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   /// Emit a 32-bit value as an instruction. This is only used for the .inst
116   /// directive, EmitInstruction should be used in other cases.
117   void emitInst(uint32_t Inst) {
118     char Buffer[4];
119 
120     // We can't just use EmitIntValue here, as that will emit a data mapping
121     // symbol, and swap the endianness on big-endian systems (instructions are
122     // always little-endian).
123     for (unsigned I = 0; I < 4; ++I) {
124       Buffer[I] = uint8_t(Inst);
125       Inst >>= 8;
126     }
127 
128     EmitA64MappingSymbol();
129     MCELFStreamer::EmitBytes(StringRef(Buffer, 4));
130   }
131 
132   /// This is one of the functions used to emit data into an ELF section, so the
133   /// AArch64 streamer overrides it to add the appropriate mapping symbol ($d)
134   /// if necessary.
135   void EmitBytes(StringRef Data) override {
136     EmitDataMappingSymbol();
137     MCELFStreamer::EmitBytes(Data);
138   }
139 
140   /// This is one of the functions used to emit data into an ELF section, so the
141   /// AArch64 streamer overrides it to add the appropriate mapping symbol ($d)
142   /// if necessary.
143   void EmitValueImpl(const MCExpr *Value, unsigned Size, SMLoc Loc) override {
144     EmitDataMappingSymbol();
145     MCELFStreamer::EmitValueImpl(Value, Size, Loc);
146   }
147 
148 private:
149   enum ElfMappingSymbol {
150     EMS_None,
151     EMS_A64,
152     EMS_Data
153   };
154 
155   void EmitDataMappingSymbol() {
156     if (LastEMS == EMS_Data)
157       return;
158     EmitMappingSymbol("$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     auto *Symbol = cast<MCSymbolELF>(getContext().getOrCreateSymbol(
171         Name + "." + Twine(MappingSymbolCounter++)));
172     EmitLabel(Symbol);
173     Symbol->setType(ELF::STT_NOTYPE);
174     Symbol->setBinding(ELF::STB_LOCAL);
175     Symbol->setExternal(false);
176   }
177 
178   int64_t MappingSymbolCounter;
179 
180   DenseMap<const MCSection *, ElfMappingSymbol> LastMappingSymbols;
181   ElfMappingSymbol LastEMS;
182 };
183 } // end anonymous namespace
184 
185 AArch64ELFStreamer &AArch64TargetELFStreamer::getStreamer() {
186   return static_cast<AArch64ELFStreamer &>(Streamer);
187 }
188 
189 void AArch64TargetELFStreamer::emitInst(uint32_t Inst) {
190   getStreamer().emitInst(Inst);
191 }
192 
193 namespace llvm {
194 MCTargetStreamer *createAArch64AsmTargetStreamer(MCStreamer &S,
195                                                  formatted_raw_ostream &OS,
196                                                  MCInstPrinter *InstPrint,
197                                                  bool isVerboseAsm) {
198   return new AArch64TargetAsmStreamer(S, OS);
199 }
200 
201 MCELFStreamer *createAArch64ELFStreamer(MCContext &Context, MCAsmBackend &TAB,
202                                         raw_pwrite_stream &OS,
203                                         MCCodeEmitter *Emitter, bool RelaxAll) {
204   AArch64ELFStreamer *S = new AArch64ELFStreamer(Context, TAB, OS, Emitter);
205   if (RelaxAll)
206     S->getAssembler().setRelaxAll(true);
207   return S;
208 }
209 
210 MCTargetStreamer *
211 createAArch64ObjectTargetStreamer(MCStreamer &S, const MCSubtargetInfo &STI) {
212   const Triple &TT = STI.getTargetTriple();
213   if (TT.isOSBinFormatELF())
214     return new AArch64TargetELFStreamer(S);
215   return nullptr;
216 }
217 }
218