//===- lib/MC/ELFObjectWriter.cpp - ELF File Writer -------------------===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// // // This file implements ELF object file writer information. // //===----------------------------------------------------------------------===// #include "llvm/MC/ELFObjectWriter.h" #include "llvm/ADT/SmallPtrSet.h" #include "llvm/ADT/STLExtras.h" #include "llvm/ADT/StringMap.h" #include "llvm/ADT/Twine.h" #include "llvm/MC/MCAssembler.h" #include "llvm/MC/MCAsmLayout.h" #include "llvm/MC/MCContext.h" #include "llvm/MC/MCELFSymbolFlags.h" #include "llvm/MC/MCExpr.h" #include "llvm/MC/MCObjectWriter.h" #include "llvm/MC/MCSectionELF.h" #include "llvm/MC/MCSymbol.h" #include "llvm/MC/MCValue.h" #include "llvm/Support/Debug.h" #include "llvm/Support/ErrorHandling.h" #include "llvm/Support/ELF.h" #include "llvm/Target/TargetAsmBackend.h" #include "../Target/X86/X86FixupKinds.h" #include using namespace llvm; static unsigned GetType(const MCSymbolData &SD) { uint32_t Type = (SD.getFlags() & (0xf << ELF_STT_Shift)) >> ELF_STT_Shift; assert(Type == ELF::STT_NOTYPE || Type == ELF::STT_OBJECT || Type == ELF::STT_FUNC || Type == ELF::STT_SECTION || Type == ELF::STT_FILE || Type == ELF::STT_COMMON || Type == ELF::STT_TLS); return Type; } static unsigned GetBinding(const MCSymbolData &SD) { uint32_t Binding = (SD.getFlags() & (0xf << ELF_STB_Shift)) >> ELF_STB_Shift; assert(Binding == ELF::STB_LOCAL || Binding == ELF::STB_GLOBAL || Binding == ELF::STB_WEAK); return Binding; } static void SetBinding(MCSymbolData &SD, unsigned Binding) { assert(Binding == ELF::STB_LOCAL || Binding == ELF::STB_GLOBAL || Binding == ELF::STB_WEAK); uint32_t OtherFlags = SD.getFlags() & ~(0xf << ELF_STB_Shift); SD.setFlags(OtherFlags | (Binding << ELF_STB_Shift)); } static unsigned GetVisibility(MCSymbolData &SD) { unsigned Visibility = (SD.getFlags() & (0xf << ELF_STV_Shift)) >> ELF_STV_Shift; assert(Visibility == ELF::STV_DEFAULT || Visibility == ELF::STV_INTERNAL || Visibility == ELF::STV_HIDDEN || Visibility == ELF::STV_PROTECTED); return Visibility; } static bool isFixupKindX86PCRel(unsigned Kind) { switch (Kind) { default: return false; case X86::reloc_pcrel_1byte: case X86::reloc_pcrel_4byte: case X86::reloc_riprel_4byte: case X86::reloc_riprel_4byte_movq_load: return true; } } static bool RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) { switch (Variant) { default: return false; case MCSymbolRefExpr::VK_GOT: case MCSymbolRefExpr::VK_PLT: case MCSymbolRefExpr::VK_GOTPCREL: case MCSymbolRefExpr::VK_TPOFF: case MCSymbolRefExpr::VK_TLSGD: case MCSymbolRefExpr::VK_GOTTPOFF: case MCSymbolRefExpr::VK_INDNTPOFF: case MCSymbolRefExpr::VK_NTPOFF: case MCSymbolRefExpr::VK_GOTNTPOFF: case MCSymbolRefExpr::VK_TLSLDM: case MCSymbolRefExpr::VK_DTPOFF: case MCSymbolRefExpr::VK_TLSLD: return true; } } namespace { class ELFObjectWriterImpl { /*static bool isFixupKindX86RIPRel(unsigned Kind) { return Kind == X86::reloc_riprel_4byte || Kind == X86::reloc_riprel_4byte_movq_load; }*/ /// ELFSymbolData - Helper struct for containing some precomputed information /// on symbols. struct ELFSymbolData { MCSymbolData *SymbolData; uint64_t StringIndex; uint32_t SectionIndex; // Support lexicographic sorting. bool operator<(const ELFSymbolData &RHS) const { if (GetType(*SymbolData) == ELF::STT_FILE) return true; if (GetType(*RHS.SymbolData) == ELF::STT_FILE) return false; return SymbolData->getSymbol().getName() < RHS.SymbolData->getSymbol().getName(); } }; /// @name Relocation Data /// @{ struct ELFRelocationEntry { // Make these big enough for both 32-bit and 64-bit uint64_t r_offset; int Index; unsigned Type; const MCSymbol *Symbol; uint64_t r_addend; // Support lexicographic sorting. bool operator<(const ELFRelocationEntry &RE) const { return RE.r_offset < r_offset; } }; SmallPtrSet UsedInReloc; SmallPtrSet WeakrefUsedInReloc; DenseMap Renames; llvm::DenseMap > Relocations; DenseMap SectionStringTableIndex; /// @} /// @name Symbol Table Data /// @{ SmallString<256> StringTable; std::vector LocalSymbolData; std::vector ExternalSymbolData; std::vector UndefinedSymbolData; /// @} int NumRegularSections; bool NeedsGOT; bool NeedsSymtabShndx; ELFObjectWriter *Writer; raw_ostream &OS; unsigned Is64Bit : 1; bool HasRelocationAddend; Triple::OSType OSType; uint16_t EMachine; // This holds the symbol table index of the last local symbol. unsigned LastLocalSymbolIndex; // This holds the .strtab section index. unsigned StringTableIndex; // This holds the .symtab section index. unsigned SymbolTableIndex; unsigned ShstrtabIndex; public: ELFObjectWriterImpl(ELFObjectWriter *_Writer, bool _Is64Bit, uint16_t _EMachine, bool _HasRelAddend, Triple::OSType _OSType) : NeedsGOT(false), NeedsSymtabShndx(false), Writer(_Writer), OS(Writer->getStream()), Is64Bit(_Is64Bit), HasRelocationAddend(_HasRelAddend), OSType(_OSType), EMachine(_EMachine) { } void Write8(uint8_t Value) { Writer->Write8(Value); } void Write16(uint16_t Value) { Writer->Write16(Value); } void Write32(uint32_t Value) { Writer->Write32(Value); } //void Write64(uint64_t Value) { Writer->Write64(Value); } void WriteZeros(unsigned N) { Writer->WriteZeros(N); } //void WriteBytes(StringRef Str, unsigned ZeroFillSize = 0) { // Writer->WriteBytes(Str, ZeroFillSize); //} void WriteWord(uint64_t W) { if (Is64Bit) Writer->Write64(W); else Writer->Write32(W); } void StringLE16(char *buf, uint16_t Value) { buf[0] = char(Value >> 0); buf[1] = char(Value >> 8); } void StringLE32(char *buf, uint32_t Value) { StringLE16(buf, uint16_t(Value >> 0)); StringLE16(buf + 2, uint16_t(Value >> 16)); } void StringLE64(char *buf, uint64_t Value) { StringLE32(buf, uint32_t(Value >> 0)); StringLE32(buf + 4, uint32_t(Value >> 32)); } void StringBE16(char *buf ,uint16_t Value) { buf[0] = char(Value >> 8); buf[1] = char(Value >> 0); } void StringBE32(char *buf, uint32_t Value) { StringBE16(buf, uint16_t(Value >> 16)); StringBE16(buf + 2, uint16_t(Value >> 0)); } void StringBE64(char *buf, uint64_t Value) { StringBE32(buf, uint32_t(Value >> 32)); StringBE32(buf + 4, uint32_t(Value >> 0)); } void String8(MCDataFragment &F, uint8_t Value) { char buf[1]; buf[0] = Value; F.getContents() += StringRef(buf, 1); } void String16(MCDataFragment &F, uint16_t Value) { char buf[2]; if (Writer->isLittleEndian()) StringLE16(buf, Value); else StringBE16(buf, Value); F.getContents() += StringRef(buf, 2); } void String32(MCDataFragment &F, uint32_t Value) { char buf[4]; if (Writer->isLittleEndian()) StringLE32(buf, Value); else StringBE32(buf, Value); F.getContents() += StringRef(buf, 4); } void String64(MCDataFragment &F, uint64_t Value) { char buf[8]; if (Writer->isLittleEndian()) StringLE64(buf, Value); else StringBE64(buf, Value); F.getContents() += StringRef(buf, 8); } void WriteHeader(uint64_t SectionDataSize, unsigned NumberOfSections); void WriteSymbolEntry(MCDataFragment *SymtabF, MCDataFragment *ShndxF, uint64_t name, uint8_t info, uint64_t value, uint64_t size, uint8_t other, uint32_t shndx, bool Reserved); void WriteSymbol(MCDataFragment *SymtabF, MCDataFragment *ShndxF, ELFSymbolData &MSD, const MCAsmLayout &Layout); typedef DenseMap SectionIndexMapTy; void WriteSymbolTable(MCDataFragment *SymtabF, MCDataFragment *ShndxF, const MCAssembler &Asm, const MCAsmLayout &Layout, unsigned NumRegularSections); void RecordRelocation(const MCAssembler &Asm, const MCAsmLayout &Layout, const MCFragment *Fragment, const MCFixup &Fixup, MCValue Target, uint64_t &FixedValue); uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm, const MCSymbol *S); /// ComputeSymbolTable - Compute the symbol table data /// /// \param StringTable [out] - The string table data. /// \param StringIndexMap [out] - Map from symbol names to offsets in the /// string table. void ComputeSymbolTable(MCAssembler &Asm, const SectionIndexMapTy &SectionIndexMap); void ComputeIndexMap(MCAssembler &Asm, SectionIndexMapTy &SectionIndexMap); void WriteRelocation(MCAssembler &Asm, MCAsmLayout &Layout, const MCSectionData &SD); void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout) { for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it) { WriteRelocation(Asm, Layout, *it); } } void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout); void ExecutePostLayoutBinding(MCAssembler &Asm); void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags, uint64_t Address, uint64_t Offset, uint64_t Size, uint32_t Link, uint32_t Info, uint64_t Alignment, uint64_t EntrySize); void WriteRelocationsFragment(const MCAssembler &Asm, MCDataFragment *F, const MCSectionData *SD); bool IsFixupFullyResolved(const MCAssembler &Asm, const MCValue Target, bool IsPCRel, const MCFragment *DF) const; void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout); }; } // Emit the ELF header. void ELFObjectWriterImpl::WriteHeader(uint64_t SectionDataSize, unsigned NumberOfSections) { // ELF Header // ---------- // // Note // ---- // emitWord method behaves differently for ELF32 and ELF64, writing // 4 bytes in the former and 8 in the latter. Write8(0x7f); // e_ident[EI_MAG0] Write8('E'); // e_ident[EI_MAG1] Write8('L'); // e_ident[EI_MAG2] Write8('F'); // e_ident[EI_MAG3] Write8(Is64Bit ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS] // e_ident[EI_DATA] Write8(Writer->isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB); Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION] // e_ident[EI_OSABI] switch (OSType) { case Triple::FreeBSD: Write8(ELF::ELFOSABI_FREEBSD); break; case Triple::Linux: Write8(ELF::ELFOSABI_LINUX); break; default: Write8(ELF::ELFOSABI_NONE); break; } Write8(0); // e_ident[EI_ABIVERSION] WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD); Write16(ELF::ET_REL); // e_type Write16(EMachine); // e_machine = target Write32(ELF::EV_CURRENT); // e_version WriteWord(0); // e_entry, no entry point in .o file WriteWord(0); // e_phoff, no program header for .o WriteWord(SectionDataSize + (Is64Bit ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr))); // e_shoff = sec hdr table off in bytes // FIXME: Make this configurable. Write32(0); // e_flags = whatever the target wants // e_ehsize = ELF header size Write16(Is64Bit ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr)); Write16(0); // e_phentsize = prog header entry size Write16(0); // e_phnum = # prog header entries = 0 // e_shentsize = Section header entry size Write16(Is64Bit ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr)); // e_shnum = # of section header ents if (NumberOfSections >= ELF::SHN_LORESERVE) Write16(0); else Write16(NumberOfSections); // e_shstrndx = Section # of '.shstrtab' if (NumberOfSections >= ELF::SHN_LORESERVE) Write16(ELF::SHN_XINDEX); else Write16(ShstrtabIndex); } void ELFObjectWriterImpl::WriteSymbolEntry(MCDataFragment *SymtabF, MCDataFragment *ShndxF, uint64_t name, uint8_t info, uint64_t value, uint64_t size, uint8_t other, uint32_t shndx, bool Reserved) { if (ShndxF) { if (shndx >= ELF::SHN_LORESERVE && !Reserved) String32(*ShndxF, shndx); else String32(*ShndxF, 0); } uint16_t Index = (shndx >= ELF::SHN_LORESERVE && !Reserved) ? uint16_t(ELF::SHN_XINDEX) : shndx; if (Is64Bit) { String32(*SymtabF, name); // st_name String8(*SymtabF, info); // st_info String8(*SymtabF, other); // st_other String16(*SymtabF, Index); // st_shndx String64(*SymtabF, value); // st_value String64(*SymtabF, size); // st_size } else { String32(*SymtabF, name); // st_name String32(*SymtabF, value); // st_value String32(*SymtabF, size); // st_size String8(*SymtabF, info); // st_info String8(*SymtabF, other); // st_other String16(*SymtabF, Index); // st_shndx } } static uint64_t SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout) { if (Data.isCommon() && Data.isExternal()) return Data.getCommonAlignment(); const MCSymbol &Symbol = Data.getSymbol(); if (!Symbol.isInSection()) return 0; if (MCFragment *FF = Data.getFragment()) return Layout.getSymbolAddress(&Data) - Layout.getSectionAddress(FF->getParent()); return 0; } static const MCSymbol &AliasedSymbol(const MCSymbol &Symbol) { const MCSymbol *S = &Symbol; while (S->isVariable()) { const MCExpr *Value = S->getVariableValue(); if (Value->getKind() != MCExpr::SymbolRef) return *S; const MCSymbolRefExpr *Ref = static_cast(Value); S = &Ref->getSymbol(); } return *S; } void ELFObjectWriterImpl::ExecutePostLayoutBinding(MCAssembler &Asm) { // The presence of symbol versions causes undefined symbols and // versions declared with @@@ to be renamed. for (MCAssembler::symbol_iterator it = Asm.symbol_begin(), ie = Asm.symbol_end(); it != ie; ++it) { const MCSymbol &Alias = it->getSymbol(); const MCSymbol &Symbol = AliasedSymbol(Alias); MCSymbolData &SD = Asm.getSymbolData(Symbol); // Undefined symbols are global, but this is the first place we // are able to set it. if (Symbol.isUndefined() && !Symbol.isVariable()) { if (GetBinding(SD) == ELF::STB_LOCAL) { SetBinding(SD, ELF::STB_GLOBAL); SetBinding(*it, ELF::STB_GLOBAL); } } // Not an alias. if (&Symbol == &Alias) continue; StringRef AliasName = Alias.getName(); size_t Pos = AliasName.find('@'); if (Pos == StringRef::npos) continue; // Aliases defined with .symvar copy the binding from the symbol they alias. // This is the first place we are able to copy this information. it->setExternal(SD.isExternal()); SetBinding(*it, GetBinding(SD)); StringRef Rest = AliasName.substr(Pos); if (!Symbol.isUndefined() && !Rest.startswith("@@@")) continue; // FIXME: produce a better error message. if (Symbol.isUndefined() && Rest.startswith("@@") && !Rest.startswith("@@@")) report_fatal_error("A @@ version cannot be undefined"); Renames.insert(std::make_pair(&Symbol, &Alias)); } } void ELFObjectWriterImpl::WriteSymbol(MCDataFragment *SymtabF, MCDataFragment *ShndxF, ELFSymbolData &MSD, const MCAsmLayout &Layout) { MCSymbolData &OrigData = *MSD.SymbolData; MCSymbolData &Data = Layout.getAssembler().getSymbolData(AliasedSymbol(OrigData.getSymbol())); bool IsReserved = Data.isCommon() || Data.getSymbol().isAbsolute() || Data.getSymbol().isVariable(); uint8_t Binding = GetBinding(OrigData); uint8_t Visibility = GetVisibility(OrigData); uint8_t Type = GetType(Data); uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift); uint8_t Other = Visibility; uint64_t Value = SymbolValue(Data, Layout); uint64_t Size = 0; const MCExpr *ESize; assert(!(Data.isCommon() && !Data.isExternal())); ESize = Data.getSize(); if (Data.getSize()) { MCValue Res; if (ESize->getKind() == MCExpr::Binary) { const MCBinaryExpr *BE = static_cast(ESize); if (BE->EvaluateAsRelocatable(Res, &Layout)) { assert(!Res.getSymA() || !Res.getSymA()->getSymbol().isDefined()); assert(!Res.getSymB() || !Res.getSymB()->getSymbol().isDefined()); Size = Res.getConstant(); } } else if (ESize->getKind() == MCExpr::Constant) { Size = static_cast(ESize)->getValue(); } else { assert(0 && "Unsupported size expression"); } } // Write out the symbol table entry WriteSymbolEntry(SymtabF, ShndxF, MSD.StringIndex, Info, Value, Size, Other, MSD.SectionIndex, IsReserved); } void ELFObjectWriterImpl::WriteSymbolTable(MCDataFragment *SymtabF, MCDataFragment *ShndxF, const MCAssembler &Asm, const MCAsmLayout &Layout, unsigned NumRegularSections) { // The string table must be emitted first because we need the index // into the string table for all the symbol names. assert(StringTable.size() && "Missing string table"); // FIXME: Make sure the start of the symbol table is aligned. // The first entry is the undefined symbol entry. WriteSymbolEntry(SymtabF, ShndxF, 0, 0, 0, 0, 0, 0, false); // Write the symbol table entries. LastLocalSymbolIndex = LocalSymbolData.size() + 1; for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) { ELFSymbolData &MSD = LocalSymbolData[i]; WriteSymbol(SymtabF, ShndxF, MSD, Layout); } // Write out a symbol table entry for each regular section. unsigned Index = 1; for (MCAssembler::const_iterator it = Asm.begin(); Index <= NumRegularSections; ++it, ++Index) { const MCSectionELF &Section = static_cast(it->getSection()); // Leave out relocations so we don't have indexes within // the relocations messed up if (Section.getType() == ELF::SHT_RELA || Section.getType() == ELF::SHT_REL) continue; WriteSymbolEntry(SymtabF, ShndxF, 0, ELF::STT_SECTION, 0, 0, ELF::STV_DEFAULT, Index, false); LastLocalSymbolIndex++; } for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) { ELFSymbolData &MSD = ExternalSymbolData[i]; MCSymbolData &Data = *MSD.SymbolData; assert(((Data.getFlags() & ELF_STB_Global) || (Data.getFlags() & ELF_STB_Weak)) && "External symbol requires STB_GLOBAL or STB_WEAK flag"); WriteSymbol(SymtabF, ShndxF, MSD, Layout); if (GetBinding(Data) == ELF::STB_LOCAL) LastLocalSymbolIndex++; } for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) { ELFSymbolData &MSD = UndefinedSymbolData[i]; MCSymbolData &Data = *MSD.SymbolData; WriteSymbol(SymtabF, ShndxF, MSD, Layout); if (GetBinding(Data) == ELF::STB_LOCAL) LastLocalSymbolIndex++; } } static bool ShouldRelocOnSymbol(const MCSymbolData &SD, const MCValue &Target, const MCFragment &F) { const MCSymbol &Symbol = SD.getSymbol(); if (Symbol.isUndefined()) return true; const MCSectionELF &Section = static_cast(Symbol.getSection()); if (SD.isExternal()) return true; MCSymbolRefExpr::VariantKind Kind = Target.getSymA()->getKind(); const MCSectionELF &Sec2 = static_cast(F.getParent()->getSection()); if (Section.getKind().isBSS()) return false; if (&Sec2 != &Section && (Kind == MCSymbolRefExpr::VK_PLT || Kind == MCSymbolRefExpr::VK_GOTPCREL || Kind == MCSymbolRefExpr::VK_GOTOFF)) return true; if (Section.getFlags() & MCSectionELF::SHF_MERGE) return Target.getConstant() != 0; return false; } // FIXME: this is currently X86/X86_64 only void ELFObjectWriterImpl::RecordRelocation(const MCAssembler &Asm, const MCAsmLayout &Layout, const MCFragment *Fragment, const MCFixup &Fixup, MCValue Target, uint64_t &FixedValue) { int64_t Addend = 0; int Index = 0; int64_t Value = Target.getConstant(); const MCSymbol *Symbol = 0; const MCSymbol *Renamed = 0; bool IsPCRel = isFixupKindX86PCRel(Fixup.getKind()); if (!Target.isAbsolute()) { Symbol = &AliasedSymbol(Target.getSymA()->getSymbol()); Renamed = Renames.lookup(Symbol); if (!Renamed) Renamed = &Target.getSymA()->getSymbol(); MCSymbolData &SD = Asm.getSymbolData(*Symbol); MCFragment *F = SD.getFragment(); if (const MCSymbolRefExpr *RefB = Target.getSymB()) { const MCSymbol &SymbolB = RefB->getSymbol(); MCSymbolData &SDB = Asm.getSymbolData(SymbolB); IsPCRel = true; MCSectionData *Sec = Fragment->getParent(); // Offset of the symbol in the section int64_t a = Layout.getSymbolAddress(&SDB) - Layout.getSectionAddress(Sec); // Ofeset of the relocation in the section int64_t b = Layout.getFragmentOffset(Fragment) + Fixup.getOffset(); Value += b - a; } // Check that this case has already been fully resolved before we get // here. if (Symbol->isDefined() && !SD.isExternal() && IsPCRel && &Fragment->getParent()->getSection() == &Symbol->getSection()) { llvm_unreachable("We don't need a relocation in this case."); return; } bool RelocOnSymbol = ShouldRelocOnSymbol(SD, Target, *Fragment); if (!RelocOnSymbol) { Index = F->getParent()->getOrdinal(); MCSectionData *FSD = F->getParent(); // Offset of the symbol in the section Value += Layout.getSymbolAddress(&SD) - Layout.getSectionAddress(FSD); } else { UsedInReloc.insert(Renamed); MCSymbolData &RenamedSD = Asm.getSymbolData(*Renamed); if (RenamedSD.getFlags() & ELF_Other_Weakref) { WeakrefUsedInReloc.insert(Symbol); } Index = -1; } Addend = Value; // Compensate for the addend on i386. if (Is64Bit) Value = 0; } FixedValue = Value; // determine the type of the relocation MCSymbolRefExpr::VariantKind Modifier = Target.getSymA()->getKind(); unsigned Type; if (Is64Bit) { if (IsPCRel) { switch (Modifier) { default: llvm_unreachable("Unimplemented"); case MCSymbolRefExpr::VK_None: Type = ELF::R_X86_64_PC32; break; case MCSymbolRefExpr::VK_PLT: Type = ELF::R_X86_64_PLT32; break; case MCSymbolRefExpr::VK_GOTPCREL: Type = ELF::R_X86_64_GOTPCREL; break; case MCSymbolRefExpr::VK_GOTTPOFF: Type = ELF::R_X86_64_GOTTPOFF; break; case MCSymbolRefExpr::VK_TLSGD: Type = ELF::R_X86_64_TLSGD; break; case MCSymbolRefExpr::VK_TLSLD: Type = ELF::R_X86_64_TLSLD; break; } } else { switch ((unsigned)Fixup.getKind()) { default: llvm_unreachable("invalid fixup kind!"); case FK_Data_8: Type = ELF::R_X86_64_64; break; case X86::reloc_signed_4byte: case X86::reloc_pcrel_4byte: assert(isInt<32>(Target.getConstant())); switch (Modifier) { default: llvm_unreachable("Unimplemented"); case MCSymbolRefExpr::VK_None: Type = ELF::R_X86_64_32S; break; case MCSymbolRefExpr::VK_GOT: Type = ELF::R_X86_64_GOT32; break; case MCSymbolRefExpr::VK_GOTPCREL: Type = ELF::R_X86_64_GOTPCREL; break; case MCSymbolRefExpr::VK_TPOFF: Type = ELF::R_X86_64_TPOFF32; break; case MCSymbolRefExpr::VK_DTPOFF: Type = ELF::R_X86_64_DTPOFF32; break; } break; case FK_Data_4: Type = ELF::R_X86_64_32; break; case FK_Data_2: Type = ELF::R_X86_64_16; break; case X86::reloc_pcrel_1byte: case FK_Data_1: Type = ELF::R_X86_64_8; break; } } } else { if (IsPCRel) { switch (Modifier) { default: llvm_unreachable("Unimplemented"); case MCSymbolRefExpr::VK_None: Type = ELF::R_386_PC32; break; case MCSymbolRefExpr::VK_PLT: Type = ELF::R_386_PLT32; break; } } else { switch ((unsigned)Fixup.getKind()) { default: llvm_unreachable("invalid fixup kind!"); case X86::reloc_global_offset_table: Type = ELF::R_386_GOTPC; break; // FIXME: Should we avoid selecting reloc_signed_4byte in 32 bit mode // instead? case X86::reloc_signed_4byte: case X86::reloc_pcrel_4byte: case FK_Data_4: switch (Modifier) { default: llvm_unreachable("Unimplemented"); case MCSymbolRefExpr::VK_None: Type = ELF::R_386_32; break; case MCSymbolRefExpr::VK_GOT: Type = ELF::R_386_GOT32; break; case MCSymbolRefExpr::VK_GOTOFF: Type = ELF::R_386_GOTOFF; break; case MCSymbolRefExpr::VK_TLSGD: Type = ELF::R_386_TLS_GD; break; case MCSymbolRefExpr::VK_TPOFF: Type = ELF::R_386_TLS_LE_32; break; case MCSymbolRefExpr::VK_INDNTPOFF: Type = ELF::R_386_TLS_IE; break; case MCSymbolRefExpr::VK_NTPOFF: Type = ELF::R_386_TLS_LE; break; case MCSymbolRefExpr::VK_GOTNTPOFF: Type = ELF::R_386_TLS_GOTIE; break; case MCSymbolRefExpr::VK_TLSLDM: Type = ELF::R_386_TLS_LDM; break; case MCSymbolRefExpr::VK_DTPOFF: Type = ELF::R_386_TLS_LDO_32; break; } break; case FK_Data_2: Type = ELF::R_386_16; break; case X86::reloc_pcrel_1byte: case FK_Data_1: Type = ELF::R_386_8; break; } } } if (RelocNeedsGOT(Modifier)) NeedsGOT = true; ELFRelocationEntry ERE; ERE.Index = Index; ERE.Type = Type; ERE.Symbol = Renamed; ERE.r_offset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset(); if (HasRelocationAddend) ERE.r_addend = Addend; else ERE.r_addend = 0; // Silence compiler warning. Relocations[Fragment->getParent()].push_back(ERE); } uint64_t ELFObjectWriterImpl::getSymbolIndexInSymbolTable(const MCAssembler &Asm, const MCSymbol *S) { MCSymbolData &SD = Asm.getSymbolData(*S); // Local symbol. if (!SD.isExternal() && !S->isUndefined()) return SD.getIndex() + /* empty symbol */ 1; // External or undefined symbol. return SD.getIndex() + NumRegularSections + /* empty symbol */ 1; } static bool isInSymtab(const MCAssembler &Asm, const MCSymbolData &Data, bool Used, bool Renamed) { if (Data.getFlags() & ELF_Other_Weakref) return false; if (Used) return true; if (Renamed) return false; const MCSymbol &Symbol = Data.getSymbol(); if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_") return true; const MCSymbol &A = AliasedSymbol(Symbol); if (!A.isVariable() && A.isUndefined() && !Data.isCommon()) return false; if (!Asm.isSymbolLinkerVisible(Symbol) && !Symbol.isUndefined()) return false; if (Symbol.isTemporary()) return false; return true; } static bool isLocal(const MCSymbolData &Data) { if (Data.isExternal()) return false; const MCSymbol &Symbol = Data.getSymbol(); if (Symbol.isUndefined() && !Symbol.isVariable()) return false; return true; } void ELFObjectWriterImpl::ComputeIndexMap(MCAssembler &Asm, SectionIndexMapTy &SectionIndexMap) { unsigned Index = 1; for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it) { const MCSectionELF &Section = static_cast(it->getSection()); SectionIndexMap[&Section] = Index++; } } void ELFObjectWriterImpl::ComputeSymbolTable(MCAssembler &Asm, const SectionIndexMapTy &SectionIndexMap) { // FIXME: Is this the correct place to do this? if (NeedsGOT) { llvm::StringRef Name = "_GLOBAL_OFFSET_TABLE_"; MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name); MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym); Data.setExternal(true); SetBinding(Data, ELF::STB_GLOBAL); } // Build section lookup table. NumRegularSections = Asm.size(); // Index 0 is always the empty string. StringMap StringIndexMap; StringTable += '\x00'; // Add the data for the symbols. for (MCAssembler::symbol_iterator it = Asm.symbol_begin(), ie = Asm.symbol_end(); it != ie; ++it) { const MCSymbol &Symbol = it->getSymbol(); bool Used = UsedInReloc.count(&Symbol); bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol); if (!isInSymtab(Asm, *it, Used || WeakrefUsed, Renames.count(&Symbol))) continue; ELFSymbolData MSD; MSD.SymbolData = it; bool Local = isLocal(*it); const MCSymbol &RefSymbol = AliasedSymbol(Symbol); if (RefSymbol.isUndefined() && !Used && WeakrefUsed) SetBinding(*it, ELF::STB_WEAK); if (it->isCommon()) { assert(!Local); MSD.SectionIndex = ELF::SHN_COMMON; } else if (Symbol.isAbsolute() || RefSymbol.isVariable()) { MSD.SectionIndex = ELF::SHN_ABS; } else if (RefSymbol.isUndefined()) { MSD.SectionIndex = ELF::SHN_UNDEF; } else { const MCSectionELF &Section = static_cast(RefSymbol.getSection()); MSD.SectionIndex = SectionIndexMap.lookup(&Section); if (MSD.SectionIndex >= ELF::SHN_LORESERVE) NeedsSymtabShndx = true; assert(MSD.SectionIndex && "Invalid section index!"); } // The @@@ in symbol version is replaced with @ in undefined symbols and // @@ in defined ones. StringRef Name = Symbol.getName(); size_t Pos = Name.find("@@@"); std::string FinalName; if (Pos != StringRef::npos) { StringRef Prefix = Name.substr(0, Pos); unsigned n = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1; StringRef Suffix = Name.substr(Pos + n); FinalName = Prefix.str() + Suffix.str(); } else { FinalName = Name.str(); } uint64_t &Entry = StringIndexMap[FinalName]; if (!Entry) { Entry = StringTable.size(); StringTable += FinalName; StringTable += '\x00'; } MSD.StringIndex = Entry; if (MSD.SectionIndex == ELF::SHN_UNDEF) UndefinedSymbolData.push_back(MSD); else if (Local) LocalSymbolData.push_back(MSD); else ExternalSymbolData.push_back(MSD); } // Symbols are required to be in lexicographic order. array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end()); array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end()); array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end()); // Set the symbol indices. Local symbols must come before all other // symbols with non-local bindings. unsigned Index = 0; for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) LocalSymbolData[i].SymbolData->setIndex(Index++); for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) ExternalSymbolData[i].SymbolData->setIndex(Index++); for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) UndefinedSymbolData[i].SymbolData->setIndex(Index++); } void ELFObjectWriterImpl::WriteRelocation(MCAssembler &Asm, MCAsmLayout &Layout, const MCSectionData &SD) { if (!Relocations[&SD].empty()) { MCContext &Ctx = Asm.getContext(); const MCSectionELF *RelaSection; const MCSectionELF &Section = static_cast(SD.getSection()); const StringRef SectionName = Section.getSectionName(); std::string RelaSectionName = HasRelocationAddend ? ".rela" : ".rel"; RelaSectionName += SectionName; unsigned EntrySize; if (HasRelocationAddend) EntrySize = Is64Bit ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela); else EntrySize = Is64Bit ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel); RelaSection = Ctx.getELFSection(RelaSectionName, HasRelocationAddend ? ELF::SHT_RELA : ELF::SHT_REL, 0, SectionKind::getReadOnly(), EntrySize); MCSectionData &RelaSD = Asm.getOrCreateSectionData(*RelaSection); RelaSD.setAlignment(Is64Bit ? 8 : 4); MCDataFragment *F = new MCDataFragment(&RelaSD); WriteRelocationsFragment(Asm, F, &SD); Asm.AddSectionToTheEnd(*Writer, RelaSD, Layout); } } void ELFObjectWriterImpl::WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags, uint64_t Address, uint64_t Offset, uint64_t Size, uint32_t Link, uint32_t Info, uint64_t Alignment, uint64_t EntrySize) { Write32(Name); // sh_name: index into string table Write32(Type); // sh_type WriteWord(Flags); // sh_flags WriteWord(Address); // sh_addr WriteWord(Offset); // sh_offset WriteWord(Size); // sh_size Write32(Link); // sh_link Write32(Info); // sh_info WriteWord(Alignment); // sh_addralign WriteWord(EntrySize); // sh_entsize } void ELFObjectWriterImpl::WriteRelocationsFragment(const MCAssembler &Asm, MCDataFragment *F, const MCSectionData *SD) { std::vector &Relocs = Relocations[SD]; // sort by the r_offset just like gnu as does array_pod_sort(Relocs.begin(), Relocs.end()); for (unsigned i = 0, e = Relocs.size(); i != e; ++i) { ELFRelocationEntry entry = Relocs[e - i - 1]; if (entry.Index < 0) entry.Index = getSymbolIndexInSymbolTable(Asm, entry.Symbol); else entry.Index += LocalSymbolData.size() + 1; if (Is64Bit) { String64(*F, entry.r_offset); struct ELF::Elf64_Rela ERE64; ERE64.setSymbolAndType(entry.Index, entry.Type); String64(*F, ERE64.r_info); if (HasRelocationAddend) String64(*F, entry.r_addend); } else { String32(*F, entry.r_offset); struct ELF::Elf32_Rela ERE32; ERE32.setSymbolAndType(entry.Index, entry.Type); String32(*F, ERE32.r_info); if (HasRelocationAddend) String32(*F, entry.r_addend); } } } void ELFObjectWriterImpl::CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout) { MCContext &Ctx = Asm.getContext(); MCDataFragment *F; unsigned EntrySize = Is64Bit ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32; unsigned NumRegularSections = Asm.size(); // We construct .shstrtab, .symtab and .strtab in this order to match gnu as. const MCSectionELF *ShstrtabSection = Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0, SectionKind::getReadOnly(), false); MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection); ShstrtabSD.setAlignment(1); ShstrtabIndex = Asm.size(); const MCSectionELF *SymtabSection = Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, SectionKind::getReadOnly(), EntrySize); MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection); SymtabSD.setAlignment(Is64Bit ? 8 : 4); SymbolTableIndex = Asm.size(); MCSectionData *SymtabShndxSD = NULL; if (NeedsSymtabShndx) { const MCSectionELF *SymtabShndxSection = Ctx.getELFSection(".symtab_shndx", ELF::SHT_SYMTAB_SHNDX, 0, SectionKind::getReadOnly(), 4); SymtabShndxSD = &Asm.getOrCreateSectionData(*SymtabShndxSection); SymtabShndxSD->setAlignment(4); } const MCSection *StrtabSection; StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0, SectionKind::getReadOnly(), false); MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection); StrtabSD.setAlignment(1); StringTableIndex = Asm.size(); WriteRelocations(Asm, Layout); // Symbol table F = new MCDataFragment(&SymtabSD); MCDataFragment *ShndxF = NULL; if (NeedsSymtabShndx) { ShndxF = new MCDataFragment(SymtabShndxSD); Asm.AddSectionToTheEnd(*Writer, *SymtabShndxSD, Layout); } WriteSymbolTable(F, ShndxF, Asm, Layout, NumRegularSections); Asm.AddSectionToTheEnd(*Writer, SymtabSD, Layout); F = new MCDataFragment(&StrtabSD); F->getContents().append(StringTable.begin(), StringTable.end()); Asm.AddSectionToTheEnd(*Writer, StrtabSD, Layout); F = new MCDataFragment(&ShstrtabSD); // Section header string table. // // The first entry of a string table holds a null character so skip // section 0. uint64_t Index = 1; F->getContents() += '\x00'; for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it) { const MCSectionELF &Section = static_cast(it->getSection()); // FIXME: We could merge suffixes like in .text and .rela.text. // Remember the index into the string table so we can write it // into the sh_name field of the section header table. SectionStringTableIndex[&it->getSection()] = Index; Index += Section.getSectionName().size() + 1; F->getContents() += Section.getSectionName(); F->getContents() += '\x00'; } Asm.AddSectionToTheEnd(*Writer, ShstrtabSD, Layout); } bool ELFObjectWriterImpl::IsFixupFullyResolved(const MCAssembler &Asm, const MCValue Target, bool IsPCRel, const MCFragment *DF) const { // If this is a PCrel relocation, find the section this fixup value is // relative to. const MCSection *BaseSection = 0; if (IsPCRel) { BaseSection = &DF->getParent()->getSection(); assert(BaseSection); } const MCSection *SectionA = 0; const MCSymbol *SymbolA = 0; if (const MCSymbolRefExpr *A = Target.getSymA()) { SymbolA = &A->getSymbol(); SectionA = &SymbolA->getSection(); } const MCSection *SectionB = 0; if (const MCSymbolRefExpr *B = Target.getSymB()) { SectionB = &B->getSymbol().getSection(); } if (!BaseSection) return SectionA == SectionB; const MCSymbolData &DataA = Asm.getSymbolData(*SymbolA); if (DataA.isExternal()) return false; return !SectionB && BaseSection == SectionA; } void ELFObjectWriterImpl::WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) { SectionIndexMapTy SectionIndexMap; ComputeIndexMap(Asm, SectionIndexMap); // Compute symbol table information. ComputeSymbolTable(Asm, SectionIndexMap); CreateMetadataSections(const_cast(Asm), const_cast(Layout)); // Add 1 for the null section. unsigned NumSections = Asm.size() + 1; uint64_t NaturalAlignment = Is64Bit ? 8 : 4; uint64_t HeaderSize = Is64Bit ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr); uint64_t FileOff = HeaderSize; for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it) { const MCSectionData &SD = *it; FileOff = RoundUpToAlignment(FileOff, SD.getAlignment()); // Get the size of the section in the output file (including padding). uint64_t Size = Layout.getSectionFileSize(&SD); FileOff += Size; } FileOff = RoundUpToAlignment(FileOff, NaturalAlignment); // Write out the ELF header ... WriteHeader(FileOff - HeaderSize, NumSections); FileOff = HeaderSize; // ... then all of the sections ... DenseMap SectionOffsetMap; for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it) { const MCSectionData &SD = *it; uint64_t Padding = OffsetToAlignment(FileOff, SD.getAlignment()); WriteZeros(Padding); FileOff += Padding; // Remember the offset into the file for this section. SectionOffsetMap[&it->getSection()] = FileOff; FileOff += Layout.getSectionFileSize(&SD); Asm.WriteSectionData(it, Layout, Writer); } uint64_t Padding = OffsetToAlignment(FileOff, NaturalAlignment); WriteZeros(Padding); FileOff += Padding; // ... and then the section header table. // Should we align the section header table? // // Null section first. uint64_t FirstSectionSize = NumSections >= ELF::SHN_LORESERVE ? NumSections : 0; uint32_t FirstSectionLink = ShstrtabIndex >= ELF::SHN_LORESERVE ? ShstrtabIndex : 0; WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, FirstSectionLink, 0, 0, 0); for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it) { const MCSectionData &SD = *it; const MCSectionELF &Section = static_cast(SD.getSection()); uint64_t sh_link = 0; uint64_t sh_info = 0; switch(Section.getType()) { case ELF::SHT_DYNAMIC: sh_link = SectionStringTableIndex[&it->getSection()]; sh_info = 0; break; case ELF::SHT_REL: case ELF::SHT_RELA: { const MCSectionELF *SymtabSection; const MCSectionELF *InfoSection; SymtabSection = Asm.getContext().getELFSection(".symtab", ELF::SHT_SYMTAB, 0, SectionKind::getReadOnly(), false); sh_link = SectionIndexMap[SymtabSection]; // Remove ".rel" and ".rela" prefixes. unsigned SecNameLen = (Section.getType() == ELF::SHT_REL) ? 4 : 5; StringRef SectionName = Section.getSectionName().substr(SecNameLen); InfoSection = Asm.getContext().getELFSection(SectionName, ELF::SHT_PROGBITS, 0, SectionKind::getReadOnly(), false); sh_info = SectionIndexMap[InfoSection]; break; } case ELF::SHT_SYMTAB: case ELF::SHT_DYNSYM: sh_link = StringTableIndex; sh_info = LastLocalSymbolIndex; break; case ELF::SHT_SYMTAB_SHNDX: sh_link = SymbolTableIndex; break; case ELF::SHT_PROGBITS: case ELF::SHT_STRTAB: case ELF::SHT_NOBITS: case ELF::SHT_NULL: case ELF::SHT_ARM_ATTRIBUTES: // Nothing to do. break; default: assert(0 && "FIXME: sh_type value not supported!"); break; } WriteSecHdrEntry(SectionStringTableIndex[&it->getSection()], Section.getType(), Section.getFlags(), 0, SectionOffsetMap.lookup(&SD.getSection()), Layout.getSectionSize(&SD), sh_link, sh_info, SD.getAlignment(), Section.getEntrySize()); } } ELFObjectWriter::ELFObjectWriter(raw_ostream &OS, bool Is64Bit, Triple::OSType OSType, uint16_t EMachine, bool IsLittleEndian, bool HasRelocationAddend) : MCObjectWriter(OS, IsLittleEndian) { Impl = new ELFObjectWriterImpl(this, Is64Bit, EMachine, HasRelocationAddend, OSType); } ELFObjectWriter::~ELFObjectWriter() { delete (ELFObjectWriterImpl*) Impl; } void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm) { ((ELFObjectWriterImpl*) Impl)->ExecutePostLayoutBinding(Asm); } void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm, const MCAsmLayout &Layout, const MCFragment *Fragment, const MCFixup &Fixup, MCValue Target, uint64_t &FixedValue) { ((ELFObjectWriterImpl*) Impl)->RecordRelocation(Asm, Layout, Fragment, Fixup, Target, FixedValue); } bool ELFObjectWriter::IsFixupFullyResolved(const MCAssembler &Asm, const MCValue Target, bool IsPCRel, const MCFragment *DF) const { return ((ELFObjectWriterImpl*) Impl)->IsFixupFullyResolved(Asm, Target, IsPCRel, DF); } void ELFObjectWriter::WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) { ((ELFObjectWriterImpl*) Impl)->WriteObject(Asm, Layout); }