SystemZMCAsmBackend.cpp

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//===-- SystemZMCAsmBackend.cpp - SystemZ 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/SystemZMCFixups.h"
#include "MCTargetDesc/SystemZMCTargetDesc.h"
#include "llvm/MC/MCAsmBackend.h"
#include "llvm/MC/MCELFObjectWriter.h"
#include "llvm/MC/MCFixupKindInfo.h"
#include "llvm/MC/MCInst.h"
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/MC/MCSubtargetInfo.h"

using namespace llvm;

// Value is a fully-resolved relocation value: Symbol + Addend [- Pivot].
// Return the bits that should be installed in a relocation field for
// fixup kind Kind.
static uint64_t extractBitsForFixup(MCFixupKind Kind, uint64_t Value) {
  if (Kind < FirstTargetFixupKind)
    return Value;

  switch (unsigned(Kind)) {
  case SystemZ::FK_390_PC12DBL:
  case SystemZ::FK_390_PC16DBL:
  case SystemZ::FK_390_PC24DBL:
  case SystemZ::FK_390_PC32DBL:
    return (int64_t)Value / 2;

  case SystemZ::FK_390_TLS_CALL:
    return 0;
  }

  llvm_unreachable("Unknown fixup kind!");
}

namespace {
class SystemZMCAsmBackend : public MCAsmBackend {
  uint8_t OSABI;
public:
  SystemZMCAsmBackend(uint8_t osABI)
      : MCAsmBackend(support::big), OSABI(osABI) {}

  // Override MCAsmBackend
  unsigned getNumFixupKinds() const override {
    return SystemZ::NumTargetFixupKinds;
  }
  const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const override;
  void applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
                  const MCValue &Target, MutableArrayRef<char> Data,
                  uint64_t Value, bool IsResolved,
                  const MCSubtargetInfo *STI) const override;
  bool mayNeedRelaxation(const MCInst &Inst,
                         const MCSubtargetInfo &STI) const override {
    return false;
  }
  bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value,
                            const MCRelaxableFragment *Fragment,
                            const MCAsmLayout &Layout) const override {
    return false;
  }
  bool writeNopData(raw_ostream &OS, uint64_t Count) const override;
  std::unique_ptr<MCObjectTargetWriter>
  createObjectTargetWriter() const override {
    return createSystemZObjectWriter(OSABI);
  }
};
} // end anonymous namespace

const MCFixupKindInfo &
SystemZMCAsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
  const static MCFixupKindInfo Infos[SystemZ::NumTargetFixupKinds] = {
    { "FK_390_PC12DBL",  4, 12, MCFixupKindInfo::FKF_IsPCRel },
    { "FK_390_PC16DBL",  0, 16, MCFixupKindInfo::FKF_IsPCRel },
    { "FK_390_PC24DBL",  0, 24, MCFixupKindInfo::FKF_IsPCRel },
    { "FK_390_PC32DBL",  0, 32, MCFixupKindInfo::FKF_IsPCRel },
    { "FK_390_TLS_CALL", 0, 0, 0 }
  };

  if (Kind < FirstTargetFixupKind)
    return MCAsmBackend::getFixupKindInfo(Kind);

  assert(unsigned(Kind - FirstTargetFixupKind) < getNumFixupKinds() &&
         "Invalid kind!");
  return Infos[Kind - FirstTargetFixupKind];
}

void SystemZMCAsmBackend::applyFixup(const MCAssembler &Asm,
                                     const MCFixup &Fixup,
                                     const MCValue &Target,
                                     MutableArrayRef<char> Data, uint64_t Value,
                                     bool IsResolved,
                                     const MCSubtargetInfo *STI) const {
  MCFixupKind Kind = Fixup.getKind();
  unsigned Offset = Fixup.getOffset();
  unsigned BitSize = getFixupKindInfo(Kind).TargetSize;
  unsigned Size = (BitSize + 7) / 8;

  assert(Offset + Size <= Data.size() && "Invalid fixup offset!");

  // Big-endian insertion of Size bytes.
  Value = extractBitsForFixup(Kind, Value);
  if (BitSize < 64)
    Value &= ((uint64_t)1 << BitSize) - 1;
  unsigned ShiftValue = (Size * 8) - 8;
  for (unsigned I = 0; I != Size; ++I) {
    Data[Offset + I] |= uint8_t(Value >> ShiftValue);
    ShiftValue -= 8;
  }
}

bool SystemZMCAsmBackend::writeNopData(raw_ostream &OS, uint64_t Count) const {
  for (uint64_t I = 0; I != Count; ++I)
    OS << '\x7';
  return true;
}

MCAsmBackend *llvm::createSystemZMCAsmBackend(const Target &T,
                                              const MCSubtargetInfo &STI,
                                              const MCRegisterInfo &MRI,
                                              const MCTargetOptions &Options) {
  uint8_t OSABI =
      MCELFObjectTargetWriter::getOSABI(STI.getTargetTriple().getOS());
  return new SystemZMCAsmBackend(OSABI);
}