third_party/llvm-7.0/llvm/lib/Target/Nios2/MCTargetDesc/Nios2AsmBackend.cpp

//===-- Nios2AsmBackend.cpp - Nios2 Asm Backend  --------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the Nios2AsmBackend class.
//
//===----------------------------------------------------------------------===//
//

#include "MCTargetDesc/Nios2AsmBackend.h"
#include "MCTargetDesc/Nios2FixupKinds.h"
#include "MCTargetDesc/Nios2MCTargetDesc.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCELFObjectWriter.h"
#include "llvm/MC/MCFixupKindInfo.h"
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/MC/MCSubtargetInfo.h"

using namespace llvm;

// Prepare value for the target space for it
static unsigned adjustFixupValue(const MCFixup &Fixup, uint64_t Value) {

  unsigned Kind = Fixup.getKind();

  // Add/subtract and shift
  switch (Kind) {
  default:
    return 0;
  case Nios2::fixup_Nios2_LO16:
    break;
  case Nios2::fixup_Nios2_HI16:
    // Get the higher 16-bits. Also add 1 if bit 15 is 1.
    Value = ((Value + 0x8000) >> 16) & 0xffff;
    break;
  }

  return Value;
}

// Calculate index for Nios2 specific little endian byte order
static unsigned calculateLEIndex(unsigned i) {
  assert(i <= 3 && "Index out of range!");

  return (1 - i / 2) * 2 + i % 2;
}

/// ApplyFixup - Apply the \p Value for given \p Fixup into the provided
/// data fragment, at the offset specified by the fixup and following the
/// fixup kind as appropriate.
void Nios2AsmBackend::applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
                                 const MCValue &Target,
                                 MutableArrayRef<char> Data, uint64_t Value,
                                 bool IsResolved) const {
  MCFixupKind Kind = Fixup.getKind();
  Value = adjustFixupValue(Fixup, Value);

  if (!Value)
    return; // Doesn't change encoding.

  // Where do we start in the object
  unsigned Offset = Fixup.getOffset();
  // Number of bytes we need to fixup
  unsigned NumBytes = (getFixupKindInfo(Kind).TargetSize + 7) / 8;
  // Grab current value, if any, from bits.
  uint64_t CurVal = 0;

  for (unsigned i = 0; i != NumBytes; ++i) {
    unsigned Idx = calculateLEIndex(i);
    CurVal |= (uint64_t)((uint8_t)Data[Offset + Idx]) << (i * 8);
  }

  uint64_t Mask = ((uint64_t)(-1) >> (64 - getFixupKindInfo(Kind).TargetSize));
  CurVal |= Value & Mask;

  // Write out the fixed up bytes back to the code/data bits.
  for (unsigned i = 0; i != NumBytes; ++i) {
    unsigned Idx = calculateLEIndex(i);
    Data[Offset + Idx] = (uint8_t)((CurVal >> (i * 8)) & 0xff);
  }
}

Optional<MCFixupKind> Nios2AsmBackend::getFixupKind(StringRef Name) const {
  return StringSwitch<Optional<MCFixupKind>>(Name)
      .Case("R_NIOS2_NONE", (MCFixupKind)Nios2::fixup_Nios2_32)
      .Case("R_NIOS2_32", FK_Data_4)
      .Default(MCAsmBackend::getFixupKind(Name));
}

//@getFixupKindInfo {
const MCFixupKindInfo &
Nios2AsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
  const static MCFixupKindInfo Infos[Nios2::NumTargetFixupKinds] = {
      // This table *must* be in same the order of fixup_* kinds in
      // Nios2FixupKinds.h.
      //
      // name                        offset  bits  flags
      {"fixup_Nios2_32", 0, 32, 0},
      {"fixup_Nios2_HI16", 0, 16, 0},
      {"fixup_Nios2_LO16", 0, 16, 0}};

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

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

std::unique_ptr<MCObjectTargetWriter>
Nios2AsmBackend::createObjectTargetWriter() const {
  return createNios2ELFObjectWriter(MCELFObjectTargetWriter::getOSABI(OSType));
}

bool Nios2AsmBackend::writeNopData(raw_ostream &OS, uint64_t Count) const {
  return true;
}

// MCAsmBackend
MCAsmBackend *llvm::createNios2AsmBackend(const Target &T,
                                          const MCSubtargetInfo &STI,
                                          const MCRegisterInfo &MRI,
                                          const MCTargetOptions &Options) {
  return new Nios2AsmBackend(T, STI.getTargetTriple().getOS());
}