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 "AArch64WinCOFFStreamer.h"
18 #include "llvm/ADT/DenseMap.h"
19 #include "llvm/ADT/StringRef.h"
20 #include "llvm/ADT/Triple.h"
21 #include "llvm/ADT/Twine.h"
22 #include "llvm/BinaryFormat/ELF.h"
23 #include "llvm/MC/MCAsmBackend.h"
24 #include "llvm/MC/MCAssembler.h"
25 #include "llvm/MC/MCCodeEmitter.h"
26 #include "llvm/MC/MCContext.h"
27 #include "llvm/MC/MCELFStreamer.h"
28 #include "llvm/MC/MCExpr.h"
29 #include "llvm/MC/MCInst.h"
30 #include "llvm/MC/MCObjectWriter.h"
31 #include "llvm/MC/MCSection.h"
32 #include "llvm/MC/MCStreamer.h"
33 #include "llvm/MC/MCSubtargetInfo.h"
34 #include "llvm/MC/MCSymbolELF.h"
35 #include "llvm/MC/MCWinCOFFStreamer.h"
36 #include "llvm/Support/Casting.h"
37 #include "llvm/Support/FormattedStream.h"
38 #include "llvm/Support/raw_ostream.h"
39 
40 using namespace llvm;
41 
42 namespace {
43 
44 class AArch64ELFStreamer;
45 
46 class AArch64TargetAsmStreamer : public AArch64TargetStreamer {
47   formatted_raw_ostream &OS;
48 
49   void emitInst(uint32_t Inst) override;
50 
51 public:
52   AArch64TargetAsmStreamer(MCStreamer &S, formatted_raw_ostream &OS);
53 };
54 
55 AArch64TargetAsmStreamer::AArch64TargetAsmStreamer(MCStreamer &S,
56                                                    formatted_raw_ostream &OS)
57   : AArch64TargetStreamer(S), OS(OS) {}
58 
59 void AArch64TargetAsmStreamer::emitInst(uint32_t Inst) {
60   OS << "\t.inst\t0x" << Twine::utohexstr(Inst) << "\n";
61 }
62 
63 /// Extend the generic ELFStreamer class so that it can emit mapping symbols at
64 /// the appropriate points in the object files. These symbols are defined in the
65 /// AArch64 ELF ABI:
66 ///    infocenter.arm.com/help/topic/com.arm.doc.ihi0056a/IHI0056A_aaelf64.pdf
67 ///
68 /// In brief: $x or $d should be emitted at the start of each contiguous region
69 /// of A64 code or data in a section. In practice, this emission does not rely
70 /// on explicit assembler directives but on inherent properties of the
71 /// directives doing the emission (e.g. ".byte" is data, "add x0, x0, x0" an
72 /// instruction).
73 ///
74 /// As a result this system is orthogonal to the DataRegion infrastructure used
75 /// by MachO. Beware!
76 class AArch64ELFStreamer : public MCELFStreamer {
77 public:
78   AArch64ELFStreamer(MCContext &Context, std::unique_ptr<MCAsmBackend> TAB,
79                      std::unique_ptr<MCObjectWriter> OW,
80                      std::unique_ptr<MCCodeEmitter> Emitter)
81       : MCELFStreamer(Context, std::move(TAB), std::move(OW),
82                       std::move(Emitter)),
83         MappingSymbolCounter(0), LastEMS(EMS_None) {}
84 
85   void ChangeSection(MCSection *Section, const MCExpr *Subsection) override {
86     // We have to keep track of the mapping symbol state of any sections we
87     // use. Each one should start off as EMS_None, which is provided as the
88     // default constructor by DenseMap::lookup.
89     LastMappingSymbols[getPreviousSection().first] = LastEMS;
90     LastEMS = LastMappingSymbols.lookup(Section);
91 
92     MCELFStreamer::ChangeSection(Section, Subsection);
93   }
94 
95   // Reset state between object emissions
96   void reset() override {
97     MappingSymbolCounter = 0;
98     MCELFStreamer::reset();
99     LastMappingSymbols.clear();
100     LastEMS = EMS_None;
101   }
102 
103   /// This function is the one used to emit instruction data into the ELF
104   /// streamer. We override it to add the appropriate mapping symbol if
105   /// necessary.
106   void EmitInstruction(const MCInst &Inst, const MCSubtargetInfo &STI,
107                        bool) override {
108     EmitA64MappingSymbol();
109     MCELFStreamer::EmitInstruction(Inst, STI);
110   }
111 
112   /// Emit a 32-bit value as an instruction. This is only used for the .inst
113   /// directive, EmitInstruction should be used in other cases.
114   void emitInst(uint32_t Inst) {
115     char Buffer[4];
116 
117     // We can't just use EmitIntValue here, as that will emit a data mapping
118     // symbol, and swap the endianness on big-endian systems (instructions are
119     // always little-endian).
120     for (unsigned I = 0; I < 4; ++I) {
121       Buffer[I] = uint8_t(Inst);
122       Inst >>= 8;
123     }
124 
125     EmitA64MappingSymbol();
126     MCELFStreamer::EmitBytes(StringRef(Buffer, 4));
127   }
128 
129   /// This is one of the functions used to emit data into an ELF section, so the
130   /// AArch64 streamer overrides it to add the appropriate mapping symbol ($d)
131   /// if necessary.
132   void EmitBytes(StringRef Data) override {
133     EmitDataMappingSymbol();
134     MCELFStreamer::EmitBytes(Data);
135   }
136 
137   /// This is one of the functions used to emit data into an ELF section, so the
138   /// AArch64 streamer overrides it to add the appropriate mapping symbol ($d)
139   /// if necessary.
140   void EmitValueImpl(const MCExpr *Value, unsigned Size, SMLoc Loc) override {
141     EmitDataMappingSymbol();
142     MCELFStreamer::EmitValueImpl(Value, Size, Loc);
143   }
144 
145   void emitFill(const MCExpr &NumBytes, uint64_t FillValue,
146                                   SMLoc Loc) override {
147     EmitDataMappingSymbol();
148     MCObjectStreamer::emitFill(NumBytes, FillValue, Loc);
149   }
150 private:
151   enum ElfMappingSymbol {
152     EMS_None,
153     EMS_A64,
154     EMS_Data
155   };
156 
157   void EmitDataMappingSymbol() {
158     if (LastEMS == EMS_Data)
159       return;
160     EmitMappingSymbol("$d");
161     LastEMS = EMS_Data;
162   }
163 
164   void EmitA64MappingSymbol() {
165     if (LastEMS == EMS_A64)
166       return;
167     EmitMappingSymbol("$x");
168     LastEMS = EMS_A64;
169   }
170 
171   void EmitMappingSymbol(StringRef Name) {
172     auto *Symbol = cast<MCSymbolELF>(getContext().getOrCreateSymbol(
173         Name + "." + Twine(MappingSymbolCounter++)));
174     EmitLabel(Symbol);
175     Symbol->setType(ELF::STT_NOTYPE);
176     Symbol->setBinding(ELF::STB_LOCAL);
177     Symbol->setExternal(false);
178   }
179 
180   int64_t MappingSymbolCounter;
181 
182   DenseMap<const MCSection *, ElfMappingSymbol> LastMappingSymbols;
183   ElfMappingSymbol LastEMS;
184 };
185 
186 } // end anonymous namespace
187 
188 namespace llvm {
189 
190 AArch64ELFStreamer &AArch64TargetELFStreamer::getStreamer() {
191   return static_cast<AArch64ELFStreamer &>(Streamer);
192 }
193 
194 void AArch64TargetELFStreamer::emitInst(uint32_t Inst) {
195   getStreamer().emitInst(Inst);
196 }
197 
198 MCTargetStreamer *createAArch64AsmTargetStreamer(MCStreamer &S,
199                                                  formatted_raw_ostream &OS,
200                                                  MCInstPrinter *InstPrint,
201                                                  bool isVerboseAsm) {
202   return new AArch64TargetAsmStreamer(S, OS);
203 }
204 
205 MCELFStreamer *createAArch64ELFStreamer(MCContext &Context,
206                                         std::unique_ptr<MCAsmBackend> TAB,
207                                         std::unique_ptr<MCObjectWriter> OW,
208                                         std::unique_ptr<MCCodeEmitter> Emitter,
209                                         bool RelaxAll) {
210   AArch64ELFStreamer *S = new AArch64ELFStreamer(
211       Context, std::move(TAB), std::move(OW), std::move(Emitter));
212   if (RelaxAll)
213     S->getAssembler().setRelaxAll(true);
214   return S;
215 }
216 
217 } // end namespace llvm
218