llvm-project/llvm/lib/Target/SystemZ/MCTargetDesc/SystemZMCAsmBackend.cpp

//===-- SystemZMCAsmBackend.cpp - SystemZ assembler backend ---------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#include "MCTargetDesc/SystemZMCTargetDesc.h"
#include "MCTargetDesc/SystemZMCFixups.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"

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_PC16DBL:
  case SystemZ::FK_390_PC32DBL:
  case SystemZ::FK_390_PLT16DBL:
  case SystemZ::FK_390_PLT32DBL:
    return (int64_t)Value / 2;
  }

  llvm_unreachable("Unknown fixup kind!");
}

// If Opcode is a relaxable interprocedural reference, return the relaxed form,
// otherwise return 0.
static unsigned getRelaxedOpcode(unsigned Opcode) {
  switch (Opcode) {
  case SystemZ::BRAS: return SystemZ::BRASL;
  }
  return 0;
}

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

  // Override MCAsmBackend
  virtual unsigned getNumFixupKinds() const LLVM_OVERRIDE {
    return SystemZ::NumTargetFixupKinds;
  }
  virtual const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const
    LLVM_OVERRIDE;
  virtual void applyFixup(const MCFixup &Fixup, char *Data, unsigned DataSize,
                          uint64_t Value) const LLVM_OVERRIDE;
  virtual bool mayNeedRelaxation(const MCInst &Inst) const LLVM_OVERRIDE;
  virtual bool fixupNeedsRelaxation(const MCFixup &Fixup,
                                    uint64_t Value,
                                    const MCRelaxableFragment *Fragment,
                                    const MCAsmLayout &Layout) const
    LLVM_OVERRIDE;
  virtual void relaxInstruction(const MCInst &Inst,
                                MCInst &Res) const LLVM_OVERRIDE;
  virtual bool writeNopData(uint64_t Count,
                            MCObjectWriter *OW) const LLVM_OVERRIDE;
  virtual MCObjectWriter *createObjectWriter(raw_ostream &OS) const
    LLVM_OVERRIDE {
    return createSystemZObjectWriter(OS, OSABI);
  }
  virtual bool doesSectionRequireSymbols(const MCSection &Section) const
    LLVM_OVERRIDE {
    return false;
  }
};
} // end anonymous namespace

const MCFixupKindInfo &
SystemZMCAsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
  const static MCFixupKindInfo Infos[SystemZ::NumTargetFixupKinds] = {
    { "FK_390_PC16DBL",  0, 16, MCFixupKindInfo::FKF_IsPCRel },
    { "FK_390_PC32DBL",  0, 32, MCFixupKindInfo::FKF_IsPCRel },
    { "FK_390_PLT16DBL", 0, 16, MCFixupKindInfo::FKF_IsPCRel },
    { "FK_390_PLT32DBL", 0, 32, MCFixupKindInfo::FKF_IsPCRel }
  };

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

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

void SystemZMCAsmBackend::applyFixup(const MCFixup &Fixup, char *Data,
                                     unsigned DataSize, uint64_t Value) const {
  MCFixupKind Kind = Fixup.getKind();
  unsigned Offset = Fixup.getOffset();
  unsigned Size = (getFixupKindInfo(Kind).TargetSize + 7) / 8;

  assert(Offset + Size <= DataSize && "Invalid fixup offset!");

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

bool SystemZMCAsmBackend::mayNeedRelaxation(const MCInst &Inst) const {
  return getRelaxedOpcode(Inst.getOpcode()) != 0;
}

bool
SystemZMCAsmBackend::fixupNeedsRelaxation(const MCFixup &Fixup,
                                          uint64_t Value,
                                          const MCRelaxableFragment *Fragment,
                                          const MCAsmLayout &Layout) const {
  // At the moment we just need to relax 16-bit fields to wider fields.
  Value = extractBitsForFixup(Fixup.getKind(), Value);
  return (int16_t)Value != (int64_t)Value;
}

void SystemZMCAsmBackend::relaxInstruction(const MCInst &Inst,
                                           MCInst &Res) const {
  unsigned Opcode = getRelaxedOpcode(Inst.getOpcode());
  assert(Opcode && "Unexpected insn to relax");
  Res = Inst;
  Res.setOpcode(Opcode);
}

bool SystemZMCAsmBackend::writeNopData(uint64_t Count,
                                       MCObjectWriter *OW) const {
  for (uint64_t I = 0; I != Count; ++I)
    OW->Write8(7);
  return true;
}

MCAsmBackend *llvm::createSystemZMCAsmBackend(const Target &T, StringRef TT,
                                              StringRef CPU) {
  uint8_t OSABI = MCELFObjectTargetWriter::getOSABI(Triple(TT).getOS());
  return new SystemZMCAsmBackend(OSABI);
}