lib/Target/AArch64/MCTargetDesc/AArch64ELFStreamer.cpp

   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