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 "AArch64ELFStreamer.h"
16 #include "AArch64MCTargetDesc.h"
17 #include "AArch64TargetStreamer.h"
18 #include "AArch64WinCOFFStreamer.h"
19 #include "llvm/ADT/DenseMap.h"
20 #include "llvm/ADT/StringRef.h"
21 #include "llvm/ADT/Triple.h"
22 #include "llvm/ADT/Twine.h"
23 #include "llvm/BinaryFormat/ELF.h"
24 #include "llvm/MC/MCAsmBackend.h"
25 #include "llvm/MC/MCAssembler.h"
26 #include "llvm/MC/MCCodeEmitter.h"
27 #include "llvm/MC/MCContext.h"
28 #include "llvm/MC/MCELFStreamer.h"
29 #include "llvm/MC/MCExpr.h"
30 #include "llvm/MC/MCInst.h"
31 #include "llvm/MC/MCObjectWriter.h"
32 #include "llvm/MC/MCSection.h"
33 #include "llvm/MC/MCStreamer.h"
34 #include "llvm/MC/MCSubtargetInfo.h"
35 #include "llvm/MC/MCSymbolELF.h"
36 #include "llvm/MC/MCWinCOFFStreamer.h"
37 #include "llvm/Support/Casting.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   void emitDirectiveVariantPCS(MCSymbol *Symbol) override {
53     OS << "\t.variant_pcs\t" << Symbol->getName() << "\n";
54   }
55 
56   void emitARM64WinCFIAllocStack(unsigned Size) override {
57     OS << "\t.seh_stackalloc\t" << Size << "\n";
58   }
59   void emitARM64WinCFISaveR19R20X(int Offset) override {
60     OS << "\t.seh_save_r19r20_x\t" << Offset << "\n";
61   }
62   void emitARM64WinCFISaveFPLR(int Offset) override {
63     OS << "\t.seh_save_fplr\t" << Offset << "\n";
64   }
65   void emitARM64WinCFISaveFPLRX(int Offset) override {
66     OS << "\t.seh_save_fplr_x\t" << Offset << "\n";
67   }
68   void emitARM64WinCFISaveReg(unsigned Reg, int Offset) override {
69     OS << "\t.seh_save_reg\tx" << Reg << ", " << Offset << "\n";
70   }
71   void emitARM64WinCFISaveRegX(unsigned Reg, int Offset) override {
72     OS << "\t.seh_save_reg_x\tx" << Reg << ", " << Offset << "\n";
73   }
74   void emitARM64WinCFISaveRegP(unsigned Reg, int Offset) override {
75     OS << "\t.seh_save_regp\tx" << Reg << ", " << Offset << "\n";
76   }
77   void emitARM64WinCFISaveRegPX(unsigned Reg, int Offset) override {
78     OS << "\t.seh_save_regp_x\tx" << Reg << ", " << Offset << "\n";
79   }
80   void emitARM64WinCFISaveLRPair(unsigned Reg, int Offset) override {
81     OS << "\t.seh_save_lrpair\tx" << Reg << ", " << Offset << "\n";
82   }
83   void emitARM64WinCFISaveFReg(unsigned Reg, int Offset) override {
84     OS << "\t.seh_save_freg\td" << Reg << ", " << Offset << "\n";
85   }
86   void emitARM64WinCFISaveFRegX(unsigned Reg, int Offset) override {
87     OS << "\t.seh_save_freg_x\td" << Reg << ", " << Offset << "\n";
88   }
89   void emitARM64WinCFISaveFRegP(unsigned Reg, int Offset) override {
90     OS << "\t.seh_save_fregp\td" << Reg << ", " << Offset << "\n";
91   }
92   void emitARM64WinCFISaveFRegPX(unsigned Reg, int Offset) override {
93     OS << "\t.seh_save_fregp_x\td" << Reg << ", " << Offset << "\n";
94   }
95   void emitARM64WinCFISetFP() override { OS << "\t.seh_set_fp\n"; }
96   void emitARM64WinCFIAddFP(unsigned Size) override {
97     OS << "\t.seh_add_fp\t" << Size << "\n";
98   }
99   void emitARM64WinCFINop() override { OS << "\t.seh_nop\n"; }
100   void emitARM64WinCFISaveNext() override { OS << "\t.seh_save_next\n"; }
101   void emitARM64WinCFIPrologEnd() override { OS << "\t.seh_endprologue\n"; }
102   void emitARM64WinCFIEpilogStart() override { OS << "\t.seh_startepilogue\n"; }
103   void emitARM64WinCFIEpilogEnd() override { OS << "\t.seh_endepilogue\n"; }
104   void emitARM64WinCFITrapFrame() override { OS << "\t.seh_trap_frame\n"; }
105   void emitARM64WinCFIMachineFrame() override { OS << "\t.seh_pushframe\n"; }
106   void emitARM64WinCFIContext() override { OS << "\t.seh_context\n"; }
107   void emitARM64WinCFIClearUnwoundToCall() override {
108     OS << "\t.seh_clear_unwound_to_call\n";
109   }
110 
111 public:
112   AArch64TargetAsmStreamer(MCStreamer &S, formatted_raw_ostream &OS);
113 };
114 
115 AArch64TargetAsmStreamer::AArch64TargetAsmStreamer(MCStreamer &S,
116                                                    formatted_raw_ostream &OS)
117   : AArch64TargetStreamer(S), OS(OS) {}
118 
119 void AArch64TargetAsmStreamer::emitInst(uint32_t Inst) {
120   OS << "\t.inst\t0x" << Twine::utohexstr(Inst) << "\n";
121 }
122 
123 /// Extend the generic ELFStreamer class so that it can emit mapping symbols at
124 /// the appropriate points in the object files. These symbols are defined in the
125 /// AArch64 ELF ABI:
126 ///    infocenter.arm.com/help/topic/com.arm.doc.ihi0056a/IHI0056A_aaelf64.pdf
127 ///
128 /// In brief: $x or $d should be emitted at the start of each contiguous region
129 /// of A64 code or data in a section. In practice, this emission does not rely
130 /// on explicit assembler directives but on inherent properties of the
131 /// directives doing the emission (e.g. ".byte" is data, "add x0, x0, x0" an
132 /// instruction).
133 ///
134 /// As a result this system is orthogonal to the DataRegion infrastructure used
135 /// by MachO. Beware!
136 class AArch64ELFStreamer : public MCELFStreamer {
137 public:
138   AArch64ELFStreamer(MCContext &Context, std::unique_ptr<MCAsmBackend> TAB,
139                      std::unique_ptr<MCObjectWriter> OW,
140                      std::unique_ptr<MCCodeEmitter> Emitter)
141       : MCELFStreamer(Context, std::move(TAB), std::move(OW),
142                       std::move(Emitter)),
143         MappingSymbolCounter(0), LastEMS(EMS_None) {}
144 
145   void changeSection(MCSection *Section, const MCExpr *Subsection) override {
146     // We have to keep track of the mapping symbol state of any sections we
147     // use. Each one should start off as EMS_None, which is provided as the
148     // default constructor by DenseMap::lookup.
149     LastMappingSymbols[getPreviousSection().first] = LastEMS;
150     LastEMS = LastMappingSymbols.lookup(Section);
151 
152     MCELFStreamer::changeSection(Section, Subsection);
153   }
154 
155   // Reset state between object emissions
156   void reset() override {
157     MappingSymbolCounter = 0;
158     MCELFStreamer::reset();
159     LastMappingSymbols.clear();
160     LastEMS = EMS_None;
161   }
162 
163   /// This function is the one used to emit instruction data into the ELF
164   /// streamer. We override it to add the appropriate mapping symbol if
165   /// necessary.
166   void emitInstruction(const MCInst &Inst,
167                        const MCSubtargetInfo &STI) override {
168     emitA64MappingSymbol();
169     MCELFStreamer::emitInstruction(Inst, STI);
170   }
171 
172   /// Emit a 32-bit value as an instruction. This is only used for the .inst
173   /// directive, EmitInstruction should be used in other cases.
174   void emitInst(uint32_t Inst) {
175     char Buffer[4];
176 
177     // We can't just use EmitIntValue here, as that will emit a data mapping
178     // symbol, and swap the endianness on big-endian systems (instructions are
179     // always little-endian).
180     for (char &C : Buffer) {
181       C = uint8_t(Inst);
182       Inst >>= 8;
183     }
184 
185     emitA64MappingSymbol();
186     MCELFStreamer::emitBytes(StringRef(Buffer, 4));
187   }
188 
189   /// This is one of the functions used to emit data into an ELF section, so the
190   /// AArch64 streamer overrides it to add the appropriate mapping symbol ($d)
191   /// if necessary.
192   void emitBytes(StringRef Data) override {
193     emitDataMappingSymbol();
194     MCELFStreamer::emitBytes(Data);
195   }
196 
197   /// This is one of the functions used to emit data into an ELF section, so the
198   /// AArch64 streamer overrides it to add the appropriate mapping symbol ($d)
199   /// if necessary.
200   void emitValueImpl(const MCExpr *Value, unsigned Size, SMLoc Loc) override {
201     emitDataMappingSymbol();
202     MCELFStreamer::emitValueImpl(Value, Size, Loc);
203   }
204 
205   void emitFill(const MCExpr &NumBytes, uint64_t FillValue,
206                                   SMLoc Loc) override {
207     emitDataMappingSymbol();
208     MCObjectStreamer::emitFill(NumBytes, FillValue, Loc);
209   }
210 private:
211   enum ElfMappingSymbol {
212     EMS_None,
213     EMS_A64,
214     EMS_Data
215   };
216 
217   void emitDataMappingSymbol() {
218     if (LastEMS == EMS_Data)
219       return;
220     emitMappingSymbol("$d");
221     LastEMS = EMS_Data;
222   }
223 
224   void emitA64MappingSymbol() {
225     if (LastEMS == EMS_A64)
226       return;
227     emitMappingSymbol("$x");
228     LastEMS = EMS_A64;
229   }
230 
231   void emitMappingSymbol(StringRef Name) {
232     auto *Symbol = cast<MCSymbolELF>(getContext().getOrCreateSymbol(
233         Name + "." + Twine(MappingSymbolCounter++)));
234     emitLabel(Symbol);
235     Symbol->setType(ELF::STT_NOTYPE);
236     Symbol->setBinding(ELF::STB_LOCAL);
237     Symbol->setExternal(false);
238   }
239 
240   int64_t MappingSymbolCounter;
241 
242   DenseMap<const MCSection *, ElfMappingSymbol> LastMappingSymbols;
243   ElfMappingSymbol LastEMS;
244 };
245 
246 } // end anonymous namespace
247 
248 AArch64ELFStreamer &AArch64TargetELFStreamer::getStreamer() {
249   return static_cast<AArch64ELFStreamer &>(Streamer);
250 }
251 
252 void AArch64TargetELFStreamer::emitInst(uint32_t Inst) {
253   getStreamer().emitInst(Inst);
254 }
255 
256 void AArch64TargetELFStreamer::emitDirectiveVariantPCS(MCSymbol *Symbol) {
257   getStreamer().getAssembler().registerSymbol(*Symbol);
258   cast<MCSymbolELF>(Symbol)->setOther(ELF::STO_AARCH64_VARIANT_PCS);
259 }
260 
261 MCTargetStreamer *
262 llvm::createAArch64AsmTargetStreamer(MCStreamer &S, formatted_raw_ostream &OS,
263                                      MCInstPrinter *InstPrint,
264                                      bool isVerboseAsm) {
265   return new AArch64TargetAsmStreamer(S, OS);
266 }
267 
268 MCELFStreamer *llvm::createAArch64ELFStreamer(
269     MCContext &Context, std::unique_ptr<MCAsmBackend> TAB,
270     std::unique_ptr<MCObjectWriter> OW, std::unique_ptr<MCCodeEmitter> Emitter,
271     bool RelaxAll) {
272   AArch64ELFStreamer *S = new AArch64ELFStreamer(
273       Context, std::move(TAB), std::move(OW), std::move(Emitter));
274   if (RelaxAll)
275     S->getAssembler().setRelaxAll(true);
276   return S;
277 }
278