Home | History | Annotate | Download | only in MC 
      1 //===- llvm/MC/MCObjectWriter.h - Object File Writer Interface --*- C++ -*-===//
      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 #ifndef LLVM_MC_MCOBJECTWRITER_H
     11 #define LLVM_MC_MCOBJECTWRITER_H
     12 
     13 #include "llvm/ADT/SmallVector.h"
     14 #include "llvm/ADT/StringRef.h"
     15 #include "llvm/Support/Endian.h"
     16 #include "llvm/Support/EndianStream.h"
     17 #include "llvm/Support/raw_ostream.h"
     18 #include <cassert>
     19 #include <cstdint>
     20 
     21 namespace llvm {
     22 
     23 class MCAsmLayout;
     24 class MCAssembler;
     25 class MCFixup;
     26 class MCFragment;
     27 class MCSymbol;
     28 class MCSymbolRefExpr;
     29 class MCValue;
     30 
     31 /// Defines the object file and target independent interfaces used by the
     32 /// assembler backend to write native file format object files.
     33 ///
     34 /// The object writer contains a few callbacks used by the assembler to allow
     35 /// the object writer to modify the assembler data structures at appropriate
     36 /// points. Once assembly is complete, the object writer is given the
     37 /// MCAssembler instance, which contains all the symbol and section data which
     38 /// should be emitted as part of writeObject().
     39 ///
     40 /// The object writer also contains a number of helper methods for writing
     41 /// binary data to the output stream.
     42 class MCObjectWriter {
     43   raw_pwrite_stream *OS;
     44 
     45 protected:
     46   unsigned IsLittleEndian : 1;
     47 
     48   // Can only create subclasses.
     49   MCObjectWriter(raw_pwrite_stream &OS, bool IsLittleEndian)
     50       : OS(&OS), IsLittleEndian(IsLittleEndian) {}
     51 
     52   unsigned getInitialOffset() {
     53     return OS->tell();
     54   }
     55 
     56 public:
     57   MCObjectWriter(const MCObjectWriter &) = delete;
     58   MCObjectWriter &operator=(const MCObjectWriter &) = delete;
     59   virtual ~MCObjectWriter();
     60 
     61   /// lifetime management
     62   virtual void reset() {}
     63 
     64   bool isLittleEndian() const { return IsLittleEndian; }
     65 
     66   raw_pwrite_stream &getStream() { return *OS; }
     67   void setStream(raw_pwrite_stream &NewOS) { OS = &NewOS; }
     68 
     69   /// \name High-Level API
     70   /// @{
     71 
     72   /// Perform any late binding of symbols (for example, to assign symbol
     73   /// indices for use when generating relocations).
     74   ///
     75   /// This routine is called by the assembler after layout and relaxation is
     76   /// complete.
     77   virtual void executePostLayoutBinding(MCAssembler &Asm,
     78                                         const MCAsmLayout &Layout) = 0;
     79 
     80   /// Record a relocation entry.
     81   ///
     82   /// This routine is called by the assembler after layout and relaxation, and
     83   /// post layout binding. The implementation is responsible for storing
     84   /// information about the relocation so that it can be emitted during
     85   /// writeObject().
     86   virtual void recordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
     87                                 const MCFragment *Fragment,
     88                                 const MCFixup &Fixup, MCValue Target,
     89                                 bool &IsPCRel, uint64_t &FixedValue) = 0;
     90 
     91   /// Check whether the difference (A - B) between two symbol references is
     92   /// fully resolved.
     93   ///
     94   /// Clients are not required to answer precisely and may conservatively return
     95   /// false, even when a difference is fully resolved.
     96   bool isSymbolRefDifferenceFullyResolved(const MCAssembler &Asm,
     97                                           const MCSymbolRefExpr *A,
     98                                           const MCSymbolRefExpr *B,
     99                                           bool InSet) const;
    100 
    101   virtual bool isSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
    102                                                       const MCSymbol &A,
    103                                                       const MCSymbol &B,
    104                                                       bool InSet) const;
    105 
    106   virtual bool isSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
    107                                                       const MCSymbol &SymA,
    108                                                       const MCFragment &FB,
    109                                                       bool InSet,
    110                                                       bool IsPCRel) const;
    111 
    112   /// Write the object file.
    113   ///
    114   /// This routine is called by the assembler after layout and relaxation is
    115   /// complete, fixups have been evaluated and applied, and relocations
    116   /// generated.
    117   virtual void writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) = 0;
    118 
    119   /// @}
    120   /// \name Binary Output
    121   /// @{
    122 
    123   void write8(uint8_t Value) { *OS << char(Value); }
    124 
    125   void writeLE16(uint16_t Value) {
    126     support::endian::Writer<support::little>(*OS).write(Value);
    127   }
    128 
    129   void writeLE32(uint32_t Value) {
    130     support::endian::Writer<support::little>(*OS).write(Value);
    131   }
    132 
    133   void writeLE64(uint64_t Value) {
    134     support::endian::Writer<support::little>(*OS).write(Value);
    135   }
    136 
    137   void writeBE16(uint16_t Value) {
    138     support::endian::Writer<support::big>(*OS).write(Value);
    139   }
    140 
    141   void writeBE32(uint32_t Value) {
    142     support::endian::Writer<support::big>(*OS).write(Value);
    143   }
    144 
    145   void writeBE64(uint64_t Value) {
    146     support::endian::Writer<support::big>(*OS).write(Value);
    147   }
    148 
    149   void write16(uint16_t Value) {
    150     if (IsLittleEndian)
    151       writeLE16(Value);
    152     else
    153       writeBE16(Value);
    154   }
    155 
    156   void write32(uint32_t Value) {
    157     if (IsLittleEndian)
    158       writeLE32(Value);
    159     else
    160       writeBE32(Value);
    161   }
    162 
    163   void write64(uint64_t Value) {
    164     if (IsLittleEndian)
    165       writeLE64(Value);
    166     else
    167       writeBE64(Value);
    168   }
    169 
    170   void WriteZeros(unsigned N) {
    171     const char Zeros[16] = {0};
    172 
    173     for (unsigned i = 0, e = N / 16; i != e; ++i)
    174       *OS << StringRef(Zeros, 16);
    175 
    176     *OS << StringRef(Zeros, N % 16);
    177   }
    178 
    179   void writeBytes(const SmallVectorImpl<char> &ByteVec,
    180                   unsigned ZeroFillSize = 0) {
    181     writeBytes(StringRef(ByteVec.data(), ByteVec.size()), ZeroFillSize);
    182   }
    183 
    184   void writeBytes(StringRef Str, unsigned ZeroFillSize = 0) {
    185     // TODO: this version may need to go away once all fragment contents are
    186     // converted to SmallVector<char, N>
    187     assert(
    188         (ZeroFillSize == 0 || Str.size() <= ZeroFillSize) &&
    189         "data size greater than fill size, unexpected large write will occur");
    190     *OS << Str;
    191     if (ZeroFillSize)
    192       WriteZeros(ZeroFillSize - Str.size());
    193   }
    194 
    195   /// @}
    196 };
    197 
    198 } // end namespace llvm
    199 
    200 #endif // LLVM_MC_MCOBJECTWRITER_H
    201