forked from OSchip/llvm-project
MC: Extract ELFObjectWriter's ELF writing functionality into an ELFWriter class. NFCI.
The idea is that we will be able to use this class to create multiple files. Differential Revision: https://reviews.llvm.org/D47048 llvm-svn: 332867
This commit is contained in:
Peter Collingbourne
parent
2602a0d40c
commit
a29fe579f4
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@ -68,9 +68,10 @@ namespace {
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using SectionIndexMapTy = DenseMap<const MCSectionELF *, uint32_t>;
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class ELFObjectWriter;
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struct ELFWriter;
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class SymbolTableWriter {
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ELFObjectWriter &EWriter;
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ELFWriter &EWriter;
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bool Is64Bit;
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// indexes we are going to write to .symtab_shndx.
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@ -84,7 +85,7 @@ class SymbolTableWriter {
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template <typename T> void write(T Value);
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public:
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SymbolTableWriter(ELFObjectWriter &EWriter, bool Is64Bit);
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SymbolTableWriter(ELFWriter &EWriter, bool Is64Bit);
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void writeSymbol(uint32_t name, uint8_t info, uint64_t value, uint64_t size,
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uint8_t other, uint32_t shndx, bool Reserved);
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@ -92,7 +93,10 @@ public:
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ArrayRef<uint32_t> getShndxIndexes() const { return ShndxIndexes; }
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};
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class ELFObjectWriter : public MCObjectWriter {
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struct ELFWriter {
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ELFObjectWriter &OWriter;
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support::endian::Writer W;
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static uint64_t SymbolValue(const MCSymbol &Sym, const MCAsmLayout &Layout);
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static bool isInSymtab(const MCAsmLayout &Layout, const MCSymbolELF &Symbol,
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bool Used, bool Renamed);
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@ -117,13 +121,6 @@ class ELFObjectWriter : public MCObjectWriter {
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}
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};
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/// The target specific ELF writer instance.
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std::unique_ptr<MCELFObjectTargetWriter> TargetObjectWriter;
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DenseMap<const MCSymbolELF *, const MCSymbolELF *> Renames;
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DenseMap<const MCSectionELF *, std::vector<ELFRelocationEntry>> Relocations;
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/// @}
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/// @name Symbol Table Data
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/// @{
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@ -144,14 +141,8 @@ class ELFObjectWriter : public MCObjectWriter {
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unsigned addToSectionTable(const MCSectionELF *Sec);
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// TargetObjectWriter wrappers.
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bool is64Bit() const { return TargetObjectWriter->is64Bit(); }
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bool hasRelocationAddend() const {
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return TargetObjectWriter->hasRelocationAddend();
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}
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unsigned getRelocType(MCContext &Ctx, const MCValue &Target,
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const MCFixup &Fixup, bool IsPCRel) const {
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return TargetObjectWriter->getRelocType(Ctx, Target, Fixup, IsPCRel);
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}
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bool is64Bit() const;
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bool hasRelocationAddend() const;
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void align(unsigned Alignment);
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@ -160,23 +151,11 @@ class ELFObjectWriter : public MCObjectWriter {
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bool ZLibStyle, unsigned Alignment);
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public:
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support::endian::Writer W;
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ELFObjectWriter(std::unique_ptr<MCELFObjectTargetWriter> MOTW,
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raw_pwrite_stream &OS, bool IsLittleEndian)
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: TargetObjectWriter(std::move(MOTW)),
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ELFWriter(ELFObjectWriter &OWriter, raw_pwrite_stream &OS,
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bool IsLittleEndian)
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: OWriter(OWriter),
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W(OS, IsLittleEndian ? support::little : support::big) {}
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~ELFObjectWriter() override = default;
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void reset() override {
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Renames.clear();
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Relocations.clear();
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StrTabBuilder.clear();
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SectionTable.clear();
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MCObjectWriter::reset();
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}
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void WriteWord(uint64_t Word) {
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if (is64Bit())
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W.write<uint64_t>(Word);
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@ -197,15 +176,6 @@ public:
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using SectionOffsetsTy =
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std::map<const MCSectionELF *, std::pair<uint64_t, uint64_t>>;
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bool shouldRelocateWithSymbol(const MCAssembler &Asm,
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const MCSymbolRefExpr *RefA,
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const MCSymbolELF *Sym, uint64_t C,
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unsigned Type) const;
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void recordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
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const MCFragment *Fragment, const MCFixup &Fixup,
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MCValue Target, uint64_t &FixedValue) override;
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// Map from a signature symbol to the group section index
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using RevGroupMapTy = DenseMap<const MCSymbol *, unsigned>;
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@ -224,9 +194,6 @@ public:
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const MCSectionELF *createStringTable(MCContext &Ctx);
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void executePostLayoutBinding(MCAssembler &Asm,
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const MCAsmLayout &Layout) override;
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void writeSectionHeader(const MCAsmLayout &Layout,
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const SectionIndexMapTy &SectionIndexMap,
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const SectionOffsetsTy &SectionOffsets);
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@ -241,26 +208,69 @@ public:
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void writeRelocations(const MCAssembler &Asm, const MCSectionELF &Sec);
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using MCObjectWriter::isSymbolRefDifferenceFullyResolvedImpl;
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bool isSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
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const MCSymbol &SymA,
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const MCFragment &FB, bool InSet,
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bool IsPCRel) const override;
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uint64_t writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
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uint64_t writeObject(MCAssembler &Asm, const MCAsmLayout &Layout);
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void writeSection(const SectionIndexMapTy &SectionIndexMap,
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uint32_t GroupSymbolIndex, uint64_t Offset, uint64_t Size,
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const MCSectionELF &Section);
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};
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class ELFObjectWriter : public MCObjectWriter {
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raw_pwrite_stream &OS;
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bool IsLittleEndian;
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/// The target specific ELF writer instance.
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std::unique_ptr<MCELFObjectTargetWriter> TargetObjectWriter;
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DenseMap<const MCSectionELF *, std::vector<ELFRelocationEntry>> Relocations;
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DenseMap<const MCSymbolELF *, const MCSymbolELF *> Renames;
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bool hasRelocationAddend() const;
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bool shouldRelocateWithSymbol(const MCAssembler &Asm,
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const MCSymbolRefExpr *RefA,
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const MCSymbolELF *Sym, uint64_t C,
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unsigned Type) const;
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public:
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ELFObjectWriter(std::unique_ptr<MCELFObjectTargetWriter> MOTW,
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raw_pwrite_stream &OS, bool IsLittleEndian)
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: OS(OS), IsLittleEndian(IsLittleEndian),
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TargetObjectWriter(std::move(MOTW)) {}
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void reset() override {
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Relocations.clear();
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Renames.clear();
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MCObjectWriter::reset();
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}
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bool isSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
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const MCSymbol &SymA,
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const MCFragment &FB, bool InSet,
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bool IsPCRel) const override;
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void recordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
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const MCFragment *Fragment, const MCFixup &Fixup,
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MCValue Target, uint64_t &FixedValue) override;
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uint64_t writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) override {
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return ELFWriter(*this, OS, IsLittleEndian).writeObject(Asm, Layout);
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}
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void executePostLayoutBinding(MCAssembler &Asm,
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const MCAsmLayout &Layout) override;
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friend struct ELFWriter;
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};
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} // end anonymous namespace
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void ELFObjectWriter::align(unsigned Alignment) {
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void ELFWriter::align(unsigned Alignment) {
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uint64_t Padding = OffsetToAlignment(W.OS.tell(), Alignment);
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W.OS.write_zeros(Padding);
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}
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unsigned ELFObjectWriter::addToSectionTable(const MCSectionELF *Sec) {
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unsigned ELFWriter::addToSectionTable(const MCSectionELF *Sec) {
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SectionTable.push_back(Sec);
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StrTabBuilder.add(Sec->getSectionName());
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return SectionTable.size();
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@ -277,7 +287,7 @@ template <typename T> void SymbolTableWriter::write(T Value) {
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EWriter.write(Value);
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}
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SymbolTableWriter::SymbolTableWriter(ELFObjectWriter &EWriter, bool Is64Bit)
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SymbolTableWriter::SymbolTableWriter(ELFWriter &EWriter, bool Is64Bit)
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: EWriter(EWriter), Is64Bit(Is64Bit), NumWritten(0) {}
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void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
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@ -316,8 +326,16 @@ void SymbolTableWriter::writeSymbol(uint32_t name, uint8_t info, uint64_t value,
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++NumWritten;
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}
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bool ELFWriter::is64Bit() const {
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return OWriter.TargetObjectWriter->is64Bit();
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}
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bool ELFWriter::hasRelocationAddend() const {
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return OWriter.hasRelocationAddend();
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}
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// Emit the ELF header.
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void ELFObjectWriter::writeHeader(const MCAssembler &Asm) {
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void ELFWriter::writeHeader(const MCAssembler &Asm) {
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// ELF Header
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// ----------
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//
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@ -336,14 +354,14 @@ void ELFObjectWriter::writeHeader(const MCAssembler &Asm) {
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W.OS << char(ELF::EV_CURRENT); // e_ident[EI_VERSION]
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// e_ident[EI_OSABI]
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W.OS << char(TargetObjectWriter->getOSABI());
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W.OS << char(OWriter.TargetObjectWriter->getOSABI());
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W.OS << char(0); // e_ident[EI_ABIVERSION]
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W.OS.write_zeros(ELF::EI_NIDENT - ELF::EI_PAD);
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W.write<uint16_t>(ELF::ET_REL); // e_type
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W.write<uint16_t>(TargetObjectWriter->getEMachine()); // e_machine = target
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W.write<uint16_t>(OWriter.TargetObjectWriter->getEMachine()); // e_machine = target
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W.write<uint32_t>(ELF::EV_CURRENT); // e_version
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WriteWord(0); // e_entry, no entry point in .o file
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@ -372,8 +390,8 @@ void ELFObjectWriter::writeHeader(const MCAssembler &Asm) {
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W.write<uint16_t>(StringTableIndex);
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}
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uint64_t ELFObjectWriter::SymbolValue(const MCSymbol &Sym,
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const MCAsmLayout &Layout) {
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uint64_t ELFWriter::SymbolValue(const MCSymbol &Sym,
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const MCAsmLayout &Layout) {
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if (Sym.isCommon() && Sym.isExternal())
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return Sym.getCommonAlignment();
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@ -387,49 +405,6 @@ uint64_t ELFObjectWriter::SymbolValue(const MCSymbol &Sym,
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return Res;
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}
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void ELFObjectWriter::executePostLayoutBinding(MCAssembler &Asm,
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const MCAsmLayout &Layout) {
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// The presence of symbol versions causes undefined symbols and
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// versions declared with @@@ to be renamed.
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for (const std::pair<StringRef, const MCSymbol *> &P : Asm.Symvers) {
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StringRef AliasName = P.first;
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const auto &Symbol = cast<MCSymbolELF>(*P.second);
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size_t Pos = AliasName.find('@');
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assert(Pos != StringRef::npos);
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StringRef Prefix = AliasName.substr(0, Pos);
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StringRef Rest = AliasName.substr(Pos);
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StringRef Tail = Rest;
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if (Rest.startswith("@@@"))
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Tail = Rest.substr(Symbol.isUndefined() ? 2 : 1);
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auto *Alias =
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cast<MCSymbolELF>(Asm.getContext().getOrCreateSymbol(Prefix + Tail));
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Asm.registerSymbol(*Alias);
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const MCExpr *Value = MCSymbolRefExpr::create(&Symbol, Asm.getContext());
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Alias->setVariableValue(Value);
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// Aliases defined with .symvar copy the binding from the symbol they alias.
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// This is the first place we are able to copy this information.
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Alias->setExternal(Symbol.isExternal());
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Alias->setBinding(Symbol.getBinding());
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if (!Symbol.isUndefined() && !Rest.startswith("@@@"))
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continue;
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// FIXME: produce a better error message.
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if (Symbol.isUndefined() && Rest.startswith("@@") &&
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!Rest.startswith("@@@"))
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report_fatal_error("A @@ version cannot be undefined");
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if (Renames.count(&Symbol) && Renames[&Symbol] != Alias)
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report_fatal_error(llvm::Twine("Multiple symbol versions defined for ") +
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Symbol.getName());
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Renames.insert(std::make_pair(&Symbol, Alias));
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}
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}
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static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
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uint8_t Type = newType;
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@ -465,9 +440,8 @@ static uint8_t mergeTypeForSet(uint8_t origType, uint8_t newType) {
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return Type;
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}
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void ELFObjectWriter::writeSymbol(SymbolTableWriter &Writer,
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uint32_t StringIndex, ELFSymbolData &MSD,
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const MCAsmLayout &Layout) {
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void ELFWriter::writeSymbol(SymbolTableWriter &Writer, uint32_t StringIndex,
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ELFSymbolData &MSD, const MCAsmLayout &Layout) {
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const auto &Symbol = cast<MCSymbolELF>(*MSD.Symbol);
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const MCSymbolELF *Base =
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cast_or_null<MCSymbolELF>(Layout.getBaseSymbol(Symbol));
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@ -508,108 +482,6 @@ void ELFObjectWriter::writeSymbol(SymbolTableWriter &Writer,
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IsReserved);
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}
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// It is always valid to create a relocation with a symbol. It is preferable
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// to use a relocation with a section if that is possible. Using the section
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// allows us to omit some local symbols from the symbol table.
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bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
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const MCSymbolRefExpr *RefA,
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const MCSymbolELF *Sym,
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uint64_t C,
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unsigned Type) const {
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// A PCRel relocation to an absolute value has no symbol (or section). We
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// represent that with a relocation to a null section.
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if (!RefA)
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return false;
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MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
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switch (Kind) {
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default:
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break;
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// The .odp creation emits a relocation against the symbol ".TOC." which
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// create a R_PPC64_TOC relocation. However the relocation symbol name
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// in final object creation should be NULL, since the symbol does not
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// really exist, it is just the reference to TOC base for the current
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// object file. Since the symbol is undefined, returning false results
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// in a relocation with a null section which is the desired result.
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case MCSymbolRefExpr::VK_PPC_TOCBASE:
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return false;
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// These VariantKind cause the relocation to refer to something other than
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// the symbol itself, like a linker generated table. Since the address of
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// symbol is not relevant, we cannot replace the symbol with the
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// section and patch the difference in the addend.
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case MCSymbolRefExpr::VK_GOT:
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case MCSymbolRefExpr::VK_PLT:
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case MCSymbolRefExpr::VK_GOTPCREL:
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case MCSymbolRefExpr::VK_PPC_GOT_LO:
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case MCSymbolRefExpr::VK_PPC_GOT_HI:
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case MCSymbolRefExpr::VK_PPC_GOT_HA:
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return true;
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}
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// An undefined symbol is not in any section, so the relocation has to point
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// to the symbol itself.
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assert(Sym && "Expected a symbol");
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if (Sym->isUndefined())
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return true;
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unsigned Binding = Sym->getBinding();
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switch(Binding) {
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default:
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llvm_unreachable("Invalid Binding");
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case ELF::STB_LOCAL:
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break;
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case ELF::STB_WEAK:
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// If the symbol is weak, it might be overridden by a symbol in another
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// file. The relocation has to point to the symbol so that the linker
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// can update it.
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return true;
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case ELF::STB_GLOBAL:
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// Global ELF symbols can be preempted by the dynamic linker. The relocation
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// has to point to the symbol for a reason analogous to the STB_WEAK case.
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return true;
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}
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// If a relocation points to a mergeable section, we have to be careful.
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// If the offset is zero, a relocation with the section will encode the
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// same information. With a non-zero offset, the situation is different.
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// For example, a relocation can point 42 bytes past the end of a string.
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// If we change such a relocation to use the section, the linker would think
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// that it pointed to another string and subtracting 42 at runtime will
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// produce the wrong value.
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if (Sym->isInSection()) {
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auto &Sec = cast<MCSectionELF>(Sym->getSection());
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unsigned Flags = Sec.getFlags();
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if (Flags & ELF::SHF_MERGE) {
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if (C != 0)
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return true;
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// It looks like gold has a bug (http://sourceware.org/PR16794) and can
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// only handle section relocations to mergeable sections if using RELA.
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if (!hasRelocationAddend())
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return true;
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}
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// Most TLS relocations use a got, so they need the symbol. Even those that
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// are just an offset (@tpoff), require a symbol in gold versions before
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// 5efeedf61e4fe720fd3e9a08e6c91c10abb66d42 (2014-09-26) which fixed
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// http://sourceware.org/PR16773.
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if (Flags & ELF::SHF_TLS)
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return true;
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}
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// If the symbol is a thumb function the final relocation must set the lowest
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// bit. With a symbol that is done by just having the symbol have that bit
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// set, so we would lose the bit if we relocated with the section.
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// FIXME: We could use the section but add the bit to the relocation value.
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if (Asm.isThumbFunc(Sym))
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return true;
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if (TargetObjectWriter->needsRelocateWithSymbol(*Sym, Type))
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return true;
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return false;
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}
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// True if the assembler knows nothing about the final value of the symbol.
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// This doesn't cover the comdat issues, since in those cases the assembler
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// can at least know that all symbols in the section will move together.
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@ -630,117 +502,8 @@ static bool isWeak(const MCSymbolELF &Sym) {
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}
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}
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void ELFObjectWriter::recordRelocation(MCAssembler &Asm,
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const MCAsmLayout &Layout,
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const MCFragment *Fragment,
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const MCFixup &Fixup, MCValue Target,
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uint64_t &FixedValue) {
|
||||
MCAsmBackend &Backend = Asm.getBackend();
|
||||
bool IsPCRel = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
|
||||
MCFixupKindInfo::FKF_IsPCRel;
|
||||
const MCSectionELF &FixupSection = cast<MCSectionELF>(*Fragment->getParent());
|
||||
uint64_t C = Target.getConstant();
|
||||
uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
|
||||
MCContext &Ctx = Asm.getContext();
|
||||
|
||||
if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
|
||||
// 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) {
|
||||
Ctx.reportError(
|
||||
Fixup.getLoc(),
|
||||
"No relocation available to represent this relative expression");
|
||||
return;
|
||||
}
|
||||
|
||||
const auto &SymB = cast<MCSymbolELF>(RefB->getSymbol());
|
||||
|
||||
if (SymB.isUndefined()) {
|
||||
Ctx.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) {
|
||||
Ctx.reportError(Fixup.getLoc(),
|
||||
"Cannot represent a difference across sections");
|
||||
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(Ctx, Target, Fixup, IsPCRel);
|
||||
uint64_t OriginalC = C;
|
||||
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;
|
||||
const auto *SectionSymbol =
|
||||
SecA ? cast<MCSymbolELF>(SecA->getBeginSymbol()) : nullptr;
|
||||
if (SectionSymbol)
|
||||
SectionSymbol->setUsedInReloc();
|
||||
ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend, SymA,
|
||||
OriginalC);
|
||||
Relocations[&FixupSection].push_back(Rec);
|
||||
return;
|
||||
}
|
||||
|
||||
const auto *RenamedSymA = SymA;
|
||||
if (SymA) {
|
||||
if (const MCSymbolELF *R = Renames.lookup(SymA))
|
||||
RenamedSymA = R;
|
||||
|
||||
if (ViaWeakRef)
|
||||
RenamedSymA->setIsWeakrefUsedInReloc();
|
||||
else
|
||||
RenamedSymA->setUsedInReloc();
|
||||
}
|
||||
ELFRelocationEntry Rec(FixupOffset, RenamedSymA, Type, Addend, SymA,
|
||||
OriginalC);
|
||||
Relocations[&FixupSection].push_back(Rec);
|
||||
}
|
||||
|
||||
bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
|
||||
const MCSymbolELF &Symbol, bool Used,
|
||||
bool Renamed) {
|
||||
bool ELFWriter::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)) {
|
||||
|
|
@ -773,7 +536,7 @@ bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
|
|||
return true;
|
||||
}
|
||||
|
||||
void ELFObjectWriter::computeSymbolTable(
|
||||
void ELFWriter::computeSymbolTable(
|
||||
MCAssembler &Asm, const MCAsmLayout &Layout,
|
||||
const SectionIndexMapTy &SectionIndexMap, const RevGroupMapTy &RevGroupMap,
|
||||
SectionOffsetsTy &SectionOffsets) {
|
||||
|
|
@ -805,7 +568,7 @@ void ELFObjectWriter::computeSymbolTable(
|
|||
bool isSignature = Symbol.isSignature();
|
||||
|
||||
if (!isInSymtab(Layout, Symbol, Used || WeakrefUsed || isSignature,
|
||||
Renames.count(&Symbol)))
|
||||
OWriter.Renames.count(&Symbol)))
|
||||
continue;
|
||||
|
||||
if (Symbol.isTemporary() && Symbol.isUndefined()) {
|
||||
|
|
@ -923,10 +686,9 @@ void ELFObjectWriter::computeSymbolTable(
|
|||
SectionOffsets[SymtabShndxSection] = std::make_pair(SecStart, SecEnd);
|
||||
}
|
||||
|
||||
MCSectionELF *
|
||||
ELFObjectWriter::createRelocationSection(MCContext &Ctx,
|
||||
const MCSectionELF &Sec) {
|
||||
if (Relocations[&Sec].empty())
|
||||
MCSectionELF *ELFWriter::createRelocationSection(MCContext &Ctx,
|
||||
const MCSectionELF &Sec) {
|
||||
if (OWriter.Relocations[&Sec].empty())
|
||||
return nullptr;
|
||||
|
||||
const StringRef SectionName = Sec.getSectionName();
|
||||
|
|
@ -951,7 +713,7 @@ ELFObjectWriter::createRelocationSection(MCContext &Ctx,
|
|||
}
|
||||
|
||||
// Include the debug info compression header.
|
||||
bool ELFObjectWriter::maybeWriteCompression(
|
||||
bool ELFWriter::maybeWriteCompression(
|
||||
uint64_t Size, SmallVectorImpl<char> &CompressedContents, bool ZLibStyle,
|
||||
unsigned Alignment) {
|
||||
if (ZLibStyle) {
|
||||
|
|
@ -985,8 +747,8 @@ bool ELFObjectWriter::maybeWriteCompression(
|
|||
return true;
|
||||
}
|
||||
|
||||
void ELFObjectWriter::writeSectionData(const MCAssembler &Asm, MCSection &Sec,
|
||||
const MCAsmLayout &Layout) {
|
||||
void ELFWriter::writeSectionData(const MCAssembler &Asm, MCSection &Sec,
|
||||
const MCAsmLayout &Layout) {
|
||||
MCSectionELF &Section = static_cast<MCSectionELF &>(Sec);
|
||||
StringRef SectionName = Section.getSectionName();
|
||||
|
||||
|
|
@ -1037,12 +799,10 @@ void ELFObjectWriter::writeSectionData(const MCAssembler &Asm, MCSection &Sec,
|
|||
W.OS << 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) {
|
||||
void ELFWriter::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) {
|
||||
W.write<uint32_t>(Name); // sh_name: index into string table
|
||||
W.write<uint32_t>(Type); // sh_type
|
||||
WriteWord(Flags); // sh_flags
|
||||
|
|
@ -1055,9 +815,9 @@ void ELFObjectWriter::WriteSecHdrEntry(uint32_t Name, uint32_t Type,
|
|||
WriteWord(EntrySize); // sh_entsize
|
||||
}
|
||||
|
||||
void ELFObjectWriter::writeRelocations(const MCAssembler &Asm,
|
||||
void ELFWriter::writeRelocations(const MCAssembler &Asm,
|
||||
const MCSectionELF &Sec) {
|
||||
std::vector<ELFRelocationEntry> &Relocs = Relocations[&Sec];
|
||||
std::vector<ELFRelocationEntry> &Relocs = OWriter.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.
|
||||
|
|
@ -1066,7 +826,7 @@ void ELFObjectWriter::writeRelocations(const MCAssembler &Asm,
|
|||
std::reverse(Relocs.begin(), Relocs.end());
|
||||
|
||||
// Sort the relocation entries. MIPS needs this.
|
||||
TargetObjectWriter->sortRelocs(Asm, Relocs);
|
||||
OWriter.TargetObjectWriter->sortRelocs(Asm, Relocs);
|
||||
|
||||
for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
|
||||
const ELFRelocationEntry &Entry = Relocs[e - i - 1];
|
||||
|
|
@ -1074,13 +834,13 @@ void ELFObjectWriter::writeRelocations(const MCAssembler &Asm,
|
|||
|
||||
if (is64Bit()) {
|
||||
write(Entry.Offset);
|
||||
if (TargetObjectWriter->getEMachine() == ELF::EM_MIPS) {
|
||||
if (OWriter.TargetObjectWriter->getEMachine() == ELF::EM_MIPS) {
|
||||
write(uint32_t(Index));
|
||||
|
||||
write(TargetObjectWriter->getRSsym(Entry.Type));
|
||||
write(TargetObjectWriter->getRType3(Entry.Type));
|
||||
write(TargetObjectWriter->getRType2(Entry.Type));
|
||||
write(TargetObjectWriter->getRType(Entry.Type));
|
||||
write(OWriter.TargetObjectWriter->getRSsym(Entry.Type));
|
||||
write(OWriter.TargetObjectWriter->getRType3(Entry.Type));
|
||||
write(OWriter.TargetObjectWriter->getRType2(Entry.Type));
|
||||
write(OWriter.TargetObjectWriter->getRType(Entry.Type));
|
||||
} else {
|
||||
struct ELF::Elf64_Rela ERE64;
|
||||
ERE64.setSymbolAndType(Index, Entry.Type);
|
||||
|
|
@ -1098,15 +858,17 @@ void ELFObjectWriter::writeRelocations(const MCAssembler &Asm,
|
|||
if (hasRelocationAddend())
|
||||
write(uint32_t(Entry.Addend));
|
||||
|
||||
if (TargetObjectWriter->getEMachine() == ELF::EM_MIPS) {
|
||||
if (uint32_t RType = TargetObjectWriter->getRType2(Entry.Type)) {
|
||||
if (OWriter.TargetObjectWriter->getEMachine() == ELF::EM_MIPS) {
|
||||
if (uint32_t RType =
|
||||
OWriter.TargetObjectWriter->getRType2(Entry.Type)) {
|
||||
write(uint32_t(Entry.Offset));
|
||||
|
||||
ERE32.setSymbolAndType(0, RType);
|
||||
write(ERE32.r_info);
|
||||
write(uint32_t(0));
|
||||
}
|
||||
if (uint32_t RType = TargetObjectWriter->getRType3(Entry.Type)) {
|
||||
if (uint32_t RType =
|
||||
OWriter.TargetObjectWriter->getRType3(Entry.Type)) {
|
||||
write(uint32_t(Entry.Offset));
|
||||
|
||||
ERE32.setSymbolAndType(0, RType);
|
||||
|
|
@ -1118,15 +880,15 @@ void ELFObjectWriter::writeRelocations(const MCAssembler &Asm,
|
|||
}
|
||||
}
|
||||
|
||||
const MCSectionELF *ELFObjectWriter::createStringTable(MCContext &Ctx) {
|
||||
const MCSectionELF *ELFWriter::createStringTable(MCContext &Ctx) {
|
||||
const MCSectionELF *StrtabSection = SectionTable[StringTableIndex - 1];
|
||||
StrTabBuilder.write(W.OS);
|
||||
return StrtabSection;
|
||||
}
|
||||
|
||||
void ELFObjectWriter::writeSection(const SectionIndexMapTy &SectionIndexMap,
|
||||
uint32_t GroupSymbolIndex, uint64_t Offset,
|
||||
uint64_t Size, const MCSectionELF &Section) {
|
||||
void ELFWriter::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;
|
||||
|
||||
|
|
@ -1174,7 +936,7 @@ void ELFObjectWriter::writeSection(const SectionIndexMapTy &SectionIndexMap,
|
|||
Section.getEntrySize());
|
||||
}
|
||||
|
||||
void ELFObjectWriter::writeSectionHeader(
|
||||
void ELFWriter::writeSectionHeader(
|
||||
const MCAsmLayout &Layout, const SectionIndexMapTy &SectionIndexMap,
|
||||
const SectionOffsetsTy &SectionOffsets) {
|
||||
const unsigned NumSections = SectionTable.size();
|
||||
|
|
@ -1205,8 +967,7 @@ void ELFObjectWriter::writeSectionHeader(
|
|||
}
|
||||
}
|
||||
|
||||
uint64_t ELFObjectWriter::writeObject(MCAssembler &Asm,
|
||||
const MCAsmLayout &Layout) {
|
||||
uint64_t ELFWriter::writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) {
|
||||
uint64_t StartOffset = W.OS.tell();
|
||||
|
||||
MCContext &Ctx = Asm.getContext();
|
||||
|
|
@ -1340,6 +1101,263 @@ uint64_t ELFObjectWriter::writeObject(MCAssembler &Asm,
|
|||
return W.OS.tell() - StartOffset;
|
||||
}
|
||||
|
||||
bool ELFObjectWriter::hasRelocationAddend() const {
|
||||
return TargetObjectWriter->hasRelocationAddend();
|
||||
}
|
||||
|
||||
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 std::pair<StringRef, const MCSymbol *> &P : Asm.Symvers) {
|
||||
StringRef AliasName = P.first;
|
||||
const auto &Symbol = cast<MCSymbolELF>(*P.second);
|
||||
size_t Pos = AliasName.find('@');
|
||||
assert(Pos != StringRef::npos);
|
||||
|
||||
StringRef Prefix = AliasName.substr(0, Pos);
|
||||
StringRef Rest = AliasName.substr(Pos);
|
||||
StringRef Tail = Rest;
|
||||
if (Rest.startswith("@@@"))
|
||||
Tail = Rest.substr(Symbol.isUndefined() ? 2 : 1);
|
||||
|
||||
auto *Alias =
|
||||
cast<MCSymbolELF>(Asm.getContext().getOrCreateSymbol(Prefix + Tail));
|
||||
Asm.registerSymbol(*Alias);
|
||||
const MCExpr *Value = MCSymbolRefExpr::create(&Symbol, Asm.getContext());
|
||||
Alias->setVariableValue(Value);
|
||||
|
||||
// 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());
|
||||
|
||||
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");
|
||||
|
||||
if (Renames.count(&Symbol) && Renames[&Symbol] != Alias)
|
||||
report_fatal_error(llvm::Twine("Multiple symbol versions defined for ") +
|
||||
Symbol.getName());
|
||||
|
||||
Renames.insert(std::make_pair(&Symbol, Alias));
|
||||
}
|
||||
}
|
||||
|
||||
// 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 MCSymbolELF *Sym,
|
||||
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_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.
|
||||
if (Sym->isInSection()) {
|
||||
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;
|
||||
}
|
||||
|
||||
void ELFObjectWriter::recordRelocation(MCAssembler &Asm,
|
||||
const MCAsmLayout &Layout,
|
||||
const MCFragment *Fragment,
|
||||
const MCFixup &Fixup, MCValue Target,
|
||||
uint64_t &FixedValue) {
|
||||
MCAsmBackend &Backend = Asm.getBackend();
|
||||
bool IsPCRel = Backend.getFixupKindInfo(Fixup.getKind()).Flags &
|
||||
MCFixupKindInfo::FKF_IsPCRel;
|
||||
const MCSectionELF &FixupSection = cast<MCSectionELF>(*Fragment->getParent());
|
||||
uint64_t C = Target.getConstant();
|
||||
uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
|
||||
MCContext &Ctx = Asm.getContext();
|
||||
|
||||
if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
|
||||
// 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) {
|
||||
Ctx.reportError(
|
||||
Fixup.getLoc(),
|
||||
"No relocation available to represent this relative expression");
|
||||
return;
|
||||
}
|
||||
|
||||
const auto &SymB = cast<MCSymbolELF>(RefB->getSymbol());
|
||||
|
||||
if (SymB.isUndefined()) {
|
||||
Ctx.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) {
|
||||
Ctx.reportError(Fixup.getLoc(),
|
||||
"Cannot represent a difference across sections");
|
||||
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 = TargetObjectWriter->getRelocType(Ctx, Target, Fixup, IsPCRel);
|
||||
uint64_t OriginalC = C;
|
||||
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;
|
||||
const auto *SectionSymbol =
|
||||
SecA ? cast<MCSymbolELF>(SecA->getBeginSymbol()) : nullptr;
|
||||
if (SectionSymbol)
|
||||
SectionSymbol->setUsedInReloc();
|
||||
ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend, SymA,
|
||||
OriginalC);
|
||||
Relocations[&FixupSection].push_back(Rec);
|
||||
return;
|
||||
}
|
||||
|
||||
const auto *RenamedSymA = SymA;
|
||||
if (SymA) {
|
||||
if (const MCSymbolELF *R = Renames.lookup(SymA))
|
||||
RenamedSymA = R;
|
||||
|
||||
if (ViaWeakRef)
|
||||
RenamedSymA->setIsWeakrefUsedInReloc();
|
||||
else
|
||||
RenamedSymA->setUsedInReloc();
|
||||
}
|
||||
ELFRelocationEntry Rec(FixupOffset, RenamedSymA, Type, Addend, SymA,
|
||||
OriginalC);
|
||||
Relocations[&FixupSection].push_back(Rec);
|
||||
}
|
||||
|
||||
bool ELFObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(
|
||||
const MCAssembler &Asm, const MCSymbol &SA, const MCFragment &FB,
|
||||
bool InSet, bool IsPCRel) const {
|
||||
|
|
|
|||
Loading…
Reference in New Issue