Note 377 // ---- 378 // emitWord method behaves differently for ELF32 and ELF64, writing 379 // 4 bytes in the former and 8 in the latter. 380 381 Write8(0x7f); // e_ident[EI_MAG0] 382 Write8('E'); // e_ident[EI_MAG1] 383 Write8('L'); // e_ident[EI_MAG2] 384 Write8('F'); // e_ident[EI_MAG3] 385 386 Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS] 387 388 // e_ident[EI_DATA] 389 Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB); 390 391 Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION] 392 // e_ident[EI_OSABI] 393 Write8(TargetObjectWriter->getOSABI()); 394 Write8(0); // e_ident[EI_ABIVERSION] 395 396 WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD); 397 398 Write16(ELF::ET_REL); // e_type 399 400 Write16(TargetObjectWriter->getEMachine()); // e_machine = target 401 402 Write32(ELF::EV_CURRENT); // e_version 403 WriteWord(0); // e_entry, no entry point in .o file 404 WriteWord(0); // e_phoff, no program header for .o 405 WriteWord(SectionDataSize + (is64Bit() ? sizeof(ELF::Elf64_Ehdr) : 406 sizeof(ELF::Elf32_Ehdr))); // e_shoff = sec hdr table off in bytes 407 408 // e_flags = whatever the target wants 409 Write32(getEFlags()); 410 411 // e_ehsize = ELF header size 412 Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr)); 413 414 Write16(0); // e_phentsize = prog header entry size 415 Write16(0); // e_phnum = # prog header entries = 0 416 417 // e_shentsize = Section header entry size 418 Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr)); 419 420 // e_shnum = # of section header ents 421 if (NumberOfSections >= ELF::SHN_LORESERVE) 422 Write16(ELF::SHN_UNDEF); 423 else 424 Write16(NumberOfSections); 425 426 // e_shstrndx = Section # of '.shstrtab' 427 if (ShstrtabIndex >= ELF::SHN_LORESERVE) 428 Write16(ELF::SHN_XINDEX); 429 else 430 Write16(ShstrtabIndex); 431 } 432 433 void ELFObjectWriter::WriteSymbolEntry(MCDataFragment *SymtabF, 434 MCDataFragment *ShndxF, 435 uint64_t name, 436 uint8_t info, uint64_t value, 437 uint64_t size, uint8_t other, 438 uint32_t shndx, 439 bool Reserved) { 440 if (ShndxF) { 441 if (shndx >= ELF::SHN_LORESERVE && !Reserved) 442 String32(*ShndxF, shndx); 443 else 444 String32(*ShndxF, 0); 445 } 446 447 uint16_t Index = (shndx >= ELF::SHN_LORESERVE && !Reserved) ? 448 uint16_t(ELF::SHN_XINDEX) : shndx; 449 450 if (is64Bit()) { 451 String32(*SymtabF, name); // st_name 452 String8(*SymtabF, info); // st_info 453 String8(*SymtabF, other); // st_other 454 String16(*SymtabF, Index); // st_shndx 455 String64(*SymtabF, value); // st_value 456 String64(*SymtabF, size); // st_size 457 } else { 458 String32(*SymtabF, name); // st_name 459 String32(*SymtabF, value); // st_value 460 String32(*SymtabF, size); // st_size 461 String8(*SymtabF, info); // st_info 462 String8(*SymtabF, other); // st_other 463 String16(*SymtabF, Index); // st_shndx 464 } 465 } 466 467 uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &Data, 468 const MCAsmLayout &Layout) { 469 if (Data.isCommon() && Data.isExternal()) 470 return Data.getCommonAlignment(); 471 472 const MCSymbol &Symbol = Data.getSymbol(); 473 474 if (Symbol.isAbsolute() && Symbol.isVariable()) { 475 if (const MCExpr *Value = Symbol.getVariableValue()) { 476 int64_t IntValue; 477 if (Value->EvaluateAsAbsolute(IntValue, Layout)) 478 return (uint64_t)IntValue; 479 } 480 } 481 482 if (!Symbol.isInSection()) 483 return 0; 484 485 486 if (Data.getFragment()) { 487 if (Data.getFlags() & ELF_Other_ThumbFunc) 488 return Layout.getSymbolOffset(&Data)+1; 489 else 490 return Layout.getSymbolOffset(&Data); 491 } 492 493 return 0; 494 } 495 496 void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm, 497 const MCAsmLayout &Layout) { 498 // The presence of symbol versions causes undefined symbols and 499 // versions declared with @@@ to be renamed. 500 501 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(), 502 ie = Asm.symbol_end(); it != ie; ++it) { 503 const MCSymbol &Alias = it->getSymbol(); 504 const MCSymbol &Symbol = Alias.AliasedSymbol(); 505 MCSymbolData &SD = Asm.getSymbolData(Symbol); 506 507 // Not an alias. 508 if (&Symbol == &Alias) 509 continue; 510 511 StringRef AliasName = Alias.getName(); 512 size_t Pos = AliasName.find('@'); 513 if (Pos == StringRef::npos) 514 continue; 515 516 // Aliases defined with .symvar copy the binding from the symbol they alias. 517 // This is the first place we are able to copy this information. 518 it->setExternal(SD.isExternal()); 519 MCELF::SetBinding(*it, MCELF::GetBinding(SD)); 520 521 StringRef Rest = AliasName.substr(Pos); 522 if (!Symbol.isUndefined() && !Rest.startswith("@@@")) 523 continue; 524 525 // FIXME: produce a better error message. 526 if (Symbol.isUndefined() && Rest.startswith("@@") && 527 !Rest.startswith("@@@")) 528 report_fatal_error("A @@ version cannot be undefined"); 529 530 Renames.insert(std::make_pair(&Symbol, &Alias)); 531 } 532 } 533 534 void ELFObjectWriter::WriteSymbol(MCDataFragment *SymtabF, 535 MCDataFragment *ShndxF, 536 ELFSymbolData &MSD, 537 const MCAsmLayout &Layout) { 538 MCSymbolData &OrigData = *MSD.SymbolData; 539 MCSymbolData &Data = 540 Layout.getAssembler().getSymbolData(OrigData.getSymbol().AliasedSymbol()); 541 542 bool IsReserved = Data.isCommon() || Data.getSymbol().isAbsolute() || 543 Data.getSymbol().isVariable(); 544 545 uint8_t Binding = MCELF::GetBinding(OrigData); 546 uint8_t Visibility = MCELF::GetVisibility(OrigData); 547 uint8_t Type = MCELF::GetType(Data); 548 549 uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift); 550 uint8_t Other = Visibility; 551 552 uint64_t Value = SymbolValue(Data, Layout); 553 uint64_t Size = 0; 554 555 assert(!(Data.isCommon() && !Data.isExternal())); 556 557 const MCExpr *ESize = Data.getSize(); 558 if (ESize) { 559 int64_t Res; 560 if (!ESize->EvaluateAsAbsolute(Res, Layout)) 561 report_fatal_error("Size expression must be absolute."); 562 Size = Res; 563 } 564 565 // Write out the symbol table entry 566 WriteSymbolEntry(SymtabF, ShndxF, MSD.StringIndex, Info, Value, 567 Size, Other, MSD.SectionIndex, IsReserved); 568 } 569 570 void ELFObjectWriter::WriteSymbolTable(MCDataFragment *SymtabF, 571 MCDataFragment *ShndxF, 572 const MCAssembler &Asm, 573 const MCAsmLayout &Layout, 574 const SectionIndexMapTy &SectionIndexMap) { 575 // The string table must be emitted first because we need the index 576 // into the string table for all the symbol names. 577 assert(StringTable.size() && "Missing string table"); 578 579 // FIXME: Make sure the start of the symbol table is aligned. 580 581 // The first entry is the undefined symbol entry. 582 WriteSymbolEntry(SymtabF, ShndxF, 0, 0, 0, 0, 0, 0, false); 583 584 // Write the symbol table entries. 585 LastLocalSymbolIndex = LocalSymbolData.size() + 1; 586 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) { 587 ELFSymbolData &MSD = LocalSymbolData[i]; 588 WriteSymbol(SymtabF, ShndxF, MSD, Layout); 589 } 590 591 // Write out a symbol table entry for each regular section. 592 for (MCAssembler::const_iterator i = Asm.begin(), e = Asm.end(); i != e; 593 ++i) { 594 const MCSectionELF &Section = 595 static_cast<const MCSectionELF&>(i->getSection()); 596 if (Section.getType() == ELF::SHT_RELA || 597 Section.getType() == ELF::SHT_REL || 598 Section.getType() == ELF::SHT_STRTAB || 599 Section.getType() == ELF::SHT_SYMTAB || 600 Section.getType() == ELF::SHT_SYMTAB_SHNDX) 601 continue; 602 WriteSymbolEntry(SymtabF, ShndxF, 0, ELF::STT_SECTION, 0, 0, 603 ELF::STV_DEFAULT, SectionIndexMap.lookup(&Section), 604 false); 605 LastLocalSymbolIndex++; 606 } 607 608 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) { 609 ELFSymbolData &MSD = ExternalSymbolData[i]; 610 MCSymbolData &Data = *MSD.SymbolData; 611 assert(((Data.getFlags() & ELF_STB_Global) || 612 (Data.getFlags() & ELF_STB_Weak)) && 613 "External symbol requires STB_GLOBAL or STB_WEAK flag"); 614 WriteSymbol(SymtabF, ShndxF, MSD, Layout); 615 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL) 616 LastLocalSymbolIndex++; 617 } 618 619 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) { 620 ELFSymbolData &MSD = UndefinedSymbolData[i]; 621 MCSymbolData &Data = *MSD.SymbolData; 622 WriteSymbol(SymtabF, ShndxF, MSD, Layout); 623 if (MCELF::GetBinding(Data) == ELF::STB_LOCAL) 624 LastLocalSymbolIndex++; 625 } 626 } 627 628 const MCSymbol *ELFObjectWriter::SymbolToReloc(const MCAssembler &Asm, 629 const MCValue &Target, 630 const MCFragment &F, 631 const MCFixup &Fixup, 632 bool IsPCRel) const { 633 const MCSymbol &Symbol = Target.getSymA()->getSymbol(); 634 const MCSymbol &ASymbol = Symbol.AliasedSymbol(); 635 const MCSymbol *Renamed = Renames.lookup(&Symbol); 636 const MCSymbolData &SD = Asm.getSymbolData(Symbol); 637 638 if (ASymbol.isUndefined()) { 639 if (Renamed) 640 return Renamed; 641 return &ASymbol; 642 } 643 644 if (SD.isExternal()) { 645 if (Renamed) 646 return Renamed; 647 return &Symbol; 648 } 649 650 const MCSectionELF &Section = 651 static_cast<const MCSectionELF&>(ASymbol.getSection()); 652 const SectionKind secKind = Section.getKind(); 653 654 if (secKind.isBSS()) 655 return ExplicitRelSym(Asm, Target, F, Fixup, IsPCRel); 656 657 if (secKind.isThreadLocal()) { 658 if (Renamed) 659 return Renamed; 660 return &Symbol; 661 } 662 663 MCSymbolRefExpr::VariantKind Kind = Target.getSymA()->getKind(); 664 const MCSectionELF &Sec2 = 665 static_cast<const MCSectionELF&>(F.getParent()->getSection()); 666 667 if (&Sec2 != &Section && 668 (Kind == MCSymbolRefExpr::VK_PLT || 669 Kind == MCSymbolRefExpr::VK_GOTPCREL || 670 Kind == MCSymbolRefExpr::VK_GOTOFF)) { 671 if (Renamed) 672 return Renamed; 673 return &Symbol; 674 } 675 676 if (Section.getFlags() & ELF::SHF_MERGE) { 677 if (Target.getConstant() == 0) 678 return ExplicitRelSym(Asm, Target, F, Fixup, IsPCRel); 679 if (Renamed) 680 return Renamed; 681 return &Symbol; 682 } 683 684 return ExplicitRelSym(Asm, Target, F, Fixup, IsPCRel); 685 686 } 687 688 689 void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm, 690 const MCAsmLayout &Layout, 691 const MCFragment *Fragment, 692 const MCFixup &Fixup, 693 MCValue Target, 694 uint64_t &FixedValue) { 695 int64_t Addend = 0; 696 int Index = 0; 697 int64_t Value = Target.getConstant(); 698 const MCSymbol *RelocSymbol = NULL; 699 700 bool IsPCRel = isFixupKindPCRel(Asm, Fixup.getKind()); 701 if (!Target.isAbsolute()) { 702 const MCSymbol &Symbol = Target.getSymA()->getSymbol(); 703 const MCSymbol &ASymbol = Symbol.AliasedSymbol(); 704 RelocSymbol = SymbolToReloc(Asm, Target, *Fragment, Fixup, IsPCRel); 705 706 if (const MCSymbolRefExpr *RefB = Target.getSymB()) { 707 const MCSymbol &SymbolB = RefB->getSymbol(); 708 MCSymbolData &SDB = Asm.getSymbolData(SymbolB); 709 IsPCRel = true; 710 711 // Offset of the symbol in the section 712 int64_t a = Layout.getSymbolOffset(&SDB); 713 714 // Offset of the relocation in the section 715 int64_t b = Layout.getFragmentOffset(Fragment) + Fixup.getOffset(); 716 Value += b - a; 717 } 718 719 if (!RelocSymbol) { 720 MCSymbolData &SD = Asm.getSymbolData(ASymbol); 721 MCFragment *F = SD.getFragment(); 722 723 Index = F->getParent()->getOrdinal() + 1; 724 725 // Offset of the symbol in the section 726 Value += Layout.getSymbolOffset(&SD); 727 } else { 728 if (Asm.getSymbolData(Symbol).getFlags() & ELF_Other_Weakref) 729 WeakrefUsedInReloc.insert(RelocSymbol); 730 else 731 UsedInReloc.insert(RelocSymbol); 732 Index = -1; 733 } 734 Addend = Value; 735 // Compensate for the addend on i386. 736 if (is64Bit()) 737 Value = 0; 738 } 739 740 FixedValue = Value; 741 unsigned Type = GetRelocType(Target, Fixup, IsPCRel, 742 (RelocSymbol != 0), Addend); 743 MCSymbolRefExpr::VariantKind Modifier = Target.isAbsolute() ? 744 MCSymbolRefExpr::VK_None : Target.getSymA()->getKind(); 745 if (RelocNeedsGOT(Modifier)) 746 NeedsGOT = true; 747 748 uint64_t RelocOffset = Layout.getFragmentOffset(Fragment) + 749 Fixup.getOffset(); 750 751 // FIXME: no tests cover this. Is adjustFixupOffset dead code? 752 TargetObjectWriter->adjustFixupOffset(Fixup, RelocOffset); 753 754 if (!hasRelocationAddend()) 755 Addend = 0; 756 757 if (is64Bit()) 758 assert(isInt<64>(Addend)); 759 else 760 assert(isInt<32>(Addend)); 761 762 ELFRelocationEntry ERE(RelocOffset, Index, Type, RelocSymbol, Addend, Fixup); 763 Relocations[Fragment->getParent()].push_back(ERE); 764 } 765 766 767 uint64_t 768 ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm, 769 const MCSymbol *S) { 770 MCSymbolData &SD = Asm.getSymbolData(*S); 771 return SD.getIndex(); 772 } 773 774 bool ELFObjectWriter::isInSymtab(const MCAssembler &Asm, 775 const MCSymbolData &Data, 776 bool Used, bool Renamed) { 777 if (Data.getFlags() & ELF_Other_Weakref) 778 return false; 779 780 if (Used) 781 return true; 782 783 if (Renamed) 784 return false; 785 786 const MCSymbol &Symbol = Data.getSymbol(); 787 788 if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_") 789 return true; 790 791 const MCSymbol &A = Symbol.AliasedSymbol(); 792 if (Symbol.isVariable() && !A.isVariable() && A.isUndefined()) 793 return false; 794 795 bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL; 796 if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal) 797 return false; 798 799 if (!Asm.isSymbolLinkerVisible(Symbol) && !Symbol.isUndefined()) 800 return false; 801 802 if (Symbol.isTemporary()) 803 return false; 804 805 return true; 806 } 807 808 bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isSignature, 809 bool isUsedInReloc) { 810 if (Data.isExternal()) 811 return false; 812 813 const MCSymbol &Symbol = Data.getSymbol(); 814 const MCSymbol &RefSymbol = Symbol.AliasedSymbol(); 815 816 if (RefSymbol.isUndefined() && !RefSymbol.isVariable()) { 817 if (isSignature && !isUsedInReloc) 818 return true; 819 820 return false; 821 } 822 823 return true; 824 } 825 826 void ELFObjectWriter::ComputeIndexMap(MCAssembler &Asm, 827 SectionIndexMapTy &SectionIndexMap, 828 const RelMapTy &RelMap) { 829 unsigned Index = 1; 830 for (MCAssembler::iterator it = Asm.begin(), 831 ie = Asm.end(); it != ie; ++it) { 832 const MCSectionELF &Section = 833 static_cast<const MCSectionELF &>(it->getSection()); 834 if (Section.getType() != ELF::SHT_GROUP) 835 continue; 836 SectionIndexMap[&Section] = Index++; 837 } 838 839 for (MCAssembler::iterator it = Asm.begin(), 840 ie = Asm.end(); it != ie; ++it) { 841 const MCSectionELF &Section = 842 static_cast<const MCSectionELF &>(it->getSection()); 843 if (Section.getType() == ELF::SHT_GROUP || 844 Section.getType() == ELF::SHT_REL || 845 Section.getType() == ELF::SHT_RELA) 846 continue; 847 SectionIndexMap[&Section] = Index++; 848 const MCSectionELF *RelSection = RelMap.lookup(&Section); 849 if (RelSection) 850 SectionIndexMap[RelSection] = Index++; 851 } 852 } 853 854 void ELFObjectWriter::ComputeSymbolTable(MCAssembler &Asm, 855 const SectionIndexMapTy &SectionIndexMap, 856 RevGroupMapTy RevGroupMap, 857 unsigned NumRegularSections) { 858 // FIXME: Is this the correct place to do this? 859 // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed? 860 if (NeedsGOT) { 861 llvm::StringRef Name = "_GLOBAL_OFFSET_TABLE_"; 862 MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name); 863 MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym); 864 Data.setExternal(true); 865 MCELF::SetBinding(Data, ELF::STB_GLOBAL); 866 } 867 868 // Index 0 is always the empty string. 869 StringMap<uint64_t> StringIndexMap; 870 StringTable += '\x00'; 871 872 // FIXME: We could optimize suffixes in strtab in the same way we 873 // optimize them in shstrtab. 874 875 // Add the data for the symbols. 876 for (MCAssembler::symbol_iterator it = Asm.symbol_begin(), 877 ie = Asm.symbol_end(); it != ie; ++it) { 878 const MCSymbol &Symbol = it->getSymbol(); 879 880 bool Used = UsedInReloc.count(&Symbol); 881 bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol); 882 bool isSignature = RevGroupMap.count(&Symbol); 883 884 if (!isInSymtab(Asm, *it, 885 Used || WeakrefUsed || isSignature, 886 Renames.count(&Symbol))) 887 continue; 888 889 ELFSymbolData MSD; 890 MSD.SymbolData = it; 891 const MCSymbol &RefSymbol = Symbol.AliasedSymbol(); 892 893 // Undefined symbols are global, but this is the first place we 894 // are able to set it. 895 bool Local = isLocal(*it, isSignature, Used); 896 if (!Local && MCELF::GetBinding(*it) == ELF::STB_LOCAL) { 897 MCSymbolData &SD = Asm.getSymbolData(RefSymbol); 898 MCELF::SetBinding(*it, ELF::STB_GLOBAL); 899 MCELF::SetBinding(SD, ELF::STB_GLOBAL); 900 } 901 902 if (RefSymbol.isUndefined() && !Used && WeakrefUsed) 903 MCELF::SetBinding(*it, ELF::STB_WEAK); 904 905 if (it->isCommon()) { 906 assert(!Local); 907 MSD.SectionIndex = ELF::SHN_COMMON; 908 } else if (Symbol.isAbsolute() || RefSymbol.isVariable()) { 909 MSD.SectionIndex = ELF::SHN_ABS; 910 } else if (RefSymbol.isUndefined()) { 911 if (isSignature && !Used) 912 MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap[&Symbol]); 913 else 914 MSD.SectionIndex = ELF::SHN_UNDEF; 915 } else { 916 const MCSectionELF &Section = 917 static_cast<const MCSectionELF&>(RefSymbol.getSection()); 918 MSD.SectionIndex = SectionIndexMap.lookup(&Section); 919 if (MSD.SectionIndex >= ELF::SHN_LORESERVE) 920 NeedsSymtabShndx = true; 921 assert(MSD.SectionIndex && "Invalid section index!"); 922 } 923 924 // The @@@ in symbol version is replaced with @ in undefined symbols and 925 // @@ in defined ones. 926 StringRef Name = Symbol.getName(); 927 SmallString<32> Buf; 928 929 size_t Pos = Name.find("@@@"); 930 if (Pos != StringRef::npos) { 931 Buf += Name.substr(0, Pos); 932 unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1; 933 Buf += Name.substr(Pos + Skip); 934 Name = Buf; 935 } 936 937 uint64_t &Entry = StringIndexMap[Name]; 938 if (!Entry) { 939 Entry = StringTable.size(); 940 StringTable += Name; 941 StringTable += '\x00'; 942 } 943 MSD.StringIndex = Entry; 944 if (MSD.SectionIndex == ELF::SHN_UNDEF) 945 UndefinedSymbolData.push_back(MSD); 946 else if (Local) 947 LocalSymbolData.push_back(MSD); 948 else 949 ExternalSymbolData.push_back(MSD); 950 } 951 952 // Symbols are required to be in lexicographic order. 953 array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end()); 954 array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end()); 955 array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end()); 956 957 // Set the symbol indices. Local symbols must come before all other 958 // symbols with non-local bindings. 959 unsigned Index = 1; 960 for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) 961 LocalSymbolData[i].SymbolData->setIndex(Index++); 962 963 Index += NumRegularSections; 964 965 for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) 966 ExternalSymbolData[i].SymbolData->setIndex(Index++); 967 for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) 968 UndefinedSymbolData[i].SymbolData->setIndex(Index++); 969 970 if (NumRegularSections > ELF::SHN_LORESERVE) 971 NeedsSymtabShndx = true; 972 } 973 974 void ELFObjectWriter::CreateRelocationSections(MCAssembler &Asm, 975 MCAsmLayout &Layout, 976 RelMapTy &RelMap) { 977 for (MCAssembler::const_iterator it = Asm.begin(), 978 ie = Asm.end(); it != ie; ++it) { 979 const MCSectionData &SD = *it; 980 if (Relocations[&SD].empty()) 981 continue; 982 983 MCContext &Ctx = Asm.getContext(); 984 const MCSectionELF &Section = 985 static_cast<const MCSectionELF&>(SD.getSection()); 986 987 const StringRef SectionName = Section.getSectionName(); 988 std::string RelaSectionName = hasRelocationAddend() ? ".rela" : ".rel"; 989 RelaSectionName += SectionName; 990 991 unsigned EntrySize; 992 if (hasRelocationAddend()) 993 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela); 994 else 995 EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel); 996 997 const MCSectionELF *RelaSection = 998 Ctx.getELFSection(RelaSectionName, hasRelocationAddend() ? 999 ELF::SHT_RELA : ELF::SHT_REL, 0, 1000 SectionKind::getReadOnly(), 1001 EntrySize, ""); 1002 RelMap[&Section] = RelaSection; 1003 Asm.getOrCreateSectionData(*RelaSection); 1004 } 1005 } 1006 1007 void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout, 1008 const RelMapTy &RelMap) { 1009 for (MCAssembler::const_iterator it = Asm.begin(), 1010 ie = Asm.end(); it != ie; ++it) { 1011 const MCSectionData &SD = *it; 1012 const MCSectionELF &Section = 1013 static_cast<const MCSectionELF&>(SD.getSection()); 1014 1015 const MCSectionELF *RelaSection = RelMap.lookup(&Section); 1016 if (!RelaSection) 1017 continue; 1018 MCSectionData &RelaSD = Asm.getOrCreateSectionData(*RelaSection); 1019 RelaSD.setAlignment(is64Bit() ? 8 : 4); 1020 1021 MCDataFragment *F = new MCDataFragment(&RelaSD); 1022 WriteRelocationsFragment(Asm, F, &*it); 1023 } 1024 } 1025 1026 void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type, 1027 uint64_t Flags, uint64_t Address, 1028 uint64_t Offset, uint64_t Size, 1029 uint32_t Link, uint32_t Info, 1030 uint64_t Alignment, 1031 uint64_t EntrySize) { 1032 Write32(Name); // sh_name: index into string table 1033 Write32(Type); // sh_type 1034 WriteWord(Flags); // sh_flags 1035 WriteWord(Address); // sh_addr 1036 WriteWord(Offset); // sh_offset 1037 WriteWord(Size); // sh_size 1038 Write32(Link); // sh_link 1039 Write32(Info); // sh_info 1040 WriteWord(Alignment); // sh_addralign 1041 WriteWord(EntrySize); // sh_entsize 1042 } 1043 1044 void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm, 1045 MCDataFragment *F, 1046 const MCSectionData *SD) { 1047 std::vector<ELFRelocationEntry> &Relocs = Relocations[SD]; 1048 1049 // Sort the relocation entries. Most targets just sort by r_offset, but some 1050 // (e.g., MIPS) have additional constraints. 1051 TargetObjectWriter->sortRelocs(Asm, Relocs); 1052 1053 for (unsigned i = 0, e = Relocs.size(); i != e; ++i) { 1054 ELFRelocationEntry entry = Relocs[e - i - 1]; 1055 1056 if (!entry.Index) 1057 ; 1058 else if (entry.Index < 0) 1059 entry.Index = getSymbolIndexInSymbolTable(Asm, entry.Symbol); 1060 else 1061 entry.Index += LocalSymbolData.size(); 1062 if (is64Bit()) { 1063 String64(*F, entry.r_offset); 1064 1065 struct ELF::Elf64_Rela ERE64; 1066 ERE64.setSymbolAndType(entry.Index, entry.Type); 1067 String64(*F, ERE64.r_info); 1068 1069 if (hasRelocationAddend()) 1070 String64(*F, entry.r_addend); 1071 } else { 1072 String32(*F, entry.r_offset); 1073 1074 struct ELF::Elf32_Rela ERE32; 1075 ERE32.setSymbolAndType(entry.Index, entry.Type); 1076 String32(*F, ERE32.r_info); 1077 1078 if (hasRelocationAddend()) 1079 String32(*F, entry.r_addend); 1080 } 1081 } 1082 } 1083 1084 static int compareBySuffix(const void *a, const void *b) { 1085 const MCSectionELF *secA = *static_cast<const MCSectionELF* const *>(a); 1086 const MCSectionELF *secB = *static_cast<const MCSectionELF* const *>(b); 1087 const StringRef &NameA = secA->getSectionName(); 1088 const StringRef &NameB = secB->getSectionName(); 1089 const unsigned sizeA = NameA.size(); 1090 const unsigned sizeB = NameB.size(); 1091 const unsigned len = std::min(sizeA, sizeB); 1092 for (unsigned int i = 0; i < len; ++i) { 1093 char ca = NameA[sizeA - i - 1]; 1094 char cb = NameB[sizeB - i - 1]; 1095 if (ca != cb) 1096 return cb - ca; 1097 } 1098 1099 return sizeB - sizeA; 1100 } 1101 1102 void ELFObjectWriter::CreateMetadataSections(MCAssembler &Asm, 1103 MCAsmLayout &Layout, 1104 SectionIndexMapTy &SectionIndexMap, 1105 const RelMapTy &RelMap) { 1106 MCContext &Ctx = Asm.getContext(); 1107 MCDataFragment *F; 1108 1109 unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32; 1110 1111 // We construct .shstrtab, .symtab and .strtab in this order to match gnu as. 1112 const MCSectionELF *ShstrtabSection = 1113 Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0, 1114 SectionKind::getReadOnly()); 1115 MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection); 1116 ShstrtabSD.setAlignment(1); 1117 1118 const MCSectionELF *SymtabSection = 1119 Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, 1120 SectionKind::getReadOnly(), 1121 EntrySize, ""); 1122 MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection); 1123 SymtabSD.setAlignment(is64Bit() ? 8 : 4); 1124 1125 MCSectionData *SymtabShndxSD = NULL; 1126 1127 if (NeedsSymtabShndx) { 1128 const MCSectionELF *SymtabShndxSection = 1129 Ctx.getELFSection(".symtab_shndx", ELF::SHT_SYMTAB_SHNDX, 0, 1130 SectionKind::getReadOnly(), 4, ""); 1131 SymtabShndxSD = &Asm.getOrCreateSectionData(*SymtabShndxSection); 1132 SymtabShndxSD->setAlignment(4); 1133 } 1134 1135 const MCSectionELF *StrtabSection; 1136 StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0, 1137 SectionKind::getReadOnly()); 1138 MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection); 1139 StrtabSD.setAlignment(1); 1140 1141 ComputeIndexMap(Asm, SectionIndexMap, RelMap); 1142 1143 ShstrtabIndex = SectionIndexMap.lookup(ShstrtabSection); 1144 SymbolTableIndex = SectionIndexMap.lookup(SymtabSection); 1145 StringTableIndex = SectionIndexMap.lookup(StrtabSection); 1146 1147 // Symbol table 1148 F = new MCDataFragment(&SymtabSD); 1149 MCDataFragment *ShndxF = NULL; 1150 if (NeedsSymtabShndx) { 1151 ShndxF = new MCDataFragment(SymtabShndxSD); 1152 } 1153 WriteSymbolTable(F, ShndxF, Asm, Layout, SectionIndexMap); 1154 1155 F = new MCDataFragment(&StrtabSD); 1156 F->getContents().append(StringTable.begin(), StringTable.end()); 1157 1158 F = new MCDataFragment(&ShstrtabSD); 1159 1160 std::vector<const MCSectionELF*> Sections; 1161 for (MCAssembler::const_iterator it = Asm.begin(), 1162 ie = Asm.end(); it != ie; ++it) { 1163 const MCSectionELF &Section = 1164 static_cast<const MCSectionELF&>(it->getSection()); 1165 Sections.push_back(&Section); 1166 } 1167 array_pod_sort(Sections.begin(), Sections.end(), compareBySuffix); 1168 1169 // Section header string table. 1170 // 1171 // The first entry of a string table holds a null character so skip 1172 // section 0. 1173 uint64_t Index = 1; 1174 F->getContents() += '\x00'; 1175 1176 for (unsigned int I = 0, E = Sections.size(); I != E; ++I) { 1177 const MCSectionELF &Section = *Sections[I]; 1178 1179 StringRef Name = Section.getSectionName(); 1180 if (I != 0) { 1181 StringRef PreviousName = Sections[I - 1]->getSectionName(); 1182 if (PreviousName.endswith(Name)) { 1183 SectionStringTableIndex[&Section] = Index - Name.size() - 1; 1184 continue; 1185 } 1186 } 1187 // Remember the index into the string table so we can write it 1188 // into the sh_name field of the section header table. 1189 SectionStringTableIndex[&Section] = Index; 1190 1191 Index += Name.size() + 1; 1192 F->getContents() += Name; 1193 F->getContents() += '\x00'; 1194 } 1195 } 1196 1197 void ELFObjectWriter::CreateIndexedSections(MCAssembler &Asm, 1198 MCAsmLayout &Layout, 1199 GroupMapTy &GroupMap, 1200 RevGroupMapTy &RevGroupMap, 1201 SectionIndexMapTy &SectionIndexMap, 1202 const RelMapTy &RelMap) { 1203 // Create the .note.GNU-stack section if needed. 1204 MCContext &Ctx = Asm.getContext(); 1205 if (Asm.getNoExecStack()) { 1206 const MCSectionELF *GnuStackSection = 1207 Ctx.getELFSection(".note.GNU-stack", ELF::SHT_PROGBITS, 0, 1208 SectionKind::getReadOnly()); 1209 Asm.getOrCreateSectionData(*GnuStackSection); 1210 } 1211 1212 // Build the groups 1213 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end(); 1214 it != ie; ++it) { 1215 const MCSectionELF &Section = 1216 static_cast<const MCSectionELF&>(it->getSection()); 1217 if (!(Section.getFlags() & ELF::SHF_GROUP)) 1218 continue; 1219 1220 const MCSymbol *SignatureSymbol = Section.getGroup(); 1221 Asm.getOrCreateSymbolData(*SignatureSymbol); 1222 const MCSectionELF *&Group = RevGroupMap[SignatureSymbol]; 1223 if (!Group) { 1224 Group = Ctx.CreateELFGroupSection(); 1225 MCSectionData &Data = Asm.getOrCreateSectionData(*Group); 1226 Data.setAlignment(4); 1227 MCDataFragment *F = new MCDataFragment(&Data); 1228 String32(*F, ELF::GRP_COMDAT); 1229 } 1230 GroupMap[Group] = SignatureSymbol; 1231 } 1232 1233 ComputeIndexMap(Asm, SectionIndexMap, RelMap); 1234 1235 // Add sections to the groups 1236 for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end(); 1237 it != ie; ++it) { 1238 const MCSectionELF &Section = 1239 static_cast<const MCSectionELF&>(it->getSection()); 1240 if (!(Section.getFlags() & ELF::SHF_GROUP)) 1241 continue; 1242 const MCSectionELF *Group = RevGroupMap[Section.getGroup()]; 1243 MCSectionData &Data = Asm.getOrCreateSectionData(*Group); 1244 // FIXME: we could use the previous fragment 1245 MCDataFragment *F = new MCDataFragment(&Data); 1246 unsigned Index = SectionIndexMap.lookup(&Section); 1247 String32(*F, Index); 1248 } 1249 } 1250 1251 void ELFObjectWriter::WriteSection(MCAssembler &Asm, 1252 const SectionIndexMapTy &SectionIndexMap, 1253 uint32_t GroupSymbolIndex, 1254 uint64_t Offset, uint64_t Size, 1255 uint64_t Alignment, 1256 const MCSectionELF &Section) { 1257 uint64_t sh_link = 0; 1258 uint64_t sh_info = 0; 1259 1260 switch(Section.getType()) { 1261 case ELF::SHT_DYNAMIC: 1262 sh_link = SectionStringTableIndex[&Section]; 1263 sh_info = 0; 1264 break; 1265 1266 case ELF::SHT_REL: 1267 case ELF::SHT_RELA: { 1268 const MCSectionELF *SymtabSection; 1269 const MCSectionELF *InfoSection; 1270 SymtabSection = Asm.getContext().getELFSection(".symtab", ELF::SHT_SYMTAB, 1271 0, 1272 SectionKind::getReadOnly()); 1273 sh_link = SectionIndexMap.lookup(SymtabSection); 1274 assert(sh_link && ".symtab not found"); 1275 1276 // Remove ".rel" and ".rela" prefixes. 1277 unsigned SecNameLen = (Section.getType() == ELF::SHT_REL) ? 4 : 5; 1278 StringRef SectionName = Section.getSectionName().substr(SecNameLen); 1279 1280 InfoSection = Asm.getContext().getELFSection(SectionName, 1281 ELF::SHT_PROGBITS, 0, 1282 SectionKind::getReadOnly()); 1283 sh_info = SectionIndexMap.lookup(InfoSection); 1284 break; 1285 } 1286 1287 case ELF::SHT_SYMTAB: 1288 case ELF::SHT_DYNSYM: 1289 sh_link = StringTableIndex; 1290 sh_info = LastLocalSymbolIndex; 1291 break; 1292 1293 case ELF::SHT_SYMTAB_SHNDX: 1294 sh_link = SymbolTableIndex; 1295 break; 1296 1297 case ELF::SHT_PROGBITS: 1298 case ELF::SHT_STRTAB: 1299 case ELF::SHT_NOBITS: 1300 case ELF::SHT_NOTE: 1301 case ELF::SHT_NULL: 1302 case ELF::SHT_ARM_ATTRIBUTES: 1303 case ELF::SHT_INIT_ARRAY: 1304 case ELF::SHT_FINI_ARRAY: 1305 case ELF::SHT_PREINIT_ARRAY: 1306 case ELF::SHT_X86_64_UNWIND: 1307 // Nothing to do. 1308 break; 1309 1310 case ELF::SHT_GROUP: 1311 sh_link = SymbolTableIndex; 1312 sh_info = GroupSymbolIndex; 1313 break; 1314 1315 default: 1316 assert(0 && "FIXME: sh_type value not supported!"); 1317 break; 1318 } 1319 1320 WriteSecHdrEntry(SectionStringTableIndex[&Section], Section.getType(), 1321 Section.getFlags(), 0, Offset, Size, sh_link, sh_info, 1322 Alignment, Section.getEntrySize()); 1323 } 1324 1325 bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) { 1326 return SD.getOrdinal() == ~UINT32_C(0) && 1327 !SD.getSection().isVirtualSection(); 1328 } 1329 1330 uint64_t ELFObjectWriter::DataSectionSize(const MCSectionData &SD) { 1331 uint64_t Ret = 0; 1332 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e; 1333 ++i) { 1334 const MCFragment &F = *i; 1335 assert(F.getKind() == MCFragment::FT_Data); 1336 Ret += cast<MCDataFragment>(F).getContents().size(); 1337 } 1338 return Ret; 1339 } 1340 1341 uint64_t ELFObjectWriter::GetSectionFileSize(const MCAsmLayout &Layout, 1342 const MCSectionData &SD) { 1343 if (IsELFMetaDataSection(SD)) 1344 return DataSectionSize(SD); 1345 return Layout.getSectionFileSize(&SD); 1346 } 1347 1348 uint64_t ELFObjectWriter::GetSectionAddressSize(const MCAsmLayout &Layout, 1349 const MCSectionData &SD) { 1350 if (IsELFMetaDataSection(SD)) 1351 return DataSectionSize(SD); 1352 return Layout.getSectionAddressSize(&SD); 1353 } 1354 1355 void ELFObjectWriter::WriteDataSectionData(MCAssembler &Asm, 1356 const MCAsmLayout &Layout, 1357 const MCSectionELF &Section) { 1358 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1359 1360 uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment()); 1361 WriteZeros(Padding); 1362 1363 if (IsELFMetaDataSection(SD)) { 1364 for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e; 1365 ++i) { 1366 const MCFragment &F = *i; 1367 assert(F.getKind() == MCFragment::FT_Data); 1368 WriteBytes(cast<MCDataFragment>(F).getContents().str()); 1369 } 1370 } else { 1371 Asm.writeSectionData(&SD, Layout); 1372 } 1373 } 1374 1375 void ELFObjectWriter::WriteSectionHeader(MCAssembler &Asm, 1376 const GroupMapTy &GroupMap, 1377 const MCAsmLayout &Layout, 1378 const SectionIndexMapTy &SectionIndexMap, 1379 const SectionOffsetMapTy &SectionOffsetMap) { 1380 const unsigned NumSections = Asm.size() + 1; 1381 1382 std::vector<const MCSectionELF*> Sections; 1383 Sections.resize(NumSections - 1); 1384 1385 for (SectionIndexMapTy::const_iterator i= 1386 SectionIndexMap.begin(), e = SectionIndexMap.end(); i != e; ++i) { 1387 const std::pair<const MCSectionELF*, uint32_t> &p = *i; 1388 Sections[p.second - 1] = p.first; 1389 } 1390 1391 // Null section first. 1392 uint64_t FirstSectionSize = 1393 NumSections >= ELF::SHN_LORESERVE ? NumSections : 0; 1394 uint32_t FirstSectionLink = 1395 ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0; 1396 WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0); 1397 1398 for (unsigned i = 0; i < NumSections - 1; ++i) { 1399 const MCSectionELF &Section = *Sections[i]; 1400 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1401 uint32_t GroupSymbolIndex; 1402 if (Section.getType() != ELF::SHT_GROUP) 1403 GroupSymbolIndex = 0; 1404 else 1405 GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm, 1406 GroupMap.lookup(&Section)); 1407 1408 uint64_t Size = GetSectionAddressSize(Layout, SD); 1409 1410 WriteSection(Asm, SectionIndexMap, GroupSymbolIndex, 1411 SectionOffsetMap.lookup(&Section), Size, 1412 SD.getAlignment(), Section); 1413 } 1414 } 1415 1416 void ELFObjectWriter::ComputeSectionOrder(MCAssembler &Asm, 1417 std::vector<const MCSectionELF*> &Sections) { 1418 for (MCAssembler::iterator it = Asm.begin(), 1419 ie = Asm.end(); it != ie; ++it) { 1420 const MCSectionELF &Section = 1421 static_cast<const MCSectionELF &>(it->getSection()); 1422 if (Section.getType() == ELF::SHT_GROUP) 1423 Sections.push_back(&Section); 1424 } 1425 1426 for (MCAssembler::iterator it = Asm.begin(), 1427 ie = Asm.end(); it != ie; ++it) { 1428 const MCSectionELF &Section = 1429 static_cast<const MCSectionELF &>(it->getSection()); 1430 if (Section.getType() != ELF::SHT_GROUP && 1431 Section.getType() != ELF::SHT_REL && 1432 Section.getType() != ELF::SHT_RELA) 1433 Sections.push_back(&Section); 1434 } 1435 1436 for (MCAssembler::iterator it = Asm.begin(), 1437 ie = Asm.end(); it != ie; ++it) { 1438 const MCSectionELF &Section = 1439 static_cast<const MCSectionELF &>(it->getSection()); 1440 if (Section.getType() == ELF::SHT_REL || 1441 Section.getType() == ELF::SHT_RELA) 1442 Sections.push_back(&Section); 1443 } 1444 } 1445 1446 void ELFObjectWriter::WriteObject(MCAssembler &Asm, 1447 const MCAsmLayout &Layout) { 1448 GroupMapTy GroupMap; 1449 RevGroupMapTy RevGroupMap; 1450 SectionIndexMapTy SectionIndexMap; 1451 1452 unsigned NumUserSections = Asm.size(); 1453 1454 DenseMap<const MCSectionELF*, const MCSectionELF*> RelMap; 1455 CreateRelocationSections(Asm, const_cast<MCAsmLayout&>(Layout), RelMap); 1456 1457 const unsigned NumUserAndRelocSections = Asm.size(); 1458 CreateIndexedSections(Asm, const_cast<MCAsmLayout&>(Layout), GroupMap, 1459 RevGroupMap, SectionIndexMap, RelMap); 1460 const unsigned AllSections = Asm.size(); 1461 const unsigned NumIndexedSections = AllSections - NumUserAndRelocSections; 1462 1463 unsigned NumRegularSections = NumUserSections + NumIndexedSections; 1464 1465 // Compute symbol table information. 1466 ComputeSymbolTable(Asm, SectionIndexMap, RevGroupMap, NumRegularSections); 1467 1468 1469 WriteRelocations(Asm, const_cast<MCAsmLayout&>(Layout), RelMap); 1470 1471 CreateMetadataSections(const_cast<MCAssembler&>(Asm), 1472 const_cast<MCAsmLayout&>(Layout), 1473 SectionIndexMap, 1474 RelMap); 1475 1476 uint64_t NaturalAlignment = is64Bit() ? 8 : 4; 1477 uint64_t HeaderSize = is64Bit() ? sizeof(ELF::Elf64_Ehdr) : 1478 sizeof(ELF::Elf32_Ehdr); 1479 uint64_t FileOff = HeaderSize; 1480 1481 std::vector<const MCSectionELF*> Sections; 1482 ComputeSectionOrder(Asm, Sections); 1483 unsigned NumSections = Sections.size(); 1484 SectionOffsetMapTy SectionOffsetMap; 1485 for (unsigned i = 0; i < NumRegularSections + 1; ++i) { 1486 const MCSectionELF &Section = *Sections[i]; 1487 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1488 1489 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment()); 1490 1491 // Remember the offset into the file for this section. 1492 SectionOffsetMap[&Section] = FileOff; 1493 1494 // Get the size of the section in the output file (including padding). 1495 FileOff += GetSectionFileSize(Layout, SD); 1496 } 1497 1498 FileOff = RoundUpToAlignment(FileOff, NaturalAlignment); 1499 1500 const unsigned SectionHeaderOffset = FileOff - HeaderSize; 1501 1502 uint64_t SectionHeaderEntrySize = is64Bit() ? 1503 sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr); 1504 FileOff += (NumSections + 1) * SectionHeaderEntrySize; 1505 1506 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) { 1507 const MCSectionELF &Section = *Sections[i]; 1508 const MCSectionData &SD = Asm.getOrCreateSectionData(Section); 1509 1510 FileOff = RoundUpToAlignment(FileOff, SD.getAlignment()); 1511 1512 // Remember the offset into the file for this section. 1513 SectionOffsetMap[&Section] = FileOff; 1514 1515 // Get the size of the section in the output file (including padding). 1516 FileOff += GetSectionFileSize(Layout, SD); 1517 } 1518 1519 // Write out the ELF header ... 1520 WriteHeader(SectionHeaderOffset, NumSections + 1); 1521 1522 // ... then the regular sections ... 1523 // + because of .shstrtab 1524 for (unsigned i = 0; i < NumRegularSections + 1; ++i) 1525 WriteDataSectionData(Asm, Layout, *Sections[i]); 1526 1527 uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment); 1528 WriteZeros(Padding); 1529 1530 // ... then the section header table ... 1531 WriteSectionHeader(Asm, GroupMap, Layout, SectionIndexMap, 1532 SectionOffsetMap); 1533 1534 // ... and then the remaining sections ... 1535 for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) 1536 WriteDataSectionData(Asm, Layout, *Sections[i]); 1537 } 1538 1539 bool 1540 ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm, 1541 const MCSymbolData &DataA, 1542 const MCFragment &FB, 1543 bool InSet, 1544 bool IsPCRel) const { 1545 if (DataA.getFlags() & ELF_STB_Weak) 1546 return false; 1547 return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl( 1548 Asm, DataA, FB,InSet, IsPCRel); 1549 } 1550 1551 MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW, 1552 raw_ostream &OS, 1553 bool IsLittleEndian) { 1554 return new ELFObjectWriter(MOTW, OS, IsLittleEndian); 1555 } 1556
