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"
25 class MCSymbolRefExpr;
28 /// Defines the object file and target independent interfaces used by the
29 /// assembler backend to write native file format object files.
31 /// The object writer contains a few callbacks used by the assembler to allow
32 /// the object writer to modify the assembler data structures at appropriate
33 /// points. Once assembly is complete, the object writer is given the
34 /// MCAssembler instance, which contains all the symbol and section data which
35 /// should be emitted as part of writeObject().
37 /// The object writer also contains a number of helper methods for writing
38 /// binary data to the output stream.
39 class MCObjectWriter {
40 MCObjectWriter(const MCObjectWriter &) = delete;
41 void operator=(const MCObjectWriter &) = delete;
43 raw_pwrite_stream *OS;
46 unsigned IsLittleEndian : 1;
48 protected: // Can only create subclasses.
49 MCObjectWriter(raw_pwrite_stream &OS, bool IsLittleEndian)
50 : OS(&OS), IsLittleEndian(IsLittleEndian) {}
52 unsigned getInitialOffset() {
57 virtual ~MCObjectWriter();
59 /// lifetime management
60 virtual void reset() {}
62 bool isLittleEndian() const { return IsLittleEndian; }
64 raw_pwrite_stream &getStream() { return *OS; }
65 void setStream(raw_pwrite_stream &NewOS) { OS = &NewOS; }
67 /// \name High-Level API
70 /// Perform any late binding of symbols (for example, to assign symbol
71 /// indices for use when generating relocations).
73 /// This routine is called by the assembler after layout and relaxation is
75 virtual void executePostLayoutBinding(MCAssembler &Asm,
76 const MCAsmLayout &Layout) = 0;
78 /// Record a relocation entry.
80 /// This routine is called by the assembler after layout and relaxation, and
81 /// post layout binding. The implementation is responsible for storing
82 /// information about the relocation so that it can be emitted during
84 virtual void recordRelocation(MCAssembler &Asm, const MCAsmLayout &Layout,
85 const MCFragment *Fragment,
86 const MCFixup &Fixup, MCValue Target,
87 bool &IsPCRel, uint64_t &FixedValue) = 0;
89 /// Check whether the difference (A - B) between two symbol references is
92 /// Clients are not required to answer precisely and may conservatively return
93 /// false, even when a difference is fully resolved.
94 bool isSymbolRefDifferenceFullyResolved(const MCAssembler &Asm,
95 const MCSymbolRefExpr *A,
96 const MCSymbolRefExpr *B,
99 virtual bool isSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
104 virtual bool isSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
105 const MCSymbol &SymA,
106 const MCFragment &FB,
110 /// True if this symbol (which is a variable) is weak. This is not
111 /// just STB_WEAK, but more generally whether or not we can evaluate
113 virtual bool isWeak(const MCSymbol &Sym) const;
115 /// Write the object file.
117 /// This routine is called by the assembler after layout and relaxation is
118 /// complete, fixups have been evaluated and applied, and relocations
120 virtual void writeObject(MCAssembler &Asm, const MCAsmLayout &Layout) = 0;
123 /// \name Binary Output
126 void write8(uint8_t Value) { *OS << char(Value); }
128 void writeLE16(uint16_t Value) {
129 support::endian::Writer<support::little>(*OS).write(Value);
132 void writeLE32(uint32_t Value) {
133 support::endian::Writer<support::little>(*OS).write(Value);
136 void writeLE64(uint64_t Value) {
137 support::endian::Writer<support::little>(*OS).write(Value);
140 void writeBE16(uint16_t Value) {
141 support::endian::Writer<support::big>(*OS).write(Value);
144 void writeBE32(uint32_t Value) {
145 support::endian::Writer<support::big>(*OS).write(Value);
148 void writeBE64(uint64_t Value) {
149 support::endian::Writer<support::big>(*OS).write(Value);
152 void write16(uint16_t Value) {
159 void write32(uint32_t Value) {
166 void write64(uint64_t Value) {
173 void WriteZeros(unsigned N) {
174 const char Zeros[16] = {0};
176 for (unsigned i = 0, e = N / 16; i != e; ++i)
177 *OS << StringRef(Zeros, 16);
179 *OS << StringRef(Zeros, N % 16);
182 void writeBytes(const SmallVectorImpl<char> &ByteVec,
183 unsigned ZeroFillSize = 0) {
184 writeBytes(StringRef(ByteVec.data(), ByteVec.size()), ZeroFillSize);
187 void writeBytes(StringRef Str, unsigned ZeroFillSize = 0) {
188 // TODO: this version may need to go away once all fragment contents are
189 // converted to SmallVector<char, N>
191 (ZeroFillSize == 0 || Str.size() <= ZeroFillSize) &&
192 "data size greater than fill size, unexpected large write will occur");
195 WriteZeros(ZeroFillSize - Str.size());
201 } // End llvm namespace