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-rw-r--r--contrib/llvm/lib/MC/ELFObjectWriter.cpp1351
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diff --git a/contrib/llvm/lib/MC/ELFObjectWriter.cpp b/contrib/llvm/lib/MC/ELFObjectWriter.cpp
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+++ b/contrib/llvm/lib/MC/ELFObjectWriter.cpp
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+//===- 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/MCExpr.h"
+#include "llvm/MC/MCFixupKindInfo.h"
+#include "llvm/MC/MCObjectWriter.h"
+#include "llvm/MC/MCSectionELF.h"
+#include "llvm/MC/MCSymbolELF.h"
+#include "llvm/MC/MCValue.h"
+#include "llvm/MC/StringTableBuilder.h"
+#include "llvm/Support/Compression.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/ELF.h"
+#include "llvm/Support/Endian.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/StringSaver.h"
+#include <vector>
+using namespace llvm;
+
+#undef DEBUG_TYPE
+#define DEBUG_TYPE "reloc-info"
+
+namespace {
+
+typedef DenseMap<const MCSectionELF *, uint32_t> SectionIndexMapTy;
+
+class ELFObjectWriter;
+
+class SymbolTableWriter {
+ ELFObjectWriter &EWriter;
+ bool Is64Bit;
+
+ // indexes we are going to write to .symtab_shndx.
+ std::vector<uint32_t> ShndxIndexes;
+
+ // The numbel of symbols written so far.
+ unsigned NumWritten;
+
+ void createSymtabShndx();
+
+ template <typename T> void write(T Value);
+
+public:
+ SymbolTableWriter(ELFObjectWriter &EWriter, bool Is64Bit);
+
+ void writeSymbol(uint32_t name, uint8_t info, uint64_t value, uint64_t size,
+ uint8_t other, uint32_t shndx, bool Reserved);
+
+ ArrayRef<uint32_t> getShndxIndexes() const { return ShndxIndexes; }
+};
+
+class ELFObjectWriter : public MCObjectWriter {
+ static bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind);
+ static uint64_t SymbolValue(const MCSymbol &Sym, const MCAsmLayout &Layout);
+ static bool isInSymtab(const MCAsmLayout &Layout, const MCSymbolELF &Symbol,
+ bool Used, bool Renamed);
+
+ /// Helper struct for containing some precomputed information on symbols.
+ struct ELFSymbolData {
+ const MCSymbolELF *Symbol;
+ uint32_t SectionIndex;
+ StringRef Name;
+
+ // Support lexicographic sorting.
+ bool operator<(const ELFSymbolData &RHS) const {
+ unsigned LHSType = Symbol->getType();
+ unsigned RHSType = RHS.Symbol->getType();
+ if (LHSType == ELF::STT_SECTION && RHSType != ELF::STT_SECTION)
+ return false;
+ if (LHSType != ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
+ return true;
+ if (LHSType == ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
+ return SectionIndex < RHS.SectionIndex;
+ return Name < RHS.Name;
+ }
+ };
+
+ /// The target specific ELF writer instance.
+ std::unique_ptr<MCELFObjectTargetWriter> TargetObjectWriter;
+
+ DenseMap<const MCSymbolELF *, const MCSymbolELF *> Renames;
+
+ llvm::DenseMap<const MCSectionELF *, std::vector<ELFRelocationEntry>>
+ Relocations;
+
+ /// @}
+ /// @name Symbol Table Data
+ /// @{
+
+ BumpPtrAllocator Alloc;
+ StringSaver VersionSymSaver{Alloc};
+ StringTableBuilder StrTabBuilder{StringTableBuilder::ELF};
+
+ /// @}
+
+ // 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;
+
+ // Sections in the order they are to be output in the section table.
+ std::vector<const MCSectionELF *> SectionTable;
+ unsigned addToSectionTable(const MCSectionELF *Sec);
+
+ // 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);
+ }
+
+ void align(unsigned Alignment);
+
+ public:
+ ELFObjectWriter(MCELFObjectTargetWriter *MOTW, raw_pwrite_stream &OS,
+ bool IsLittleEndian)
+ : MCObjectWriter(OS, IsLittleEndian), TargetObjectWriter(MOTW) {}
+
+ void reset() override {
+ Renames.clear();
+ Relocations.clear();
+ StrTabBuilder.clear();
+ SectionTable.clear();
+ MCObjectWriter::reset();
+ }
+
+ ~ELFObjectWriter() override;
+
+ void WriteWord(uint64_t W) {
+ if (is64Bit())
+ write64(W);
+ else
+ write32(W);
+ }
+
+ template <typename T> void write(T Val) {
+ if (IsLittleEndian)
+ support::endian::Writer<support::little>(getStream()).write(Val);
+ else
+ support::endian::Writer<support::big>(getStream()).write(Val);
+ }
+
+ void writeHeader(const MCAssembler &Asm);
+
+ void writeSymbol(SymbolTableWriter &Writer, uint32_t StringIndex,
+ ELFSymbolData &MSD, const MCAsmLayout &Layout);
+
+ // Start and end offset of each section
+ typedef std::map<const MCSectionELF *, std::pair<uint64_t, uint64_t>>
+ SectionOffsetsTy;
+
+ bool shouldRelocateWithSymbol(const MCAssembler &Asm,
+ const MCSymbolRefExpr *RefA,
+ const MCSymbol *Sym, uint64_t C,
+ unsigned Type) const;
+
+ void recordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
+ const MCFragment *Fragment, const MCFixup &Fixup,
+ MCValue Target, bool &IsPCRel,
+ uint64_t &FixedValue) override;
+
+ // Map from a signature symbol to the group section index
+ typedef DenseMap<const MCSymbol *, unsigned> RevGroupMapTy;
+
+ /// 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.
+ void computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
+ const SectionIndexMapTy &SectionIndexMap,
+ const RevGroupMapTy &RevGroupMap,
+ SectionOffsetsTy &SectionOffsets);
+
+ MCSectionELF *createRelocationSection(MCContext &Ctx,
+ const MCSectionELF &Sec);
+
+ const MCSectionELF *createStringTable(MCContext &Ctx);
+
+ void executePostLayoutBinding(MCAssembler &Asm,
+ const MCAsmLayout &Layout) override;
+
+ void writeSectionHeader(const MCAsmLayout &Layout,
+ const SectionIndexMapTy &SectionIndexMap,
+ const SectionOffsetsTy &SectionOffsets);
+
+ void writeSectionData(const MCAssembler &Asm, MCSection &Sec,
+ const MCAsmLayout &Layout);
+
+ 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 writeRelocations(const MCAssembler &Asm, const MCSectionELF &Sec);
+
+ bool isSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
+ const MCSymbol &SymA,
+ const MCFragment &FB,
+ bool InSet,
+ bool IsPCRel) const override;
+
+ bool isWeak(const MCSymbol &Sym) const override;
+
+ void writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
+ void writeSection(const SectionIndexMapTy &SectionIndexMap,
+ uint32_t GroupSymbolIndex, uint64_t Offset, uint64_t Size,
+ const MCSectionELF &Section);
+ };
+}
+
+void ELFObjectWriter::align(unsigned Alignment) {
+ uint64_t Padding = OffsetToAlignment(getStream().tell(), Alignment);
+ WriteZeros(Padding);
+}
+
+unsigned ELFObjectWriter::addToSectionTable(const MCSectionELF *Sec) {
+ SectionTable.push_back(Sec);
+ StrTabBuilder.add(Sec->getSectionName());
+ return SectionTable.size();
+}
+
+void SymbolTableWriter::createSymtabShndx() {
+ if (!ShndxIndexes.empty())
+ return;
+
+ ShndxIndexes.resize(NumWritten);
+}
+
+template <typename T> void SymbolTableWriter::write(T Value) {
+ EWriter.write(Value);
+}
+
+SymbolTableWriter::SymbolTableWriter(ELFObjectWriter &EWriter, bool Is64Bit)
+ : EWriter(EWriter), Is64Bit(Is64Bit), 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 (!ShndxIndexes.empty()) {
+ if (LargeIndex)
+ ShndxIndexes.push_back(shndx);
+ else
+ ShndxIndexes.push_back(0);
+ }
+
+ uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
+
+ if (Is64Bit) {
+ write(name); // st_name
+ write(info); // st_info
+ write(other); // st_other
+ write(Index); // st_shndx
+ write(value); // st_value
+ write(size); // st_size
+ } else {
+ write(name); // st_name
+ write(uint32_t(value)); // st_value
+ write(uint32_t(size)); // st_size
+ write(info); // st_info
+ write(other); // st_other
+ write(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;
+}
+
+ELFObjectWriter::~ELFObjectWriter()
+{}
+
+// Emit the ELF header.
+void ELFObjectWriter::writeHeader(const MCAssembler &Asm) {
+ // ELF Header
+ // ----------
+ //
+ // Note
+ // ----
+ // emitWord method behaves differently for ELF32 and ELF64, writing
+ // 4 bytes in the former and 8 in the latter.
+
+ writeBytes(ELF::ElfMagic); // e_ident[EI_MAG0] to 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(0); // 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
+ write16(0);
+
+ // e_shstrndx = Section # of '.shstrtab'
+ assert(StringTableIndex < ELF::SHN_LORESERVE);
+ write16(StringTableIndex);
+}
+
+uint64_t ELFObjectWriter::SymbolValue(const MCSymbol &Sym,
+ const MCAsmLayout &Layout) {
+ if (Sym.isCommon() && Sym.isExternal())
+ return Sym.getCommonAlignment();
+
+ uint64_t Res;
+ if (!Layout.getSymbolOffset(Sym, Res))
+ return 0;
+
+ if (Layout.getAssembler().isThumbFunc(&Sym))
+ 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 (const MCSymbol &A : Asm.symbols()) {
+ const auto &Alias = cast<MCSymbolELF>(A);
+ // Not an alias.
+ if (!Alias.isVariable())
+ continue;
+ auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
+ if (!Ref)
+ continue;
+ const auto &Symbol = cast<MCSymbolELF>(Ref->getSymbol());
+
+ 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.
+ Alias.setExternal(Symbol.isExternal());
+ Alias.setBinding(Symbol.getBinding());
+
+ 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,
+ uint32_t StringIndex, ELFSymbolData &MSD,
+ const MCAsmLayout &Layout) {
+ const auto &Symbol = cast<MCSymbolELF>(*MSD.Symbol);
+ const MCSymbolELF *Base =
+ cast_or_null<MCSymbolELF>(Layout.getBaseSymbol(Symbol));
+
+ // This has to be in sync with when computeSymbolTable uses SHN_ABS or
+ // SHN_COMMON.
+ bool IsReserved = !Base || Symbol.isCommon();
+
+ // Binding and Type share the same byte as upper and lower nibbles
+ uint8_t Binding = Symbol.getBinding();
+ uint8_t Type = Symbol.getType();
+ if (Base) {
+ Type = mergeTypeForSet(Type, Base->getType());
+ }
+ uint8_t Info = (Binding << 4) | Type;
+
+ // Other and Visibility share the same byte with Visibility using the lower
+ // 2 bits
+ uint8_t Visibility = Symbol.getVisibility();
+ uint8_t Other = Symbol.getOther() | Visibility;
+
+ uint64_t Value = SymbolValue(*MSD.Symbol, Layout);
+ uint64_t Size = 0;
+
+ const MCExpr *ESize = MSD.Symbol->getSize();
+ if (!ESize && Base)
+ ESize = Base->getSize();
+
+ if (ESize) {
+ int64_t Res;
+ if (!ESize->evaluateKnownAbsolute(Res, Layout))
+ report_fatal_error("Size expression must be absolute.");
+ Size = Res;
+ }
+
+ // Write out the symbol table entry
+ Writer.writeSymbol(StringIndex, Info, Value, Size, Other, MSD.SectionIndex,
+ IsReserved);
+}
+
+// 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 MCSymbol *S, uint64_t C,
+ unsigned Type) const {
+ const auto *Sym = cast_or_null<MCSymbolELF>(S);
+ // 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.
+ assert(Sym && "Expected a symbol");
+ if (Sym->isUndefined())
+ return true;
+
+ unsigned Binding = Sym->getBinding();
+ 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<MCSectionELF>(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 gold versions before
+ // 5efeedf61e4fe720fd3e9a08e6c91c10abb66d42 (2014-09-26) which fixed
+ // http://sourceware.org/PR16773.
+ 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(*Sym, Type))
+ return true;
+ return false;
+}
+
+// True if the assembler knows nothing about the final value of the symbol.
+// This doesn't cover the comdat issues, since in those cases the assembler
+// can at least know that all symbols in the section will move together.
+static bool isWeak(const MCSymbolELF &Sym) {
+ if (Sym.getType() == ELF::STT_GNU_IFUNC)
+ return true;
+
+ switch (Sym.getBinding()) {
+ default:
+ llvm_unreachable("Unknown binding");
+ case ELF::STB_LOCAL:
+ return false;
+ case ELF::STB_GLOBAL:
+ return false;
+ case ELF::STB_WEAK:
+ case ELF::STB_GNU_UNIQUE:
+ return true;
+ }
+}
+
+void ELFObjectWriter::recordRelocation(MCAssembler &Asm,
+ const MCAsmLayout &Layout,
+ const MCFragment *Fragment,
+ const MCFixup &Fixup, MCValue Target,
+ bool &IsPCRel, uint64_t &FixedValue) {
+ const MCSectionELF &FixupSection = cast<MCSectionELF>(*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().reportError(
+ Fixup.getLoc(),
+ "No relocation available to represent this relative expression");
+ return;
+ }
+
+ const auto &SymB = cast<MCSymbolELF>(RefB->getSymbol());
+
+ if (SymB.isUndefined()) {
+ Asm.getContext().reportError(
+ Fixup.getLoc(),
+ Twine("symbol '") + SymB.getName() +
+ "' can not be undefined in a subtraction expression");
+ return;
+ }
+
+ assert(!SymB.isAbsolute() && "Should have been folded");
+ const MCSection &SecB = SymB.getSection();
+ if (&SecB != &FixupSection) {
+ Asm.getContext().reportError(
+ Fixup.getLoc(), "Cannot represent a difference across sections");
+ return;
+ }
+
+ if (::isWeak(SymB)) {
+ Asm.getContext().reportError(
+ Fixup.getLoc(), "Cannot represent a subtraction with a weak symbol");
+ return;
+ }
+
+ uint64_t SymBOffset = Layout.getSymbolOffset(SymB);
+ 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 auto *SymA = RefA ? cast<MCSymbolELF>(&RefA->getSymbol()) : nullptr;
+
+ bool ViaWeakRef = false;
+ if (SymA && SymA->isVariable()) {
+ const MCExpr *Expr = SymA->getVariableValue();
+ if (const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr)) {
+ if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF) {
+ SymA = cast<MCSymbolELF>(&Inner->getSymbol());
+ ViaWeakRef = true;
+ }
+ }
+ }
+
+ unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
+ bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymA, C, Type);
+ if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
+ C += Layout.getSymbolOffset(*SymA);
+
+ uint64_t Addend = 0;
+ if (hasRelocationAddend()) {
+ Addend = C;
+ C = 0;
+ }
+
+ FixedValue = C;
+
+ if (!RelocateWithSymbol) {
+ const MCSection *SecA =
+ (SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
+ auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
+ const auto *SectionSymbol =
+ ELFSec ? cast<MCSymbolELF>(ELFSec->getBeginSymbol()) : nullptr;
+ if (SectionSymbol)
+ SectionSymbol->setUsedInReloc();
+ ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend);
+ Relocations[&FixupSection].push_back(Rec);
+ return;
+ }
+
+ if (SymA) {
+ if (const MCSymbolELF *R = Renames.lookup(SymA))
+ SymA = R;
+
+ if (ViaWeakRef)
+ SymA->setIsWeakrefUsedInReloc();
+ else
+ SymA->setUsedInReloc();
+ }
+ ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
+ Relocations[&FixupSection].push_back(Rec);
+ return;
+}
+
+bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
+ const MCSymbolELF &Symbol, bool Used,
+ bool Renamed) {
+ if (Symbol.isVariable()) {
+ const MCExpr *Expr = Symbol.getVariableValue();
+ if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
+ if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
+ return false;
+ }
+ }
+
+ if (Used)
+ return true;
+
+ if (Renamed)
+ return false;
+
+ if (Symbol.isVariable() && Symbol.isUndefined()) {
+ // FIXME: this is here just to diagnose the case of a var = commmon_sym.
+ Layout.getBaseSymbol(Symbol);
+ return false;
+ }
+
+ if (Symbol.isUndefined() && !Symbol.isBindingSet())
+ return false;
+
+ if (Symbol.isTemporary())
+ return false;
+
+ if (Symbol.getType() == ELF::STT_SECTION)
+ return false;
+
+ return true;
+}
+
+void ELFObjectWriter::computeSymbolTable(
+ MCAssembler &Asm, const MCAsmLayout &Layout,
+ const SectionIndexMapTy &SectionIndexMap, const RevGroupMapTy &RevGroupMap,
+ SectionOffsetsTy &SectionOffsets) {
+ MCContext &Ctx = Asm.getContext();
+ SymbolTableWriter Writer(*this, is64Bit());
+
+ // Symbol table
+ unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
+ MCSectionELF *SymtabSection =
+ Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, EntrySize, "");
+ SymtabSection->setAlignment(is64Bit() ? 8 : 4);
+ SymbolTableIndex = addToSectionTable(SymtabSection);
+
+ align(SymtabSection->getAlignment());
+ uint64_t SecStart = getStream().tell();
+
+ // The first entry is the undefined symbol entry.
+ Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
+
+ std::vector<ELFSymbolData> LocalSymbolData;
+ std::vector<ELFSymbolData> ExternalSymbolData;
+
+ // Add the data for the symbols.
+ bool HasLargeSectionIndex = false;
+ for (const MCSymbol &S : Asm.symbols()) {
+ const auto &Symbol = cast<MCSymbolELF>(S);
+ bool Used = Symbol.isUsedInReloc();
+ bool WeakrefUsed = Symbol.isWeakrefUsedInReloc();
+ bool isSignature = Symbol.isSignature();
+
+ if (!isInSymtab(Layout, Symbol, Used || WeakrefUsed || isSignature,
+ Renames.count(&Symbol)))
+ continue;
+
+ if (Symbol.isTemporary() && Symbol.isUndefined()) {
+ Ctx.reportError(SMLoc(), "Undefined temporary symbol");
+ continue;
+ }
+
+ ELFSymbolData MSD;
+ MSD.Symbol = cast<MCSymbolELF>(&Symbol);
+
+ bool Local = Symbol.getBinding() == ELF::STB_LOCAL;
+ assert(Local || !Symbol.isTemporary());
+
+ if (Symbol.isAbsolute()) {
+ MSD.SectionIndex = ELF::SHN_ABS;
+ } else if (Symbol.isCommon()) {
+ assert(!Local);
+ MSD.SectionIndex = ELF::SHN_COMMON;
+ } else if (Symbol.isUndefined()) {
+ if (isSignature && !Used) {
+ MSD.SectionIndex = RevGroupMap.lookup(&Symbol);
+ if (MSD.SectionIndex >= ELF::SHN_LORESERVE)
+ HasLargeSectionIndex = true;
+ } else {
+ MSD.SectionIndex = ELF::SHN_UNDEF;
+ }
+ } else {
+ const MCSectionELF &Section =
+ static_cast<const MCSectionELF &>(Symbol.getSection());
+ MSD.SectionIndex = SectionIndexMap.lookup(&Section);
+ assert(MSD.SectionIndex && "Invalid section index!");
+ if (MSD.SectionIndex >= ELF::SHN_LORESERVE)
+ HasLargeSectionIndex = true;
+ }
+
+ // The @@@ in symbol version is replaced with @ in undefined symbols and @@
+ // in defined ones.
+ //
+ // FIXME: All name handling should be done before we get to the writer,
+ // including dealing with GNU-style version suffixes. Fixing this isn't
+ // trivial.
+ //
+ // We thus have to be careful to not perform the symbol version replacement
+ // blindly:
+ //
+ // The ELF format is used on Windows by the MCJIT engine. Thus, on
+ // Windows, the ELFObjectWriter can encounter symbols mangled using the MS
+ // Visual Studio C++ name mangling scheme. Symbols mangled using the MSVC
+ // C++ name mangling can legally have "@@@" as a sub-string. In that case,
+ // the EFLObjectWriter should not interpret the "@@@" sub-string as
+ // specifying GNU-style symbol versioning. The ELFObjectWriter therefore
+ // checks for the MSVC C++ name mangling prefix which is either "?", "@?",
+ // "__imp_?" or "__imp_@?".
+ //
+ // It would have been interesting to perform the MS mangling prefix check
+ // only when the target triple is of the form *-pc-windows-elf. But, it
+ // seems that this information is not easily accessible from the
+ // ELFObjectWriter.
+ StringRef Name = Symbol.getName();
+ SmallString<32> Buf;
+ if (!Name.startswith("?") && !Name.startswith("@?") &&
+ !Name.startswith("__imp_?") && !Name.startswith("__imp_@?")) {
+ // This symbol isn't following the MSVC C++ name mangling convention. We
+ // can thus safely interpret the @@@ in symbol names as specifying symbol
+ // versioning.
+ 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 = VersionSymSaver.save(Buf.c_str());
+ }
+ }
+
+ // Sections have their own string table
+ if (Symbol.getType() != ELF::STT_SECTION) {
+ MSD.Name = Name;
+ StrTabBuilder.add(Name);
+ }
+
+ if (Local)
+ LocalSymbolData.push_back(MSD);
+ else
+ ExternalSymbolData.push_back(MSD);
+ }
+
+ // This holds the .symtab_shndx section index.
+ unsigned SymtabShndxSectionIndex = 0;
+
+ if (HasLargeSectionIndex) {
+ MCSectionELF *SymtabShndxSection =
+ Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 4, "");
+ SymtabShndxSectionIndex = addToSectionTable(SymtabShndxSection);
+ SymtabShndxSection->setAlignment(4);
+ }
+
+ ArrayRef<std::string> FileNames = Asm.getFileNames();
+ for (const std::string &Name : FileNames)
+ StrTabBuilder.add(Name);
+
+ StrTabBuilder.finalize();
+
+ for (const std::string &Name : FileNames)
+ Writer.writeSymbol(StrTabBuilder.getOffset(Name),
+ ELF::STT_FILE | ELF::STB_LOCAL, 0, 0, ELF::STV_DEFAULT,
+ ELF::SHN_ABS, true);
+
+ // Symbols are required to be in lexicographic order.
+ array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
+ array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
+
+ // Set the symbol indices. Local symbols must come before all other
+ // symbols with non-local bindings.
+ unsigned Index = FileNames.size() + 1;
+
+ for (ELFSymbolData &MSD : LocalSymbolData) {
+ unsigned StringIndex = MSD.Symbol->getType() == ELF::STT_SECTION
+ ? 0
+ : StrTabBuilder.getOffset(MSD.Name);
+ MSD.Symbol->setIndex(Index++);
+ writeSymbol(Writer, StringIndex, MSD, Layout);
+ }
+
+ // Write the symbol table entries.
+ LastLocalSymbolIndex = Index;
+
+ for (ELFSymbolData &MSD : ExternalSymbolData) {
+ unsigned StringIndex = StrTabBuilder.getOffset(MSD.Name);
+ MSD.Symbol->setIndex(Index++);
+ writeSymbol(Writer, StringIndex, MSD, Layout);
+ assert(MSD.Symbol->getBinding() != ELF::STB_LOCAL);
+ }
+
+ uint64_t SecEnd = getStream().tell();
+ SectionOffsets[SymtabSection] = std::make_pair(SecStart, SecEnd);
+
+ ArrayRef<uint32_t> ShndxIndexes = Writer.getShndxIndexes();
+ if (ShndxIndexes.empty()) {
+ assert(SymtabShndxSectionIndex == 0);
+ return;
+ }
+ assert(SymtabShndxSectionIndex != 0);
+
+ SecStart = getStream().tell();
+ const MCSectionELF *SymtabShndxSection =
+ SectionTable[SymtabShndxSectionIndex - 1];
+ for (uint32_t Index : ShndxIndexes)
+ write(Index);
+ SecEnd = getStream().tell();
+ SectionOffsets[SymtabShndxSection] = std::make_pair(SecStart, SecEnd);
+}
+
+MCSectionELF *
+ELFObjectWriter::createRelocationSection(MCContext &Ctx,
+ const MCSectionELF &Sec) {
+ if (Relocations[&Sec].empty())
+ return nullptr;
+
+ const StringRef SectionName = Sec.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;
+ if (Sec.getFlags() & ELF::SHF_GROUP)
+ Flags = ELF::SHF_GROUP;
+
+ MCSectionELF *RelaSection = Ctx.createELFRelSection(
+ RelaSectionName, hasRelocationAddend() ? ELF::SHT_RELA : ELF::SHT_REL,
+ Flags, EntrySize, Sec.getGroup(), &Sec);
+ RelaSection->setAlignment(is64Bit() ? 8 : 4);
+ return RelaSection;
+}
+
+// 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<char> &CompressedContents) {
+ 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<char *>(&Size),
+ reinterpret_cast<char *>(&Size + 1),
+ CompressedContents.begin() + Magic.size());
+ return true;
+}
+
+void ELFObjectWriter::writeSectionData(const MCAssembler &Asm, MCSection &Sec,
+ const MCAsmLayout &Layout) {
+ MCSectionELF &Section = static_cast<MCSectionELF &>(Sec);
+ 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 (!Asm.getContext().getAsmInfo()->compressDebugSections() ||
+ !SectionName.startswith(".debug_") || SectionName == ".debug_frame") {
+ Asm.writeSectionData(&Section, Layout);
+ return;
+ }
+
+ SmallVector<char, 128> UncompressedData;
+ raw_svector_ostream VecOS(UncompressedData);
+ raw_pwrite_stream &OldStream = getStream();
+ setStream(VecOS);
+ Asm.writeSectionData(&Section, Layout);
+ setStream(OldStream);
+
+ SmallVector<char, 128> CompressedContents;
+ zlib::Status Success = zlib::compress(
+ StringRef(UncompressedData.data(), UncompressedData.size()),
+ CompressedContents);
+ if (Success != zlib::StatusOK) {
+ getStream() << UncompressedData;
+ return;
+ }
+
+ if (!prependCompressionHeader(UncompressedData.size(), CompressedContents)) {
+ getStream() << UncompressedData;
+ return;
+ }
+ Asm.getContext().renameELFSection(&Section,
+ (".z" + SectionName.drop_front(1)).str());
+ getStream() << CompressedContents;
+}
+
+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
+}
+
+void ELFObjectWriter::writeRelocations(const MCAssembler &Asm,
+ const MCSectionELF &Sec) {
+ std::vector<ELFRelocationEntry> &Relocs = Relocations[&Sec];
+
+ // We record relocations by pushing to the end of a vector. Reverse the vector
+ // to get the relocations in the order they were created.
+ // In most cases that is not important, but it can be for special sections
+ // (.eh_frame) or specific relocations (TLS optimizations on SystemZ).
+ std::reverse(Relocs.begin(), Relocs.end());
+
+ // Sort the relocation entries. MIPS needs this.
+ TargetObjectWriter->sortRelocs(Asm, Relocs);
+
+ for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
+ const ELFRelocationEntry &Entry = Relocs[e - i - 1];
+ unsigned Index = Entry.Symbol ? Entry.Symbol->getIndex() : 0;
+
+ if (is64Bit()) {
+ write(Entry.Offset);
+ if (TargetObjectWriter->isN64()) {
+ write(uint32_t(Index));
+
+ write(TargetObjectWriter->getRSsym(Entry.Type));
+ write(TargetObjectWriter->getRType3(Entry.Type));
+ write(TargetObjectWriter->getRType2(Entry.Type));
+ write(TargetObjectWriter->getRType(Entry.Type));
+ } else {
+ struct ELF::Elf64_Rela ERE64;
+ ERE64.setSymbolAndType(Index, Entry.Type);
+ write(ERE64.r_info);
+ }
+ if (hasRelocationAddend())
+ write(Entry.Addend);
+ } else {
+ write(uint32_t(Entry.Offset));
+
+ struct ELF::Elf32_Rela ERE32;
+ ERE32.setSymbolAndType(Index, Entry.Type);
+ write(ERE32.r_info);
+
+ if (hasRelocationAddend())
+ write(uint32_t(Entry.Addend));
+ }
+ }
+}
+
+const MCSectionELF *ELFObjectWriter::createStringTable(MCContext &Ctx) {
+ const MCSectionELF *StrtabSection = SectionTable[StringTableIndex - 1];
+ getStream() << StrTabBuilder.data();
+ return StrtabSection;
+}
+
+void ELFObjectWriter::writeSection(const SectionIndexMapTy &SectionIndexMap,
+ uint32_t GroupSymbolIndex, uint64_t Offset,
+ uint64_t Size, const MCSectionELF &Section) {
+ uint64_t sh_link = 0;
+ uint64_t sh_info = 0;
+
+ switch(Section.getType()) {
+ default:
+ // Nothing to do.
+ break;
+
+ case ELF::SHT_DYNAMIC:
+ llvm_unreachable("SHT_DYNAMIC in a relocatable object");
+
+ case ELF::SHT_REL:
+ case ELF::SHT_RELA: {
+ sh_link = SymbolTableIndex;
+ assert(sh_link && ".symtab not found");
+ const MCSectionELF *InfoSection = Section.getAssociatedSection();
+ 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_GROUP:
+ sh_link = SymbolTableIndex;
+ sh_info = GroupSymbolIndex;
+ break;
+ }
+
+ if (TargetObjectWriter->getEMachine() == ELF::EM_ARM &&
+ Section.getType() == ELF::SHT_ARM_EXIDX)
+ sh_link = SectionIndexMap.lookup(Section.getAssociatedSection());
+
+ WriteSecHdrEntry(StrTabBuilder.getOffset(Section.getSectionName()),
+ Section.getType(), Section.getFlags(), 0, Offset, Size,
+ sh_link, sh_info, Section.getAlignment(),
+ Section.getEntrySize());
+}
+
+void ELFObjectWriter::writeSectionHeader(
+ const MCAsmLayout &Layout, const SectionIndexMapTy &SectionIndexMap,
+ const SectionOffsetsTy &SectionOffsets) {
+ const unsigned NumSections = SectionTable.size();
+
+ // Null section first.
+ uint64_t FirstSectionSize =
+ (NumSections + 1) >= ELF::SHN_LORESERVE ? NumSections + 1 : 0;
+ WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, 0, 0, 0, 0);
+
+ for (const MCSectionELF *Section : SectionTable) {
+ uint32_t GroupSymbolIndex;
+ unsigned Type = Section->getType();
+ if (Type != ELF::SHT_GROUP)
+ GroupSymbolIndex = 0;
+ else
+ GroupSymbolIndex = Section->getGroup()->getIndex();
+
+ const std::pair<uint64_t, uint64_t> &Offsets =
+ SectionOffsets.find(Section)->second;
+ uint64_t Size;
+ if (Type == ELF::SHT_NOBITS)
+ Size = Layout.getSectionAddressSize(Section);
+ else
+ Size = Offsets.second - Offsets.first;
+
+ writeSection(SectionIndexMap, GroupSymbolIndex, Offsets.first, Size,
+ *Section);
+ }
+}
+
+void ELFObjectWriter::writeObject(MCAssembler &Asm,
+ const MCAsmLayout &Layout) {
+ MCContext &Ctx = Asm.getContext();
+ MCSectionELF *StrtabSection =
+ Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
+ StringTableIndex = addToSectionTable(StrtabSection);
+
+ RevGroupMapTy RevGroupMap;
+ SectionIndexMapTy SectionIndexMap;
+
+ std::map<const MCSymbol *, std::vector<const MCSectionELF *>> GroupMembers;
+
+ // Write out the ELF header ...
+ writeHeader(Asm);
+
+ // ... then the sections ...
+ SectionOffsetsTy SectionOffsets;
+ std::vector<MCSectionELF *> Groups;
+ std::vector<MCSectionELF *> Relocations;
+ for (MCSection &Sec : Asm) {
+ MCSectionELF &Section = static_cast<MCSectionELF &>(Sec);
+
+ align(Section.getAlignment());
+
+ // Remember the offset into the file for this section.
+ uint64_t SecStart = getStream().tell();
+
+ const MCSymbolELF *SignatureSymbol = Section.getGroup();
+ writeSectionData(Asm, Section, Layout);
+
+ uint64_t SecEnd = getStream().tell();
+ SectionOffsets[&Section] = std::make_pair(SecStart, SecEnd);
+
+ MCSectionELF *RelSection = createRelocationSection(Ctx, Section);
+
+ if (SignatureSymbol) {
+ Asm.registerSymbol(*SignatureSymbol);
+ unsigned &GroupIdx = RevGroupMap[SignatureSymbol];
+ if (!GroupIdx) {
+ MCSectionELF *Group = Ctx.createELFGroupSection(SignatureSymbol);
+ GroupIdx = addToSectionTable(Group);
+ Group->setAlignment(4);
+ Groups.push_back(Group);
+ }
+ std::vector<const MCSectionELF *> &Members =
+ GroupMembers[SignatureSymbol];
+ Members.push_back(&Section);
+ if (RelSection)
+ Members.push_back(RelSection);
+ }
+
+ SectionIndexMap[&Section] = addToSectionTable(&Section);
+ if (RelSection) {
+ SectionIndexMap[RelSection] = addToSectionTable(RelSection);
+ Relocations.push_back(RelSection);
+ }
+ }
+
+ for (MCSectionELF *Group : Groups) {
+ align(Group->getAlignment());
+
+ // Remember the offset into the file for this section.
+ uint64_t SecStart = getStream().tell();
+
+ const MCSymbol *SignatureSymbol = Group->getGroup();
+ assert(SignatureSymbol);
+ write(uint32_t(ELF::GRP_COMDAT));
+ for (const MCSectionELF *Member : GroupMembers[SignatureSymbol]) {
+ uint32_t SecIndex = SectionIndexMap.lookup(Member);
+ write(SecIndex);
+ }
+
+ uint64_t SecEnd = getStream().tell();
+ SectionOffsets[Group] = std::make_pair(SecStart, SecEnd);
+ }
+
+ // Compute symbol table information.
+ computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap, SectionOffsets);
+
+ for (MCSectionELF *RelSection : Relocations) {
+ align(RelSection->getAlignment());
+
+ // Remember the offset into the file for this section.
+ uint64_t SecStart = getStream().tell();
+
+ writeRelocations(Asm, *RelSection->getAssociatedSection());
+
+ uint64_t SecEnd = getStream().tell();
+ SectionOffsets[RelSection] = std::make_pair(SecStart, SecEnd);
+ }
+
+ {
+ uint64_t SecStart = getStream().tell();
+ const MCSectionELF *Sec = createStringTable(Ctx);
+ uint64_t SecEnd = getStream().tell();
+ SectionOffsets[Sec] = std::make_pair(SecStart, SecEnd);
+ }
+
+ uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
+ align(NaturalAlignment);
+
+ const unsigned SectionHeaderOffset = getStream().tell();
+
+ // ... then the section header table ...
+ writeSectionHeader(Layout, SectionIndexMap, SectionOffsets);
+
+ uint16_t NumSections = (SectionTable.size() + 1 >= ELF::SHN_LORESERVE)
+ ? (uint16_t)ELF::SHN_UNDEF
+ : SectionTable.size() + 1;
+ if (sys::IsLittleEndianHost != IsLittleEndian)
+ sys::swapByteOrder(NumSections);
+ unsigned NumSectionsOffset;
+
+ if (is64Bit()) {
+ uint64_t Val = SectionHeaderOffset;
+ if (sys::IsLittleEndianHost != IsLittleEndian)
+ sys::swapByteOrder(Val);
+ getStream().pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
+ offsetof(ELF::Elf64_Ehdr, e_shoff));
+ NumSectionsOffset = offsetof(ELF::Elf64_Ehdr, e_shnum);
+ } else {
+ uint32_t Val = SectionHeaderOffset;
+ if (sys::IsLittleEndianHost != IsLittleEndian)
+ sys::swapByteOrder(Val);
+ getStream().pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
+ offsetof(ELF::Elf32_Ehdr, e_shoff));
+ NumSectionsOffset = offsetof(ELF::Elf32_Ehdr, e_shnum);
+ }
+ getStream().pwrite(reinterpret_cast<char *>(&NumSections),
+ sizeof(NumSections), NumSectionsOffset);
+}
+
+bool ELFObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(
+ const MCAssembler &Asm, const MCSymbol &SA, const MCFragment &FB,
+ bool InSet, bool IsPCRel) const {
+ const auto &SymA = cast<MCSymbolELF>(SA);
+ if (IsPCRel) {
+ assert(!InSet);
+ if (::isWeak(SymA))
+ return false;
+ }
+ return MCObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(Asm, SymA, FB,
+ InSet, IsPCRel);
+}
+
+bool ELFObjectWriter::isWeak(const MCSymbol &S) const {
+ const auto &Sym = cast<MCSymbolELF>(S);
+ if (::isWeak(Sym))
+ return true;
+
+ // It is invalid to replace a reference to a global in a comdat
+ // with a reference to a local since out of comdat references
+ // to a local are forbidden.
+ // We could try to return false for more cases, like the reference
+ // being in the same comdat or Sym being an alias to another global,
+ // but it is not clear if it is worth the effort.
+ if (Sym.getBinding() != ELF::STB_GLOBAL)
+ return false;
+
+ if (!Sym.isInSection())
+ return false;
+
+ const auto &Sec = cast<MCSectionELF>(Sym.getSection());
+ return Sec.getGroup();
+}
+
+MCObjectWriter *llvm::createELFObjectWriter(MCELFObjectTargetWriter *MOTW,
+ raw_pwrite_stream &OS,
+ bool IsLittleEndian) {
+ return new ELFObjectWriter(MOTW, OS, IsLittleEndian);
+}
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