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      1 //===- lib/MC/MCObjectWriter.cpp - MCObjectWriter implementation ----------===//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 
     10 #include "llvm/MC/MCAssembler.h"
     11 #include "llvm/MC/MCExpr.h"
     12 #include "llvm/MC/MCObjectWriter.h"
     13 #include "llvm/MC/MCSymbol.h"
     14 
     15 using namespace llvm;
     16 
     17 MCObjectWriter::~MCObjectWriter() {
     18 }
     19 
     20 /// Utility function to encode a SLEB128 value.
     21 void MCObjectWriter::EncodeSLEB128(int64_t Value, raw_ostream &OS) {
     22   bool More;
     23   do {
     24     uint8_t Byte = Value & 0x7f;
     25     // NOTE: this assumes that this signed shift is an arithmetic right shift.
     26     Value >>= 7;
     27     More = !((((Value == 0 ) && ((Byte & 0x40) == 0)) ||
     28               ((Value == -1) && ((Byte & 0x40) != 0))));
     29     if (More)
     30       Byte |= 0x80; // Mark this byte that that more bytes will follow.
     31     OS << char(Byte);
     32   } while (More);
     33 }
     34 
     35 /// Utility function to encode a ULEB128 value.
     36 void MCObjectWriter::EncodeULEB128(uint64_t Value, raw_ostream &OS) {
     37   do {
     38     uint8_t Byte = Value & 0x7f;
     39     Value >>= 7;
     40     if (Value != 0)
     41       Byte |= 0x80; // Mark this byte that that more bytes will follow.
     42     OS << char(Byte);
     43   } while (Value != 0);
     44 }
     45 
     46 bool
     47 MCObjectWriter::IsSymbolRefDifferenceFullyResolved(const MCAssembler &Asm,
     48                                                    const MCSymbolRefExpr *A,
     49                                                    const MCSymbolRefExpr *B,
     50                                                    bool InSet) const {
     51   // Modified symbol references cannot be resolved.
     52   if (A->getKind() != MCSymbolRefExpr::VK_None ||
     53       B->getKind() != MCSymbolRefExpr::VK_None)
     54     return false;
     55 
     56   const MCSymbol &SA = A->getSymbol();
     57   const MCSymbol &SB = B->getSymbol();
     58   if (SA.AliasedSymbol().isUndefined() || SB.AliasedSymbol().isUndefined())
     59     return false;
     60 
     61   const MCSymbolData &DataA = Asm.getSymbolData(SA);
     62   const MCSymbolData &DataB = Asm.getSymbolData(SB);
     63 
     64   return IsSymbolRefDifferenceFullyResolvedImpl(Asm, DataA,
     65                                                 *DataB.getFragment(),
     66                                                 InSet,
     67                                                 false);
     68 }
     69 
     70 bool
     71 MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
     72                                                       const MCSymbolData &DataA,
     73                                                       const MCFragment &FB,
     74                                                       bool InSet,
     75                                                       bool IsPCRel) const {
     76   const MCSection &SecA = DataA.getSymbol().AliasedSymbol().getSection();
     77   const MCSection &SecB = FB.getParent()->getSection();
     78   // On ELF and COFF  A - B is absolute if A and B are in the same section.
     79   return &SecA == &SecB;
     80 }
     81