1//===- lib/MC/AArch64ELFStreamer.cpp - ELF Object Output for AArch64 ------===//
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// This file assembles .s files and emits AArch64 ELF .o object files. Different
11// from generic ELF streamer in emitting mapping symbols ($x and $d) to delimit
12// regions of data and code.
13//
14//===----------------------------------------------------------------------===//
15
16#include "llvm/MC/MCELFStreamer.h"
17#include "llvm/ADT/SmallPtrSet.h"
18#include "llvm/ADT/StringExtras.h"
19#include "llvm/ADT/Twine.h"
20#include "llvm/MC/MCAsmBackend.h"
21#include "llvm/MC/MCAsmInfo.h"
22#include "llvm/MC/MCAssembler.h"
23#include "llvm/MC/MCCodeEmitter.h"
24#include "llvm/MC/MCContext.h"
25#include "llvm/MC/MCELF.h"
26#include "llvm/MC/MCELFStreamer.h"
27#include "llvm/MC/MCELFSymbolFlags.h"
28#include "llvm/MC/MCExpr.h"
29#include "llvm/MC/MCInst.h"
30#include "llvm/MC/MCObjectStreamer.h"
31#include "llvm/MC/MCSection.h"
32#include "llvm/MC/MCSectionELF.h"
33#include "llvm/MC/MCStreamer.h"
34#include "llvm/MC/MCSymbol.h"
35#include "llvm/MC/MCValue.h"
36#include "llvm/Support/Debug.h"
37#include "llvm/Support/ELF.h"
38#include "llvm/Support/ErrorHandling.h"
39#include "llvm/Support/FormattedStream.h"
40#include "llvm/Support/raw_ostream.h"
41
42using namespace llvm;
43
44namespace {
45
46class AArch64ELFStreamer;
47
48class AArch64TargetAsmStreamer : public AArch64TargetStreamer {
49  formatted_raw_ostream &OS;
50
51  void emitInst(uint32_t Inst) override;
52
53public:
54  AArch64TargetAsmStreamer(MCStreamer &S, formatted_raw_ostream &OS);
55};
56
57AArch64TargetAsmStreamer::AArch64TargetAsmStreamer(MCStreamer &S,
58                                                   formatted_raw_ostream &OS)
59  : AArch64TargetStreamer(S), OS(OS) {}
60
61void AArch64TargetAsmStreamer::emitInst(uint32_t Inst) {
62  OS << "\t.inst\t0x" << utohexstr(Inst) << "\n";
63}
64
65class AArch64TargetELFStreamer : public AArch64TargetStreamer {
66private:
67  AArch64ELFStreamer &getStreamer();
68
69  void emitInst(uint32_t Inst) override;
70
71public:
72  AArch64TargetELFStreamer(MCStreamer &S) : AArch64TargetStreamer(S) {}
73};
74
75/// Extend the generic ELFStreamer class so that it can emit mapping symbols at
76/// the appropriate points in the object files. These symbols are defined in the
77/// AArch64 ELF ABI:
78///    infocenter.arm.com/help/topic/com.arm.doc.ihi0056a/IHI0056A_aaelf64.pdf
79///
80/// In brief: $x or $d should be emitted at the start of each contiguous region
81/// of A64 code or data in a section. In practice, this emission does not rely
82/// on explicit assembler directives but on inherent properties of the
83/// directives doing the emission (e.g. ".byte" is data, "add x0, x0, x0" an
84/// instruction).
85///
86/// As a result this system is orthogonal to the DataRegion infrastructure used
87/// by MachO. Beware!
88class AArch64ELFStreamer : public MCELFStreamer {
89public:
90  friend class AArch64TargetELFStreamer;
91
92  AArch64ELFStreamer(MCContext &Context, MCAsmBackend &TAB,
93                     raw_pwrite_stream &OS, MCCodeEmitter *Emitter)
94      : MCELFStreamer(Context, TAB, OS, Emitter), MappingSymbolCounter(0),
95        LastEMS(EMS_None) {}
96
97  ~AArch64ELFStreamer() override {}
98
99  void ChangeSection(const MCSection *Section,
100                     const MCExpr *Subsection) override {
101    // We have to keep track of the mapping symbol state of any sections we
102    // use. Each one should start off as EMS_None, which is provided as the
103    // default constructor by DenseMap::lookup.
104    LastMappingSymbols[getPreviousSection().first] = LastEMS;
105    LastEMS = LastMappingSymbols.lookup(Section);
106
107    MCELFStreamer::ChangeSection(Section, Subsection);
108  }
109
110  /// This function is the one used to emit instruction data into the ELF
111  /// streamer. We override it to add the appropriate mapping symbol if
112  /// necessary.
113  void EmitInstruction(const MCInst &Inst,
114                       const MCSubtargetInfo &STI) override {
115    EmitA64MappingSymbol();
116    MCELFStreamer::EmitInstruction(Inst, STI);
117  }
118
119  void emitInst(uint32_t Inst) {
120    char Buffer[4];
121    const bool LittleEndian = getContext().getAsmInfo()->isLittleEndian();
122
123    EmitA64MappingSymbol();
124    for (unsigned II = 0; II != 4; ++II) {
125      const unsigned I = LittleEndian ? (4 - II - 1) : II;
126      Buffer[4 - II - 1] = uint8_t(Inst >> I * CHAR_BIT);
127    }
128    MCELFStreamer::EmitBytes(StringRef(Buffer, 4));
129  }
130
131  /// This is one of the functions used to emit data into an ELF section, so the
132  /// AArch64 streamer overrides it to add the appropriate mapping symbol ($d)
133  /// if necessary.
134  void EmitBytes(StringRef Data) override {
135    EmitDataMappingSymbol();
136    MCELFStreamer::EmitBytes(Data);
137  }
138
139  /// This is one of the functions used to emit data into an ELF section, so the
140  /// AArch64 streamer overrides it to add the appropriate mapping symbol ($d)
141  /// if necessary.
142  void EmitValueImpl(const MCExpr *Value, unsigned Size,
143                     const SMLoc &Loc) override {
144    EmitDataMappingSymbol();
145    MCELFStreamer::EmitValueImpl(Value, Size);
146  }
147
148private:
149  enum ElfMappingSymbol {
150    EMS_None,
151    EMS_A64,
152    EMS_Data
153  };
154
155  void EmitDataMappingSymbol() {
156    if (LastEMS == EMS_Data)
157      return;
158    EmitMappingSymbol("$d");
159    LastEMS = EMS_Data;
160  }
161
162  void EmitA64MappingSymbol() {
163    if (LastEMS == EMS_A64)
164      return;
165    EmitMappingSymbol("$x");
166    LastEMS = EMS_A64;
167  }
168
169  void EmitMappingSymbol(StringRef Name) {
170    MCSymbol *Start = getContext().CreateTempSymbol();
171    EmitLabel(Start);
172
173    MCSymbol *Symbol = getContext().GetOrCreateSymbol(
174        Name + "." + Twine(MappingSymbolCounter++));
175
176    MCSymbolData &SD = getAssembler().getOrCreateSymbolData(*Symbol);
177    MCELF::SetType(SD, ELF::STT_NOTYPE);
178    MCELF::SetBinding(SD, ELF::STB_LOCAL);
179    SD.setExternal(false);
180    auto Sec = getCurrentSection().first;
181    assert(Sec && "need a section");
182    Symbol->setSection(*Sec);
183
184    const MCExpr *Value = MCSymbolRefExpr::Create(Start, getContext());
185    Symbol->setVariableValue(Value);
186  }
187
188  int64_t MappingSymbolCounter;
189
190  DenseMap<const MCSection *, ElfMappingSymbol> LastMappingSymbols;
191  ElfMappingSymbol LastEMS;
192
193  /// @}
194};
195} // end anonymous namespace
196
197AArch64ELFStreamer &AArch64TargetELFStreamer::getStreamer() {
198  return static_cast<AArch64ELFStreamer &>(Streamer);
199}
200
201void AArch64TargetELFStreamer::emitInst(uint32_t Inst) {
202  getStreamer().emitInst(Inst);
203}
204
205namespace llvm {
206MCTargetStreamer *createAArch64AsmTargetStreamer(MCStreamer &S,
207                                                 formatted_raw_ostream &OS,
208                                                 MCInstPrinter *InstPrint,
209                                                 bool isVerboseAsm) {
210  return new AArch64TargetAsmStreamer(S, OS);
211}
212
213MCELFStreamer *createAArch64ELFStreamer(MCContext &Context, MCAsmBackend &TAB,
214                                        raw_pwrite_stream &OS,
215                                        MCCodeEmitter *Emitter, bool RelaxAll) {
216  AArch64ELFStreamer *S = new AArch64ELFStreamer(Context, TAB, OS, Emitter);
217  if (RelaxAll)
218    S->getAssembler().setRelaxAll(true);
219  return S;
220}
221
222MCTargetStreamer *
223createAArch64ObjectTargetStreamer(MCStreamer &S, const MCSubtargetInfo &STI) {
224  Triple TT(STI.getTargetTriple());
225  if (TT.getObjectFormat() == Triple::ELF)
226    return new AArch64TargetELFStreamer(S);
227  return nullptr;
228}
229}
230