| //===- subzero/src/IceELFObjectWriter.cpp - ELF object file writer --------===// |
| // |
| // The Subzero Code Generator |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| /// |
| /// \file |
| /// \brief Defines the writer for ELF relocatable object files. |
| /// |
| //===----------------------------------------------------------------------===// |
| |
| #include "IceELFObjectWriter.h" |
| |
| #include "IceAssembler.h" |
| #include "IceDefs.h" |
| #include "IceELFSection.h" |
| #include "IceELFStreamer.h" |
| #include "IceGlobalContext.h" |
| #include "IceGlobalInits.h" |
| #include "IceInst.h" |
| #include "IceOperand.h" |
| |
| #include "llvm/Support/ELF.h" |
| #include "llvm/Support/MathExtras.h" |
| |
| namespace Ice { |
| |
| namespace { |
| |
| constexpr struct { |
| bool IsELF64; |
| uint16_t ELFMachine; |
| uint32_t ELFFlags; |
| } ELFTargetInfo[TargetArch_NUM] = { |
| #define X(tag, str, is_elf64, e_machine, e_flags) \ |
| {is_elf64, e_machine, e_flags}, |
| TARGETARCH_TABLE |
| #undef X |
| }; |
| |
| bool isELF64(const ClFlags &Flags) { |
| const TargetArch Arch = Flags.getTargetArch(); |
| if (Arch >= TargetArch_NUM) { |
| llvm_unreachable("Invalid target arch for isELF64"); |
| return false; |
| } |
| |
| if (Flags.getApplicationBinaryInterface() == ABI_PNaCl && |
| !Flags.getUseSandboxing()) { |
| // Unsandboxed PNaCl code is always ELF32 (pexes are ILP32.) |
| return false; |
| } |
| |
| return ELFTargetInfo[Arch].IsELF64; |
| } |
| |
| uint16_t getELFMachine(TargetArch Arch) { |
| if (Arch < TargetArch_NUM) |
| return ELFTargetInfo[Arch].ELFMachine; |
| llvm_unreachable("Invalid target arch for getELFMachine"); |
| return EM_NONE; |
| } |
| |
| uint32_t getELFFlags(TargetArch Arch) { |
| if (Arch < TargetArch_NUM) |
| return ELFTargetInfo[Arch].ELFFlags; |
| llvm_unreachable("Invalid target arch for getELFFlags"); |
| return 0; |
| } |
| |
| } // end of anonymous namespace |
| |
| ELFObjectWriter::ELFObjectWriter(GlobalContext &Ctx, ELFStreamer &Out) |
| : Ctx(Ctx), Str(Out), ELF64(isELF64(getFlags())) { |
| // Create the special bookkeeping sections now. |
| constexpr char NullSectionName[] = ""; |
| NullSection = new (Ctx.allocate<ELFSection>()) |
| ELFSection(NullSectionName, SHT_NULL, 0, 0, 0); |
| |
| constexpr char ShStrTabName[] = ".shstrtab"; |
| ShStrTab = new (Ctx.allocate<ELFStringTableSection>()) |
| ELFStringTableSection(ShStrTabName, SHT_STRTAB, 0, 1, 0); |
| ShStrTab->add(ShStrTabName); |
| |
| constexpr char SymTabName[] = ".symtab"; |
| const Elf64_Xword SymTabAlign = ELF64 ? 8 : 4; |
| const Elf64_Xword SymTabEntSize = |
| ELF64 ? sizeof(Elf64_Sym) : sizeof(Elf32_Sym); |
| static_assert(sizeof(Elf64_Sym) == 24 && sizeof(Elf32_Sym) == 16, |
| "Elf_Sym sizes cannot be derived from sizeof"); |
| SymTab = createSection<ELFSymbolTableSection>(SymTabName, SHT_SYMTAB, 0, |
| SymTabAlign, SymTabEntSize); |
| SymTab->createNullSymbol(NullSection, &Ctx); |
| |
| constexpr char StrTabName[] = ".strtab"; |
| StrTab = |
| createSection<ELFStringTableSection>(StrTabName, SHT_STRTAB, 0, 1, 0); |
| } |
| |
| template <typename T> |
| T *ELFObjectWriter::createSection(const std::string &Name, Elf64_Word ShType, |
| Elf64_Xword ShFlags, Elf64_Xword ShAddralign, |
| Elf64_Xword ShEntsize) { |
| assert(!SectionNumbersAssigned); |
| T *NewSection = |
| new (Ctx.allocate<T>()) T(Name, ShType, ShFlags, ShAddralign, ShEntsize); |
| ShStrTab->add(Name); |
| return NewSection; |
| } |
| |
| ELFRelocationSection * |
| ELFObjectWriter::createRelocationSection(const ELFSection *RelatedSection) { |
| // Choice of RELA vs REL is actually separate from elf64 vs elf32, but in |
| // practice we've only had .rela for elf64 (x86-64). In the future, the two |
| // properties may need to be decoupled and the ShEntSize can vary more. |
| const Elf64_Word ShType = ELF64 ? SHT_RELA : SHT_REL; |
| const std::string RelPrefix = ELF64 ? ".rela" : ".rel"; |
| const std::string RelSectionName = RelPrefix + RelatedSection->getName(); |
| const Elf64_Xword ShAlign = ELF64 ? 8 : 4; |
| const Elf64_Xword ShEntSize = ELF64 ? sizeof(Elf64_Rela) : sizeof(Elf32_Rel); |
| static_assert(sizeof(Elf64_Rela) == 24 && sizeof(Elf32_Rel) == 8, |
| "Elf_Rel/Rela sizes cannot be derived from sizeof"); |
| constexpr Elf64_Xword ShFlags = 0; |
| ELFRelocationSection *RelSection = createSection<ELFRelocationSection>( |
| RelSectionName, ShType, ShFlags, ShAlign, ShEntSize); |
| RelSection->setRelatedSection(RelatedSection); |
| return RelSection; |
| } |
| |
| template <typename UserSectionList> |
| void ELFObjectWriter::assignRelSectionNumInPairs(SizeT &CurSectionNumber, |
| UserSectionList &UserSections, |
| RelSectionList &RelSections, |
| SectionList &AllSections) { |
| RelSectionList::iterator RelIt = RelSections.begin(); |
| RelSectionList::iterator RelE = RelSections.end(); |
| for (ELFSection *UserSection : UserSections) { |
| UserSection->setNumber(CurSectionNumber++); |
| UserSection->setNameStrIndex(ShStrTab->getIndex(UserSection->getName())); |
| AllSections.push_back(UserSection); |
| if (RelIt != RelE) { |
| ELFRelocationSection *RelSection = *RelIt; |
| if (RelSection->getRelatedSection() == UserSection) { |
| RelSection->setInfoNum(UserSection->getNumber()); |
| RelSection->setNumber(CurSectionNumber++); |
| RelSection->setNameStrIndex(ShStrTab->getIndex(RelSection->getName())); |
| AllSections.push_back(RelSection); |
| ++RelIt; |
| } |
| } |
| } |
| // Should finish with UserIt at the same time as RelIt. |
| assert(RelIt == RelE); |
| return; |
| } |
| |
| void ELFObjectWriter::assignRelLinkNum(SizeT SymTabNumber, |
| RelSectionList &RelSections) { |
| for (ELFRelocationSection *S : RelSections) { |
| S->setLinkNum(SymTabNumber); |
| } |
| } |
| |
| void ELFObjectWriter::assignSectionNumbersInfo(SectionList &AllSections) { |
| // Go through each section, assigning them section numbers and and fill in |
| // the size for sections that aren't incrementally updated. |
| assert(!SectionNumbersAssigned); |
| SizeT CurSectionNumber = 0; |
| NullSection->setNumber(CurSectionNumber++); |
| // The rest of the fields are initialized to 0, and stay that way. |
| AllSections.push_back(NullSection); |
| |
| assignRelSectionNumInPairs<TextSectionList>(CurSectionNumber, TextSections, |
| RelTextSections, AllSections); |
| assignRelSectionNumInPairs<DataSectionList>(CurSectionNumber, DataSections, |
| RelDataSections, AllSections); |
| for (ELFSection *BSSSection : BSSSections) { |
| BSSSection->setNumber(CurSectionNumber++); |
| BSSSection->setNameStrIndex(ShStrTab->getIndex(BSSSection->getName())); |
| AllSections.push_back(BSSSection); |
| } |
| assignRelSectionNumInPairs<DataSectionList>(CurSectionNumber, RODataSections, |
| RelRODataSections, AllSections); |
| |
| ShStrTab->setNumber(CurSectionNumber++); |
| ShStrTab->setNameStrIndex(ShStrTab->getIndex(ShStrTab->getName())); |
| AllSections.push_back(ShStrTab); |
| |
| SymTab->setNumber(CurSectionNumber++); |
| SymTab->setNameStrIndex(ShStrTab->getIndex(SymTab->getName())); |
| AllSections.push_back(SymTab); |
| |
| StrTab->setNumber(CurSectionNumber++); |
| StrTab->setNameStrIndex(ShStrTab->getIndex(StrTab->getName())); |
| AllSections.push_back(StrTab); |
| |
| SymTab->setLinkNum(StrTab->getNumber()); |
| SymTab->setInfoNum(SymTab->getNumLocals()); |
| |
| assignRelLinkNum(SymTab->getNumber(), RelTextSections); |
| assignRelLinkNum(SymTab->getNumber(), RelDataSections); |
| assignRelLinkNum(SymTab->getNumber(), RelRODataSections); |
| SectionNumbersAssigned = true; |
| } |
| |
| Elf64_Off ELFObjectWriter::alignFileOffset(Elf64_Xword Align) { |
| Elf64_Off OffsetInFile = Str.tell(); |
| Elf64_Xword AlignDiff = Utils::OffsetToAlignment(OffsetInFile, Align); |
| if (AlignDiff == 0) |
| return OffsetInFile; |
| Str.writeZeroPadding(AlignDiff); |
| OffsetInFile += AlignDiff; |
| return OffsetInFile; |
| } |
| |
| void ELFObjectWriter::writeFunctionCode(GlobalString FuncName, bool IsInternal, |
| Assembler *Asm) { |
| assert(!SectionNumbersAssigned); |
| TimerMarker T_func(&Ctx, FuncName.toStringOrEmpty()); |
| TimerMarker Timer(TimerStack::TT_writeELF, &Ctx); |
| ELFTextSection *Section = nullptr; |
| ELFRelocationSection *RelSection = nullptr; |
| const bool FunctionSections = getFlags().getFunctionSections(); |
| if (TextSections.empty() || FunctionSections) { |
| std::string SectionName = ".text"; |
| if (FunctionSections) |
| SectionName += "." + FuncName; |
| constexpr Elf64_Xword ShFlags = SHF_ALLOC | SHF_EXECINSTR; |
| const Elf64_Xword ShAlign = 1 << Asm->getBundleAlignLog2Bytes(); |
| Section = createSection<ELFTextSection>(SectionName, SHT_PROGBITS, ShFlags, |
| ShAlign, 0); |
| Elf64_Off OffsetInFile = alignFileOffset(Section->getSectionAlign()); |
| Section->setFileOffset(OffsetInFile); |
| TextSections.push_back(Section); |
| RelSection = createRelocationSection(Section); |
| RelTextSections.push_back(RelSection); |
| } else { |
| Section = TextSections[0]; |
| RelSection = RelTextSections[0]; |
| } |
| const RelocOffsetT OffsetInSection = Section->getCurrentSize(); |
| // Function symbols are set to 0 size in the symbol table, in contrast to |
| // data symbols which have a proper size. |
| constexpr SizeT SymbolSize = 0; |
| uint8_t SymbolType; |
| uint8_t SymbolBinding; |
| if (IsInternal && !getFlags().getDisableInternal()) { |
| SymbolType = STT_NOTYPE; |
| SymbolBinding = STB_LOCAL; |
| } else { |
| SymbolType = STT_FUNC; |
| SymbolBinding = STB_GLOBAL; |
| } |
| SymTab->createDefinedSym(FuncName, SymbolType, SymbolBinding, Section, |
| OffsetInSection, SymbolSize); |
| StrTab->add(FuncName); |
| |
| // Copy the fixup information from per-function Assembler memory to the |
| // object writer's memory, for writing later. |
| const auto &Fixups = Asm->fixups(); |
| if (!Fixups.empty()) { |
| if (!RelSection->isRela()) { |
| // This is a non-rela section, so we need to update the instruction stream |
| // with the relocation addends. |
| for (const auto *Fixup : Fixups) { |
| Fixup->emitOffset(Asm); |
| } |
| } |
| RelSection->addRelocations(OffsetInSection, Asm->fixups(), SymTab); |
| } |
| Section->appendData(Str, Asm->getBufferView()); |
| } |
| |
| namespace { |
| |
| ELFObjectWriter::SectionType |
| classifyGlobalSection(const VariableDeclaration *Var) { |
| if (Var->getIsConstant()) |
| return ELFObjectWriter::ROData; |
| if (Var->hasNonzeroInitializer()) |
| return ELFObjectWriter::Data; |
| return ELFObjectWriter::BSS; |
| } |
| |
| // Partition the Vars list by SectionType into VarsBySection. If TranslateOnly |
| // is non-empty, then only the TranslateOnly variable is kept for emission. |
| void partitionGlobalsBySection(const VariableDeclarationList &Vars, |
| VariableDeclarationPartition VarsBySection[]) { |
| for (VariableDeclaration *Var : Vars) { |
| if (getFlags().matchTranslateOnly(Var->getName(), 0)) { |
| size_t Section = classifyGlobalSection(Var); |
| assert(Section < ELFObjectWriter::NumSectionTypes); |
| VarsBySection[Section].push_back(Var); |
| } |
| } |
| } |
| |
| } // end of anonymous namespace |
| |
| void ELFObjectWriter::writeTargetRODataSection(const std::string &Name, |
| Elf64_Word ShType, |
| Elf64_Xword ShFlags, |
| Elf64_Xword ShAddralign, |
| Elf64_Xword ShEntsize, |
| const llvm::StringRef &SecData) { |
| TimerMarker Timer(TimerStack::TT_writeELF, &Ctx); |
| assert(!SectionNumbersAssigned); |
| ELFDataSection *Section = createSection<ELFDataSection>( |
| Name, ShType, ShFlags, ShAddralign, ShEntsize); |
| Section->setFileOffset(alignFileOffset(ShAddralign)); |
| Section->appendData(Str, llvm::StringRef(SecData.data(), SecData.size())); |
| RODataSections.push_back(Section); |
| } |
| |
| void ELFObjectWriter::writeDataSection(const VariableDeclarationList &Vars, |
| FixupKind RelocationKind, |
| const std::string &SectionSuffix, |
| bool IsPIC) { |
| TimerMarker Timer(TimerStack::TT_writeELF, &Ctx); |
| assert(!SectionNumbersAssigned); |
| VariableDeclarationPartition VarsBySection[ELFObjectWriter::NumSectionTypes]; |
| for (auto &SectionList : VarsBySection) |
| SectionList.reserve(Vars.size()); |
| partitionGlobalsBySection(Vars, VarsBySection); |
| size_t I = 0; |
| for (auto &SectionList : VarsBySection) { |
| writeDataOfType(static_cast<SectionType>(I++), SectionList, RelocationKind, |
| SectionSuffix, IsPIC); |
| } |
| } |
| |
| namespace { |
| std::string MangleSectionName(const char Base[], const std::string &Suffix) { |
| if (Suffix.empty()) |
| return Base; |
| return Base + ("." + Suffix); |
| } |
| } // end of anonymous namespace |
| |
| // TODO(jvoung): Handle fdata-sections. |
| void ELFObjectWriter::writeDataOfType(SectionType ST, |
| const VariableDeclarationPartition &Vars, |
| FixupKind RelocationKind, |
| const std::string &SectionSuffix, |
| bool IsPIC) { |
| if (Vars.empty()) |
| return; |
| ELFDataSection *Section; |
| ELFRelocationSection *RelSection; |
| Elf64_Xword ShAddralign = 1; |
| for (VariableDeclaration *Var : Vars) { |
| Elf64_Xword Align = Var->getAlignment(); |
| ShAddralign = std::max(ShAddralign, Align); |
| } |
| constexpr Elf64_Xword ShEntsize = 0; // non-uniform data element size. |
| // Lift this out, so it can be re-used if we do fdata-sections? |
| switch (ST) { |
| case ROData: { |
| const std::string SectionName = |
| MangleSectionName(IsPIC ? ".data.rel.ro" : ".rodata", SectionSuffix); |
| const Elf64_Xword ShFlags = IsPIC ? (SHF_ALLOC | SHF_WRITE) : SHF_ALLOC; |
| Section = createSection<ELFDataSection>(SectionName, SHT_PROGBITS, ShFlags, |
| ShAddralign, ShEntsize); |
| Section->setFileOffset(alignFileOffset(ShAddralign)); |
| RODataSections.push_back(Section); |
| RelSection = createRelocationSection(Section); |
| RelRODataSections.push_back(RelSection); |
| break; |
| } |
| case Data: { |
| const std::string SectionName = MangleSectionName(".data", SectionSuffix); |
| constexpr Elf64_Xword ShFlags = SHF_ALLOC | SHF_WRITE; |
| Section = createSection<ELFDataSection>(SectionName, SHT_PROGBITS, ShFlags, |
| ShAddralign, ShEntsize); |
| Section->setFileOffset(alignFileOffset(ShAddralign)); |
| DataSections.push_back(Section); |
| RelSection = createRelocationSection(Section); |
| RelDataSections.push_back(RelSection); |
| break; |
| } |
| case BSS: { |
| const std::string SectionName = MangleSectionName(".bss", SectionSuffix); |
| constexpr Elf64_Xword ShFlags = SHF_ALLOC | SHF_WRITE; |
| Section = createSection<ELFDataSection>(SectionName, SHT_NOBITS, ShFlags, |
| ShAddralign, ShEntsize); |
| Section->setFileOffset(alignFileOffset(ShAddralign)); |
| BSSSections.push_back(Section); |
| break; |
| } |
| case NumSectionTypes: |
| llvm::report_fatal_error("Unknown SectionType"); |
| break; |
| } |
| |
| constexpr uint8_t SymbolType = STT_OBJECT; |
| for (VariableDeclaration *Var : Vars) { |
| // If the variable declaration does not have an initializer, its symtab |
| // entry will be created separately. |
| if (!Var->hasInitializer()) |
| continue; |
| constexpr Elf64_Xword MinAlign = 1; |
| const auto Align = std::max<Elf64_Xword>(MinAlign, Var->getAlignment()); |
| Section->padToAlignment(Str, Align); |
| SizeT SymbolSize = Var->getNumBytes(); |
| bool IsExternal = Var->isExternal() || getFlags().getDisableInternal(); |
| const uint8_t SymbolBinding = IsExternal ? STB_GLOBAL : STB_LOCAL; |
| GlobalString Name = Var->getName(); |
| SymTab->createDefinedSym(Name, SymbolType, SymbolBinding, Section, |
| Section->getCurrentSize(), SymbolSize); |
| StrTab->add(Name); |
| if (!Var->hasNonzeroInitializer()) { |
| assert(ST == BSS || ST == ROData); |
| if (ST == ROData) |
| Section->appendZeros(Str, SymbolSize); |
| else |
| Section->setSize(Section->getCurrentSize() + SymbolSize); |
| } else { |
| assert(ST != BSS); |
| for (const auto *Init : Var->getInitializers()) { |
| switch (Init->getKind()) { |
| case VariableDeclaration::Initializer::DataInitializerKind: { |
| const auto &Data = |
| llvm::cast<VariableDeclaration::DataInitializer>(Init) |
| ->getContents(); |
| Section->appendData(Str, llvm::StringRef(Data.data(), Data.size())); |
| break; |
| } |
| case VariableDeclaration::Initializer::ZeroInitializerKind: |
| Section->appendZeros(Str, Init->getNumBytes()); |
| break; |
| case VariableDeclaration::Initializer::RelocInitializerKind: { |
| const auto *Reloc = |
| llvm::cast<VariableDeclaration::RelocInitializer>(Init); |
| AssemblerFixup NewFixup; |
| NewFixup.set_position(Section->getCurrentSize()); |
| NewFixup.set_kind(Reloc->hasFixup() ? Reloc->getFixup() |
| : RelocationKind); |
| assert(NewFixup.kind() != llvm::ELF::R_ARM_NONE); |
| NewFixup.set_value(Ctx.getConstantSym( |
| Reloc->getOffset(), Reloc->getDeclaration()->getName())); |
| RelSection->addRelocation(NewFixup); |
| Section->appendRelocationOffset(Str, RelSection->isRela(), |
| Reloc->getOffset()); |
| break; |
| } |
| } |
| } |
| } |
| } |
| } |
| |
| void ELFObjectWriter::writeInitialELFHeader() { |
| TimerMarker Timer(TimerStack::TT_writeELF, &Ctx); |
| assert(!SectionNumbersAssigned); |
| constexpr Elf64_Off DummySHOffset = 0; |
| constexpr SizeT DummySHStrIndex = 0; |
| constexpr SizeT DummyNumSections = 0; |
| if (ELF64) { |
| writeELFHeaderInternal<true>(DummySHOffset, DummySHStrIndex, |
| DummyNumSections); |
| } else { |
| writeELFHeaderInternal<false>(DummySHOffset, DummySHStrIndex, |
| DummyNumSections); |
| } |
| } |
| |
| template <bool IsELF64> |
| void ELFObjectWriter::writeELFHeaderInternal(Elf64_Off SectionHeaderOffset, |
| SizeT SectHeaderStrIndex, |
| SizeT NumSections) { |
| // Write the e_ident: magic number, class, etc. The e_ident is byte order and |
| // ELF class independent. |
| Str.writeBytes(llvm::StringRef(ElfMagic, strlen(ElfMagic))); |
| Str.write8(IsELF64 ? ELFCLASS64 : ELFCLASS32); |
| Str.write8(ELFDATA2LSB); |
| Str.write8(EV_CURRENT); |
| Str.write8(ELFOSABI_NONE); |
| constexpr uint8_t ELF_ABIVersion = 0; |
| Str.write8(ELF_ABIVersion); |
| Str.writeZeroPadding(EI_NIDENT - EI_PAD); |
| |
| // TODO(jvoung): Handle and test > 64K sections. See the generic ABI doc: |
| // https://refspecs.linuxbase.org/elf/gabi4+/ch4.eheader.html e_shnum should |
| // be 0 and then actual number of sections is stored in the sh_size member of |
| // the 0th section. |
| assert(NumSections < SHN_LORESERVE); |
| assert(SectHeaderStrIndex < SHN_LORESERVE); |
| |
| const TargetArch Arch = getFlags().getTargetArch(); |
| // Write the rest of the file header, which does depend on byte order and ELF |
| // class. |
| Str.writeLE16(ET_REL); // e_type |
| Str.writeLE16(getELFMachine(getFlags().getTargetArch())); // e_machine |
| Str.writeELFWord<IsELF64>(1); // e_version |
| // Since this is for a relocatable object, there is no entry point, and no |
| // program headers. |
| Str.writeAddrOrOffset<IsELF64>(0); // e_entry |
| Str.writeAddrOrOffset<IsELF64>(0); // e_phoff |
| Str.writeAddrOrOffset<IsELF64>(SectionHeaderOffset); // e_shoff |
| Str.writeELFWord<IsELF64>(getELFFlags(Arch)); // e_flags |
| Str.writeLE16(IsELF64 ? sizeof(Elf64_Ehdr) : sizeof(Elf32_Ehdr)); // e_ehsize |
| static_assert(sizeof(Elf64_Ehdr) == 64 && sizeof(Elf32_Ehdr) == 52, |
| "Elf_Ehdr sizes cannot be derived from sizeof"); |
| Str.writeLE16(0); // e_phentsize |
| Str.writeLE16(0); // e_phnum |
| Str.writeLE16(IsELF64 ? sizeof(Elf64_Shdr) |
| : sizeof(Elf32_Shdr)); // e_shentsize |
| static_assert(sizeof(Elf64_Shdr) == 64 && sizeof(Elf32_Shdr) == 40, |
| "Elf_Shdr sizes cannot be derived from sizeof"); |
| Str.writeLE16(static_cast<Elf64_Half>(NumSections)); // e_shnum |
| Str.writeLE16(static_cast<Elf64_Half>(SectHeaderStrIndex)); // e_shstrndx |
| } |
| |
| template <typename ConstType> void ELFObjectWriter::writeConstantPool(Type Ty) { |
| TimerMarker Timer(TimerStack::TT_writeELF, &Ctx); |
| ConstantList Pool = Ctx.getConstantPool(Ty); |
| if (Pool.empty()) { |
| return; |
| } |
| SizeT Align = typeAlignInBytes(Ty); |
| size_t EntSize = typeWidthInBytes(Ty); |
| char Buf[20]; |
| SizeT WriteAmt = std::min(EntSize, llvm::array_lengthof(Buf)); |
| // Check that we write the full PrimType. |
| assert(WriteAmt == EntSize); |
| // Assume that writing WriteAmt bytes at a time allows us to avoid aligning |
| // between entries. |
| assert(WriteAmt % Align == 0); |
| constexpr Elf64_Xword ShFlags = SHF_ALLOC | SHF_MERGE; |
| std::string SecBuffer; |
| llvm::raw_string_ostream SecStrBuf(SecBuffer); |
| SecStrBuf << ".rodata.cst" << WriteAmt; |
| ELFDataSection *Section = createSection<ELFDataSection>( |
| SecStrBuf.str(), SHT_PROGBITS, ShFlags, Align, WriteAmt); |
| RODataSections.push_back(Section); |
| SizeT OffsetInSection = 0; |
| // The symbol table entry doesn't need to know the defined symbol's size |
| // since this is in a section with a fixed Entry Size. |
| constexpr SizeT SymbolSize = 0; |
| Section->setFileOffset(alignFileOffset(Align)); |
| |
| // Write the data. |
| for (Constant *C : Pool) { |
| if (!C->getShouldBePooled()) |
| continue; |
| auto *Const = llvm::cast<ConstType>(C); |
| GlobalString SymName = Const->getLabelName(); |
| SymTab->createDefinedSym(SymName, STT_NOTYPE, STB_LOCAL, Section, |
| OffsetInSection, SymbolSize); |
| StrTab->add(SymName); |
| typename ConstType::PrimType Value = Const->getValue(); |
| memcpy(Buf, &Value, WriteAmt); |
| Str.writeBytes(llvm::StringRef(Buf, WriteAmt)); |
| OffsetInSection += WriteAmt; |
| } |
| Section->setSize(OffsetInSection); |
| } |
| |
| // Instantiate known needed versions of the template, since we are defining the |
| // function in the .cpp file instead of the .h file. We may need to instantiate |
| // constant pools for integers as well if we do constant-pooling of large |
| // integers to remove them from the instruction stream (fewer bytes controlled |
| // by an attacker). |
| template void ELFObjectWriter::writeConstantPool<ConstantFloat>(Type Ty); |
| |
| template void ELFObjectWriter::writeConstantPool<ConstantDouble>(Type Ty); |
| |
| template void ELFObjectWriter::writeConstantPool<ConstantInteger32>(Type Ty); |
| |
| void ELFObjectWriter::writeAllRelocationSections() { |
| writeRelocationSections(RelTextSections); |
| writeRelocationSections(RelDataSections); |
| writeRelocationSections(RelRODataSections); |
| } |
| |
| void ELFObjectWriter::writeJumpTable(const JumpTableData &JT, |
| FixupKind RelocationKind, bool IsPIC) { |
| TimerMarker Timer(TimerStack::TT_writeELF, &Ctx); |
| ELFDataSection *Section; |
| ELFRelocationSection *RelSection; |
| const Elf64_Xword PointerSize = typeWidthInBytes(getPointerType()); |
| const Elf64_Xword ShAddralign = PointerSize; |
| const Elf64_Xword ShEntsize = PointerSize; |
| const std::string SectionName = MangleSectionName( |
| IsPIC ? ".data.rel.ro" : ".rodata", JT.getSectionName()); |
| Section = createSection<ELFDataSection>(SectionName, SHT_PROGBITS, SHF_ALLOC, |
| ShAddralign, ShEntsize); |
| Section->setFileOffset(alignFileOffset(ShAddralign)); |
| RODataSections.push_back(Section); |
| RelSection = createRelocationSection(Section); |
| RelRODataSections.push_back(RelSection); |
| |
| constexpr uint8_t SymbolType = STT_OBJECT; |
| Section->padToAlignment(Str, PointerSize); |
| const bool IsExternal = getFlags().getDisableInternal(); |
| const uint8_t SymbolBinding = IsExternal ? STB_GLOBAL : STB_LOCAL; |
| const auto JumpTableName = JT.getName(); |
| SymTab->createDefinedSym(JumpTableName, SymbolType, SymbolBinding, Section, |
| Section->getCurrentSize(), PointerSize); |
| StrTab->add(JumpTableName); |
| |
| for (intptr_t TargetOffset : JT.getTargetOffsets()) { |
| AssemblerFixup NewFixup; |
| NewFixup.set_position(Section->getCurrentSize()); |
| NewFixup.set_kind(RelocationKind); |
| NewFixup.set_value(Ctx.getConstantSym(TargetOffset, JT.getFunctionName())); |
| RelSection->addRelocation(NewFixup); |
| Section->appendRelocationOffset(Str, RelSection->isRela(), TargetOffset); |
| } |
| } |
| |
| void ELFObjectWriter::setUndefinedSyms(const ConstantList &UndefSyms) { |
| TimerMarker Timer(TimerStack::TT_writeELF, &Ctx); |
| for (const Constant *S : UndefSyms) { |
| const auto *Sym = llvm::cast<ConstantRelocatable>(S); |
| GlobalString Name = Sym->getName(); |
| assert(Name.hasStdString()); |
| assert(Sym->getOffset() == 0); |
| SymTab->noteUndefinedSym(Name, NullSection); |
| StrTab->add(Name); |
| } |
| } |
| |
| void ELFObjectWriter::writeRelocationSections(RelSectionList &RelSections) { |
| for (ELFRelocationSection *RelSec : RelSections) { |
| Elf64_Off Offset = alignFileOffset(RelSec->getSectionAlign()); |
| RelSec->setFileOffset(Offset); |
| RelSec->setSize(RelSec->getSectionDataSize()); |
| if (ELF64) { |
| RelSec->writeData<true>(Str, SymTab); |
| } else { |
| RelSec->writeData<false>(Str, SymTab); |
| } |
| } |
| } |
| |
| void ELFObjectWriter::writeNonUserSections() { |
| TimerMarker Timer(TimerStack::TT_writeELF, &Ctx); |
| |
| // Write out the shstrtab now that all sections are known. |
| ShStrTab->doLayout(); |
| ShStrTab->setSize(ShStrTab->getSectionDataSize()); |
| Elf64_Off ShStrTabOffset = alignFileOffset(ShStrTab->getSectionAlign()); |
| ShStrTab->setFileOffset(ShStrTabOffset); |
| Str.writeBytes(ShStrTab->getSectionData()); |
| |
| SectionList AllSections; |
| assignSectionNumbersInfo(AllSections); |
| |
| // Finalize the regular StrTab and fix up references in the SymTab. |
| StrTab->doLayout(); |
| StrTab->setSize(StrTab->getSectionDataSize()); |
| |
| SymTab->updateIndices(StrTab); |
| |
| Elf64_Off SymTabOffset = alignFileOffset(SymTab->getSectionAlign()); |
| SymTab->setFileOffset(SymTabOffset); |
| SymTab->setSize(SymTab->getSectionDataSize()); |
| SymTab->writeData(Str, ELF64); |
| |
| Elf64_Off StrTabOffset = alignFileOffset(StrTab->getSectionAlign()); |
| StrTab->setFileOffset(StrTabOffset); |
| Str.writeBytes(StrTab->getSectionData()); |
| |
| writeAllRelocationSections(); |
| |
| // Write out the section headers. |
| const size_t ShdrAlign = ELF64 ? 8 : 4; |
| Elf64_Off ShOffset = alignFileOffset(ShdrAlign); |
| for (const auto S : AllSections) { |
| if (ELF64) |
| S->writeHeader<true>(Str); |
| else |
| S->writeHeader<false>(Str); |
| } |
| |
| // Finally write the updated ELF header w/ the correct number of sections. |
| Str.seek(0); |
| if (ELF64) { |
| writeELFHeaderInternal<true>(ShOffset, ShStrTab->getNumber(), |
| AllSections.size()); |
| } else { |
| writeELFHeaderInternal<false>(ShOffset, ShStrTab->getNumber(), |
| AllSections.size()); |
| } |
| } |
| |
| } // end of namespace Ice |
