text: //===-- PPCAsmBackend.cpp - PPC Assembler Backend -------------------------===//
  //
  // 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
  //
  //===----------------------------------------------------------------------===//
  
  #include "MCTargetDesc/PPCFixupKinds.h"
  #include "MCTargetDesc/PPCMCTargetDesc.h"
  #include "llvm/BinaryFormat/ELF.h"
  #include "llvm/BinaryFormat/MachO.h"
  #include "llvm/MC/MCAsmBackend.h"
  #include "llvm/MC/MCAssembler.h"
  #include "llvm/MC/MCELFObjectWriter.h"
  #include "llvm/MC/MCFixupKindInfo.h"
  #include "llvm/MC/MCMachObjectWriter.h"
  #include "llvm/MC/MCObjectWriter.h"
  #include "llvm/MC/MCSectionMachO.h"
  #include "llvm/MC/MCSubtargetInfo.h"
  #include "llvm/MC/MCSymbolELF.h"
  #include "llvm/MC/MCValue.h"
  #include "llvm/Support/ErrorHandling.h"
  #include "llvm/Support/TargetRegistry.h"
  using namespace llvm;
  
  static uint64_t adjustFixupValue(unsigned Kind, uint64_t Value) {
    switch (Kind) {
    default:
      llvm_unreachable("Unknown fixup kind!");
    case FK_NONE:
    case FK_Data_1:
    case FK_Data_2:
    case FK_Data_4:
    case FK_Data_8:
    case PPC::fixup_ppc_nofixup:
      return Value;
    case PPC::fixup_ppc_brcond14:
    case PPC::fixup_ppc_brcond14abs:
      return Value & 0xfffc;
    case PPC::fixup_ppc_br24:
    case PPC::fixup_ppc_br24abs:
      return Value & 0x3fffffc;
    case PPC::fixup_ppc_half16:
      return Value & 0xffff;
    case PPC::fixup_ppc_half16ds:
      return Value & 0xfffc;
    }
  }
  
  static unsigned getFixupKindNumBytes(unsigned Kind) {
    switch (Kind) {
    default:
      llvm_unreachable("Unknown fixup kind!");
    case FK_NONE:
      return 0;
    case FK_Data_1:
      return 1;
    case FK_Data_2:
    case PPC::fixup_ppc_half16:
    case PPC::fixup_ppc_half16ds:
      return 2;
    case FK_Data_4:
    case PPC::fixup_ppc_brcond14:
    case PPC::fixup_ppc_brcond14abs:
    case PPC::fixup_ppc_br24:
    case PPC::fixup_ppc_br24abs:
      return 4;
    case FK_Data_8:
      return 8;
    case PPC::fixup_ppc_nofixup:
      return 0;
    }
  }
  
  namespace {
  
  class PPCAsmBackend : public MCAsmBackend {
  protected:
    Triple TT;
  public:
    PPCAsmBackend(const Target &T, const Triple &TT)
        : MCAsmBackend(TT.isLittleEndian() ? support::little : support::big),
          TT(TT) {}
  
    unsigned getNumFixupKinds() const override {
      return PPC::NumTargetFixupKinds;
    }
  
    const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const override {
      const static MCFixupKindInfo InfosBE[PPC::NumTargetFixupKinds] = {
        // name                    offset  bits  flags
        { "fixup_ppc_br24",        6,      24,   MCFixupKindInfo::FKF_IsPCRel },
        { "fixup_ppc_brcond14",    16,     14,   MCFixupKindInfo::FKF_IsPCRel },
        { "fixup_ppc_br24abs",     6,      24,   0 },
        { "fixup_ppc_brcond14abs", 16,     14,   0 },
        { "fixup_ppc_half16",       0,     16,   0 },
        { "fixup_ppc_half16ds",     0,     14,   0 },
        { "fixup_ppc_nofixup",      0,      0,   0 }
      };
      const static MCFixupKindInfo InfosLE[PPC::NumTargetFixupKinds] = {
        // name                    offset  bits  flags
        { "fixup_ppc_br24",        2,      24,   MCFixupKindInfo::FKF_IsPCRel },
        { "fixup_ppc_brcond14",    2,      14,   MCFixupKindInfo::FKF_IsPCRel },
        { "fixup_ppc_br24abs",     2,      24,   0 },
        { "fixup_ppc_brcond14abs", 2,      14,   0 },
        { "fixup_ppc_half16",      0,      16,   0 },
        { "fixup_ppc_half16ds",    2,      14,   0 },
        { "fixup_ppc_nofixup",     0,       0,   0 }
      };
  
      if (Kind < FirstTargetFixupKind)
        return MCAsmBackend::getFixupKindInfo(Kind);
  
      assert(unsigned(Kind - FirstTargetFixupKind) < getNumFixupKinds() &&
             "Invalid kind!");
      return (Endian == support::little
                  ? InfosLE
                  : InfosBE)[Kind - FirstTargetFixupKind];
    }
  
    void applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
                    const MCValue &Target, MutableArrayRef<char> Data,
                    uint64_t Value, bool IsResolved,
                    const MCSubtargetInfo *STI) const override {
      Value = adjustFixupValue(Fixup.getKind(), Value);
      if (!Value) return;           // Doesn't change encoding.
  
      unsigned Offset = Fixup.getOffset();
      unsigned NumBytes = getFixupKindNumBytes(Fixup.getKind());
  
      // For each byte of the fragment that the fixup touches, mask in the bits
      // from the fixup value. The Value has been "split up" into the appropriate
      // bitfields above.
      for (unsigned i = 0; i != NumBytes; ++i) {
        unsigned Idx = Endian == support::little ? i : (NumBytes - 1 - i);
        Data[Offset + i] |= uint8_t((Value >> (Idx * 8)) & 0xff);
      }
    }
  
    bool shouldForceRelocation(const MCAssembler &Asm, const MCFixup &Fixup,
                               const MCValue &Target) override {
      switch ((unsigned)Fixup.getKind()) {
      default:
        return false;
      case FK_NONE:
        return true;
      case PPC::fixup_ppc_br24:
      case PPC::fixup_ppc_br24abs:
        // If the target symbol has a local entry point we must not attempt
        // to resolve the fixup directly.  Emit a relocation and leave
        // resolution of the final target address to the linker.
        if (const MCSymbolRefExpr *A = Target.getSymA()) {
          if (const auto *S = dyn_cast<MCSymbolELF>(&A->getSymbol())) {
            // The "other" values are stored in the last 6 bits of the second
            // byte. The traditional defines for STO values assume the full byte
            // and thus the shift to pack it.
            unsigned Other = S->getOther() << 2;
            if ((Other & ELF::STO_PPC64_LOCAL_MASK) != 0)
              return true;
          }
        }
        return false;
      }
    }
  
    bool mayNeedRelaxation(const MCInst &Inst,
                           const MCSubtargetInfo &STI) const override {
      // FIXME.
      return false;
    }
  
    bool fixupNeedsRelaxation(const MCFixup &Fixup,
                              uint64_t Value,
                              const MCRelaxableFragment *DF,
                              const MCAsmLayout &Layout) const override {
      // FIXME.
      llvm_unreachable("relaxInstruction() unimplemented");
    }
  
    void relaxInstruction(const MCInst &Inst, const MCSubtargetInfo &STI,
                          MCInst &Res) const override {
      // FIXME.
      llvm_unreachable("relaxInstruction() unimplemented");
    }
  
    bool writeNopData(raw_ostream &OS, uint64_t Count) const override {
      uint64_t NumNops = Count / 4;
      for (uint64_t i = 0; i != NumNops; ++i)
        support::endian::write<uint32_t>(OS, 0x60000000, Endian);
  
      OS.write_zeros(Count % 4);
  
      return true;
    }
  };
  } // end anonymous namespace
  
  
  // FIXME: This should be in a separate file.
  namespace {
  
  class ELFPPCAsmBackend : public PPCAsmBackend {
  public:
    ELFPPCAsmBackend(const Target &T, const Triple &TT) : PPCAsmBackend(T, TT) {}
  
    std::unique_ptr<MCObjectTargetWriter>
    createObjectTargetWriter() const override {
      uint8_t OSABI = MCELFObjectTargetWriter::getOSABI(TT.getOS());
      bool Is64 = TT.isPPC64();
      return createPPCELFObjectWriter(Is64, OSABI);
    }
  
    Optional<MCFixupKind> getFixupKind(StringRef Name) const override;
  };
  
  class XCOFFPPCAsmBackend : public PPCAsmBackend {
  public:
    XCOFFPPCAsmBackend(const Target &T, const Triple &TT)
        : PPCAsmBackend(T, TT) {}
  
    std::unique_ptr<MCObjectTargetWriter>
    createObjectTargetWriter() const override {
      return createPPCXCOFFObjectWriter(TT.isArch64Bit());
    }
  };
  
  } // end anonymous namespace
  
  Optional<MCFixupKind> ELFPPCAsmBackend::getFixupKind(StringRef Name) const {
    if (TT.isPPC64()) {
      if (Name == "R_PPC64_NONE")
        return FK_NONE;
    } else {
      if (Name == "R_PPC_NONE")
        return FK_NONE;
    }
    return MCAsmBackend::getFixupKind(Name);
  }
  
  MCAsmBackend *llvm::createPPCAsmBackend(const Target &T,
                                          const MCSubtargetInfo &STI,
                                          const MCRegisterInfo &MRI,
                                          const MCTargetOptions &Options) {
    const Triple &TT = STI.getTargetTriple();
    if (TT.isOSBinFormatXCOFF())
      return new XCOFFPPCAsmBackend(T, TT);
  
    return new ELFPPCAsmBackend(T, TT);
  }
  