//===- 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/MCELFObjectWriter.h" #include "llvm/ADT/STLExtras.h" #include "llvm/ADT/SmallPtrSet.h" #include "llvm/ADT/SmallString.h" #include "llvm/ADT/StringMap.h" #include "llvm/MC/MCAsmBackend.h" #include "llvm/MC/MCAsmInfo.h" #include "llvm/MC/MCAsmLayout.h" #include "llvm/MC/MCAssembler.h" #include "llvm/MC/MCContext.h" #include "llvm/MC/MCELF.h" #include "llvm/MC/MCELFSymbolFlags.h" #include "llvm/MC/MCExpr.h" #include "llvm/MC/MCFixupKindInfo.h" #include "llvm/MC/MCObjectWriter.h" #include "llvm/MC/MCSectionELF.h" #include "llvm/MC/MCValue.h" #include "llvm/Object/StringTableBuilder.h" #include "llvm/Support/Compression.h" #include "llvm/Support/Debug.h" #include "llvm/Support/Endian.h" #include "llvm/Support/ELF.h" #include "llvm/Support/ErrorHandling.h" #include using namespace llvm; #undef DEBUG_TYPE #define DEBUG_TYPE "reloc-info" namespace { class FragmentWriter { bool IsLittleEndian; public: FragmentWriter(bool IsLittleEndian); template void write(MCDataFragment &F, T Val); }; typedef DenseMap SectionIndexMapTy; class SymbolTableWriter { MCAssembler &Asm; FragmentWriter &FWriter; bool Is64Bit; SectionIndexMapTy &SectionIndexMap; // The symbol .symtab fragment we are writting to. MCDataFragment *SymtabF; // .symtab_shndx fragment we are writting to. MCDataFragment *ShndxF; // The numbel of symbols written so far. unsigned NumWritten; void createSymtabShndx(); template void write(MCDataFragment &F, T Value); public: SymbolTableWriter(MCAssembler &Asm, FragmentWriter &FWriter, bool Is64Bit, SectionIndexMapTy &SectionIndexMap, MCDataFragment *SymtabF); void writeSymbol(uint32_t name, uint8_t info, uint64_t value, uint64_t size, uint8_t other, uint32_t shndx, bool Reserved); }; struct ELFRelocationEntry { uint64_t Offset; // Where is the relocation. bool UseSymbol; // Relocate with a symbol, not the section. union { const MCSymbol *Symbol; // The symbol to relocate with. const MCSectionData *Section; // The section to relocate with. }; unsigned Type; // The type of the relocation. uint64_t Addend; // The addend to use. ELFRelocationEntry(uint64_t Offset, const MCSymbol *Symbol, unsigned Type, uint64_t Addend) : Offset(Offset), UseSymbol(true), Symbol(Symbol), Type(Type), Addend(Addend) {} ELFRelocationEntry(uint64_t Offset, const MCSectionData *Section, unsigned Type, uint64_t Addend) : Offset(Offset), UseSymbol(false), Section(Section), Type(Type), Addend(Addend) {} }; class ELFObjectWriter : public MCObjectWriter { FragmentWriter FWriter; protected: static bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind); static bool RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant); static uint64_t SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout); static bool isInSymtab(const MCAsmLayout &Layout, const MCSymbolData &Data, bool Used, bool Renamed); static bool isLocal(const MCSymbolData &Data, bool isUsedInReloc); static bool IsELFMetaDataSection(const MCSectionData &SD); static uint64_t DataSectionSize(const MCSectionData &SD); static uint64_t GetSectionFileSize(const MCAsmLayout &Layout, const MCSectionData &SD); static uint64_t GetSectionAddressSize(const MCAsmLayout &Layout, const MCSectionData &SD); void WriteDataSectionData(MCAssembler &Asm, const MCAsmLayout &Layout, const MCSectionELF &Section); /*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; StringRef Name; // Support lexicographic sorting. bool operator<(const ELFSymbolData &RHS) const { return Name < RHS.Name; } }; /// The target specific ELF writer instance. std::unique_ptr TargetObjectWriter; SmallPtrSet UsedInReloc; SmallPtrSet WeakrefUsedInReloc; DenseMap Renames; llvm::DenseMap> Relocations; StringTableBuilder ShStrTabBuilder; /// @} /// @name Symbol Table Data /// @{ StringTableBuilder StrTabBuilder; std::vector FileSymbolData; std::vector LocalSymbolData; std::vector ExternalSymbolData; std::vector UndefinedSymbolData; /// @} bool NeedsGOT; // 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; // TargetObjectWriter wrappers. bool is64Bit() const { return TargetObjectWriter->is64Bit(); } bool hasRelocationAddend() const { return TargetObjectWriter->hasRelocationAddend(); } unsigned GetRelocType(const MCValue &Target, const MCFixup &Fixup, bool IsPCRel) const { return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel); } public: ELFObjectWriter(MCELFObjectTargetWriter *MOTW, raw_ostream &_OS, bool IsLittleEndian) : MCObjectWriter(_OS, IsLittleEndian), FWriter(IsLittleEndian), TargetObjectWriter(MOTW), NeedsGOT(false) {} virtual ~ELFObjectWriter(); void WriteWord(uint64_t W) { if (is64Bit()) Write64(W); else Write32(W); } template void write(MCDataFragment &F, T Value) { FWriter.write(F, Value); } void WriteHeader(const MCAssembler &Asm, uint64_t SectionDataSize, unsigned NumberOfSections); void WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD, const MCAsmLayout &Layout); void WriteSymbolTable(MCDataFragment *SymtabF, MCAssembler &Asm, const MCAsmLayout &Layout, SectionIndexMapTy &SectionIndexMap); bool shouldRelocateWithSymbol(const MCAssembler &Asm, const MCSymbolRefExpr *RefA, const MCSymbolData *SD, uint64_t C, unsigned Type) const; void RecordRelocation(const MCAssembler &Asm, const MCAsmLayout &Layout, const MCFragment *Fragment, const MCFixup &Fixup, MCValue Target, bool &IsPCRel, uint64_t &FixedValue) override; uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm, const MCSymbol *S); // Map from a group section to the signature symbol typedef DenseMap GroupMapTy; // Map from a signature symbol to the group section typedef DenseMap RevGroupMapTy; // Map from a section to the section with the relocations typedef DenseMap RelMapTy; // Map from a section to its offset typedef DenseMap SectionOffsetMapTy; /// Compute the symbol table data /// /// \param Asm - The assembler. /// \param SectionIndexMap - Maps a section to its index. /// \param RevGroupMap - Maps a signature symbol to the group section. /// \param NumRegularSections - Number of non-relocation sections. void computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout, const SectionIndexMapTy &SectionIndexMap, RevGroupMapTy RevGroupMap, unsigned NumRegularSections); void ComputeIndexMap(MCAssembler &Asm, SectionIndexMapTy &SectionIndexMap, const RelMapTy &RelMap); void CreateRelocationSections(MCAssembler &Asm, MCAsmLayout &Layout, RelMapTy &RelMap); void CompressDebugSections(MCAssembler &Asm, MCAsmLayout &Layout); void WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout, const RelMapTy &RelMap); void CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout, SectionIndexMapTy &SectionIndexMap, const RelMapTy &RelMap); // Create the sections that show up in the symbol table. Currently // those are the .note.GNU-stack section and the group sections. void CreateIndexedSections(MCAssembler &Asm, MCAsmLayout &Layout, GroupMapTy &GroupMap, RevGroupMapTy &RevGroupMap, SectionIndexMapTy &SectionIndexMap, const RelMapTy &RelMap); void ExecutePostLayoutBinding(MCAssembler &Asm, const MCAsmLayout &Layout) override; void WriteSectionHeader(MCAssembler &Asm, const GroupMapTy &GroupMap, const MCAsmLayout &Layout, const SectionIndexMapTy &SectionIndexMap, const SectionOffsetMapTy &SectionOffsetMap); void ComputeSectionOrder(MCAssembler &Asm, std::vector &Sections); 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 IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm, const MCSymbolData &DataA, const MCFragment &FB, bool InSet, bool IsPCRel) const override; void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override; void WriteSection(MCAssembler &Asm, const SectionIndexMapTy &SectionIndexMap, uint32_t GroupSymbolIndex, uint64_t Offset, uint64_t Size, uint64_t Alignment, const MCSectionELF &Section); }; } FragmentWriter::FragmentWriter(bool IsLittleEndian) : IsLittleEndian(IsLittleEndian) {} template void FragmentWriter::write(MCDataFragment &F, T Val) { if (IsLittleEndian) Val = support::endian::byte_swap(Val); else Val = support::endian::byte_swap(Val); const char *Start = (const char *)&Val; F.getContents().append(Start, Start + sizeof(T)); } void SymbolTableWriter::createSymtabShndx() { if (ShndxF) return; MCContext &Ctx = Asm.getContext(); const MCSectionELF *SymtabShndxSection = Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, SectionKind::getReadOnly(), 4, ""); MCSectionData *SymtabShndxSD = &Asm.getOrCreateSectionData(*SymtabShndxSection); SymtabShndxSD->setAlignment(4); ShndxF = new MCDataFragment(SymtabShndxSD); unsigned Index = SectionIndexMap.size() + 1; SectionIndexMap[SymtabShndxSection] = Index; for (unsigned I = 0; I < NumWritten; ++I) write(*ShndxF, uint32_t(0)); } template void SymbolTableWriter::write(MCDataFragment &F, T Value) { FWriter.write(F, Value); } SymbolTableWriter::SymbolTableWriter(MCAssembler &Asm, FragmentWriter &FWriter, bool Is64Bit, SectionIndexMapTy &SectionIndexMap, MCDataFragment *SymtabF) : Asm(Asm), FWriter(FWriter), Is64Bit(Is64Bit), SectionIndexMap(SectionIndexMap), SymtabF(SymtabF), ShndxF(nullptr), NumWritten(0) {} void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value, uint64_t size, uint8_t other, uint32_t shndx, bool Reserved) { bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved; if (LargeIndex) createSymtabShndx(); if (ShndxF) { if (LargeIndex) write(*ShndxF, shndx); else write(*ShndxF, uint32_t(0)); } uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx; raw_svector_ostream OS(SymtabF->getContents()); if (Is64Bit) { write(*SymtabF, name); // st_name write(*SymtabF, info); // st_info write(*SymtabF, other); // st_other write(*SymtabF, Index); // st_shndx write(*SymtabF, value); // st_value write(*SymtabF, size); // st_size } else { write(*SymtabF, name); // st_name write(*SymtabF, uint32_t(value)); // st_value write(*SymtabF, uint32_t(size)); // st_size write(*SymtabF, info); // st_info write(*SymtabF, other); // st_other write(*SymtabF, Index); // st_shndx } ++NumWritten; } bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) { const MCFixupKindInfo &FKI = Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind); return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel; } bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) { switch (Variant) { default: return false; case MCSymbolRefExpr::VK_GOT: case MCSymbolRefExpr::VK_PLT: case MCSymbolRefExpr::VK_GOTPCREL: case MCSymbolRefExpr::VK_GOTOFF: 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; } } ELFObjectWriter::~ELFObjectWriter() {} // Emit the ELF header. void ELFObjectWriter::WriteHeader(const MCAssembler &Asm, 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(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB); Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION] // e_ident[EI_OSABI] Write8(TargetObjectWriter->getOSABI()); Write8(0); // e_ident[EI_ABIVERSION] WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD); Write16(ELF::ET_REL); // e_type Write16(TargetObjectWriter->getEMachine()); // 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 // e_flags = whatever the target wants Write32(Asm.getELFHeaderEFlags()); // 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(ELF::SHN_UNDEF); else Write16(NumberOfSections); // e_shstrndx = Section # of '.shstrtab' if (ShstrtabIndex >= ELF::SHN_LORESERVE) Write16(ELF::SHN_XINDEX); else Write16(ShstrtabIndex); } uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout) { if (Data.isCommon() && Data.isExternal()) return Data.getCommonAlignment(); uint64_t Res; if (!Layout.getSymbolOffset(&Data, Res)) return 0; if (Layout.getAssembler().isThumbFunc(&Data.getSymbol())) Res |= 1; return Res; } void ELFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm, const MCAsmLayout &Layout) { // The presence of symbol versions causes undefined symbols and // versions declared with @@@ to be renamed. for (MCSymbolData &OriginalData : Asm.symbols()) { const MCSymbol &Alias = OriginalData.getSymbol(); // Not an alias. if (!Alias.isVariable()) continue; auto *Ref = dyn_cast(Alias.getVariableValue()); if (!Ref) continue; const MCSymbol &Symbol = Ref->getSymbol(); MCSymbolData &SD = Asm.getSymbolData(Symbol); 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. OriginalData.setExternal(SD.isExternal()); MCELF::SetBinding(OriginalData, MCELF::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)); } } static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) { uint8_t Type = newType; // Propagation rules: // IFUNC > FUNC > OBJECT > NOTYPE // TLS_OBJECT > OBJECT > NOTYPE // // dont let the new type degrade the old type switch (origType) { default: break; case ELF::STT_GNU_IFUNC: if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS) Type = ELF::STT_GNU_IFUNC; break; case ELF::STT_FUNC: if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS) Type = ELF::STT_FUNC; break; case ELF::STT_OBJECT: if (Type == ELF::STT_NOTYPE) Type = ELF::STT_OBJECT; break; case ELF::STT_TLS: if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE || Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC) Type = ELF::STT_TLS; break; } return Type; } void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD, const MCAsmLayout &Layout) { MCSymbolData &OrigData = *MSD.SymbolData; assert((!OrigData.getFragment() || (&OrigData.getFragment()->getParent()->getSection() == &OrigData.getSymbol().getSection())) && "The symbol's section doesn't match the fragment's symbol"); const MCSymbol *Base = Layout.getBaseSymbol(OrigData.getSymbol()); // This has to be in sync with when computeSymbolTable uses SHN_ABS or // SHN_COMMON. bool IsReserved = !Base || OrigData.isCommon(); // Binding and Type share the same byte as upper and lower nibbles uint8_t Binding = MCELF::GetBinding(OrigData); uint8_t Type = MCELF::GetType(OrigData); MCSymbolData *BaseSD = nullptr; if (Base) { BaseSD = &Layout.getAssembler().getSymbolData(*Base); Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD)); } uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift); // Other and Visibility share the same byte with Visibility using the lower // 2 bits uint8_t Visibility = MCELF::GetVisibility(OrigData); uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift); Other |= Visibility; uint64_t Value = SymbolValue(OrigData, Layout); uint64_t Size = 0; const MCExpr *ESize = OrigData.getSize(); if (!ESize && Base) ESize = BaseSD->getSize(); if (ESize) { int64_t Res; if (!ESize->EvaluateAsAbsolute(Res, Layout)) report_fatal_error("Size expression must be absolute."); Size = Res; } // Write out the symbol table entry Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other, MSD.SectionIndex, IsReserved); } void ELFObjectWriter::WriteSymbolTable(MCDataFragment *SymtabF, MCAssembler &Asm, const MCAsmLayout &Layout, SectionIndexMapTy &SectionIndexMap) { // The string table must be emitted first because we need the index // into the string table for all the symbol names. // FIXME: Make sure the start of the symbol table is aligned. SymbolTableWriter Writer(Asm, FWriter, is64Bit(), SectionIndexMap, SymtabF); // The first entry is the undefined symbol entry. Writer.writeSymbol(0, 0, 0, 0, 0, 0, false); for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) { Writer.writeSymbol(FileSymbolData[i], ELF::STT_FILE | ELF::STB_LOCAL, 0, 0, ELF::STV_DEFAULT, ELF::SHN_ABS, true); } // Write the symbol table entries. LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1; for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) { ELFSymbolData &MSD = LocalSymbolData[i]; WriteSymbol(Writer, MSD, Layout); } // Write out a symbol table entry for each regular section. for (MCAssembler::const_iterator i = Asm.begin(), e = Asm.end(); i != e; ++i) { const MCSectionELF &Section = static_cast(i->getSection()); if (Section.getType() == ELF::SHT_RELA || Section.getType() == ELF::SHT_REL || Section.getType() == ELF::SHT_STRTAB || Section.getType() == ELF::SHT_SYMTAB || Section.getType() == ELF::SHT_SYMTAB_SHNDX) continue; Writer.writeSymbol(0, ELF::STT_SECTION, 0, 0, ELF::STV_DEFAULT, SectionIndexMap.lookup(&Section), 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(Writer, MSD, Layout); if (MCELF::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(Writer, MSD, Layout); if (MCELF::GetBinding(Data) == ELF::STB_LOCAL) LastLocalSymbolIndex++; } } // It is always valid to create a relocation with a symbol. It is preferable // to use a relocation with a section if that is possible. Using the section // allows us to omit some local symbols from the symbol table. bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm, const MCSymbolRefExpr *RefA, const MCSymbolData *SD, uint64_t C, unsigned Type) const { // A PCRel relocation to an absolute value has no symbol (or section). We // represent that with a relocation to a null section. if (!RefA) return false; MCSymbolRefExpr::VariantKind Kind = RefA->getKind(); switch (Kind) { default: break; // The .odp creation emits a relocation against the symbol ".TOC." which // create a R_PPC64_TOC relocation. However the relocation symbol name // in final object creation should be NULL, since the symbol does not // really exist, it is just the reference to TOC base for the current // object file. Since the symbol is undefined, returning false results // in a relocation with a null section which is the desired result. case MCSymbolRefExpr::VK_PPC_TOCBASE: return false; // These VariantKind cause the relocation to refer to something other than // the symbol itself, like a linker generated table. Since the address of // symbol is not relevant, we cannot replace the symbol with the // section and patch the difference in the addend. case MCSymbolRefExpr::VK_GOT: case MCSymbolRefExpr::VK_PLT: case MCSymbolRefExpr::VK_GOTPCREL: case MCSymbolRefExpr::VK_Mips_GOT: case MCSymbolRefExpr::VK_PPC_GOT_LO: case MCSymbolRefExpr::VK_PPC_GOT_HI: case MCSymbolRefExpr::VK_PPC_GOT_HA: return true; } // An undefined symbol is not in any section, so the relocation has to point // to the symbol itself. const MCSymbol &Sym = SD->getSymbol(); if (Sym.isUndefined()) return true; unsigned Binding = MCELF::GetBinding(*SD); switch(Binding) { default: llvm_unreachable("Invalid Binding"); case ELF::STB_LOCAL: break; case ELF::STB_WEAK: // If the symbol is weak, it might be overridden by a symbol in another // file. The relocation has to point to the symbol so that the linker // can update it. return true; case ELF::STB_GLOBAL: // Global ELF symbols can be preempted by the dynamic linker. The relocation // has to point to the symbol for a reason analogous to the STB_WEAK case. return true; } // If a relocation points to a mergeable section, we have to be careful. // If the offset is zero, a relocation with the section will encode the // same information. With a non-zero offset, the situation is different. // For example, a relocation can point 42 bytes past the end of a string. // If we change such a relocation to use the section, the linker would think // that it pointed to another string and subtracting 42 at runtime will // produce the wrong value. auto &Sec = cast(Sym.getSection()); unsigned Flags = Sec.getFlags(); if (Flags & ELF::SHF_MERGE) { if (C != 0) return true; // It looks like gold has a bug (http://sourceware.org/PR16794) and can // only handle section relocations to mergeable sections if using RELA. if (!hasRelocationAddend()) return true; } // Most TLS relocations use a got, so they need the symbol. Even those that // are just an offset (@tpoff), require a symbol in some linkers (gold, // but not bfd ld). if (Flags & ELF::SHF_TLS) return true; // If the symbol is a thumb function the final relocation must set the lowest // bit. With a symbol that is done by just having the symbol have that bit // set, so we would lose the bit if we relocated with the section. // FIXME: We could use the section but add the bit to the relocation value. if (Asm.isThumbFunc(&Sym)) return true; if (TargetObjectWriter->needsRelocateWithSymbol(Type)) return true; return false; } static const MCSymbol *getWeakRef(const MCSymbolRefExpr &Ref) { const MCSymbol &Sym = Ref.getSymbol(); if (Ref.getKind() == MCSymbolRefExpr::VK_WEAKREF) return &Sym; if (!Sym.isVariable()) return nullptr; const MCExpr *Expr = Sym.getVariableValue(); const auto *Inner = dyn_cast(Expr); if (!Inner) return nullptr; if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF) return &Inner->getSymbol(); return nullptr; } void ELFObjectWriter::RecordRelocation(const MCAssembler &Asm, const MCAsmLayout &Layout, const MCFragment *Fragment, const MCFixup &Fixup, MCValue Target, bool &IsPCRel, uint64_t &FixedValue) { const MCSectionData *FixupSection = Fragment->getParent(); uint64_t C = Target.getConstant(); uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset(); if (const MCSymbolRefExpr *RefB = Target.getSymB()) { assert(RefB->getKind() == MCSymbolRefExpr::VK_None && "Should not have constructed this"); // Let A, B and C being the components of Target and R be the location of // the fixup. If the fixup is not pcrel, we want to compute (A - B + C). // If it is pcrel, we want to compute (A - B + C - R). // In general, ELF has no relocations for -B. It can only represent (A + C) // or (A + C - R). If B = R + K and the relocation is not pcrel, we can // replace B to implement it: (A - R - K + C) if (IsPCRel) Asm.getContext().FatalError( Fixup.getLoc(), "No relocation available to represent this relative expression"); const MCSymbol &SymB = RefB->getSymbol(); if (SymB.isUndefined()) Asm.getContext().FatalError( Fixup.getLoc(), Twine("symbol '") + SymB.getName() + "' can not be undefined in a subtraction expression"); assert(!SymB.isAbsolute() && "Should have been folded"); const MCSection &SecB = SymB.getSection(); if (&SecB != &FixupSection->getSection()) Asm.getContext().FatalError( Fixup.getLoc(), "Cannot represent a difference across sections"); const MCSymbolData &SymBD = Asm.getSymbolData(SymB); uint64_t SymBOffset = Layout.getSymbolOffset(&SymBD); uint64_t K = SymBOffset - FixupOffset; IsPCRel = true; C -= K; } // We either rejected the fixup or folded B into C at this point. const MCSymbolRefExpr *RefA = Target.getSymA(); const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr; const MCSymbolData *SymAD = SymA ? &Asm.getSymbolData(*SymA) : nullptr; unsigned Type = GetRelocType(Target, Fixup, IsPCRel); bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymAD, C, Type); if (!RelocateWithSymbol && SymA && !SymA->isUndefined()) C += Layout.getSymbolOffset(SymAD); uint64_t Addend = 0; if (hasRelocationAddend()) { Addend = C; C = 0; } FixedValue = C; // FIXME: What is this!?!? MCSymbolRefExpr::VariantKind Modifier = RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None; if (RelocNeedsGOT(Modifier)) NeedsGOT = true; if (!RelocateWithSymbol) { const MCSection *SecA = (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr; const MCSectionData *SecAD = SecA ? &Asm.getSectionData(*SecA) : nullptr; ELFRelocationEntry Rec(FixupOffset, SecAD, Type, Addend); Relocations[FixupSection].push_back(Rec); return; } if (SymA) { if (const MCSymbol *R = Renames.lookup(SymA)) SymA = R; if (const MCSymbol *WeakRef = getWeakRef(*RefA)) WeakrefUsedInReloc.insert(WeakRef); else UsedInReloc.insert(SymA); } ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend); Relocations[FixupSection].push_back(Rec); return; } uint64_t ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm, const MCSymbol *S) { const MCSymbolData &SD = Asm.getSymbolData(*S); return SD.getIndex(); } bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout, const MCSymbolData &Data, bool Used, bool Renamed) { const MCSymbol &Symbol = Data.getSymbol(); if (Symbol.isVariable()) { const MCExpr *Expr = Symbol.getVariableValue(); if (const MCSymbolRefExpr *Ref = dyn_cast(Expr)) { if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF) return false; } } if (Used) return true; if (Renamed) return false; if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_") return true; if (Symbol.isVariable()) { const MCSymbol *Base = Layout.getBaseSymbol(Symbol); if (Base && Base->isUndefined()) return false; } bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL; if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal) return false; if (Symbol.isTemporary()) return false; return true; } bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isUsedInReloc) { if (Data.isExternal()) return false; const MCSymbol &Symbol = Data.getSymbol(); if (Symbol.isDefined()) return true; if (isUsedInReloc) return false; return true; } void ELFObjectWriter::ComputeIndexMap(MCAssembler &Asm, SectionIndexMapTy &SectionIndexMap, const RelMapTy &RelMap) { unsigned Index = 1; for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it) { const MCSectionELF &Section = static_cast(it->getSection()); if (Section.getType() != ELF::SHT_GROUP) continue; SectionIndexMap[&Section] = Index++; } for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it) { const MCSectionELF &Section = static_cast(it->getSection()); if (Section.getType() == ELF::SHT_GROUP || Section.getType() == ELF::SHT_REL || Section.getType() == ELF::SHT_RELA) continue; SectionIndexMap[&Section] = Index++; const MCSectionELF *RelSection = RelMap.lookup(&Section); if (RelSection) SectionIndexMap[RelSection] = Index++; } } void ELFObjectWriter::computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout, const SectionIndexMapTy &SectionIndexMap, RevGroupMapTy RevGroupMap, unsigned NumRegularSections) { // FIXME: Is this the correct place to do this? // FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed? if (NeedsGOT) { StringRef Name = "_GLOBAL_OFFSET_TABLE_"; MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name); MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym); Data.setExternal(true); MCELF::SetBinding(Data, ELF::STB_GLOBAL); } // Add the data for the symbols. for (MCSymbolData &SD : Asm.symbols()) { const MCSymbol &Symbol = SD.getSymbol(); bool Used = UsedInReloc.count(&Symbol); bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol); bool isSignature = RevGroupMap.count(&Symbol); if (!isInSymtab(Layout, SD, Used || WeakrefUsed || isSignature, Renames.count(&Symbol))) continue; ELFSymbolData MSD; MSD.SymbolData = &SD; const MCSymbol *BaseSymbol = Layout.getBaseSymbol(Symbol); // Undefined symbols are global, but this is the first place we // are able to set it. bool Local = isLocal(SD, Used); if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) { assert(BaseSymbol); MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol); MCELF::SetBinding(SD, ELF::STB_GLOBAL); MCELF::SetBinding(BaseData, ELF::STB_GLOBAL); } if (!BaseSymbol) { MSD.SectionIndex = ELF::SHN_ABS; } else if (SD.isCommon()) { assert(!Local); MSD.SectionIndex = ELF::SHN_COMMON; } else if (BaseSymbol->isUndefined()) { if (isSignature && !Used) MSD.SectionIndex = SectionIndexMap.lookup(RevGroupMap[&Symbol]); else MSD.SectionIndex = ELF::SHN_UNDEF; if (!Used && WeakrefUsed) MCELF::SetBinding(SD, ELF::STB_WEAK); } else { const MCSectionELF &Section = static_cast(BaseSymbol->getSection()); MSD.SectionIndex = SectionIndexMap.lookup(&Section); assert(MSD.SectionIndex && "Invalid section index!"); } // The @@@ in symbol version is replaced with @ in undefined symbols and // @@ in defined ones. StringRef Name = Symbol.getName(); SmallString<32> Buf; size_t Pos = Name.find("@@@"); if (Pos != StringRef::npos) { Buf += Name.substr(0, Pos); unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1; Buf += Name.substr(Pos + Skip); Name = Buf; } MSD.Name = StrTabBuilder.add(Name); if (MSD.SectionIndex == ELF::SHN_UNDEF) UndefinedSymbolData.push_back(MSD); else if (Local) LocalSymbolData.push_back(MSD); else ExternalSymbolData.push_back(MSD); } for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i) StrTabBuilder.add(*i); StrTabBuilder.finalize(); for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i) FileSymbolData.push_back(StrTabBuilder.getOffset(*i)); for (ELFSymbolData& MSD : LocalSymbolData) MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name); for (ELFSymbolData& MSD : ExternalSymbolData) MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name); for (ELFSymbolData& MSD : UndefinedSymbolData) MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name); // 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 = FileSymbolData.size() + 1; for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) LocalSymbolData[i].SymbolData->setIndex(Index++); Index += NumRegularSections; 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 ELFObjectWriter::CreateRelocationSections(MCAssembler &Asm, MCAsmLayout &Layout, RelMapTy &RelMap) { for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it) { const MCSectionData &SD = *it; if (Relocations[&SD].empty()) continue; MCContext &Ctx = Asm.getContext(); 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); unsigned Flags = 0; StringRef Group = ""; if (Section.getFlags() & ELF::SHF_GROUP) { Flags = ELF::SHF_GROUP; Group = Section.getGroup()->getName(); } const MCSectionELF *RelaSection = Ctx.getELFSection(RelaSectionName, hasRelocationAddend() ? ELF::SHT_RELA : ELF::SHT_REL, Flags, SectionKind::getReadOnly(), EntrySize, Group); RelMap[&Section] = RelaSection; Asm.getOrCreateSectionData(*RelaSection); } } static SmallVector getUncompressedData(MCAsmLayout &Layout, MCSectionData::FragmentListType &Fragments) { SmallVector UncompressedData; for (const MCFragment &F : Fragments) { const SmallVectorImpl *Contents; switch (F.getKind()) { case MCFragment::FT_Data: Contents = &cast(F).getContents(); break; case MCFragment::FT_Dwarf: Contents = &cast(F).getContents(); break; case MCFragment::FT_DwarfFrame: Contents = &cast(F).getContents(); break; default: llvm_unreachable( "Not expecting any other fragment types in a debug_* section"); } UncompressedData.append(Contents->begin(), Contents->end()); } return UncompressedData; } // Include the debug info compression header: // "ZLIB" followed by 8 bytes representing the uncompressed size of the section, // useful for consumers to preallocate a buffer to decompress into. static bool prependCompressionHeader(uint64_t Size, SmallVectorImpl &CompressedContents) { static const StringRef Magic = "ZLIB"; if (Size <= Magic.size() + sizeof(Size) + CompressedContents.size()) return false; if (sys::IsLittleEndianHost) sys::swapByteOrder(Size); CompressedContents.insert(CompressedContents.begin(), Magic.size() + sizeof(Size), 0); std::copy(Magic.begin(), Magic.end(), CompressedContents.begin()); std::copy(reinterpret_cast(&Size), reinterpret_cast(&Size + 1), CompressedContents.begin() + Magic.size()); return true; } // Return a single fragment containing the compressed contents of the whole // section. Null if the section was not compressed for any reason. static std::unique_ptr getCompressedFragment(MCAsmLayout &Layout, MCSectionData::FragmentListType &Fragments) { std::unique_ptr CompressedFragment(new MCDataFragment()); // Gather the uncompressed data from all the fragments, recording the // alignment fragment, if seen, and any fixups. SmallVector UncompressedData = getUncompressedData(Layout, Fragments); SmallVectorImpl &CompressedContents = CompressedFragment->getContents(); zlib::Status Success = zlib::compress( StringRef(UncompressedData.data(), UncompressedData.size()), CompressedContents); if (Success != zlib::StatusOK) return nullptr; if (!prependCompressionHeader(UncompressedData.size(), CompressedContents)) return nullptr; return CompressedFragment; } typedef DenseMap> DefiningSymbolMap; static void UpdateSymbols(const MCAsmLayout &Layout, const std::vector &Symbols, MCFragment &NewFragment) { for (MCSymbolData *Sym : Symbols) { Sym->setOffset(Sym->getOffset() + Layout.getFragmentOffset(Sym->getFragment())); Sym->setFragment(&NewFragment); } } static void CompressDebugSection(MCAssembler &Asm, MCAsmLayout &Layout, const DefiningSymbolMap &DefiningSymbols, const MCSectionELF &Section, MCSectionData &SD) { StringRef SectionName = Section.getSectionName(); MCSectionData::FragmentListType &Fragments = SD.getFragmentList(); std::unique_ptr CompressedFragment = getCompressedFragment(Layout, Fragments); // Leave the section as-is if the fragments could not be compressed. if (!CompressedFragment) return; // Update the fragment+offsets of any symbols referring to fragments in this // section to refer to the new fragment. auto I = DefiningSymbols.find(&SD); if (I != DefiningSymbols.end()) UpdateSymbols(Layout, I->second, *CompressedFragment); // Invalidate the layout for the whole section since it will have new and // different fragments now. Layout.invalidateFragmentsFrom(&Fragments.front()); Fragments.clear(); // Complete the initialization of the new fragment CompressedFragment->setParent(&SD); CompressedFragment->setLayoutOrder(0); Fragments.push_back(CompressedFragment.release()); // Rename from .debug_* to .zdebug_* Asm.getContext().renameELFSection(&Section, (".z" + SectionName.drop_front(1)).str()); } void ELFObjectWriter::CompressDebugSections(MCAssembler &Asm, MCAsmLayout &Layout) { if (!Asm.getContext().getAsmInfo()->compressDebugSections()) return; DefiningSymbolMap DefiningSymbols; for (MCSymbolData &SD : Asm.symbols()) if (MCFragment *F = SD.getFragment()) DefiningSymbols[F->getParent()].push_back(&SD); for (MCSectionData &SD : Asm) { const MCSectionELF &Section = static_cast(SD.getSection()); StringRef SectionName = Section.getSectionName(); // Compressing debug_frame requires handling alignment fragments which is // more work (possibly generalizing MCAssembler.cpp:writeFragment to allow // for writing to arbitrary buffers) for little benefit. if (!SectionName.startswith(".debug_") || SectionName == ".debug_frame") continue; CompressDebugSection(Asm, Layout, DefiningSymbols, Section, SD); } } void ELFObjectWriter::WriteRelocations(MCAssembler &Asm, MCAsmLayout &Layout, const RelMapTy &RelMap) { for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it) { const MCSectionData &SD = *it; const MCSectionELF &Section = static_cast(SD.getSection()); const MCSectionELF *RelaSection = RelMap.lookup(&Section); if (!RelaSection) continue; MCSectionData &RelaSD = Asm.getOrCreateSectionData(*RelaSection); RelaSD.setAlignment(is64Bit() ? 8 : 4); MCDataFragment *F = new MCDataFragment(&RelaSD); WriteRelocationsFragment(Asm, F, &*it); } } void ELFObjectWriter::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 } // ELF doesn't require relocations to be in any order. We sort by the r_offset, // just to match gnu as for easier comparison. The use type is an arbitrary way // of making the sort deterministic. static int cmpRel(const ELFRelocationEntry *AP, const ELFRelocationEntry *BP) { const ELFRelocationEntry &A = *AP; const ELFRelocationEntry &B = *BP; if (A.Offset != B.Offset) return B.Offset - A.Offset; if (B.Type != A.Type) return A.Type - B.Type; llvm_unreachable("ELFRelocs might be unstable!"); } static void sortRelocs(const MCAssembler &Asm, std::vector &Relocs) { array_pod_sort(Relocs.begin(), Relocs.end(), cmpRel); } void ELFObjectWriter::WriteRelocationsFragment(const MCAssembler &Asm, MCDataFragment *F, const MCSectionData *SD) { std::vector &Relocs = Relocations[SD]; sortRelocs(Asm, Relocs); for (unsigned i = 0, e = Relocs.size(); i != e; ++i) { const ELFRelocationEntry &Entry = Relocs[e - i - 1]; unsigned Index; if (Entry.UseSymbol) { Index = getSymbolIndexInSymbolTable(Asm, Entry.Symbol); } else { const MCSectionData *Sec = Entry.Section; if (Sec) Index = Sec->getOrdinal() + FileSymbolData.size() + LocalSymbolData.size() + 1; else Index = 0; } if (is64Bit()) { write(*F, Entry.Offset); if (TargetObjectWriter->isN64()) { write(*F, uint32_t(Index)); write(*F, TargetObjectWriter->getRSsym(Entry.Type)); write(*F, TargetObjectWriter->getRType3(Entry.Type)); write(*F, TargetObjectWriter->getRType2(Entry.Type)); write(*F, TargetObjectWriter->getRType(Entry.Type)); } else { struct ELF::Elf64_Rela ERE64; ERE64.setSymbolAndType(Index, Entry.Type); write(*F, ERE64.r_info); } if (hasRelocationAddend()) write(*F, Entry.Addend); } else { write(*F, uint32_t(Entry.Offset)); struct ELF::Elf32_Rela ERE32; ERE32.setSymbolAndType(Index, Entry.Type); write(*F, ERE32.r_info); if (hasRelocationAddend()) write(*F, uint32_t(Entry.Addend)); } } } void ELFObjectWriter::CreateMetadataSections(MCAssembler &Asm, MCAsmLayout &Layout, SectionIndexMapTy &SectionIndexMap, const RelMapTy &RelMap) { MCContext &Ctx = Asm.getContext(); MCDataFragment *F; unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32; // 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()); MCSectionData &ShstrtabSD = Asm.getOrCreateSectionData(*ShstrtabSection); ShstrtabSD.setAlignment(1); const MCSectionELF *SymtabSection = Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, SectionKind::getReadOnly(), EntrySize, ""); MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection); SymtabSD.setAlignment(is64Bit() ? 8 : 4); const MCSectionELF *StrtabSection; StrtabSection = Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0, SectionKind::getReadOnly()); MCSectionData &StrtabSD = Asm.getOrCreateSectionData(*StrtabSection); StrtabSD.setAlignment(1); ComputeIndexMap(Asm, SectionIndexMap, RelMap); ShstrtabIndex = SectionIndexMap.lookup(ShstrtabSection); SymbolTableIndex = SectionIndexMap.lookup(SymtabSection); StringTableIndex = SectionIndexMap.lookup(StrtabSection); // Symbol table F = new MCDataFragment(&SymtabSD); WriteSymbolTable(F, Asm, Layout, SectionIndexMap); F = new MCDataFragment(&StrtabSD); F->getContents().append(StrTabBuilder.data().begin(), StrTabBuilder.data().end()); F = new MCDataFragment(&ShstrtabSD); // Section header string table. for (auto it = Asm.begin(), ie = Asm.end(); it != ie; ++it) { const MCSectionELF &Section = static_cast(it->getSection()); ShStrTabBuilder.add(Section.getSectionName()); } ShStrTabBuilder.finalize(); F->getContents().append(ShStrTabBuilder.data().begin(), ShStrTabBuilder.data().end()); } void ELFObjectWriter::CreateIndexedSections(MCAssembler &Asm, MCAsmLayout &Layout, GroupMapTy &GroupMap, RevGroupMapTy &RevGroupMap, SectionIndexMapTy &SectionIndexMap, const RelMapTy &RelMap) { // Create the .note.GNU-stack section if needed. MCContext &Ctx = Asm.getContext(); if (Asm.getNoExecStack()) { const MCSectionELF *GnuStackSection = Ctx.getELFSection(".note.GNU-stack", ELF::SHT_PROGBITS, 0, SectionKind::getReadOnly()); Asm.getOrCreateSectionData(*GnuStackSection); } // Build the groups for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it) { const MCSectionELF &Section = static_cast(it->getSection()); if (!(Section.getFlags() & ELF::SHF_GROUP)) continue; const MCSymbol *SignatureSymbol = Section.getGroup(); Asm.getOrCreateSymbolData(*SignatureSymbol); const MCSectionELF *&Group = RevGroupMap[SignatureSymbol]; if (!Group) { Group = Ctx.CreateELFGroupSection(); MCSectionData &Data = Asm.getOrCreateSectionData(*Group); Data.setAlignment(4); MCDataFragment *F = new MCDataFragment(&Data); write(*F, uint32_t(ELF::GRP_COMDAT)); } GroupMap[Group] = SignatureSymbol; } ComputeIndexMap(Asm, SectionIndexMap, RelMap); // Add sections to the groups for (MCAssembler::const_iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it) { const MCSectionELF &Section = static_cast(it->getSection()); if (!(Section.getFlags() & ELF::SHF_GROUP)) continue; const MCSectionELF *Group = RevGroupMap[Section.getGroup()]; MCSectionData &Data = Asm.getOrCreateSectionData(*Group); // FIXME: we could use the previous fragment MCDataFragment *F = new MCDataFragment(&Data); uint32_t Index = SectionIndexMap.lookup(&Section); write(*F, Index); } } void ELFObjectWriter::WriteSection(MCAssembler &Asm, const SectionIndexMapTy &SectionIndexMap, uint32_t GroupSymbolIndex, uint64_t Offset, uint64_t Size, uint64_t Alignment, const MCSectionELF &Section) { uint64_t sh_link = 0; uint64_t sh_info = 0; switch(Section.getType()) { case ELF::SHT_DYNAMIC: sh_link = ShStrTabBuilder.getOffset(Section.getSectionName()); 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()); sh_link = SectionIndexMap.lookup(SymtabSection); assert(sh_link && ".symtab not found"); // Remove ".rel" and ".rela" prefixes. unsigned SecNameLen = (Section.getType() == ELF::SHT_REL) ? 4 : 5; StringRef SectionName = Section.getSectionName().substr(SecNameLen); StringRef GroupName = Section.getGroup() ? Section.getGroup()->getName() : ""; InfoSection = Asm.getContext().getELFSection(SectionName, ELF::SHT_PROGBITS, 0, SectionKind::getReadOnly(), 0, GroupName); sh_info = SectionIndexMap.lookup(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_NOTE: case ELF::SHT_NULL: case ELF::SHT_ARM_ATTRIBUTES: case ELF::SHT_INIT_ARRAY: case ELF::SHT_FINI_ARRAY: case ELF::SHT_PREINIT_ARRAY: case ELF::SHT_X86_64_UNWIND: case ELF::SHT_MIPS_REGINFO: case ELF::SHT_MIPS_OPTIONS: // Nothing to do. break; case ELF::SHT_GROUP: sh_link = SymbolTableIndex; sh_info = GroupSymbolIndex; break; default: llvm_unreachable("FIXME: sh_type value not supported!"); } if (TargetObjectWriter->getEMachine() == ELF::EM_ARM && Section.getType() == ELF::SHT_ARM_EXIDX) { StringRef SecName(Section.getSectionName()); if (SecName == ".ARM.exidx") { sh_link = SectionIndexMap.lookup( Asm.getContext().getELFSection(".text", ELF::SHT_PROGBITS, ELF::SHF_EXECINSTR | ELF::SHF_ALLOC, SectionKind::getText())); } else if (SecName.startswith(".ARM.exidx")) { StringRef GroupName = Section.getGroup() ? Section.getGroup()->getName() : ""; sh_link = SectionIndexMap.lookup(Asm.getContext().getELFSection( SecName.substr(sizeof(".ARM.exidx") - 1), ELF::SHT_PROGBITS, ELF::SHF_EXECINSTR | ELF::SHF_ALLOC, SectionKind::getText(), 0, GroupName)); } } WriteSecHdrEntry(ShStrTabBuilder.getOffset(Section.getSectionName()), Section.getType(), Section.getFlags(), 0, Offset, Size, sh_link, sh_info, Alignment, Section.getEntrySize()); } bool ELFObjectWriter::IsELFMetaDataSection(const MCSectionData &SD) { return SD.getOrdinal() == ~UINT32_C(0) && !SD.getSection().isVirtualSection(); } uint64_t ELFObjectWriter::DataSectionSize(const MCSectionData &SD) { uint64_t Ret = 0; for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e; ++i) { const MCFragment &F = *i; assert(F.getKind() == MCFragment::FT_Data); Ret += cast(F).getContents().size(); } return Ret; } uint64_t ELFObjectWriter::GetSectionFileSize(const MCAsmLayout &Layout, const MCSectionData &SD) { if (IsELFMetaDataSection(SD)) return DataSectionSize(SD); return Layout.getSectionFileSize(&SD); } uint64_t ELFObjectWriter::GetSectionAddressSize(const MCAsmLayout &Layout, const MCSectionData &SD) { if (IsELFMetaDataSection(SD)) return DataSectionSize(SD); return Layout.getSectionAddressSize(&SD); } void ELFObjectWriter::WriteDataSectionData(MCAssembler &Asm, const MCAsmLayout &Layout, const MCSectionELF &Section) { const MCSectionData &SD = Asm.getOrCreateSectionData(Section); uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment()); WriteZeros(Padding); if (IsELFMetaDataSection(SD)) { for (MCSectionData::const_iterator i = SD.begin(), e = SD.end(); i != e; ++i) { const MCFragment &F = *i; assert(F.getKind() == MCFragment::FT_Data); WriteBytes(cast(F).getContents()); } } else { Asm.writeSectionData(&SD, Layout); } } void ELFObjectWriter::WriteSectionHeader(MCAssembler &Asm, const GroupMapTy &GroupMap, const MCAsmLayout &Layout, const SectionIndexMapTy &SectionIndexMap, const SectionOffsetMapTy &SectionOffsetMap) { const unsigned NumSections = Asm.size() + 1; std::vector Sections; Sections.resize(NumSections - 1); for (SectionIndexMapTy::const_iterator i= SectionIndexMap.begin(), e = SectionIndexMap.end(); i != e; ++i) { const std::pair &p = *i; Sections[p.second - 1] = p.first; } // 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 (unsigned i = 0; i < NumSections - 1; ++i) { const MCSectionELF &Section = *Sections[i]; const MCSectionData &SD = Asm.getOrCreateSectionData(Section); uint32_t GroupSymbolIndex; if (Section.getType() != ELF::SHT_GROUP) GroupSymbolIndex = 0; else GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm, GroupMap.lookup(&Section)); uint64_t Size = GetSectionAddressSize(Layout, SD); WriteSection(Asm, SectionIndexMap, GroupSymbolIndex, SectionOffsetMap.lookup(&Section), Size, SD.getAlignment(), Section); } } void ELFObjectWriter::ComputeSectionOrder(MCAssembler &Asm, std::vector &Sections) { for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it) { const MCSectionELF &Section = static_cast(it->getSection()); if (Section.getType() == ELF::SHT_GROUP) Sections.push_back(&Section); } for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it) { const MCSectionELF &Section = static_cast(it->getSection()); if (Section.getType() != ELF::SHT_GROUP && Section.getType() != ELF::SHT_REL && Section.getType() != ELF::SHT_RELA) Sections.push_back(&Section); } for (MCAssembler::iterator it = Asm.begin(), ie = Asm.end(); it != ie; ++it) { const MCSectionELF &Section = static_cast(it->getSection()); if (Section.getType() == ELF::SHT_REL || Section.getType() == ELF::SHT_RELA) Sections.push_back(&Section); } } void ELFObjectWriter::WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) { GroupMapTy GroupMap; RevGroupMapTy RevGroupMap; SectionIndexMapTy SectionIndexMap; unsigned NumUserSections = Asm.size(); CompressDebugSections(Asm, const_cast(Layout)); DenseMap RelMap; CreateRelocationSections(Asm, const_cast(Layout), RelMap); const unsigned NumUserAndRelocSections = Asm.size(); CreateIndexedSections(Asm, const_cast(Layout), GroupMap, RevGroupMap, SectionIndexMap, RelMap); const unsigned AllSections = Asm.size(); const unsigned NumIndexedSections = AllSections - NumUserAndRelocSections; unsigned NumRegularSections = NumUserSections + NumIndexedSections; // Compute symbol table information. computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap, NumRegularSections); WriteRelocations(Asm, const_cast(Layout), RelMap); CreateMetadataSections(const_cast(Asm), const_cast(Layout), SectionIndexMap, RelMap); uint64_t NaturalAlignment = is64Bit() ? 8 : 4; uint64_t HeaderSize = is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr); uint64_t FileOff = HeaderSize; std::vector Sections; ComputeSectionOrder(Asm, Sections); unsigned NumSections = Sections.size(); SectionOffsetMapTy SectionOffsetMap; for (unsigned i = 0; i < NumRegularSections + 1; ++i) { const MCSectionELF &Section = *Sections[i]; const MCSectionData &SD = Asm.getOrCreateSectionData(Section); FileOff = RoundUpToAlignment(FileOff, SD.getAlignment()); // Remember the offset into the file for this section. SectionOffsetMap[&Section] = FileOff; // Get the size of the section in the output file (including padding). FileOff += GetSectionFileSize(Layout, SD); } FileOff = RoundUpToAlignment(FileOff, NaturalAlignment); const unsigned SectionHeaderOffset = FileOff - HeaderSize; uint64_t SectionHeaderEntrySize = is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr); FileOff += (NumSections + 1) * SectionHeaderEntrySize; for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) { const MCSectionELF &Section = *Sections[i]; const MCSectionData &SD = Asm.getOrCreateSectionData(Section); FileOff = RoundUpToAlignment(FileOff, SD.getAlignment()); // Remember the offset into the file for this section. SectionOffsetMap[&Section] = FileOff; // Get the size of the section in the output file (including padding). FileOff += GetSectionFileSize(Layout, SD); } // Write out the ELF header ... WriteHeader(Asm, SectionHeaderOffset, NumSections + 1); // ... then the regular sections ... // + because of .shstrtab for (unsigned i = 0; i < NumRegularSections + 1; ++i) WriteDataSectionData(Asm, Layout, *Sections[i]); uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment); WriteZeros(Padding); // ... then the section header table ... WriteSectionHeader(Asm, GroupMap, Layout, SectionIndexMap, SectionOffsetMap); // ... and then the remaining sections ... for (unsigned i = NumRegularSections + 1; i < NumSections; ++i) WriteDataSectionData(Asm, Layout, *Sections[i]); } bool ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm, const MCSymbolData &DataA, const MCFragment &FB, bool InSet, bool IsPCRel) const { if (DataA.getFlags() & ELF_STB_Weak || MCELF::GetType(DataA) == ELF::STT_GNU_IFUNC) return false; return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl( Asm, DataA, FB,InSet, IsPCRel); } MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW, raw_ostream &OS, bool IsLittleEndian) { return new ELFObjectWriter(MOTW, OS, IsLittleEndian); }