1 //===-- WebAssemblyAsmBackend.cpp - WebAssembly Assembler Backend ---------===// 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 /// \file 11 /// \brief This file implements the WebAssemblyAsmBackend class. 12 /// 13 //===----------------------------------------------------------------------===// 14 15 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h" 16 #include "llvm/MC/MCAsmBackend.h" 17 #include "llvm/MC/MCAssembler.h" 18 #include "llvm/MC/MCDirectives.h" 19 #include "llvm/MC/MCELFObjectWriter.h" 20 #include "llvm/MC/MCExpr.h" 21 #include "llvm/MC/MCFixupKindInfo.h" 22 #include "llvm/MC/MCObjectWriter.h" 23 #include "llvm/MC/MCSubtargetInfo.h" 24 #include "llvm/MC/MCSymbol.h" 25 #include "llvm/Support/ErrorHandling.h" 26 #include "llvm/Support/raw_ostream.h" 27 using namespace llvm; 28 29 namespace { 30 class WebAssemblyAsmBackend final : public MCAsmBackend { 31 bool Is64Bit; 32 33 public: 34 explicit WebAssemblyAsmBackend(bool Is64Bit) 35 : MCAsmBackend(), Is64Bit(Is64Bit) {} 36 ~WebAssemblyAsmBackend() override {} 37 38 void applyFixup(const MCFixup &Fixup, char *Data, unsigned DataSize, 39 uint64_t Value, bool IsPCRel) const override; 40 41 MCObjectWriter *createObjectWriter(raw_pwrite_stream &OS) const override; 42 43 // No instruction requires relaxation 44 bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value, 45 const MCRelaxableFragment *DF, 46 const MCAsmLayout &Layout) const override { 47 return false; 48 } 49 50 unsigned getNumFixupKinds() const override { 51 // We currently just use the generic fixups in MCFixup.h and don't have any 52 // target-specific fixups. 53 return 0; 54 } 55 56 bool mayNeedRelaxation(const MCInst &Inst) const override { return false; } 57 58 void relaxInstruction(const MCInst &Inst, const MCSubtargetInfo &STI, 59 MCInst &Res) const override {} 60 61 bool writeNopData(uint64_t Count, MCObjectWriter *OW) const override; 62 }; 63 64 bool WebAssemblyAsmBackend::writeNopData(uint64_t Count, 65 MCObjectWriter *OW) const { 66 if (Count == 0) 67 return true; 68 69 // FIXME: Do something. 70 return false; 71 } 72 73 void WebAssemblyAsmBackend::applyFixup(const MCFixup &Fixup, char *Data, 74 unsigned DataSize, uint64_t Value, 75 bool IsPCRel) const { 76 const MCFixupKindInfo &Info = getFixupKindInfo(Fixup.getKind()); 77 assert(Info.Flags == 0 && "WebAssembly does not use MCFixupKindInfo flags"); 78 79 unsigned NumBytes = (Info.TargetSize + 7) / 8; 80 if (Value == 0) 81 return; // Doesn't change encoding. 82 83 // Shift the value into position. 84 Value <<= Info.TargetOffset; 85 86 unsigned Offset = Fixup.getOffset(); 87 assert(Offset + NumBytes <= DataSize && "Invalid fixup offset!"); 88 89 // For each byte of the fragment that the fixup touches, mask in the 90 // bits from the fixup value. 91 for (unsigned i = 0; i != NumBytes; ++i) 92 Data[Offset + i] |= uint8_t((Value >> (i * 8)) & 0xff); 93 } 94 95 MCObjectWriter * 96 WebAssemblyAsmBackend::createObjectWriter(raw_pwrite_stream &OS) const { 97 return createWebAssemblyELFObjectWriter(OS, Is64Bit, 0); 98 } 99 } // end anonymous namespace 100 101 MCAsmBackend *llvm::createWebAssemblyAsmBackend(const Triple &TT) { 102 return new WebAssemblyAsmBackend(TT.isArch64Bit()); 103 } 104
