1 //===-- llvm/MC/MCObjectWriter.h - Object File Writer Interface -*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 #ifndef LLVM_MC_MCOBJECTWRITER_H
11 #define LLVM_MC_MCOBJECTWRITER_H
13 #include "llvm/ADT/SmallVector.h"
14 #include "llvm/Support/Compiler.h"
15 #include "llvm/Support/DataTypes.h"
16 #include "llvm/Support/EndianStream.h"
17 #include "llvm/Support/raw_ostream.h"
26 class MCSymbolRefExpr;
29 /// MCObjectWriter - Defines the object file and target independent interfaces
30 /// used by the assembler backend to write native file format object files.
32 /// The object writer contains a few callbacks used by the assembler to allow
33 /// the object writer to modify the assembler data structures at appropriate
34 /// points. Once assembly is complete, the object writer is given the
35 /// MCAssembler instance, which contains all the symbol and section data which
36 /// should be emitted as part of WriteObject().
38 /// The object writer also contains a number of helper methods for writing
39 /// binary data to the output stream.
40 class MCObjectWriter {
41 MCObjectWriter(const MCObjectWriter &) = delete;
42 void operator=(const MCObjectWriter &) = delete;
47 unsigned IsLittleEndian : 1;
49 protected: // Can only create subclasses.
50 MCObjectWriter(raw_ostream &OS, bool IsLittleEndian)
51 : OS(OS), IsLittleEndian(IsLittleEndian) {}
54 virtual ~MCObjectWriter();
56 /// lifetime management
57 virtual void reset() { }
59 bool isLittleEndian() const { return IsLittleEndian; }
61 raw_ostream &getStream() { return OS; }
63 /// @name High-Level API
66 /// \brief Perform any late binding of symbols (for example, to assign symbol
67 /// indices for use when generating relocations).
69 /// This routine is called by the assembler after layout and relaxation is
71 virtual void ExecutePostLayoutBinding(MCAssembler &Asm,
72 const MCAsmLayout &Layout) = 0;
74 /// \brief Record a relocation entry.
76 /// This routine is called by the assembler after layout and relaxation, and
77 /// post layout binding. The implementation is responsible for storing
78 /// information about the relocation so that it can be emitted during
80 virtual void RecordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
81 const MCFragment *Fragment,
82 const MCFixup &Fixup, MCValue Target,
83 bool &IsPCRel, uint64_t &FixedValue) = 0;
85 /// \brief Check whether the difference (A - B) between two symbol
86 /// references is fully resolved.
88 /// Clients are not required to answer precisely and may conservatively return
89 /// false, even when a difference is fully resolved.
90 bool IsSymbolRefDifferenceFullyResolved(const MCAssembler &Asm,
91 const MCSymbolRefExpr *A,
92 const MCSymbolRefExpr *B,
95 virtual bool IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
96 const MCSymbolData &DataA,
97 const MCSymbolData *DataB,
102 /// \brief True if this symbol (which is a variable) is weak. This is not
103 /// just STB_WEAK, but more generally whether or not we can evaluate
105 virtual bool isWeak(const MCSymbolData &SD) const;
107 /// \brief Write the object file.
109 /// This routine is called by the assembler after layout and relaxation is
110 /// complete, fixups have been evaluated and applied, and relocations
112 virtual void WriteObject(MCAssembler &Asm,
113 const MCAsmLayout &Layout) = 0;
116 /// @name Binary Output
119 void Write8(uint8_t Value) {
123 void WriteLE16(uint16_t Value) {
124 support::endian::Writer<support::little>(OS).write(Value);
127 void WriteLE32(uint32_t Value) {
128 support::endian::Writer<support::little>(OS).write(Value);
131 void WriteLE64(uint64_t Value) {
132 support::endian::Writer<support::little>(OS).write(Value);
135 void WriteBE16(uint16_t Value) {
136 support::endian::Writer<support::big>(OS).write(Value);
139 void WriteBE32(uint32_t Value) {
140 support::endian::Writer<support::big>(OS).write(Value);
143 void WriteBE64(uint64_t Value) {
144 support::endian::Writer<support::big>(OS).write(Value);
147 void Write16(uint16_t Value) {
154 void Write32(uint32_t Value) {
161 void Write64(uint64_t Value) {
168 void WriteZeros(unsigned N) {
169 const char Zeros[16] = { 0 };
171 for (unsigned i = 0, e = N / 16; i != e; ++i)
172 OS << StringRef(Zeros, 16);
174 OS << StringRef(Zeros, N % 16);
177 void WriteBytes(const SmallVectorImpl<char> &ByteVec, unsigned ZeroFillSize = 0) {
178 WriteBytes(StringRef(ByteVec.data(), ByteVec.size()), ZeroFillSize);
181 void WriteBytes(StringRef Str, unsigned ZeroFillSize = 0) {
182 // TODO: this version may need to go away once all fragment contents are
183 // converted to SmallVector<char, N>
184 assert((ZeroFillSize == 0 || Str.size () <= ZeroFillSize) &&
185 "data size greater than fill size, unexpected large write will occur");
188 WriteZeros(ZeroFillSize - Str.size());
195 } // End llvm namespace