forked from OSchip/llvm-project
1519 lines
51 KiB
C++
1519 lines
51 KiB
C++
//===- lib/MC/ELFObjectWriter.cpp - ELF File Writer -----------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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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/ADT/ArrayRef.h"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/STLExtras.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/StringRef.h"
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#include "llvm/ADT/Twine.h"
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#include "llvm/ADT/iterator.h"
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#include "llvm/BinaryFormat/ELF.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/MCELFObjectWriter.h"
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#include "llvm/MC/MCExpr.h"
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#include "llvm/MC/MCFixup.h"
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#include "llvm/MC/MCFixupKindInfo.h"
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#include "llvm/MC/MCFragment.h"
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#include "llvm/MC/MCObjectWriter.h"
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#include "llvm/MC/MCSection.h"
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#include "llvm/MC/MCSectionELF.h"
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#include "llvm/MC/MCSymbol.h"
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#include "llvm/MC/MCSymbolELF.h"
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#include "llvm/MC/MCTargetOptions.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/Alignment.h"
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#include "llvm/Support/Casting.h"
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#include "llvm/Support/Compression.h"
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#include "llvm/Support/Endian.h"
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#include "llvm/Support/EndianStream.h"
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#include "llvm/Support/Error.h"
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#include "llvm/Support/ErrorHandling.h"
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#include "llvm/Support/Host.h"
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#include "llvm/Support/LEB128.h"
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#include "llvm/Support/MathExtras.h"
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#include "llvm/Support/SMLoc.h"
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#include "llvm/Support/raw_ostream.h"
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#include <algorithm>
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#include <cassert>
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#include <cstddef>
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#include <cstdint>
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#include <map>
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#include <memory>
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#include <string>
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#include <utility>
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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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using SectionIndexMapTy = DenseMap<const MCSectionELF *, uint32_t>;
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class ELFObjectWriter;
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struct ELFWriter;
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bool isDwoSection(const MCSectionELF &Sec) {
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return Sec.getName().endswith(".dwo");
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}
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class SymbolTableWriter {
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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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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(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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ArrayRef<uint32_t> getShndxIndexes() const { return ShndxIndexes; }
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};
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struct ELFWriter {
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ELFObjectWriter &OWriter;
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support::endian::Writer W;
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enum DwoMode {
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AllSections,
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NonDwoOnly,
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DwoOnly,
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} Mode;
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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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/// Helper struct for containing some precomputed information on symbols.
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struct ELFSymbolData {
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const MCSymbolELF *Symbol;
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StringRef Name;
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uint32_t SectionIndex;
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uint32_t Order;
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};
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/// @}
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/// @name Symbol Table Data
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/// @{
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StringTableBuilder StrTabBuilder{StringTableBuilder::ELF};
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/// @}
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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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// 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;
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bool usesRela(const MCSectionELF &Sec) const;
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uint64_t align(unsigned Alignment);
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bool maybeWriteCompression(uint64_t Size,
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SmallVectorImpl<uint8_t> &CompressedContents,
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unsigned Alignment);
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public:
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ELFWriter(ELFObjectWriter &OWriter, raw_pwrite_stream &OS,
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bool IsLittleEndian, DwoMode Mode)
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: OWriter(OWriter),
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W(OS, IsLittleEndian ? support::little : support::big), Mode(Mode) {}
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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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else
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W.write<uint32_t>(Word);
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}
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template <typename T> void write(T Val) {
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W.write(Val);
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}
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void writeHeader(const MCAssembler &Asm);
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void writeSymbol(SymbolTableWriter &Writer, uint32_t StringIndex,
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ELFSymbolData &MSD, const MCAsmLayout &Layout);
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// Start and end offset of each section
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using SectionOffsetsTy =
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std::map<const MCSectionELF *, std::pair<uint64_t, uint64_t>>;
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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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/// 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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SectionOffsetsTy &SectionOffsets);
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void writeAddrsigSection();
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MCSectionELF *createRelocationSection(MCContext &Ctx,
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const MCSectionELF &Sec);
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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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void writeSectionData(const MCAssembler &Asm, MCSection &Sec,
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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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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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/// 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 SeenGnuAbi = false;
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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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: TargetObjectWriter(std::move(MOTW)) {}
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void reset() override {
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SeenGnuAbi = false;
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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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virtual bool checkRelocation(MCContext &Ctx, SMLoc Loc,
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const MCSectionELF *From,
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const MCSectionELF *To) {
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return true;
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}
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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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void executePostLayoutBinding(MCAssembler &Asm,
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const MCAsmLayout &Layout) override;
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void markGnuAbi() override { SeenGnuAbi = true; }
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bool seenGnuAbi() const { return SeenGnuAbi; }
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friend struct ELFWriter;
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};
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class ELFSingleObjectWriter : public ELFObjectWriter {
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raw_pwrite_stream &OS;
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bool IsLittleEndian;
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public:
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ELFSingleObjectWriter(std::unique_ptr<MCELFObjectTargetWriter> MOTW,
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raw_pwrite_stream &OS, bool IsLittleEndian)
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: ELFObjectWriter(std::move(MOTW)), OS(OS),
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IsLittleEndian(IsLittleEndian) {}
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uint64_t writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) override {
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return ELFWriter(*this, OS, IsLittleEndian, ELFWriter::AllSections)
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.writeObject(Asm, Layout);
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}
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friend struct ELFWriter;
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};
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class ELFDwoObjectWriter : public ELFObjectWriter {
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raw_pwrite_stream &OS, &DwoOS;
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bool IsLittleEndian;
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public:
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ELFDwoObjectWriter(std::unique_ptr<MCELFObjectTargetWriter> MOTW,
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raw_pwrite_stream &OS, raw_pwrite_stream &DwoOS,
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bool IsLittleEndian)
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: ELFObjectWriter(std::move(MOTW)), OS(OS), DwoOS(DwoOS),
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IsLittleEndian(IsLittleEndian) {}
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virtual bool checkRelocation(MCContext &Ctx, SMLoc Loc,
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const MCSectionELF *From,
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const MCSectionELF *To) override {
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if (isDwoSection(*From)) {
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Ctx.reportError(Loc, "A dwo section may not contain relocations");
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return false;
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}
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if (To && isDwoSection(*To)) {
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Ctx.reportError(Loc, "A relocation may not refer to a dwo section");
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return false;
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}
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return true;
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}
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uint64_t writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) override {
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uint64_t Size = ELFWriter(*this, OS, IsLittleEndian, ELFWriter::NonDwoOnly)
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.writeObject(Asm, Layout);
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Size += ELFWriter(*this, DwoOS, IsLittleEndian, ELFWriter::DwoOnly)
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.writeObject(Asm, Layout);
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return Size;
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}
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};
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} // end anonymous namespace
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uint64_t ELFWriter::align(unsigned Alignment) {
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uint64_t Offset = W.OS.tell(), NewOffset = alignTo(Offset, Alignment);
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W.OS.write_zeros(NewOffset - Offset);
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return NewOffset;
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}
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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->getName());
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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(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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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 ELFWriter::is64Bit() const {
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return OWriter.TargetObjectWriter->is64Bit();
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}
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bool ELFWriter::usesRela(const MCSectionELF &Sec) const {
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return OWriter.hasRelocationAddend() &&
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Sec.getType() != ELF::SHT_LLVM_CALL_GRAPH_PROFILE;
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}
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// Emit the ELF header.
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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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// 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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W.OS << ELF::ElfMagic; // e_ident[EI_MAG0] to e_ident[EI_MAG3]
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W.OS << char(is64Bit() ? ELF::ELFCLASS64 : ELF::ELFCLASS32); // e_ident[EI_CLASS]
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// e_ident[EI_DATA]
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W.OS << char(W.Endian == support::little ? ELF::ELFDATA2LSB
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: ELF::ELFDATA2MSB);
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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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uint8_t OSABI = OWriter.TargetObjectWriter->getOSABI();
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W.OS << char(OSABI == ELF::ELFOSABI_NONE && OWriter.seenGnuAbi()
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? int(ELF::ELFOSABI_GNU)
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: OSABI);
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// e_ident[EI_ABIVERSION]
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W.OS << char(OWriter.TargetObjectWriter->getABIVersion());
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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>(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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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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W.write<uint32_t>(Asm.getELFHeaderEFlags());
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// e_ehsize = ELF header size
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W.write<uint16_t>(is64Bit() ? sizeof(ELF::Elf64_Ehdr)
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: sizeof(ELF::Elf32_Ehdr));
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W.write<uint16_t>(0); // e_phentsize = prog header entry size
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W.write<uint16_t>(0); // e_phnum = # prog header entries = 0
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// e_shentsize = Section header entry size
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W.write<uint16_t>(is64Bit() ? sizeof(ELF::Elf64_Shdr)
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: sizeof(ELF::Elf32_Shdr));
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// e_shnum = # of section header ents
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W.write<uint16_t>(0);
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// e_shstrndx = Section # of '.strtab'
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assert(StringTableIndex < ELF::SHN_LORESERVE);
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W.write<uint16_t>(StringTableIndex);
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}
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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())
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return Sym.getCommonAlignment();
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uint64_t Res;
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if (!Layout.getSymbolOffset(Sym, Res))
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return 0;
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if (Layout.getAssembler().isThumbFunc(&Sym))
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Res |= 1;
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return Res;
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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 ||
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Type == ELF::STT_GNU_IFUNC || Type == ELF::STT_FUNC)
|
|
Type = ELF::STT_TLS;
|
|
break;
|
|
}
|
|
|
|
return Type;
|
|
}
|
|
|
|
static bool isIFunc(const MCSymbolELF *Symbol) {
|
|
while (Symbol->getType() != ELF::STT_GNU_IFUNC) {
|
|
const MCSymbolRefExpr *Value;
|
|
if (!Symbol->isVariable() ||
|
|
!(Value = dyn_cast<MCSymbolRefExpr>(Symbol->getVariableValue())) ||
|
|
Value->getKind() != MCSymbolRefExpr::VK_None ||
|
|
mergeTypeForSet(Symbol->getType(), ELF::STT_GNU_IFUNC) != ELF::STT_GNU_IFUNC)
|
|
return false;
|
|
Symbol = &cast<MCSymbolELF>(Value->getSymbol());
|
|
}
|
|
return true;
|
|
}
|
|
|
|
void ELFWriter::writeSymbol(SymbolTableWriter &Writer, uint32_t StringIndex,
|
|
ELFSymbolData &MSD, const MCAsmLayout &Layout) {
|
|
const auto &Symbol = cast<MCSymbolELF>(*MSD.Symbol);
|
|
const MCSymbolELF *Base =
|
|
cast_or_null<MCSymbolELF>(Layout.getBaseSymbol(Symbol));
|
|
|
|
// This has to be in sync with when computeSymbolTable uses SHN_ABS or
|
|
// SHN_COMMON.
|
|
bool IsReserved = !Base || Symbol.isCommon();
|
|
|
|
// Binding and Type share the same byte as upper and lower nibbles
|
|
uint8_t Binding = Symbol.getBinding();
|
|
uint8_t Type = Symbol.getType();
|
|
if (isIFunc(&Symbol))
|
|
Type = ELF::STT_GNU_IFUNC;
|
|
if (Base) {
|
|
Type = mergeTypeForSet(Type, Base->getType());
|
|
}
|
|
uint8_t Info = (Binding << 4) | Type;
|
|
|
|
// Other and Visibility share the same byte with Visibility using the lower
|
|
// 2 bits
|
|
uint8_t Visibility = Symbol.getVisibility();
|
|
uint8_t Other = Symbol.getOther() | Visibility;
|
|
|
|
uint64_t Value = SymbolValue(*MSD.Symbol, Layout);
|
|
uint64_t Size = 0;
|
|
|
|
const MCExpr *ESize = MSD.Symbol->getSize();
|
|
if (!ESize && Base) {
|
|
// For expressions like .set y, x+1, if y's size is unset, inherit from x.
|
|
ESize = Base->getSize();
|
|
|
|
// For `.size x, 2; y = x; .size y, 1; z = y; z1 = z; .symver y, y@v1`, z,
|
|
// z1, and y@v1's st_size equals y's. However, `Base` is `x` which will give
|
|
// us 2. Follow the MCSymbolRefExpr assignment chain, which covers most
|
|
// needs. MCBinaryExpr is not handled.
|
|
const MCSymbolELF *Sym = &Symbol;
|
|
while (Sym->isVariable()) {
|
|
if (auto *Expr =
|
|
dyn_cast<MCSymbolRefExpr>(Sym->getVariableValue(false))) {
|
|
Sym = cast<MCSymbolELF>(&Expr->getSymbol());
|
|
if (!Sym->getSize())
|
|
continue;
|
|
ESize = Sym->getSize();
|
|
}
|
|
break;
|
|
}
|
|
}
|
|
|
|
if (ESize) {
|
|
int64_t Res;
|
|
if (!ESize->evaluateKnownAbsolute(Res, Layout))
|
|
report_fatal_error("Size expression must be absolute.");
|
|
Size = Res;
|
|
}
|
|
|
|
// Write out the symbol table entry
|
|
Writer.writeSymbol(StringIndex, Info, Value, Size, Other, MSD.SectionIndex,
|
|
IsReserved);
|
|
}
|
|
|
|
bool ELFWriter::isInSymtab(const MCAsmLayout &Layout, const MCSymbolELF &Symbol,
|
|
bool Used, bool Renamed) {
|
|
if (Symbol.isVariable()) {
|
|
const MCExpr *Expr = Symbol.getVariableValue();
|
|
// Target Expressions that are always inlined do not appear in the symtab
|
|
if (const auto *T = dyn_cast<MCTargetExpr>(Expr))
|
|
if (T->inlineAssignedExpr())
|
|
return false;
|
|
if (const MCSymbolRefExpr *Ref = dyn_cast<MCSymbolRefExpr>(Expr)) {
|
|
if (Ref->getKind() == MCSymbolRefExpr::VK_WEAKREF)
|
|
return false;
|
|
}
|
|
}
|
|
|
|
if (Used)
|
|
return true;
|
|
|
|
if (Renamed)
|
|
return false;
|
|
|
|
if (Symbol.isVariable() && Symbol.isUndefined()) {
|
|
// FIXME: this is here just to diagnose the case of a var = commmon_sym.
|
|
Layout.getBaseSymbol(Symbol);
|
|
return false;
|
|
}
|
|
|
|
if (Symbol.isTemporary())
|
|
return false;
|
|
|
|
if (Symbol.getType() == ELF::STT_SECTION)
|
|
return false;
|
|
|
|
return true;
|
|
}
|
|
|
|
void ELFWriter::computeSymbolTable(
|
|
MCAssembler &Asm, const MCAsmLayout &Layout,
|
|
const SectionIndexMapTy &SectionIndexMap, const RevGroupMapTy &RevGroupMap,
|
|
SectionOffsetsTy &SectionOffsets) {
|
|
MCContext &Ctx = Asm.getContext();
|
|
SymbolTableWriter Writer(*this, is64Bit());
|
|
|
|
// Symbol table
|
|
unsigned EntrySize = is64Bit() ? ELF::SYMENTRY_SIZE64 : ELF::SYMENTRY_SIZE32;
|
|
MCSectionELF *SymtabSection =
|
|
Ctx.getELFSection(".symtab", ELF::SHT_SYMTAB, 0, EntrySize);
|
|
SymtabSection->setAlignment(is64Bit() ? Align(8) : Align(4));
|
|
SymbolTableIndex = addToSectionTable(SymtabSection);
|
|
|
|
uint64_t SecStart = align(SymtabSection->getAlignment());
|
|
|
|
// The first entry is the undefined symbol entry.
|
|
Writer.writeSymbol(0, 0, 0, 0, 0, 0, false);
|
|
|
|
std::vector<ELFSymbolData> LocalSymbolData;
|
|
std::vector<ELFSymbolData> ExternalSymbolData;
|
|
MutableArrayRef<std::pair<std::string, size_t>> FileNames =
|
|
Asm.getFileNames();
|
|
for (const std::pair<std::string, size_t> &F : FileNames)
|
|
StrTabBuilder.add(F.first);
|
|
|
|
// Add the data for the symbols.
|
|
bool HasLargeSectionIndex = false;
|
|
for (auto It : llvm::enumerate(Asm.symbols())) {
|
|
const auto &Symbol = cast<MCSymbolELF>(It.value());
|
|
bool Used = Symbol.isUsedInReloc();
|
|
bool WeakrefUsed = Symbol.isWeakrefUsedInReloc();
|
|
bool isSignature = Symbol.isSignature();
|
|
|
|
if (!isInSymtab(Layout, Symbol, Used || WeakrefUsed || isSignature,
|
|
OWriter.Renames.count(&Symbol)))
|
|
continue;
|
|
|
|
if (Symbol.isTemporary() && Symbol.isUndefined()) {
|
|
Ctx.reportError(SMLoc(), "Undefined temporary symbol " + Symbol.getName());
|
|
continue;
|
|
}
|
|
|
|
ELFSymbolData MSD;
|
|
MSD.Symbol = cast<MCSymbolELF>(&Symbol);
|
|
MSD.Order = It.index();
|
|
|
|
bool Local = Symbol.getBinding() == ELF::STB_LOCAL;
|
|
assert(Local || !Symbol.isTemporary());
|
|
|
|
if (Symbol.isAbsolute()) {
|
|
MSD.SectionIndex = ELF::SHN_ABS;
|
|
} else if (Symbol.isCommon()) {
|
|
if (Symbol.isTargetCommon()) {
|
|
MSD.SectionIndex = Symbol.getIndex();
|
|
} else {
|
|
assert(!Local);
|
|
MSD.SectionIndex = ELF::SHN_COMMON;
|
|
}
|
|
} else if (Symbol.isUndefined()) {
|
|
if (isSignature && !Used) {
|
|
MSD.SectionIndex = RevGroupMap.lookup(&Symbol);
|
|
if (MSD.SectionIndex >= ELF::SHN_LORESERVE)
|
|
HasLargeSectionIndex = true;
|
|
} else {
|
|
MSD.SectionIndex = ELF::SHN_UNDEF;
|
|
}
|
|
} else {
|
|
const MCSectionELF &Section =
|
|
static_cast<const MCSectionELF &>(Symbol.getSection());
|
|
|
|
// We may end up with a situation when section symbol is technically
|
|
// defined, but should not be. That happens because we explicitly
|
|
// pre-create few .debug_* sections to have accessors.
|
|
// And if these sections were not really defined in the code, but were
|
|
// referenced, we simply error out.
|
|
if (!Section.isRegistered()) {
|
|
assert(static_cast<const MCSymbolELF &>(Symbol).getType() ==
|
|
ELF::STT_SECTION);
|
|
Ctx.reportError(SMLoc(),
|
|
"Undefined section reference: " + Symbol.getName());
|
|
continue;
|
|
}
|
|
|
|
if (Mode == NonDwoOnly && isDwoSection(Section))
|
|
continue;
|
|
MSD.SectionIndex = SectionIndexMap.lookup(&Section);
|
|
assert(MSD.SectionIndex && "Invalid section index!");
|
|
if (MSD.SectionIndex >= ELF::SHN_LORESERVE)
|
|
HasLargeSectionIndex = true;
|
|
}
|
|
|
|
StringRef Name = Symbol.getName();
|
|
|
|
// Sections have their own string table
|
|
if (Symbol.getType() != ELF::STT_SECTION) {
|
|
MSD.Name = Name;
|
|
StrTabBuilder.add(Name);
|
|
}
|
|
|
|
if (Local)
|
|
LocalSymbolData.push_back(MSD);
|
|
else
|
|
ExternalSymbolData.push_back(MSD);
|
|
}
|
|
|
|
// This holds the .symtab_shndx section index.
|
|
unsigned SymtabShndxSectionIndex = 0;
|
|
|
|
if (HasLargeSectionIndex) {
|
|
MCSectionELF *SymtabShndxSection =
|
|
Ctx.getELFSection(".symtab_shndx", ELF::SHT_SYMTAB_SHNDX, 0, 4);
|
|
SymtabShndxSectionIndex = addToSectionTable(SymtabShndxSection);
|
|
SymtabShndxSection->setAlignment(Align(4));
|
|
}
|
|
|
|
StrTabBuilder.finalize();
|
|
|
|
// Make the first STT_FILE precede previous local symbols.
|
|
unsigned Index = 1;
|
|
auto FileNameIt = FileNames.begin();
|
|
if (!FileNames.empty())
|
|
FileNames[0].second = 0;
|
|
|
|
for (ELFSymbolData &MSD : LocalSymbolData) {
|
|
// Emit STT_FILE symbols before their associated local symbols.
|
|
for (; FileNameIt != FileNames.end() && FileNameIt->second <= MSD.Order;
|
|
++FileNameIt) {
|
|
Writer.writeSymbol(StrTabBuilder.getOffset(FileNameIt->first),
|
|
ELF::STT_FILE | ELF::STB_LOCAL, 0, 0, ELF::STV_DEFAULT,
|
|
ELF::SHN_ABS, true);
|
|
++Index;
|
|
}
|
|
|
|
unsigned StringIndex = MSD.Symbol->getType() == ELF::STT_SECTION
|
|
? 0
|
|
: StrTabBuilder.getOffset(MSD.Name);
|
|
MSD.Symbol->setIndex(Index++);
|
|
writeSymbol(Writer, StringIndex, MSD, Layout);
|
|
}
|
|
for (; FileNameIt != FileNames.end(); ++FileNameIt) {
|
|
Writer.writeSymbol(StrTabBuilder.getOffset(FileNameIt->first),
|
|
ELF::STT_FILE | ELF::STB_LOCAL, 0, 0, ELF::STV_DEFAULT,
|
|
ELF::SHN_ABS, true);
|
|
++Index;
|
|
}
|
|
|
|
// Write the symbol table entries.
|
|
LastLocalSymbolIndex = Index;
|
|
|
|
for (ELFSymbolData &MSD : ExternalSymbolData) {
|
|
unsigned StringIndex = StrTabBuilder.getOffset(MSD.Name);
|
|
MSD.Symbol->setIndex(Index++);
|
|
writeSymbol(Writer, StringIndex, MSD, Layout);
|
|
assert(MSD.Symbol->getBinding() != ELF::STB_LOCAL);
|
|
}
|
|
|
|
uint64_t SecEnd = W.OS.tell();
|
|
SectionOffsets[SymtabSection] = std::make_pair(SecStart, SecEnd);
|
|
|
|
ArrayRef<uint32_t> ShndxIndexes = Writer.getShndxIndexes();
|
|
if (ShndxIndexes.empty()) {
|
|
assert(SymtabShndxSectionIndex == 0);
|
|
return;
|
|
}
|
|
assert(SymtabShndxSectionIndex != 0);
|
|
|
|
SecStart = W.OS.tell();
|
|
const MCSectionELF *SymtabShndxSection =
|
|
SectionTable[SymtabShndxSectionIndex - 1];
|
|
for (uint32_t Index : ShndxIndexes)
|
|
write(Index);
|
|
SecEnd = W.OS.tell();
|
|
SectionOffsets[SymtabShndxSection] = std::make_pair(SecStart, SecEnd);
|
|
}
|
|
|
|
void ELFWriter::writeAddrsigSection() {
|
|
for (const MCSymbol *Sym : OWriter.AddrsigSyms)
|
|
encodeULEB128(Sym->getIndex(), W.OS);
|
|
}
|
|
|
|
MCSectionELF *ELFWriter::createRelocationSection(MCContext &Ctx,
|
|
const MCSectionELF &Sec) {
|
|
if (OWriter.Relocations[&Sec].empty())
|
|
return nullptr;
|
|
|
|
const StringRef SectionName = Sec.getName();
|
|
bool Rela = usesRela(Sec);
|
|
std::string RelaSectionName = Rela ? ".rela" : ".rel";
|
|
RelaSectionName += SectionName;
|
|
|
|
unsigned EntrySize;
|
|
if (Rela)
|
|
EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rela) : sizeof(ELF::Elf32_Rela);
|
|
else
|
|
EntrySize = is64Bit() ? sizeof(ELF::Elf64_Rel) : sizeof(ELF::Elf32_Rel);
|
|
|
|
unsigned Flags = ELF::SHF_INFO_LINK;
|
|
if (Sec.getFlags() & ELF::SHF_GROUP)
|
|
Flags = ELF::SHF_GROUP;
|
|
|
|
MCSectionELF *RelaSection = Ctx.createELFRelSection(
|
|
RelaSectionName, Rela ? ELF::SHT_RELA : ELF::SHT_REL, Flags, EntrySize,
|
|
Sec.getGroup(), &Sec);
|
|
RelaSection->setAlignment(is64Bit() ? Align(8) : Align(4));
|
|
return RelaSection;
|
|
}
|
|
|
|
// Include the debug info compression header.
|
|
bool ELFWriter::maybeWriteCompression(
|
|
uint64_t Size, SmallVectorImpl<uint8_t> &CompressedContents,
|
|
unsigned Alignment) {
|
|
uint64_t HdrSize =
|
|
is64Bit() ? sizeof(ELF::Elf32_Chdr) : sizeof(ELF::Elf64_Chdr);
|
|
if (Size <= HdrSize + CompressedContents.size())
|
|
return false;
|
|
// Platform specific header is followed by compressed data.
|
|
if (is64Bit()) {
|
|
// Write Elf64_Chdr header.
|
|
write(static_cast<ELF::Elf64_Word>(ELF::ELFCOMPRESS_ZLIB));
|
|
write(static_cast<ELF::Elf64_Word>(0)); // ch_reserved field.
|
|
write(static_cast<ELF::Elf64_Xword>(Size));
|
|
write(static_cast<ELF::Elf64_Xword>(Alignment));
|
|
} else {
|
|
// Write Elf32_Chdr header otherwise.
|
|
write(static_cast<ELF::Elf32_Word>(ELF::ELFCOMPRESS_ZLIB));
|
|
write(static_cast<ELF::Elf32_Word>(Size));
|
|
write(static_cast<ELF::Elf32_Word>(Alignment));
|
|
}
|
|
return true;
|
|
}
|
|
|
|
void ELFWriter::writeSectionData(const MCAssembler &Asm, MCSection &Sec,
|
|
const MCAsmLayout &Layout) {
|
|
MCSectionELF &Section = static_cast<MCSectionELF &>(Sec);
|
|
StringRef SectionName = Section.getName();
|
|
|
|
auto &MC = Asm.getContext();
|
|
const auto &MAI = MC.getAsmInfo();
|
|
|
|
bool CompressionEnabled =
|
|
MAI->compressDebugSections() != DebugCompressionType::None;
|
|
if (!CompressionEnabled || !SectionName.startswith(".debug_")) {
|
|
Asm.writeSectionData(W.OS, &Section, Layout);
|
|
return;
|
|
}
|
|
|
|
assert((MAI->compressDebugSections() == DebugCompressionType::Z ||
|
|
MAI->compressDebugSections() == DebugCompressionType::GNU) &&
|
|
"expected zlib or zlib-gnu style compression");
|
|
|
|
SmallVector<char, 128> UncompressedData;
|
|
raw_svector_ostream VecOS(UncompressedData);
|
|
Asm.writeSectionData(VecOS, &Section, Layout);
|
|
|
|
SmallVector<uint8_t, 128> CompressedContents;
|
|
compression::zlib::compress(
|
|
makeArrayRef(reinterpret_cast<uint8_t *>(UncompressedData.data()),
|
|
UncompressedData.size()),
|
|
CompressedContents);
|
|
|
|
bool ZlibStyle = MAI->compressDebugSections() == DebugCompressionType::Z;
|
|
if (!maybeWriteCompression(UncompressedData.size(), CompressedContents,
|
|
Sec.getAlignment())) {
|
|
W.OS << UncompressedData;
|
|
return;
|
|
}
|
|
|
|
if (ZlibStyle) {
|
|
// Set the compressed flag. That is zlib style.
|
|
Section.setFlags(Section.getFlags() | ELF::SHF_COMPRESSED);
|
|
// Alignment field should reflect the requirements of
|
|
// the compressed section header.
|
|
Section.setAlignment(is64Bit() ? Align(8) : Align(4));
|
|
} else {
|
|
// Add "z" prefix to section name. This is zlib-gnu style.
|
|
MC.renameELFSection(&Section, (".z" + SectionName.drop_front(1)).str());
|
|
}
|
|
W.OS << toStringRef(CompressedContents);
|
|
}
|
|
|
|
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
|
|
WriteWord(Address); // sh_addr
|
|
WriteWord(Offset); // sh_offset
|
|
WriteWord(Size); // sh_size
|
|
W.write<uint32_t>(Link); // sh_link
|
|
W.write<uint32_t>(Info); // sh_info
|
|
WriteWord(Alignment); // sh_addralign
|
|
WriteWord(EntrySize); // sh_entsize
|
|
}
|
|
|
|
void ELFWriter::writeRelocations(const MCAssembler &Asm,
|
|
const MCSectionELF &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.
|
|
// In most cases that is not important, but it can be for special sections
|
|
// (.eh_frame) or specific relocations (TLS optimizations on SystemZ).
|
|
std::reverse(Relocs.begin(), Relocs.end());
|
|
|
|
// Sort the relocation entries. MIPS needs this.
|
|
OWriter.TargetObjectWriter->sortRelocs(Asm, Relocs);
|
|
|
|
const bool Rela = usesRela(Sec);
|
|
for (unsigned i = 0, e = Relocs.size(); i != e; ++i) {
|
|
const ELFRelocationEntry &Entry = Relocs[e - i - 1];
|
|
unsigned Index = Entry.Symbol ? Entry.Symbol->getIndex() : 0;
|
|
|
|
if (is64Bit()) {
|
|
write(Entry.Offset);
|
|
if (OWriter.TargetObjectWriter->getEMachine() == ELF::EM_MIPS) {
|
|
write(uint32_t(Index));
|
|
|
|
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);
|
|
write(ERE64.r_info);
|
|
}
|
|
if (Rela)
|
|
write(Entry.Addend);
|
|
} else {
|
|
write(uint32_t(Entry.Offset));
|
|
|
|
struct ELF::Elf32_Rela ERE32;
|
|
ERE32.setSymbolAndType(Index, Entry.Type);
|
|
write(ERE32.r_info);
|
|
|
|
if (Rela)
|
|
write(uint32_t(Entry.Addend));
|
|
|
|
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 =
|
|
OWriter.TargetObjectWriter->getRType3(Entry.Type)) {
|
|
write(uint32_t(Entry.Offset));
|
|
|
|
ERE32.setSymbolAndType(0, RType);
|
|
write(ERE32.r_info);
|
|
write(uint32_t(0));
|
|
}
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
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;
|
|
|
|
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 MCSection *InfoSection = Section.getLinkedToSection();
|
|
sh_info = SectionIndexMap.lookup(cast<MCSectionELF>(InfoSection));
|
|
break;
|
|
}
|
|
|
|
case ELF::SHT_SYMTAB:
|
|
sh_link = StringTableIndex;
|
|
sh_info = LastLocalSymbolIndex;
|
|
break;
|
|
|
|
case ELF::SHT_SYMTAB_SHNDX:
|
|
case ELF::SHT_LLVM_CALL_GRAPH_PROFILE:
|
|
case ELF::SHT_LLVM_ADDRSIG:
|
|
sh_link = SymbolTableIndex;
|
|
break;
|
|
|
|
case ELF::SHT_GROUP:
|
|
sh_link = SymbolTableIndex;
|
|
sh_info = GroupSymbolIndex;
|
|
break;
|
|
}
|
|
|
|
if (Section.getFlags() & ELF::SHF_LINK_ORDER) {
|
|
// If the value in the associated metadata is not a definition, Sym will be
|
|
// undefined. Represent this with sh_link=0.
|
|
const MCSymbol *Sym = Section.getLinkedToSymbol();
|
|
if (Sym && Sym->isInSection()) {
|
|
const MCSectionELF *Sec = cast<MCSectionELF>(&Sym->getSection());
|
|
sh_link = SectionIndexMap.lookup(Sec);
|
|
}
|
|
}
|
|
|
|
WriteSecHdrEntry(StrTabBuilder.getOffset(Section.getName()),
|
|
Section.getType(), Section.getFlags(), 0, Offset, Size,
|
|
sh_link, sh_info, Section.getAlignment(),
|
|
Section.getEntrySize());
|
|
}
|
|
|
|
void ELFWriter::writeSectionHeader(
|
|
const MCAsmLayout &Layout, const SectionIndexMapTy &SectionIndexMap,
|
|
const SectionOffsetsTy &SectionOffsets) {
|
|
const unsigned NumSections = SectionTable.size();
|
|
|
|
// Null section first.
|
|
uint64_t FirstSectionSize =
|
|
(NumSections + 1) >= ELF::SHN_LORESERVE ? NumSections + 1 : 0;
|
|
WriteSecHdrEntry(0, 0, 0, 0, 0, FirstSectionSize, 0, 0, 0, 0);
|
|
|
|
for (const MCSectionELF *Section : SectionTable) {
|
|
uint32_t GroupSymbolIndex;
|
|
unsigned Type = Section->getType();
|
|
if (Type != ELF::SHT_GROUP)
|
|
GroupSymbolIndex = 0;
|
|
else
|
|
GroupSymbolIndex = Section->getGroup()->getIndex();
|
|
|
|
const std::pair<uint64_t, uint64_t> &Offsets =
|
|
SectionOffsets.find(Section)->second;
|
|
uint64_t Size;
|
|
if (Type == ELF::SHT_NOBITS)
|
|
Size = Layout.getSectionAddressSize(Section);
|
|
else
|
|
Size = Offsets.second - Offsets.first;
|
|
|
|
writeSection(SectionIndexMap, GroupSymbolIndex, Offsets.first, Size,
|
|
*Section);
|
|
}
|
|
}
|
|
|
|
uint64_t ELFWriter::writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) {
|
|
uint64_t StartOffset = W.OS.tell();
|
|
|
|
MCContext &Ctx = Asm.getContext();
|
|
MCSectionELF *StrtabSection =
|
|
Ctx.getELFSection(".strtab", ELF::SHT_STRTAB, 0);
|
|
StringTableIndex = addToSectionTable(StrtabSection);
|
|
|
|
RevGroupMapTy RevGroupMap;
|
|
SectionIndexMapTy SectionIndexMap;
|
|
|
|
std::map<const MCSymbol *, std::vector<const MCSectionELF *>> GroupMembers;
|
|
|
|
// Write out the ELF header ...
|
|
writeHeader(Asm);
|
|
|
|
// ... then the sections ...
|
|
SectionOffsetsTy SectionOffsets;
|
|
std::vector<MCSectionELF *> Groups;
|
|
std::vector<MCSectionELF *> Relocations;
|
|
for (MCSection &Sec : Asm) {
|
|
MCSectionELF &Section = static_cast<MCSectionELF &>(Sec);
|
|
if (Mode == NonDwoOnly && isDwoSection(Section))
|
|
continue;
|
|
if (Mode == DwoOnly && !isDwoSection(Section))
|
|
continue;
|
|
|
|
// Remember the offset into the file for this section.
|
|
const uint64_t SecStart = align(Section.getAlignment());
|
|
|
|
const MCSymbolELF *SignatureSymbol = Section.getGroup();
|
|
writeSectionData(Asm, Section, Layout);
|
|
|
|
uint64_t SecEnd = W.OS.tell();
|
|
SectionOffsets[&Section] = std::make_pair(SecStart, SecEnd);
|
|
|
|
MCSectionELF *RelSection = createRelocationSection(Ctx, Section);
|
|
|
|
if (SignatureSymbol) {
|
|
unsigned &GroupIdx = RevGroupMap[SignatureSymbol];
|
|
if (!GroupIdx) {
|
|
MCSectionELF *Group =
|
|
Ctx.createELFGroupSection(SignatureSymbol, Section.isComdat());
|
|
GroupIdx = addToSectionTable(Group);
|
|
Group->setAlignment(Align(4));
|
|
Groups.push_back(Group);
|
|
}
|
|
std::vector<const MCSectionELF *> &Members =
|
|
GroupMembers[SignatureSymbol];
|
|
Members.push_back(&Section);
|
|
if (RelSection)
|
|
Members.push_back(RelSection);
|
|
}
|
|
|
|
SectionIndexMap[&Section] = addToSectionTable(&Section);
|
|
if (RelSection) {
|
|
SectionIndexMap[RelSection] = addToSectionTable(RelSection);
|
|
Relocations.push_back(RelSection);
|
|
}
|
|
|
|
OWriter.TargetObjectWriter->addTargetSectionFlags(Ctx, Section);
|
|
}
|
|
|
|
for (MCSectionELF *Group : Groups) {
|
|
// Remember the offset into the file for this section.
|
|
const uint64_t SecStart = align(Group->getAlignment());
|
|
|
|
const MCSymbol *SignatureSymbol = Group->getGroup();
|
|
assert(SignatureSymbol);
|
|
write(uint32_t(Group->isComdat() ? unsigned(ELF::GRP_COMDAT) : 0));
|
|
for (const MCSectionELF *Member : GroupMembers[SignatureSymbol]) {
|
|
uint32_t SecIndex = SectionIndexMap.lookup(Member);
|
|
write(SecIndex);
|
|
}
|
|
|
|
uint64_t SecEnd = W.OS.tell();
|
|
SectionOffsets[Group] = std::make_pair(SecStart, SecEnd);
|
|
}
|
|
|
|
if (Mode == DwoOnly) {
|
|
// dwo files don't have symbol tables or relocations, but they do have
|
|
// string tables.
|
|
StrTabBuilder.finalize();
|
|
} else {
|
|
MCSectionELF *AddrsigSection;
|
|
if (OWriter.EmitAddrsigSection) {
|
|
AddrsigSection = Ctx.getELFSection(".llvm_addrsig", ELF::SHT_LLVM_ADDRSIG,
|
|
ELF::SHF_EXCLUDE);
|
|
addToSectionTable(AddrsigSection);
|
|
}
|
|
|
|
// Compute symbol table information.
|
|
computeSymbolTable(Asm, Layout, SectionIndexMap, RevGroupMap,
|
|
SectionOffsets);
|
|
|
|
for (MCSectionELF *RelSection : Relocations) {
|
|
// Remember the offset into the file for this section.
|
|
const uint64_t SecStart = align(RelSection->getAlignment());
|
|
|
|
writeRelocations(Asm,
|
|
cast<MCSectionELF>(*RelSection->getLinkedToSection()));
|
|
|
|
uint64_t SecEnd = W.OS.tell();
|
|
SectionOffsets[RelSection] = std::make_pair(SecStart, SecEnd);
|
|
}
|
|
|
|
if (OWriter.EmitAddrsigSection) {
|
|
uint64_t SecStart = W.OS.tell();
|
|
writeAddrsigSection();
|
|
uint64_t SecEnd = W.OS.tell();
|
|
SectionOffsets[AddrsigSection] = std::make_pair(SecStart, SecEnd);
|
|
}
|
|
}
|
|
|
|
{
|
|
uint64_t SecStart = W.OS.tell();
|
|
StrTabBuilder.write(W.OS);
|
|
SectionOffsets[StrtabSection] = std::make_pair(SecStart, W.OS.tell());
|
|
}
|
|
|
|
const uint64_t SectionHeaderOffset = align(is64Bit() ? 8 : 4);
|
|
|
|
// ... then the section header table ...
|
|
writeSectionHeader(Layout, SectionIndexMap, SectionOffsets);
|
|
|
|
uint16_t NumSections = support::endian::byte_swap<uint16_t>(
|
|
(SectionTable.size() + 1 >= ELF::SHN_LORESERVE) ? (uint16_t)ELF::SHN_UNDEF
|
|
: SectionTable.size() + 1,
|
|
W.Endian);
|
|
unsigned NumSectionsOffset;
|
|
|
|
auto &Stream = static_cast<raw_pwrite_stream &>(W.OS);
|
|
if (is64Bit()) {
|
|
uint64_t Val =
|
|
support::endian::byte_swap<uint64_t>(SectionHeaderOffset, W.Endian);
|
|
Stream.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
|
|
offsetof(ELF::Elf64_Ehdr, e_shoff));
|
|
NumSectionsOffset = offsetof(ELF::Elf64_Ehdr, e_shnum);
|
|
} else {
|
|
uint32_t Val =
|
|
support::endian::byte_swap<uint32_t>(SectionHeaderOffset, W.Endian);
|
|
Stream.pwrite(reinterpret_cast<char *>(&Val), sizeof(Val),
|
|
offsetof(ELF::Elf32_Ehdr, e_shoff));
|
|
NumSectionsOffset = offsetof(ELF::Elf32_Ehdr, e_shnum);
|
|
}
|
|
Stream.pwrite(reinterpret_cast<char *>(&NumSections), sizeof(NumSections),
|
|
NumSectionsOffset);
|
|
|
|
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 MCAssembler::Symver &S : Asm.Symvers) {
|
|
StringRef AliasName = S.Name;
|
|
const auto &Symbol = cast<MCSymbolELF>(*S.Sym);
|
|
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->setBinding(Symbol.getBinding());
|
|
Alias->setVisibility(Symbol.getVisibility());
|
|
Alias->setOther(Symbol.getOther());
|
|
|
|
if (!Symbol.isUndefined() && S.KeepOriginalSym)
|
|
continue;
|
|
|
|
if (Symbol.isUndefined() && Rest.startswith("@@") &&
|
|
!Rest.startswith("@@@")) {
|
|
Asm.getContext().reportError(S.Loc, "default version symbol " +
|
|
AliasName + " must be defined");
|
|
continue;
|
|
}
|
|
|
|
if (Renames.count(&Symbol) && Renames[&Symbol] != Alias) {
|
|
Asm.getContext().reportError(S.Loc, Twine("multiple versions for ") +
|
|
Symbol.getName());
|
|
continue;
|
|
}
|
|
|
|
Renames.insert(std::make_pair(&Symbol, Alias));
|
|
}
|
|
|
|
for (const MCSymbol *&Sym : AddrsigSyms) {
|
|
if (const MCSymbol *R = Renames.lookup(cast<MCSymbolELF>(Sym)))
|
|
Sym = R;
|
|
if (Sym->isInSection() && Sym->getName().startswith(".L"))
|
|
Sym = Sym->getSection().getBeginSymbol();
|
|
Sym->setUsedInReloc();
|
|
}
|
|
}
|
|
|
|
// 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_GOTPCREL_NORELAX:
|
|
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:
|
|
case ELF::STB_GNU_UNIQUE:
|
|
// 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;
|
|
}
|
|
|
|
// Keep symbol type for a local ifunc because it may result in an IRELATIVE
|
|
// reloc that the dynamic loader will use to resolve the address at startup
|
|
// time.
|
|
if (Sym->getType() == ELF::STT_GNU_IFUNC)
|
|
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;
|
|
|
|
// gold<2.34 incorrectly ignored the addend for R_386_GOTOFF (9)
|
|
// (http://sourceware.org/PR16794).
|
|
if (TargetObjectWriter->getEMachine() == ELF::EM_386 &&
|
|
Type == ELF::R_386_GOTOFF)
|
|
return true;
|
|
|
|
// ld.lld handles R_MIPS_HI16/R_MIPS_LO16 separately, not as a whole, so
|
|
// it doesn't know that an R_MIPS_HI16 with implicit addend 1 and an
|
|
// R_MIPS_LO16 with implicit addend -32768 represents 32768, which is in
|
|
// range of a MergeInputSection. We could introduce a new RelExpr member
|
|
// (like R_RISCV_PC_INDIRECT for R_RISCV_PCREL_HI20 / R_RISCV_PCREL_LO12)
|
|
// but the complexity is unnecessary given that GNU as keeps the original
|
|
// symbol for this case as well.
|
|
if (TargetObjectWriter->getEMachine() == ELF::EM_MIPS &&
|
|
!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()) {
|
|
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;
|
|
}
|
|
|
|
assert(!IsPCRel && "should have been folded");
|
|
IsPCRel = true;
|
|
C += FixupOffset - Layout.getSymbolOffset(SymB);
|
|
}
|
|
|
|
// 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;
|
|
}
|
|
}
|
|
}
|
|
|
|
const MCSectionELF *SecA = (SymA && SymA->isInSection())
|
|
? cast<MCSectionELF>(&SymA->getSection())
|
|
: nullptr;
|
|
if (!checkRelocation(Ctx, Fixup.getLoc(), &FixupSection, SecA))
|
|
return;
|
|
|
|
unsigned Type = TargetObjectWriter->getRelocType(Ctx, Target, Fixup, IsPCRel);
|
|
const auto *Parent = cast<MCSectionELF>(Fragment->getParent());
|
|
// Emiting relocation with sybmol for CG Profile to help with --cg-profile.
|
|
bool RelocateWithSymbol =
|
|
shouldRelocateWithSymbol(Asm, RefA, SymA, C, Type) ||
|
|
(Parent->getType() == ELF::SHT_LLVM_CALL_GRAPH_PROFILE);
|
|
uint64_t Addend = 0;
|
|
|
|
FixedValue = !RelocateWithSymbol && SymA && !SymA->isUndefined()
|
|
? C + Layout.getSymbolOffset(*SymA)
|
|
: C;
|
|
if (hasRelocationAddend()) {
|
|
Addend = FixedValue;
|
|
FixedValue = 0;
|
|
}
|
|
|
|
if (!RelocateWithSymbol) {
|
|
const auto *SectionSymbol =
|
|
SecA ? cast<MCSymbolELF>(SecA->getBeginSymbol()) : nullptr;
|
|
if (SectionSymbol)
|
|
SectionSymbol->setUsedInReloc();
|
|
ELFRelocationEntry Rec(FixupOffset, SectionSymbol, Type, Addend, SymA, C);
|
|
Relocations[&FixupSection].push_back(Rec);
|
|
return;
|
|
}
|
|
|
|
const MCSymbolELF *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, C);
|
|
Relocations[&FixupSection].push_back(Rec);
|
|
}
|
|
|
|
bool ELFObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(
|
|
const MCAssembler &Asm, const MCSymbol &SA, const MCFragment &FB,
|
|
bool InSet, bool IsPCRel) const {
|
|
const auto &SymA = cast<MCSymbolELF>(SA);
|
|
if (IsPCRel) {
|
|
assert(!InSet);
|
|
if (SymA.getBinding() != ELF::STB_LOCAL ||
|
|
SymA.getType() == ELF::STT_GNU_IFUNC)
|
|
return false;
|
|
}
|
|
return MCObjectWriter::isSymbolRefDifferenceFullyResolvedImpl(Asm, SymA, FB,
|
|
InSet, IsPCRel);
|
|
}
|
|
|
|
std::unique_ptr<MCObjectWriter>
|
|
llvm::createELFObjectWriter(std::unique_ptr<MCELFObjectTargetWriter> MOTW,
|
|
raw_pwrite_stream &OS, bool IsLittleEndian) {
|
|
return std::make_unique<ELFSingleObjectWriter>(std::move(MOTW), OS,
|
|
IsLittleEndian);
|
|
}
|
|
|
|
std::unique_ptr<MCObjectWriter>
|
|
llvm::createELFDwoObjectWriter(std::unique_ptr<MCELFObjectTargetWriter> MOTW,
|
|
raw_pwrite_stream &OS, raw_pwrite_stream &DwoOS,
|
|
bool IsLittleEndian) {
|
|
return std::make_unique<ELFDwoObjectWriter>(std::move(MOTW), OS, DwoOS,
|
|
IsLittleEndian);
|
|
}
|