MCELFObjectWriter.h

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//===- llvm/MC/MCELFObjectWriter.h - ELF Object Writer ----------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_MC_MCELFOBJECTWRITER_H
#define LLVM_MC_MCELFOBJECTWRITER_H
 
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/BinaryFormat/ELF.h"
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/MC/MCSectionELF.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/TargetParser/Triple.h"
#include <cstdint>
#include <memory>
#include <optional>
#include <vector>
 
namespace llvm {
 
class MCAssembler;
class MCContext;
class MCFixup;
class MCSymbol;
class MCSymbolELF;
class MCTargetOptions;
class MCValue;
 
struct ELFRelocationEntry {
  uint64_t Offset; // Where is the relocation.
  const MCSymbolELF *Symbol; // The symbol to relocate with.
  unsigned Type;   // The type of the relocation.
  uint64_t Addend; // The addend to use.
  const MCSymbolELF *OriginalSymbol; // The original value of Symbol if we changed it.
 
  ELFRelocationEntry(uint64_t Offset, const MCSymbolELF *Symbol, unsigned Type,
                     uint64_t Addend, const MCSymbolELF *OriginalSymbol)
      : Offset(Offset), Symbol(Symbol), Type(Type), Addend(Addend),
        OriginalSymbol(OriginalSymbol) {}
 
  void print(raw_ostream &Out) const {
    Out << "Off=" << Offset << ", Sym=" << Symbol << ", Type=" << Type
        << ", Addend=" << Addend << ", OriginalSymbol=" << OriginalSymbol;
  }
 
  LLVM_DUMP_METHOD void dump() const { print(errs()); }
};
 
class MCELFObjectTargetWriter : public MCObjectTargetWriter {
  const uint8_t OSABI;
  const uint8_t ABIVersion;
  const uint16_t EMachine;
  const unsigned HasRelocationAddend : 1;
  const unsigned Is64Bit : 1;
 
protected:
  MCELFObjectTargetWriter(bool Is64Bit_, uint8_t OSABI_, uint16_t EMachine_,
                          bool HasRelocationAddend_, uint8_t ABIVersion_ = 0);
 
public:
  virtual ~MCELFObjectTargetWriter() = default;
 
  Triple::ObjectFormatType getFormat() const override { return Triple::ELF; }
  static bool classof(const MCObjectTargetWriter *W) {
    return W->getFormat() == Triple::ELF;
  }
 
  static uint8_t getOSABI(Triple::OSType OSType) {
    switch (OSType) {
      case Triple::HermitCore:
        return ELF::ELFOSABI_STANDALONE;
      case Triple::PS4:
      case Triple::FreeBSD:
        return ELF::ELFOSABI_FREEBSD;
      case Triple::Solaris:
        return ELF::ELFOSABI_SOLARIS;
      case Triple::OpenBSD:
        return ELF::ELFOSABI_OPENBSD;
      default:
        return ELF::ELFOSABI_NONE;
    }
  }
 
  virtual unsigned getRelocType(MCContext &Ctx, const MCValue &Target,
                                const MCFixup &Fixup, bool IsPCRel) const = 0;
 
  virtual bool needsRelocateWithSymbol(const MCValue &Val, const MCSymbol &Sym,
                                       unsigned Type) const;
 
  virtual void sortRelocs(const MCAssembler &Asm,
                          std::vector<ELFRelocationEntry> &Relocs);
 
  /// \name Accessors
  /// @{
  uint8_t getOSABI() const { return OSABI; }
  uint8_t getABIVersion() const { return ABIVersion; }
  uint16_t getEMachine() const { return EMachine; }
  bool hasRelocationAddend() const { return HasRelocationAddend; }
  bool is64Bit() const { return Is64Bit; }
  /// @}
 
  // Instead of changing everyone's API we pack the N64 Type fields
  // into the existing 32 bit data unsigned.
#define R_TYPE_SHIFT 0
#define R_TYPE_MASK 0xffffff00
#define R_TYPE2_SHIFT 8
#define R_TYPE2_MASK 0xffff00ff
#define R_TYPE3_SHIFT 16
#define R_TYPE3_MASK 0xff00ffff
#define R_SSYM_SHIFT 24
#define R_SSYM_MASK 0x00ffffff
 
  // N64 relocation type accessors
  uint8_t getRType(uint32_t Type) const {
    return (unsigned)((Type >> R_TYPE_SHIFT) & 0xff);
  }
  uint8_t getRType2(uint32_t Type) const {
    return (unsigned)((Type >> R_TYPE2_SHIFT) & 0xff);
  }
  uint8_t getRType3(uint32_t Type) const {
    return (unsigned)((Type >> R_TYPE3_SHIFT) & 0xff);
  }
  uint8_t getRSsym(uint32_t Type) const {
    return (unsigned)((Type >> R_SSYM_SHIFT) & 0xff);
  }
 
  // N64 relocation type setting
  static unsigned setRTypes(unsigned Value1, unsigned Value2, unsigned Value3) {
    return ((Value1 & 0xff) << R_TYPE_SHIFT) |
           ((Value2 & 0xff) << R_TYPE2_SHIFT) |
           ((Value3 & 0xff) << R_TYPE3_SHIFT);
  }
  unsigned setRSsym(unsigned Value, unsigned Type) const {
    return (Type & R_SSYM_MASK) | ((Value & 0xff) << R_SSYM_SHIFT);
  }
 
  // On AArch64, return a new section to be added to the ELF object that
  // contains relocations used to describe every symbol that should have memory
  // tags applied. Returns nullptr if no such section is necessary (i.e. there's
  // no tagged globals).
  virtual MCSectionELF *getMemtagRelocsSection(MCContext &Ctx) const {
    return nullptr;
  }
};
 
class ELFObjectWriter final : public MCObjectWriter {
  unsigned ELFHeaderEFlags = 0;
 
public:
  std::unique_ptr<MCELFObjectTargetWriter> TargetObjectWriter;
  raw_pwrite_stream &OS;
  raw_pwrite_stream *DwoOS = nullptr;
 
  DenseMap<const MCSectionELF *, std::vector<ELFRelocationEntry>> Relocations;
  DenseMap<const MCSymbolELF *, const MCSymbolELF *> Renames;
  bool IsLittleEndian = false;
  bool SeenGnuAbi = false;
  std::optional<uint8_t> OverrideABIVersion;
 
  struct Symver {
    SMLoc Loc;
    const MCSymbol *Sym;
    StringRef Name;
    // True if .symver *, *@@@* or .symver *, *, remove.
    bool KeepOriginalSym;
  };
  SmallVector<Symver, 0> Symvers;
 
  ELFObjectWriter(std::unique_ptr<MCELFObjectTargetWriter> MOTW,
                  raw_pwrite_stream &OS, bool IsLittleEndian);
  ELFObjectWriter(std::unique_ptr<MCELFObjectTargetWriter> MOTW,
                  raw_pwrite_stream &OS, raw_pwrite_stream &DwoOS,
                  bool IsLittleEndian);
 
  void reset() override;
  void executePostLayoutBinding(MCAssembler &Asm) override;
  void recordRelocation(MCAssembler &Asm, const MCFragment *Fragment,
                        const MCFixup &Fixup, MCValue Target,
                        uint64_t &FixedValue) override;
  bool isSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
                                              const MCSymbol &SymA,
                                              const MCFragment &FB, bool InSet,
                                              bool IsPCRel) const override;
  uint64_t writeObject(MCAssembler &Asm) override;
 
  bool hasRelocationAddend() const;
  bool usesRela(const MCTargetOptions *TO, const MCSectionELF &Sec) const;
 
  bool shouldRelocateWithSymbol(const MCAssembler &Asm, const MCValue &Val,
                                const MCSymbolELF *Sym, uint64_t C,
                                unsigned Type) const;
 
  bool checkRelocation(MCContext &Ctx, SMLoc Loc, const MCSectionELF *From,
                       const MCSectionELF *To);
 
  unsigned getELFHeaderEFlags() const { return ELFHeaderEFlags; }
  void setELFHeaderEFlags(unsigned Flags) { ELFHeaderEFlags = Flags; }
 
  // Mark that we have seen GNU ABI usage (e.g. SHF_GNU_RETAIN, STB_GNU_UNIQUE).
  void markGnuAbi() { SeenGnuAbi = true; }
  bool seenGnuAbi() const { return SeenGnuAbi; }
 
  // Override the default e_ident[EI_ABIVERSION] in the ELF header.
  void setOverrideABIVersion(uint8_t V) { OverrideABIVersion = V; }
};
} // end namespace llvm
 
#endif // LLVM_MC_MCELFOBJECTWRITER_H