1 //===- lib/MC/AArch64ELFStreamer.cpp - ELF Object Output for AArch64 ------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file assembles .s files and emits AArch64 ELF .o object files. Different
10 // from generic ELF streamer in emitting mapping symbols ($x and $d) to delimit
11 // regions of data and code.
12 //
13 //===----------------------------------------------------------------------===//
14 
15 #include "AArch64TargetStreamer.h"
16 #include "AArch64WinCOFFStreamer.h"
17 #include "llvm/ADT/DenseMap.h"
18 #include "llvm/ADT/StringRef.h"
19 #include "llvm/ADT/Triple.h"
20 #include "llvm/ADT/Twine.h"
21 #include "llvm/BinaryFormat/ELF.h"
22 #include "llvm/MC/MCAsmBackend.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/MCObjectWriter.h"
30 #include "llvm/MC/MCSection.h"
31 #include "llvm/MC/MCStreamer.h"
32 #include "llvm/MC/MCSubtargetInfo.h"
33 #include "llvm/MC/MCSymbolELF.h"
34 #include "llvm/MC/MCWinCOFFStreamer.h"
35 #include "llvm/Support/Casting.h"
36 #include "llvm/Support/FormattedStream.h"
37 #include "llvm/Support/raw_ostream.h"
38 
39 using namespace llvm;
40 
41 namespace {
42 
43 class AArch64ELFStreamer;
44 
45 class AArch64TargetAsmStreamer : public AArch64TargetStreamer {
46   formatted_raw_ostream &OS;
47 
48   void emitInst(uint32_t Inst) override;
49 
50 public:
51   AArch64TargetAsmStreamer(MCStreamer &S, formatted_raw_ostream &OS);
52 };
53 
54 AArch64TargetAsmStreamer::AArch64TargetAsmStreamer(MCStreamer &S,
55                                                    formatted_raw_ostream &OS)
56   : AArch64TargetStreamer(S), OS(OS) {}
57 
58 void AArch64TargetAsmStreamer::emitInst(uint32_t Inst) {
59   OS << "\t.inst\t0x" << Twine::utohexstr(Inst) << "\n";
60 }
61 
62 /// Extend the generic ELFStreamer class so that it can emit mapping symbols at
63 /// the appropriate points in the object files. These symbols are defined in the
64 /// AArch64 ELF ABI:
65 ///    infocenter.arm.com/help/topic/com.arm.doc.ihi0056a/IHI0056A_aaelf64.pdf
66 ///
67 /// In brief: $x or $d should be emitted at the start of each contiguous region
68 /// of A64 code or data in a section. In practice, this emission does not rely
69 /// on explicit assembler directives but on inherent properties of the
70 /// directives doing the emission (e.g. ".byte" is data, "add x0, x0, x0" an
71 /// instruction).
72 ///
73 /// As a result this system is orthogonal to the DataRegion infrastructure used
74 /// by MachO. Beware!
75 class AArch64ELFStreamer : public MCELFStreamer {
76 public:
77   AArch64ELFStreamer(MCContext &Context, std::unique_ptr<MCAsmBackend> TAB,
78                      std::unique_ptr<MCObjectWriter> OW,
79                      std::unique_ptr<MCCodeEmitter> Emitter)
80       : MCELFStreamer(Context, std::move(TAB), std::move(OW),
81                       std::move(Emitter)),
82         MappingSymbolCounter(0), LastEMS(EMS_None) {}
83 
84   void ChangeSection(MCSection *Section, const MCExpr *Subsection) override {
85     // We have to keep track of the mapping symbol state of any sections we
86     // use. Each one should start off as EMS_None, which is provided as the
87     // default constructor by DenseMap::lookup.
88     LastMappingSymbols[getPreviousSection().first] = LastEMS;
89     LastEMS = LastMappingSymbols.lookup(Section);
90 
91     MCELFStreamer::ChangeSection(Section, Subsection);
92   }
93 
94   // Reset state between object emissions
95   void reset() override {
96     MappingSymbolCounter = 0;
97     MCELFStreamer::reset();
98     LastMappingSymbols.clear();
99     LastEMS = EMS_None;
100   }
101 
102   /// This function is the one used to emit instruction data into the ELF
103   /// streamer. We override it to add the appropriate mapping symbol if
104   /// necessary.
105   void EmitInstruction(const MCInst &Inst,
106                        const MCSubtargetInfo &STI) override {
107     EmitA64MappingSymbol();
108     MCELFStreamer::EmitInstruction(Inst, STI);
109   }
110 
111   /// Emit a 32-bit value as an instruction. This is only used for the .inst
112   /// directive, EmitInstruction should be used in other cases.
113   void emitInst(uint32_t Inst) {
114     char Buffer[4];
115 
116     // We can't just use EmitIntValue here, as that will emit a data mapping
117     // symbol, and swap the endianness on big-endian systems (instructions are
118     // always little-endian).
119     for (unsigned I = 0; I < 4; ++I) {
120       Buffer[I] = uint8_t(Inst);
121       Inst >>= 8;
122     }
123 
124     EmitA64MappingSymbol();
125     MCELFStreamer::EmitBytes(StringRef(Buffer, 4));
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 EmitBytes(StringRef Data) override {
132     EmitDataMappingSymbol();
133     MCELFStreamer::EmitBytes(Data);
134   }
135 
136   /// This is one of the functions used to emit data into an ELF section, so the
137   /// AArch64 streamer overrides it to add the appropriate mapping symbol ($d)
138   /// if necessary.
139   void EmitValueImpl(const MCExpr *Value, unsigned Size, SMLoc Loc) override {
140     EmitDataMappingSymbol();
141     MCELFStreamer::EmitValueImpl(Value, Size, Loc);
142   }
143 
144   void emitFill(const MCExpr &NumBytes, uint64_t FillValue,
145                                   SMLoc Loc) override {
146     EmitDataMappingSymbol();
147     MCObjectStreamer::emitFill(NumBytes, FillValue, Loc);
148   }
149 private:
150   enum ElfMappingSymbol {
151     EMS_None,
152     EMS_A64,
153     EMS_Data
154   };
155 
156   void EmitDataMappingSymbol() {
157     if (LastEMS == EMS_Data)
158       return;
159     EmitMappingSymbol("$d");
160     LastEMS = EMS_Data;
161   }
162 
163   void EmitA64MappingSymbol() {
164     if (LastEMS == EMS_A64)
165       return;
166     EmitMappingSymbol("$x");
167     LastEMS = EMS_A64;
168   }
169 
170   void EmitMappingSymbol(StringRef Name) {
171     auto *Symbol = cast<MCSymbolELF>(getContext().getOrCreateSymbol(
172         Name + "." + Twine(MappingSymbolCounter++)));
173     EmitLabel(Symbol);
174     Symbol->setType(ELF::STT_NOTYPE);
175     Symbol->setBinding(ELF::STB_LOCAL);
176     Symbol->setExternal(false);
177   }
178 
179   int64_t MappingSymbolCounter;
180 
181   DenseMap<const MCSection *, ElfMappingSymbol> LastMappingSymbols;
182   ElfMappingSymbol LastEMS;
183 };
184 
185 } // end anonymous namespace
186 
187 namespace llvm {
188 
189 AArch64ELFStreamer &AArch64TargetELFStreamer::getStreamer() {
190   return static_cast<AArch64ELFStreamer &>(Streamer);
191 }
192 
193 void AArch64TargetELFStreamer::emitInst(uint32_t Inst) {
194   getStreamer().emitInst(Inst);
195 }
196 
197 MCTargetStreamer *createAArch64AsmTargetStreamer(MCStreamer &S,
198                                                  formatted_raw_ostream &OS,
199                                                  MCInstPrinter *InstPrint,
200                                                  bool isVerboseAsm) {
201   return new AArch64TargetAsmStreamer(S, OS);
202 }
203 
204 MCELFStreamer *createAArch64ELFStreamer(MCContext &Context,
205                                         std::unique_ptr<MCAsmBackend> TAB,
206                                         std::unique_ptr<MCObjectWriter> OW,
207                                         std::unique_ptr<MCCodeEmitter> Emitter,
208                                         bool RelaxAll) {
209   AArch64ELFStreamer *S = new AArch64ELFStreamer(
210       Context, std::move(TAB), std::move(OW), std::move(Emitter));
211   if (RelaxAll)
212     S->getAssembler().setRelaxAll(true);
213   return S;
214 }
215 
216 } // end namespace llvm
217