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