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      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   void emitInst(uint32_t Inst) {
    116     EmitA64MappingSymbol();
    117     MCELFStreamer::EmitIntValue(Inst, 4);
    118   }
    119 
    120   /// This is one of the functions used to emit data into an ELF section, so the
    121   /// AArch64 streamer overrides it to add the appropriate mapping symbol ($d)
    122   /// if necessary.
    123   void EmitBytes(StringRef Data) override {
    124     EmitDataMappingSymbol();
    125     MCELFStreamer::EmitBytes(Data);
    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 ($d)
    130   /// if necessary.
    131   void EmitValueImpl(const MCExpr *Value, unsigned Size, SMLoc Loc) override {
    132     EmitDataMappingSymbol();
    133     MCELFStreamer::EmitValueImpl(Value, Size, Loc);
    134   }
    135 
    136 private:
    137   enum ElfMappingSymbol {
    138     EMS_None,
    139     EMS_A64,
    140     EMS_Data
    141   };
    142 
    143   void EmitDataMappingSymbol() {
    144     if (LastEMS == EMS_Data)
    145       return;
    146     EmitMappingSymbol("$d");
    147     LastEMS = EMS_Data;
    148   }
    149 
    150   void EmitA64MappingSymbol() {
    151     if (LastEMS == EMS_A64)
    152       return;
    153     EmitMappingSymbol("$x");
    154     LastEMS = EMS_A64;
    155   }
    156 
    157   void EmitMappingSymbol(StringRef Name) {
    158     auto *Symbol = cast<MCSymbolELF>(getContext().getOrCreateSymbol(
    159         Name + "." + Twine(MappingSymbolCounter++)));
    160     EmitLabel(Symbol);
    161     Symbol->setType(ELF::STT_NOTYPE);
    162     Symbol->setBinding(ELF::STB_LOCAL);
    163     Symbol->setExternal(false);
    164   }
    165 
    166   int64_t MappingSymbolCounter;
    167 
    168   DenseMap<const MCSection *, ElfMappingSymbol> LastMappingSymbols;
    169   ElfMappingSymbol LastEMS;
    170 };
    171 } // end anonymous namespace
    172 
    173 AArch64ELFStreamer &AArch64TargetELFStreamer::getStreamer() {
    174   return static_cast<AArch64ELFStreamer &>(Streamer);
    175 }
    176 
    177 void AArch64TargetELFStreamer::emitInst(uint32_t Inst) {
    178   getStreamer().emitInst(Inst);
    179 }
    180 
    181 namespace llvm {
    182 MCTargetStreamer *createAArch64AsmTargetStreamer(MCStreamer &S,
    183                                                  formatted_raw_ostream &OS,
    184                                                  MCInstPrinter *InstPrint,
    185                                                  bool isVerboseAsm) {
    186   return new AArch64TargetAsmStreamer(S, OS);
    187 }
    188 
    189 MCELFStreamer *createAArch64ELFStreamer(MCContext &Context, MCAsmBackend &TAB,
    190                                         raw_pwrite_stream &OS,
    191                                         MCCodeEmitter *Emitter, bool RelaxAll) {
    192   AArch64ELFStreamer *S = new AArch64ELFStreamer(Context, TAB, OS, Emitter);
    193   if (RelaxAll)
    194     S->getAssembler().setRelaxAll(true);
    195   return S;
    196 }
    197 
    198 MCTargetStreamer *
    199 createAArch64ObjectTargetStreamer(MCStreamer &S, const MCSubtargetInfo &STI) {
    200   const Triple &TT = STI.getTargetTriple();
    201   if (TT.isOSBinFormatELF())
    202     return new AArch64TargetELFStreamer(S);
    203   return nullptr;
    204 }
    205 }
    206