//===-- 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/ADT/StringSwitch.h"
#include "llvm/MC/MCAsmBackend.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCContext.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,
                                    const MCFixup &Fixup, MCContext &Ctx) {
  if (Kind < FirstTargetFixupKind)
    return Value;

  auto checkFixupInRange = [&](int64_t Min, int64_t Max) -> bool {
    int64_t SVal = int64_t(Value);
    if (SVal < Min || SVal > Max) {
      Ctx.reportError(Fixup.getLoc(), "operand out of range (" + Twine(SVal) +
                                          " not between " + Twine(Min) +
                                          " and " + Twine(Max) + ")");
      return false;
    }
    return true;
  };

  auto handlePCRelFixupValue = [&](unsigned W) -> uint64_t {
    if (Value % 2 != 0)
      Ctx.reportError(Fixup.getLoc(), "Non-even PC relative offset.");
    if (!checkFixupInRange(minIntN(W) * 2, maxIntN(W) * 2))
      return 0;
    return (int64_t)Value / 2;
  };

  switch (unsigned(Kind)) {
  case SystemZ::FK_390_PC12DBL:
    return handlePCRelFixupValue(12);
  case SystemZ::FK_390_PC16DBL:
    return handlePCRelFixupValue(16);
  case SystemZ::FK_390_PC24DBL:
    return handlePCRelFixupValue(24);
  case SystemZ::FK_390_PC32DBL:
    return handlePCRelFixupValue(32);

  case SystemZ::FK_390_12:
    if (!checkFixupInRange(0, maxUIntN(12)))
      return 0;
    return Value;

  case SystemZ::FK_390_20: {
    if (!checkFixupInRange(minIntN(20), maxIntN(20)))
      return 0;
    // The high byte of a 20 bit displacement value comes first.
    uint64_t DLo = Value & 0xfff;
    uint64_t DHi = (Value >> 12) & 0xff;
    return (DLo << 8) | DHi;
  }

  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;
  }
  std::optional<MCFixupKind> getFixupKind(StringRef Name) const override;
  const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const override;
  bool shouldForceRelocation(const MCAssembler &Asm, const MCFixup &Fixup,
                             const MCValue &Target) 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 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 MCSubtargetInfo *STI) const override;
  std::unique_ptr<MCObjectTargetWriter>
  createObjectTargetWriter() const override {
    return createSystemZObjectWriter(OSABI);
  }
};
} // end anonymous namespace

std::optional<MCFixupKind>
SystemZMCAsmBackend::getFixupKind(StringRef Name) const {
  unsigned Type = llvm::StringSwitch<unsigned>(Name)
#define ELF_RELOC(X, Y) .Case(#X, Y)
#include "llvm/BinaryFormat/ELFRelocs/SystemZ.def"
#undef ELF_RELOC
			.Case("BFD_RELOC_NONE", ELF::R_390_NONE)
			.Case("BFD_RELOC_8", ELF::R_390_8)
			.Case("BFD_RELOC_16", ELF::R_390_16)
			.Case("BFD_RELOC_32", ELF::R_390_32)
			.Case("BFD_RELOC_64", ELF::R_390_64)
			.Default(-1u);
  if (Type != -1u)
    return static_cast<MCFixupKind>(FirstLiteralRelocationKind + Type);
  return std::nullopt;
}

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 },
    { "FK_390_12",       4, 12, 0 },
    { "FK_390_20",       4, 20, 0 }
  };

  // Fixup kinds from .reloc directive are like R_390_NONE. They
  // do not require any extra processing.
  if (Kind >= FirstLiteralRelocationKind)
    return MCAsmBackend::getFixupKindInfo(FK_NONE);

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

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

bool SystemZMCAsmBackend::shouldForceRelocation(const MCAssembler &,
						const MCFixup &Fixup,
						const MCValue &) {
  return Fixup.getKind() >= FirstLiteralRelocationKind;
}

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();
  if (Kind >= FirstLiteralRelocationKind)
    return;
  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, Fixup, Asm.getContext());
  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 MCSubtargetInfo *STI) 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);
}