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Transition one API from `MCSymbolData` to `MCSymbol`. The function needs both, and the backpointer from `MCSymbolData` to `MCSymbol` is going away. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@237498 91177308-0d34-0410-b5e6-96231b3b80d8
1508 lines
52 KiB
C++
1508 lines
52 KiB
C++
//===- lib/MC/ELFObjectWriter.cpp - ELF File Writer -----------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements ELF object file writer information.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/MC/MCELFObjectWriter.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/SmallString.h"
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#include "llvm/ADT/StringMap.h"
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#include "llvm/MC/MCAsmBackend.h"
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#include "llvm/MC/MCAsmInfo.h"
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#include "llvm/MC/MCAsmLayout.h"
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#include "llvm/MC/MCAssembler.h"
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#include "llvm/MC/MCContext.h"
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#include "llvm/MC/MCELF.h"
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#include "llvm/MC/MCELFSymbolFlags.h"
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#include "llvm/MC/MCExpr.h"
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#include "llvm/MC/MCFixupKindInfo.h"
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#include "llvm/MC/MCObjectWriter.h"
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#include "llvm/MC/MCSectionELF.h"
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#include "llvm/MC/MCValue.h"
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#include "llvm/MC/StringTableBuilder.h"
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#include "llvm/Support/Compression.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/ELF.h"
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#include "llvm/Support/Endian.h"
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#include "llvm/Support/ErrorHandling.h"
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#include <vector>
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using namespace llvm;
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#undef DEBUG_TYPE
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#define DEBUG_TYPE "reloc-info"
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namespace {
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typedef DenseMap<const MCSectionELF *, uint32_t> SectionIndexMapTy;
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class ELFObjectWriter;
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class SymbolTableWriter {
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ELFObjectWriter &EWriter;
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bool Is64Bit;
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// indexes we are going to write to .symtab_shndx.
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std::vector<uint32_t> ShndxIndexes;
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// The numbel of symbols written so far.
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unsigned NumWritten;
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void createSymtabShndx();
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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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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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ArrayRef<uint32_t> getShndxIndexes() const { return ShndxIndexes; }
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};
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class ELFObjectWriter : public MCObjectWriter {
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static bool isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind);
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static bool RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant);
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static uint64_t SymbolValue(MCSymbolData &Data, const MCAsmLayout &Layout);
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static bool isInSymtab(const MCAsmLayout &Layout, const MCSymbolData &Data,
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bool Used, bool Renamed);
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static bool isLocal(const MCSymbolData &Data, bool isUsedInReloc);
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/// Helper struct for containing some precomputed information on symbols.
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struct ELFSymbolData {
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MCSymbolData *SymbolData;
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uint64_t StringIndex;
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uint32_t SectionIndex;
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StringRef Name;
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// Support lexicographic sorting.
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bool operator<(const ELFSymbolData &RHS) const {
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unsigned LHSType = MCELF::GetType(*SymbolData);
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unsigned RHSType = MCELF::GetType(*RHS.SymbolData);
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if (LHSType == ELF::STT_SECTION && RHSType != ELF::STT_SECTION)
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return false;
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if (LHSType != ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
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return true;
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if (LHSType == ELF::STT_SECTION && RHSType == ELF::STT_SECTION)
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return SectionIndex < RHS.SectionIndex;
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return Name < RHS.Name;
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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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SmallPtrSet<const MCSymbol *, 16> UsedInReloc;
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SmallPtrSet<const MCSymbol *, 16> WeakrefUsedInReloc;
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DenseMap<const MCSymbol *, const MCSymbol *> Renames;
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llvm::DenseMap<const MCSectionELF *, std::vector<ELFRelocationEntry>>
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Relocations;
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StringTableBuilder ShStrTabBuilder;
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/// @}
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/// @name Symbol Table Data
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/// @{
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StringTableBuilder StrTabBuilder;
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std::vector<uint64_t> FileSymbolData;
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std::vector<ELFSymbolData> LocalSymbolData;
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std::vector<ELFSymbolData> ExternalSymbolData;
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std::vector<ELFSymbolData> UndefinedSymbolData;
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/// @}
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bool NeedsGOT;
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// This holds the symbol table index of the last local symbol.
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unsigned LastLocalSymbolIndex;
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// This holds the .strtab section index.
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unsigned StringTableIndex;
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// This holds the .symtab section index.
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unsigned SymbolTableIndex;
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unsigned ShstrtabIndex;
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// Sections in the order they are to be output in the section table.
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std::vector<const MCSectionELF *> SectionTable;
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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(const MCValue &Target, const MCFixup &Fixup,
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bool IsPCRel) const {
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return TargetObjectWriter->GetRelocType(Target, Fixup, IsPCRel);
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}
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public:
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ELFObjectWriter(MCELFObjectTargetWriter *MOTW, raw_pwrite_stream &OS,
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bool IsLittleEndian)
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: MCObjectWriter(OS, IsLittleEndian), TargetObjectWriter(MOTW),
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NeedsGOT(false) {}
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void reset() override {
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UsedInReloc.clear();
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WeakrefUsedInReloc.clear();
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Renames.clear();
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Relocations.clear();
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ShStrTabBuilder.clear();
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StrTabBuilder.clear();
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FileSymbolData.clear();
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LocalSymbolData.clear();
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ExternalSymbolData.clear();
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UndefinedSymbolData.clear();
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NeedsGOT = false;
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SectionTable.clear();
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MCObjectWriter::reset();
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}
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~ELFObjectWriter() override;
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void WriteWord(uint64_t W) {
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if (is64Bit())
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Write64(W);
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else
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Write32(W);
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}
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template <typename T> void write(T Val) {
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if (IsLittleEndian)
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support::endian::Writer<support::little>(OS).write(Val);
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else
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support::endian::Writer<support::big>(OS).write(Val);
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}
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void writeHeader(const MCAssembler &Asm);
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void WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
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const MCAsmLayout &Layout);
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// Start and end offset of each section
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typedef std::map<const MCSectionELF *, std::pair<uint64_t, uint64_t>>
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SectionOffsetsTy;
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void WriteSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
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SectionOffsetsTy &SectionOffsets);
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bool shouldRelocateWithSymbol(const MCAssembler &Asm,
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const MCSymbolRefExpr *RefA,
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const MCSymbolData *SD, 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, bool &IsPCRel,
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uint64_t &FixedValue) override;
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uint64_t getSymbolIndexInSymbolTable(const MCAssembler &Asm,
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const MCSymbol *S);
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// Map from a signature symbol to the group section index
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typedef DenseMap<const MCSymbol *, unsigned> RevGroupMapTy;
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/// Compute the symbol table data
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///
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/// \param Asm - The assembler.
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/// \param SectionIndexMap - Maps a section to its index.
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/// \param RevGroupMap - Maps a signature symbol to the group section.
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void computeSymbolTable(MCAssembler &Asm, const MCAsmLayout &Layout,
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const SectionIndexMapTy &SectionIndexMap,
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const RevGroupMapTy &RevGroupMap);
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const MCSectionELF *createRelocationSection(MCAssembler &Asm,
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const MCSectionELF &Sec);
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const MCSectionELF *createSectionHeaderStringTable();
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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(MCAssembler &Asm, const MCAsmLayout &Layout,
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const SectionIndexMapTy &SectionIndexMap,
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const SectionOffsetsTy &SectionOffsets);
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void writeSectionData(const MCAssembler &Asm, const MCSectionData &SD,
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const MCAsmLayout &Layout);
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void WriteSecHdrEntry(uint32_t Name, uint32_t Type, uint64_t Flags,
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uint64_t Address, uint64_t Offset, uint64_t Size,
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uint32_t Link, uint32_t Info, uint64_t Alignment,
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uint64_t EntrySize);
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void writeRelocations(const MCAssembler &Asm, const MCSectionELF &Sec);
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bool IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
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const MCSymbol &SymA,
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const MCFragment &FB,
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bool InSet,
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bool IsPCRel) const override;
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bool isWeak(const MCSymbolData &SD) const override;
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void WriteObject(MCAssembler &Asm, const MCAsmLayout &Layout) override;
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void writeSection(MCAssembler &Asm,
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const SectionIndexMapTy &SectionIndexMap,
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uint32_t GroupSymbolIndex,
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uint64_t Offset, uint64_t Size, uint64_t Alignment,
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const MCSectionELF &Section);
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};
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}
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unsigned ELFObjectWriter::addToSectionTable(const MCSectionELF *Sec) {
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SectionTable.push_back(Sec);
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ShStrTabBuilder.add(Sec->getSectionName());
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return SectionTable.size();
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}
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void SymbolTableWriter::createSymtabShndx() {
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if (!ShndxIndexes.empty())
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return;
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ShndxIndexes.resize(NumWritten);
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}
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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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: 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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uint64_t size, uint8_t other,
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uint32_t shndx, bool Reserved) {
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bool LargeIndex = shndx >= ELF::SHN_LORESERVE && !Reserved;
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if (LargeIndex)
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createSymtabShndx();
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if (!ShndxIndexes.empty()) {
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if (LargeIndex)
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ShndxIndexes.push_back(shndx);
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else
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ShndxIndexes.push_back(0);
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}
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uint16_t Index = LargeIndex ? uint16_t(ELF::SHN_XINDEX) : shndx;
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if (Is64Bit) {
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write(name); // st_name
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write(info); // st_info
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write(other); // st_other
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write(Index); // st_shndx
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write(value); // st_value
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write(size); // st_size
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} else {
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write(name); // st_name
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write(uint32_t(value)); // st_value
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write(uint32_t(size)); // st_size
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write(info); // st_info
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write(other); // st_other
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write(Index); // st_shndx
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}
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++NumWritten;
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}
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bool ELFObjectWriter::isFixupKindPCRel(const MCAssembler &Asm, unsigned Kind) {
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const MCFixupKindInfo &FKI =
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Asm.getBackend().getFixupKindInfo((MCFixupKind) Kind);
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return FKI.Flags & MCFixupKindInfo::FKF_IsPCRel;
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}
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bool ELFObjectWriter::RelocNeedsGOT(MCSymbolRefExpr::VariantKind Variant) {
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switch (Variant) {
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default:
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return false;
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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_GOTOFF:
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case MCSymbolRefExpr::VK_TPOFF:
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case MCSymbolRefExpr::VK_TLSGD:
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case MCSymbolRefExpr::VK_GOTTPOFF:
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case MCSymbolRefExpr::VK_INDNTPOFF:
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case MCSymbolRefExpr::VK_NTPOFF:
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case MCSymbolRefExpr::VK_GOTNTPOFF:
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case MCSymbolRefExpr::VK_TLSLDM:
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case MCSymbolRefExpr::VK_DTPOFF:
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case MCSymbolRefExpr::VK_TLSLD:
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return true;
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}
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}
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ELFObjectWriter::~ELFObjectWriter()
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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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// ELF Header
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// ----------
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//
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// Note
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// ----
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// emitWord method behaves differently for ELF32 and ELF64, writing
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// 4 bytes in the former and 8 in the latter.
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WriteBytes(ELF::ElfMagic); // e_ident[EI_MAG0] to e_ident[EI_MAG3]
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Write8(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
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// e_ident[EI_DATA]
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Write8(isLittleEndian() ? ELF::ELFDATA2LSB : ELF::ELFDATA2MSB);
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Write8(ELF::EV_CURRENT); // e_ident[EI_VERSION]
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// e_ident[EI_OSABI]
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Write8(TargetObjectWriter->getOSABI());
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Write8(0); // e_ident[EI_ABIVERSION]
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WriteZeros(ELF::EI_NIDENT - ELF::EI_PAD);
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Write16(ELF::ET_REL); // e_type
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Write16(TargetObjectWriter->getEMachine()); // e_machine = target
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Write32(ELF::EV_CURRENT); // e_version
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WriteWord(0); // e_entry, no entry point in .o file
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WriteWord(0); // e_phoff, no program header for .o
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WriteWord(0); // e_shoff = sec hdr table off in bytes
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// e_flags = whatever the target wants
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Write32(Asm.getELFHeaderEFlags());
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// e_ehsize = ELF header size
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Write16(is64Bit() ? sizeof(ELF::Elf64_Ehdr) : sizeof(ELF::Elf32_Ehdr));
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Write16(0); // e_phentsize = prog header entry size
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Write16(0); // e_phnum = # prog header entries = 0
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// e_shentsize = Section header entry size
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Write16(is64Bit() ? sizeof(ELF::Elf64_Shdr) : sizeof(ELF::Elf32_Shdr));
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// e_shnum = # of section header ents
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Write16(0);
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// e_shstrndx = Section # of '.shstrtab'
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assert(ShstrtabIndex < ELF::SHN_LORESERVE);
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Write16(ShstrtabIndex);
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}
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uint64_t ELFObjectWriter::SymbolValue(MCSymbolData &Data,
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const MCAsmLayout &Layout) {
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if (Data.isCommon() && Data.isExternal())
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return Data.getCommonAlignment();
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uint64_t Res;
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if (!Layout.getSymbolOffset(&Data, Res))
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return 0;
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if (Layout.getAssembler().isThumbFunc(&Data.getSymbol()))
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Res |= 1;
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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 MCSymbol &Alias : Asm.symbols()) {
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MCSymbolData &OriginalData = Alias.getData();
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// Not an alias.
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if (!Alias.isVariable())
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continue;
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auto *Ref = dyn_cast<MCSymbolRefExpr>(Alias.getVariableValue());
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if (!Ref)
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continue;
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const MCSymbol &Symbol = Ref->getSymbol();
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MCSymbolData &SD = Asm.getSymbolData(Symbol);
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StringRef AliasName = Alias.getName();
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size_t Pos = AliasName.find('@');
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if (Pos == StringRef::npos)
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continue;
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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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OriginalData.setExternal(SD.isExternal());
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MCELF::SetBinding(OriginalData, MCELF::GetBinding(SD));
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StringRef Rest = AliasName.substr(Pos);
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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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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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// Propagation rules:
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// IFUNC > FUNC > OBJECT > NOTYPE
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// TLS_OBJECT > OBJECT > NOTYPE
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//
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// dont let the new type degrade the old type
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switch (origType) {
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default:
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break;
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case ELF::STT_GNU_IFUNC:
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if (Type == ELF::STT_FUNC || Type == ELF::STT_OBJECT ||
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Type == ELF::STT_NOTYPE || Type == ELF::STT_TLS)
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Type = ELF::STT_GNU_IFUNC;
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break;
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case ELF::STT_FUNC:
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if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
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Type == ELF::STT_TLS)
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Type = ELF::STT_FUNC;
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break;
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case ELF::STT_OBJECT:
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if (Type == ELF::STT_NOTYPE)
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Type = ELF::STT_OBJECT;
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break;
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case ELF::STT_TLS:
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|
if (Type == ELF::STT_OBJECT || Type == ELF::STT_NOTYPE ||
|
|
Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
|
|
Type = ELF::STT_TLS;
|
|
break;
|
|
}
|
|
|
|
return Type;
|
|
}
|
|
|
|
void ELFObjectWriter::WriteSymbol(SymbolTableWriter &Writer, ELFSymbolData &MSD,
|
|
const MCAsmLayout &Layout) {
|
|
MCSymbolData &OrigData = *MSD.SymbolData;
|
|
assert((!OrigData.getFragment() ||
|
|
(&OrigData.getFragment()->getParent()->getSection() ==
|
|
&OrigData.getSymbol().getSection())) &&
|
|
"The symbol's section doesn't match the fragment's symbol");
|
|
const MCSymbol *Base = Layout.getBaseSymbol(OrigData.getSymbol());
|
|
|
|
// This has to be in sync with when computeSymbolTable uses SHN_ABS or
|
|
// SHN_COMMON.
|
|
bool IsReserved = !Base || OrigData.isCommon();
|
|
|
|
// Binding and Type share the same byte as upper and lower nibbles
|
|
uint8_t Binding = MCELF::GetBinding(OrigData);
|
|
uint8_t Type = MCELF::GetType(OrigData);
|
|
MCSymbolData *BaseSD = nullptr;
|
|
if (Base) {
|
|
BaseSD = &Layout.getAssembler().getSymbolData(*Base);
|
|
Type = mergeTypeForSet(Type, MCELF::GetType(*BaseSD));
|
|
}
|
|
uint8_t Info = (Binding << ELF_STB_Shift) | (Type << ELF_STT_Shift);
|
|
|
|
// Other and Visibility share the same byte with Visibility using the lower
|
|
// 2 bits
|
|
uint8_t Visibility = MCELF::GetVisibility(OrigData);
|
|
uint8_t Other = MCELF::getOther(OrigData) << (ELF_STO_Shift - ELF_STV_Shift);
|
|
Other |= Visibility;
|
|
|
|
uint64_t Value = SymbolValue(OrigData, Layout);
|
|
uint64_t Size = 0;
|
|
|
|
const MCExpr *ESize = OrigData.getSize();
|
|
if (!ESize && Base)
|
|
ESize = BaseSD->getSize();
|
|
|
|
if (ESize) {
|
|
int64_t Res;
|
|
if (!ESize->evaluateKnownAbsolute(Res, Layout))
|
|
report_fatal_error("Size expression must be absolute.");
|
|
Size = Res;
|
|
}
|
|
|
|
// Write out the symbol table entry
|
|
Writer.writeSymbol(MSD.StringIndex, Info, Value, Size, Other,
|
|
MSD.SectionIndex, IsReserved);
|
|
}
|
|
|
|
void ELFObjectWriter::WriteSymbolTable(MCAssembler &Asm,
|
|
const MCAsmLayout &Layout,
|
|
SectionOffsetsTy &SectionOffsets) {
|
|
|
|
MCContext &Ctx = Asm.getContext();
|
|
|
|
unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
|
|
|
|
// Symbol table
|
|
const MCSectionELF *SymtabSection =
|
|
Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, EntrySize, "");
|
|
MCSectionData &SymtabSD = Asm.getOrCreateSectionData(*SymtabSection);
|
|
SymtabSD.setAlignment(is64Bit() ? 8 : 4);
|
|
SymbolTableIndex = addToSectionTable(SymtabSection);
|
|
|
|
// The string table must be emitted first because we need the index
|
|
// into the string table for all the symbol names.
|
|
|
|
SymbolTableWriter Writer(*this, is64Bit());
|
|
|
|
uint64_t Padding = OffsetToAlignment(OS.tell(), SymtabSD.getAlignment());
|
|
WriteZeros(Padding);
|
|
|
|
uint64_t SecStart = OS.tell();
|
|
|
|
// The first entry is the undefined symbol entry.
|
|
Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
|
|
|
|
for (unsigned i = 0, e = FileSymbolData.size(); i != e; ++i) {
|
|
Writer.writeSymbol(FileSymbolData[i], ELF::STT_FILE | ELF::STB_LOCAL, 0, 0,
|
|
ELF::STV_DEFAULT, ELF::SHN_ABS, true);
|
|
}
|
|
|
|
// Write the symbol table entries.
|
|
LastLocalSymbolIndex = FileSymbolData.size() + LocalSymbolData.size() + 1;
|
|
|
|
for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i) {
|
|
ELFSymbolData &MSD = LocalSymbolData[i];
|
|
WriteSymbol(Writer, MSD, Layout);
|
|
}
|
|
|
|
for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i) {
|
|
ELFSymbolData &MSD = ExternalSymbolData[i];
|
|
MCSymbolData &Data = *MSD.SymbolData;
|
|
assert(((Data.getFlags() & ELF_STB_Global) ||
|
|
(Data.getFlags() & ELF_STB_Weak)) &&
|
|
"External symbol requires STB_GLOBAL or STB_WEAK flag");
|
|
WriteSymbol(Writer, MSD, Layout);
|
|
if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
|
|
LastLocalSymbolIndex++;
|
|
}
|
|
|
|
for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i) {
|
|
ELFSymbolData &MSD = UndefinedSymbolData[i];
|
|
MCSymbolData &Data = *MSD.SymbolData;
|
|
WriteSymbol(Writer, MSD, Layout);
|
|
if (MCELF::GetBinding(Data) == ELF::STB_LOCAL)
|
|
LastLocalSymbolIndex++;
|
|
}
|
|
|
|
uint64_t SecEnd = OS.tell();
|
|
SectionOffsets[SymtabSection] = std::make_pair(SecStart, SecEnd);
|
|
|
|
ArrayRef<uint32_t> ShndxIndexes = Writer.getShndxIndexes();
|
|
if (ShndxIndexes.empty())
|
|
return;
|
|
|
|
SecStart = OS.tell();
|
|
const MCSectionELF *SymtabShndxSection =
|
|
Ctx.getELFSection(".symtab_shndxr", ELF::SHT_SYMTAB_SHNDX, 0, 4, "");
|
|
addToSectionTable(SymtabShndxSection);
|
|
MCSectionData *SymtabShndxSD =
|
|
&Asm.getOrCreateSectionData(*SymtabShndxSection);
|
|
SymtabShndxSD->setAlignment(4);
|
|
for (uint32_t Index : ShndxIndexes)
|
|
write(Index);
|
|
SecEnd = OS.tell();
|
|
SectionOffsets[SymtabShndxSection] = std::make_pair(SecStart, SecEnd);
|
|
}
|
|
|
|
// It is always valid to create a relocation with a symbol. It is preferable
|
|
// to use a relocation with a section if that is possible. Using the section
|
|
// allows us to omit some local symbols from the symbol table.
|
|
bool ELFObjectWriter::shouldRelocateWithSymbol(const MCAssembler &Asm,
|
|
const MCSymbolRefExpr *RefA,
|
|
const MCSymbolData *SD,
|
|
uint64_t C,
|
|
unsigned Type) const {
|
|
// A PCRel relocation to an absolute value has no symbol (or section). We
|
|
// represent that with a relocation to a null section.
|
|
if (!RefA)
|
|
return false;
|
|
|
|
MCSymbolRefExpr::VariantKind Kind = RefA->getKind();
|
|
switch (Kind) {
|
|
default:
|
|
break;
|
|
// The .odp creation emits a relocation against the symbol ".TOC." which
|
|
// create a R_PPC64_TOC relocation. However the relocation symbol name
|
|
// in final object creation should be NULL, since the symbol does not
|
|
// really exist, it is just the reference to TOC base for the current
|
|
// object file. Since the symbol is undefined, returning false results
|
|
// in a relocation with a null section which is the desired result.
|
|
case MCSymbolRefExpr::VK_PPC_TOCBASE:
|
|
return false;
|
|
|
|
// These VariantKind cause the relocation to refer to something other than
|
|
// the symbol itself, like a linker generated table. Since the address of
|
|
// symbol is not relevant, we cannot replace the symbol with the
|
|
// section and patch the difference in the addend.
|
|
case MCSymbolRefExpr::VK_GOT:
|
|
case MCSymbolRefExpr::VK_PLT:
|
|
case MCSymbolRefExpr::VK_GOTPCREL:
|
|
case MCSymbolRefExpr::VK_Mips_GOT:
|
|
case MCSymbolRefExpr::VK_PPC_GOT_LO:
|
|
case MCSymbolRefExpr::VK_PPC_GOT_HI:
|
|
case MCSymbolRefExpr::VK_PPC_GOT_HA:
|
|
return true;
|
|
}
|
|
|
|
// An undefined symbol is not in any section, so the relocation has to point
|
|
// to the symbol itself.
|
|
const MCSymbol &Sym = SD->getSymbol();
|
|
if (Sym.isUndefined())
|
|
return true;
|
|
|
|
unsigned Binding = MCELF::GetBinding(*SD);
|
|
switch(Binding) {
|
|
default:
|
|
llvm_unreachable("Invalid Binding");
|
|
case ELF::STB_LOCAL:
|
|
break;
|
|
case ELF::STB_WEAK:
|
|
// If the symbol is weak, it might be overridden by a symbol in another
|
|
// file. The relocation has to point to the symbol so that the linker
|
|
// can update it.
|
|
return true;
|
|
case ELF::STB_GLOBAL:
|
|
// Global ELF symbols can be preempted by the dynamic linker. The relocation
|
|
// has to point to the symbol for a reason analogous to the STB_WEAK case.
|
|
return true;
|
|
}
|
|
|
|
// If a relocation points to a mergeable section, we have to be careful.
|
|
// If the offset is zero, a relocation with the section will encode the
|
|
// same information. With a non-zero offset, the situation is different.
|
|
// For example, a relocation can point 42 bytes past the end of a string.
|
|
// If we change such a relocation to use the section, the linker would think
|
|
// that it pointed to another string and subtracting 42 at runtime will
|
|
// produce the wrong value.
|
|
auto &Sec = cast<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(*SD, Type))
|
|
return true;
|
|
return false;
|
|
}
|
|
|
|
static const MCSymbol *getWeakRef(const MCSymbolRefExpr &Ref) {
|
|
const MCSymbol &Sym = Ref.getSymbol();
|
|
|
|
if (Ref.getKind() == MCSymbolRefExpr::VK_WEAKREF)
|
|
return &Sym;
|
|
|
|
if (!Sym.isVariable())
|
|
return nullptr;
|
|
|
|
const MCExpr *Expr = Sym.getVariableValue();
|
|
const auto *Inner = dyn_cast<MCSymbolRefExpr>(Expr);
|
|
if (!Inner)
|
|
return nullptr;
|
|
|
|
if (Inner->getKind() == MCSymbolRefExpr::VK_WEAKREF)
|
|
return &Inner->getSymbol();
|
|
return nullptr;
|
|
}
|
|
|
|
// 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 MCSymbolData &D) {
|
|
if (MCELF::GetType(D) == ELF::STT_GNU_IFUNC)
|
|
return true;
|
|
|
|
switch (MCELF::GetBinding(D)) {
|
|
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 MCSectionData *FixupSectionD = Fragment->getParent();
|
|
const MCSectionELF &FixupSection =
|
|
cast<MCSectionELF>(FixupSectionD->getSection());
|
|
uint64_t C = Target.getConstant();
|
|
uint64_t FixupOffset = Layout.getFragmentOffset(Fragment) + Fixup.getOffset();
|
|
|
|
if (const MCSymbolRefExpr *RefB = Target.getSymB()) {
|
|
assert(RefB->getKind() == MCSymbolRefExpr::VK_None &&
|
|
"Should not have constructed this");
|
|
|
|
// Let A, B and C being the components of Target and R be the location of
|
|
// the fixup. If the fixup is not pcrel, we want to compute (A - B + C).
|
|
// If it is pcrel, we want to compute (A - B + C - R).
|
|
|
|
// In general, ELF has no relocations for -B. It can only represent (A + C)
|
|
// or (A + C - R). If B = R + K and the relocation is not pcrel, we can
|
|
// replace B to implement it: (A - R - K + C)
|
|
if (IsPCRel)
|
|
Asm.getContext().FatalError(
|
|
Fixup.getLoc(),
|
|
"No relocation available to represent this relative expression");
|
|
|
|
const MCSymbol &SymB = RefB->getSymbol();
|
|
|
|
if (SymB.isUndefined())
|
|
Asm.getContext().FatalError(
|
|
Fixup.getLoc(),
|
|
Twine("symbol '") + SymB.getName() +
|
|
"' can not be undefined in a subtraction expression");
|
|
|
|
assert(!SymB.isAbsolute() && "Should have been folded");
|
|
const MCSection &SecB = SymB.getSection();
|
|
if (&SecB != &FixupSection)
|
|
Asm.getContext().FatalError(
|
|
Fixup.getLoc(), "Cannot represent a difference across sections");
|
|
|
|
const MCSymbolData &SymBD = Asm.getSymbolData(SymB);
|
|
if (::isWeak(SymBD))
|
|
Asm.getContext().FatalError(
|
|
Fixup.getLoc(), "Cannot represent a subtraction with a weak symbol");
|
|
|
|
uint64_t SymBOffset = Layout.getSymbolOffset(&SymBD);
|
|
uint64_t K = SymBOffset - FixupOffset;
|
|
IsPCRel = true;
|
|
C -= K;
|
|
}
|
|
|
|
// We either rejected the fixup or folded B into C at this point.
|
|
const MCSymbolRefExpr *RefA = Target.getSymA();
|
|
const MCSymbol *SymA = RefA ? &RefA->getSymbol() : nullptr;
|
|
const MCSymbolData *SymAD = SymA ? &Asm.getSymbolData(*SymA) : nullptr;
|
|
|
|
unsigned Type = GetRelocType(Target, Fixup, IsPCRel);
|
|
bool RelocateWithSymbol = shouldRelocateWithSymbol(Asm, RefA, SymAD, C, Type);
|
|
if (!RelocateWithSymbol && SymA && !SymA->isUndefined())
|
|
C += Layout.getSymbolOffset(SymAD);
|
|
|
|
uint64_t Addend = 0;
|
|
if (hasRelocationAddend()) {
|
|
Addend = C;
|
|
C = 0;
|
|
}
|
|
|
|
FixedValue = C;
|
|
|
|
// FIXME: What is this!?!?
|
|
MCSymbolRefExpr::VariantKind Modifier =
|
|
RefA ? RefA->getKind() : MCSymbolRefExpr::VK_None;
|
|
if (RelocNeedsGOT(Modifier))
|
|
NeedsGOT = true;
|
|
|
|
if (!RelocateWithSymbol) {
|
|
const MCSection *SecA =
|
|
(SymA && !SymA->isUndefined()) ? &SymA->getSection() : nullptr;
|
|
auto *ELFSec = cast_or_null<MCSectionELF>(SecA);
|
|
MCSymbol *SectionSymbol =
|
|
ELFSec ? Asm.getContext().getOrCreateSectionSymbol(*ELFSec)
|
|
: nullptr;
|
|
ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend);
|
|
Relocations[&FixupSection].push_back(Rec);
|
|
return;
|
|
}
|
|
|
|
if (SymA) {
|
|
if (const MCSymbol *R = Renames.lookup(SymA))
|
|
SymA = R;
|
|
|
|
if (const MCSymbol *WeakRef = getWeakRef(*RefA))
|
|
WeakrefUsedInReloc.insert(WeakRef);
|
|
else
|
|
UsedInReloc.insert(SymA);
|
|
}
|
|
ELFRelocationEntry Rec(FixupOffset, SymA, Type, Addend);
|
|
Relocations[&FixupSection].push_back(Rec);
|
|
return;
|
|
}
|
|
|
|
|
|
uint64_t
|
|
ELFObjectWriter::getSymbolIndexInSymbolTable(const MCAssembler &Asm,
|
|
const MCSymbol *S) {
|
|
const MCSymbolData &SD = Asm.getSymbolData(*S);
|
|
return SD.getIndex();
|
|
}
|
|
|
|
bool ELFObjectWriter::isInSymtab(const MCAsmLayout &Layout,
|
|
const MCSymbolData &Data, bool Used,
|
|
bool Renamed) {
|
|
const MCSymbol &Symbol = Data.getSymbol();
|
|
if (Symbol.isVariable()) {
|
|
const MCExpr *Expr = Symbol.getVariableValue();
|
|
if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
|
|
if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
|
|
return false;
|
|
}
|
|
}
|
|
|
|
if (Used)
|
|
return true;
|
|
|
|
if (Renamed)
|
|
return false;
|
|
|
|
if (Symbol.getName() == "_GLOBAL_OFFSET_TABLE_")
|
|
return true;
|
|
|
|
if (Symbol.isVariable()) {
|
|
const MCSymbol *Base = Layout.getBaseSymbol(Symbol);
|
|
if (Base && Base->isUndefined())
|
|
return false;
|
|
}
|
|
|
|
bool IsGlobal = MCELF::GetBinding(Data) == ELF::STB_GLOBAL;
|
|
if (!Symbol.isVariable() && Symbol.isUndefined() && !IsGlobal)
|
|
return false;
|
|
|
|
if (Symbol.isTemporary())
|
|
return false;
|
|
|
|
return true;
|
|
}
|
|
|
|
bool ELFObjectWriter::isLocal(const MCSymbolData &Data, bool isUsedInReloc) {
|
|
if (Data.isExternal())
|
|
return false;
|
|
|
|
const MCSymbol &Symbol = Data.getSymbol();
|
|
if (Symbol.isDefined())
|
|
return true;
|
|
|
|
if (isUsedInReloc)
|
|
return false;
|
|
|
|
return true;
|
|
}
|
|
|
|
void ELFObjectWriter::computeSymbolTable(
|
|
MCAssembler &Asm, const MCAsmLayout &Layout,
|
|
const SectionIndexMapTy &SectionIndexMap,
|
|
const RevGroupMapTy &RevGroupMap) {
|
|
// FIXME: Is this the correct place to do this?
|
|
// FIXME: Why is an undefined reference to _GLOBAL_OFFSET_TABLE_ needed?
|
|
if (NeedsGOT) {
|
|
StringRef Name = "_GLOBAL_OFFSET_TABLE_";
|
|
MCSymbol *Sym = Asm.getContext().GetOrCreateSymbol(Name);
|
|
MCSymbolData &Data = Asm.getOrCreateSymbolData(*Sym);
|
|
Data.setExternal(true);
|
|
MCELF::SetBinding(Data, ELF::STB_GLOBAL);
|
|
}
|
|
|
|
// Add the data for the symbols.
|
|
for (const MCSymbol &Symbol : Asm.symbols()) {
|
|
MCSymbolData &SD = Symbol.getData();
|
|
|
|
bool Used = UsedInReloc.count(&Symbol);
|
|
bool WeakrefUsed = WeakrefUsedInReloc.count(&Symbol);
|
|
bool isSignature = RevGroupMap.count(&Symbol);
|
|
|
|
if (!isInSymtab(Layout, SD,
|
|
Used || WeakrefUsed || isSignature,
|
|
Renames.count(&Symbol)))
|
|
continue;
|
|
|
|
ELFSymbolData MSD;
|
|
MSD.SymbolData = &SD;
|
|
const MCSymbol *BaseSymbol = Layout.getBaseSymbol(Symbol);
|
|
|
|
// Undefined symbols are global, but this is the first place we
|
|
// are able to set it.
|
|
bool Local = isLocal(SD, Used);
|
|
if (!Local && MCELF::GetBinding(SD) == ELF::STB_LOCAL) {
|
|
assert(BaseSymbol);
|
|
MCSymbolData &BaseData = Asm.getSymbolData(*BaseSymbol);
|
|
MCELF::SetBinding(SD, ELF::STB_GLOBAL);
|
|
MCELF::SetBinding(BaseData, ELF::STB_GLOBAL);
|
|
}
|
|
|
|
if (!BaseSymbol) {
|
|
MSD.SectionIndex = ELF::SHN_ABS;
|
|
} else if (SD.isCommon()) {
|
|
assert(!Local);
|
|
MSD.SectionIndex = ELF::SHN_COMMON;
|
|
} else if (BaseSymbol->isUndefined()) {
|
|
if (isSignature && !Used)
|
|
MSD.SectionIndex = RevGroupMap.lookup(&Symbol);
|
|
else
|
|
MSD.SectionIndex = ELF::SHN_UNDEF;
|
|
if (!Used && WeakrefUsed)
|
|
MCELF::SetBinding(SD, ELF::STB_WEAK);
|
|
} else {
|
|
const MCSectionELF &Section =
|
|
static_cast<const MCSectionELF&>(BaseSymbol->getSection());
|
|
MSD.SectionIndex = SectionIndexMap.lookup(&Section);
|
|
assert(MSD.SectionIndex && "Invalid section index!");
|
|
}
|
|
|
|
// The @@@ in symbol version is replaced with @ in undefined symbols and @@
|
|
// in defined ones.
|
|
//
|
|
// 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();
|
|
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.
|
|
SmallString<32> Buf;
|
|
size_t Pos = Name.find("@@@");
|
|
if (Pos != StringRef::npos) {
|
|
Buf += Name.substr(0, Pos);
|
|
unsigned Skip = MSD.SectionIndex == ELF::SHN_UNDEF ? 2 : 1;
|
|
Buf += Name.substr(Pos + Skip);
|
|
Name = Buf;
|
|
}
|
|
}
|
|
|
|
// Sections have their own string table
|
|
if (MCELF::GetType(SD) != ELF::STT_SECTION)
|
|
MSD.Name = StrTabBuilder.add(Name);
|
|
|
|
if (MSD.SectionIndex == ELF::SHN_UNDEF)
|
|
UndefinedSymbolData.push_back(MSD);
|
|
else if (Local)
|
|
LocalSymbolData.push_back(MSD);
|
|
else
|
|
ExternalSymbolData.push_back(MSD);
|
|
}
|
|
|
|
for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
|
|
StrTabBuilder.add(*i);
|
|
|
|
StrTabBuilder.finalize(StringTableBuilder::ELF);
|
|
|
|
for (auto i = Asm.file_names_begin(), e = Asm.file_names_end(); i != e; ++i)
|
|
FileSymbolData.push_back(StrTabBuilder.getOffset(*i));
|
|
|
|
for (ELFSymbolData &MSD : LocalSymbolData)
|
|
MSD.StringIndex = MCELF::GetType(*MSD.SymbolData) == ELF::STT_SECTION
|
|
? 0
|
|
: StrTabBuilder.getOffset(MSD.Name);
|
|
for (ELFSymbolData &MSD : ExternalSymbolData)
|
|
MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
|
|
for (ELFSymbolData& MSD : UndefinedSymbolData)
|
|
MSD.StringIndex = StrTabBuilder.getOffset(MSD.Name);
|
|
|
|
// Symbols are required to be in lexicographic order.
|
|
array_pod_sort(LocalSymbolData.begin(), LocalSymbolData.end());
|
|
array_pod_sort(ExternalSymbolData.begin(), ExternalSymbolData.end());
|
|
array_pod_sort(UndefinedSymbolData.begin(), UndefinedSymbolData.end());
|
|
|
|
// Set the symbol indices. Local symbols must come before all other
|
|
// symbols with non-local bindings.
|
|
unsigned Index = FileSymbolData.size() + 1;
|
|
for (unsigned i = 0, e = LocalSymbolData.size(); i != e; ++i)
|
|
LocalSymbolData[i].SymbolData->setIndex(Index++);
|
|
|
|
for (unsigned i = 0, e = ExternalSymbolData.size(); i != e; ++i)
|
|
ExternalSymbolData[i].SymbolData->setIndex(Index++);
|
|
for (unsigned i = 0, e = UndefinedSymbolData.size(); i != e; ++i)
|
|
UndefinedSymbolData[i].SymbolData->setIndex(Index++);
|
|
}
|
|
|
|
const MCSectionELF *
|
|
ELFObjectWriter::createRelocationSection(MCAssembler &Asm,
|
|
const MCSectionELF &Sec) {
|
|
if (Relocations[&Sec].empty())
|
|
return nullptr;
|
|
|
|
MCContext &Ctx = Asm.getContext();
|
|
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;
|
|
|
|
const MCSectionELF *RelaSection = Ctx.createELFRelSection(
|
|
RelaSectionName, hasRelocationAddend() ? ELF::SHT_RELA : ELF::SHT_REL,
|
|
Flags, EntrySize, Sec.getGroup(), &Sec);
|
|
MCSectionData &RelSD = Asm.getOrCreateSectionData(*RelaSection);
|
|
RelSD.setAlignment(is64Bit() ? 8 : 4);
|
|
return RelaSection;
|
|
}
|
|
|
|
static SmallVector<char, 128>
|
|
getUncompressedData(const MCAsmLayout &Layout,
|
|
const MCSectionData::FragmentListType &Fragments) {
|
|
SmallVector<char, 128> UncompressedData;
|
|
for (const MCFragment &F : Fragments) {
|
|
const SmallVectorImpl<char> *Contents;
|
|
switch (F.getKind()) {
|
|
case MCFragment::FT_Data:
|
|
Contents = &cast<MCDataFragment>(F).getContents();
|
|
break;
|
|
case MCFragment::FT_Dwarf:
|
|
Contents = &cast<MCDwarfLineAddrFragment>(F).getContents();
|
|
break;
|
|
case MCFragment::FT_DwarfFrame:
|
|
Contents = &cast<MCDwarfCallFrameFragment>(F).getContents();
|
|
break;
|
|
default:
|
|
llvm_unreachable(
|
|
"Not expecting any other fragment types in a debug_* section");
|
|
}
|
|
UncompressedData.append(Contents->begin(), Contents->end());
|
|
}
|
|
return UncompressedData;
|
|
}
|
|
|
|
// Include the debug info compression header:
|
|
// "ZLIB" followed by 8 bytes representing the uncompressed size of the section,
|
|
// useful for consumers to preallocate a buffer to decompress into.
|
|
static bool
|
|
prependCompressionHeader(uint64_t Size,
|
|
SmallVectorImpl<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,
|
|
const MCSectionData &SD,
|
|
const MCAsmLayout &Layout) {
|
|
const MCSectionELF &Section =
|
|
static_cast<const MCSectionELF &>(SD.getSection());
|
|
StringRef SectionName = Section.getSectionName();
|
|
|
|
// Compressing debug_frame requires handling alignment fragments which is
|
|
// more work (possibly generalizing MCAssembler.cpp:writeFragment to allow
|
|
// for writing to arbitrary buffers) for little benefit.
|
|
if (!Asm.getContext().getAsmInfo()->compressDebugSections() ||
|
|
!SectionName.startswith(".debug_") || SectionName == ".debug_frame") {
|
|
Asm.writeSectionData(&SD, Layout);
|
|
return;
|
|
}
|
|
|
|
// Gather the uncompressed data from all the fragments.
|
|
const MCSectionData::FragmentListType &Fragments = SD.getFragmentList();
|
|
SmallVector<char, 128> UncompressedData =
|
|
getUncompressedData(Layout, Fragments);
|
|
|
|
SmallVector<char, 128> CompressedContents;
|
|
zlib::Status Success = zlib::compress(
|
|
StringRef(UncompressedData.data(), UncompressedData.size()),
|
|
CompressedContents);
|
|
if (Success != zlib::StatusOK) {
|
|
Asm.writeSectionData(&SD, Layout);
|
|
return;
|
|
}
|
|
|
|
if (!prependCompressionHeader(UncompressedData.size(), CompressedContents)) {
|
|
Asm.writeSectionData(&SD, Layout);
|
|
return;
|
|
}
|
|
Asm.getContext().renameELFSection(&Section,
|
|
(".z" + SectionName.drop_front(1)).str());
|
|
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) {
|
|
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];
|
|
|
|
// Sort the relocation entries. Most targets just sort by Offset, but some
|
|
// (e.g., MIPS) have additional constraints.
|
|
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 ? getSymbolIndexInSymbolTable(Asm, Entry.Symbol) : 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::createSectionHeaderStringTable() {
|
|
const MCSectionELF *ShstrtabSection = SectionTable[ShstrtabIndex - 1];
|
|
ShStrTabBuilder.finalize(StringTableBuilder::ELF);
|
|
OS << ShStrTabBuilder.data();
|
|
return ShstrtabSection;
|
|
}
|
|
|
|
const MCSectionELF *ELFObjectWriter::createStringTable(MCContext &Ctx) {
|
|
const MCSectionELF *StrtabSection =
|
|
Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
|
|
StringTableIndex = addToSectionTable(StrtabSection);
|
|
OS << StrTabBuilder.data();
|
|
return StrtabSection;
|
|
}
|
|
|
|
void ELFObjectWriter::writeSection(MCAssembler &Asm,
|
|
const SectionIndexMapTy &SectionIndexMap,
|
|
uint32_t GroupSymbolIndex,
|
|
uint64_t Offset, uint64_t Size,
|
|
uint64_t Alignment,
|
|
const MCSectionELF &Section) {
|
|
uint64_t sh_link = 0;
|
|
uint64_t sh_info = 0;
|
|
|
|
switch(Section.getType()) {
|
|
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(ShStrTabBuilder.getOffset(Section.getSectionName()),
|
|
Section.getType(),
|
|
Section.getFlags(), 0, Offset, Size, sh_link, sh_info,
|
|
Alignment, Section.getEntrySize());
|
|
}
|
|
|
|
void ELFObjectWriter::writeSectionHeader(
|
|
MCAssembler &Asm, 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) {
|
|
const MCSectionData &SD = Asm.getOrCreateSectionData(*Section);
|
|
uint32_t GroupSymbolIndex;
|
|
unsigned Type = Section->getType();
|
|
if (Type != ELF::SHT_GROUP)
|
|
GroupSymbolIndex = 0;
|
|
else
|
|
GroupSymbolIndex = getSymbolIndexInSymbolTable(Asm, Section->getGroup());
|
|
|
|
const std::pair<uint64_t, uint64_t> &Offsets =
|
|
SectionOffsets.find(Section)->second;
|
|
uint64_t Size = Type == ELF::SHT_NOBITS ? Layout.getSectionAddressSize(&SD)
|
|
: Offsets.second - Offsets.first;
|
|
|
|
writeSection(Asm, SectionIndexMap, GroupSymbolIndex, Offsets.first, Size,
|
|
SD.getAlignment(), *Section);
|
|
}
|
|
}
|
|
|
|
void ELFObjectWriter::WriteObject(MCAssembler &Asm,
|
|
const MCAsmLayout &Layout) {
|
|
MCContext &Ctx = Asm.getContext();
|
|
const MCSectionELF *ShstrtabSection =
|
|
Ctx.getELFSection(".shstrtab", ELF::SHT_STRTAB, 0);
|
|
ShstrtabIndex = addToSectionTable(ShstrtabSection);
|
|
|
|
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;
|
|
bool ComputedSymtab = false;
|
|
for (const MCSectionData &SD : Asm) {
|
|
const MCSectionELF &Section =
|
|
static_cast<const MCSectionELF &>(SD.getSection());
|
|
|
|
uint64_t Padding = OffsetToAlignment(OS.tell(), SD.getAlignment());
|
|
WriteZeros(Padding);
|
|
|
|
// Remember the offset into the file for this section.
|
|
uint64_t SecStart = OS.tell();
|
|
|
|
const MCSymbol *SignatureSymbol = Section.getGroup();
|
|
unsigned Type = Section.getType();
|
|
if (Type == ELF::SHT_GROUP) {
|
|
assert(SignatureSymbol);
|
|
write(uint32_t(ELF::GRP_COMDAT));
|
|
for (const MCSectionELF *Member : GroupMembers[SignatureSymbol]) {
|
|
uint32_t SecIndex = SectionIndexMap.lookup(Member);
|
|
write(SecIndex);
|
|
}
|
|
} else if (Type == ELF::SHT_REL || Type == ELF::SHT_RELA) {
|
|
if (!ComputedSymtab) {
|
|
// Compute symbol table information.
|
|
computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap);
|
|
ComputedSymtab = true;
|
|
}
|
|
writeRelocations(Asm, *Section.getAssociatedSection());
|
|
} else {
|
|
writeSectionData(Asm, SD, Layout);
|
|
}
|
|
|
|
uint64_t SecEnd = OS.tell();
|
|
SectionOffsets[&Section] = std::make_pair(SecStart, SecEnd);
|
|
|
|
if (Type == ELF::SHT_GROUP || Type == ELF::SHT_REL || Type == ELF::SHT_RELA)
|
|
continue;
|
|
|
|
const MCSectionELF *RelSection = createRelocationSection(Asm, Section);
|
|
|
|
if (SignatureSymbol) {
|
|
Asm.getOrCreateSymbolData(*SignatureSymbol);
|
|
unsigned &GroupIdx = RevGroupMap[SignatureSymbol];
|
|
if (!GroupIdx) {
|
|
const MCSectionELF *Group = Ctx.createELFGroupSection(SignatureSymbol);
|
|
GroupIdx = addToSectionTable(Group);
|
|
MCSectionData *GroupD = &Asm.getOrCreateSectionData(*Group);
|
|
GroupD->setAlignment(4);
|
|
}
|
|
GroupMembers[SignatureSymbol].push_back(&Section);
|
|
if (RelSection)
|
|
GroupMembers[SignatureSymbol].push_back(RelSection);
|
|
}
|
|
|
|
SectionIndexMap[&Section] = addToSectionTable(&Section);
|
|
if (RelSection)
|
|
SectionIndexMap[RelSection] = addToSectionTable(RelSection);
|
|
}
|
|
|
|
if (!ComputedSymtab) {
|
|
// Compute symbol table information.
|
|
computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap);
|
|
ComputedSymtab = true;
|
|
}
|
|
|
|
WriteSymbolTable(Asm, Layout, SectionOffsets);
|
|
|
|
{
|
|
uint64_t SecStart = OS.tell();
|
|
const MCSectionELF *Sec = createStringTable(Ctx);
|
|
uint64_t SecEnd = OS.tell();
|
|
SectionOffsets[Sec] = std::make_pair(SecStart, SecEnd);
|
|
}
|
|
|
|
{
|
|
uint64_t SecStart = OS.tell();
|
|
const MCSectionELF *Sec = createSectionHeaderStringTable();
|
|
uint64_t SecEnd = OS.tell();
|
|
SectionOffsets[Sec] = std::make_pair(SecStart, SecEnd);
|
|
}
|
|
|
|
uint64_t NaturalAlignment = is64Bit() ? 8 : 4;
|
|
uint64_t Padding = OffsetToAlignment(OS.tell(), NaturalAlignment);
|
|
WriteZeros(Padding);
|
|
|
|
const unsigned SectionHeaderOffset = OS.tell();
|
|
|
|
// ... then the section header table ...
|
|
writeSectionHeader(Asm, 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);
|
|
OS.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);
|
|
OS.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
|
|
offsetof(ELF::Elf32_Ehdr, e_shoff));
|
|
NumSectionsOffset = offsetof(ELF::Elf32_Ehdr, e_shnum);
|
|
}
|
|
OS.pwrite(reinterpret_cast<char *>(&NumSections), sizeof(NumSections),
|
|
NumSectionsOffset);
|
|
}
|
|
|
|
bool ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
|
|
const MCAssembler &Asm, const MCSymbol &SymA, const MCFragment &FB,
|
|
bool InSet, bool IsPCRel) const {
|
|
if (IsPCRel) {
|
|
assert(!InSet);
|
|
if (::isWeak(SymA.getData()))
|
|
return false;
|
|
}
|
|
return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(Asm, SymA, FB,
|
|
InSet, IsPCRel);
|
|
}
|
|
|
|
bool ELFObjectWriter::isWeak(const MCSymbolData &SD) const {
|
|
if (::isWeak(SD))
|
|
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 (MCELF::GetBinding(SD) != ELF::STB_GLOBAL)
|
|
return false;
|
|
|
|
const MCSymbol &Sym = SD.getSymbol();
|
|
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);
|
|
}
|