llvm-mirror/lib/MC/MCObjectWriter.cpp

//===- lib/MC/MCObjectWriter.cpp - MCObjectWriter implementation ----------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCObjectWriter.h"
#include "llvm/MC/MCSymbol.h"

using namespace llvm;

MCObjectWriter::~MCObjectWriter() {
}

/// Utility function to encode a SLEB128 value.
void MCObjectWriter::EncodeSLEB128(int64_t Value, raw_ostream &OS) {
  bool More;
  do {
    uint8_t Byte = Value & 0x7f;
    // NOTE: this assumes that this signed shift is an arithmetic right shift.
    Value >>= 7;
    More = !((((Value == 0 ) && ((Byte & 0x40) == 0)) ||
              ((Value == -1) && ((Byte & 0x40) != 0))));
    if (More)
      Byte |= 0x80; // Mark this byte that that more bytes will follow.
    OS << char(Byte);
  } while (More);
}

/// Utility function to encode a ULEB128 value.
void MCObjectWriter::EncodeULEB128(uint64_t Value, raw_ostream &OS,
                                   unsigned Padding) {
  do {
    uint8_t Byte = Value & 0x7f;
    Value >>= 7;
    if (Value != 0 || Padding != 0)
      Byte |= 0x80; // Mark this byte that that more bytes will follow.
    OS << char(Byte);
  } while (Value != 0);

  // Pad with 0x80 and emit a null byte at the end.
  if (Padding != 0) {
    for (; Padding != 1; --Padding)
      OS << '\x80';
    OS << '\x00';
  }
}

bool
MCObjectWriter::IsSymbolRefDifferenceFullyResolved(const MCAssembler &Asm,
                                                   const MCSymbolRefExpr *A,
                                                   const MCSymbolRefExpr *B,
                                                   bool InSet) const {
  // Modified symbol references cannot be resolved.
  if (A->getKind() != MCSymbolRefExpr::VK_None ||
      B->getKind() != MCSymbolRefExpr::VK_None)
    return false;

  const MCSymbol &SA = A->getSymbol();
  const MCSymbol &SB = B->getSymbol();
  if (SA.AliasedSymbol().isUndefined() || SB.AliasedSymbol().isUndefined())
    return false;

  const MCSymbolData &DataA = Asm.getSymbolData(SA);
  const MCSymbolData &DataB = Asm.getSymbolData(SB);

  return IsSymbolRefDifferenceFullyResolvedImpl(Asm, DataA,
                                                *DataB.getFragment(),
                                                InSet,
                                                false);
}

bool
MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
                                                      const MCSymbolData &DataA,
                                                      const MCFragment &FB,
                                                      bool InSet,
                                                      bool IsPCRel) const {
  const MCSection &SecA = DataA.getSymbol().AliasedSymbol().getSection();
  const MCSection &SecB = FB.getParent()->getSection();
  // On ELF and COFF  A - B is absolute if A and B are in the same section.
  return &SecA == &SecB;
}