1 //===-- WebAssemblyAsmBackend.cpp - WebAssembly Assembler Backend ---------===// 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 /// \file 10 /// This file implements the WebAssemblyAsmBackend class. 11 /// 12 //===----------------------------------------------------------------------===// 13 14 #include "MCTargetDesc/WebAssemblyFixupKinds.h" 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/MCExpr.h" 20 #include "llvm/MC/MCFixupKindInfo.h" 21 #include "llvm/MC/MCObjectWriter.h" 22 #include "llvm/MC/MCSubtargetInfo.h" 23 #include "llvm/MC/MCSymbol.h" 24 #include "llvm/MC/MCWasmObjectWriter.h" 25 #include "llvm/Support/ErrorHandling.h" 26 #include "llvm/Support/raw_ostream.h" 27 28 using namespace llvm; 29 30 namespace { 31 32 class WebAssemblyAsmBackend final : public MCAsmBackend { 33 bool Is64Bit; 34 bool IsEmscripten; 35 36 public: 37 explicit WebAssemblyAsmBackend(bool Is64Bit, bool IsEmscripten) 38 : MCAsmBackend(support::little), Is64Bit(Is64Bit), 39 IsEmscripten(IsEmscripten) {} 40 41 unsigned getNumFixupKinds() const override { 42 return WebAssembly::NumTargetFixupKinds; 43 } 44 45 const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const override; 46 47 void applyFixup(const MCAssembler &Asm, const MCFixup &Fixup, 48 const MCValue &Target, MutableArrayRef<char> Data, 49 uint64_t Value, bool IsPCRel, 50 const MCSubtargetInfo *STI) const override; 51 52 std::unique_ptr<MCObjectTargetWriter> 53 createObjectTargetWriter() const override; 54 55 // No instruction requires relaxation 56 bool fixupNeedsRelaxation(const MCFixup &Fixup, uint64_t Value, 57 const MCRelaxableFragment *DF, 58 const MCAsmLayout &Layout) const override { 59 return false; 60 } 61 62 bool mayNeedRelaxation(const MCInst &Inst, 63 const MCSubtargetInfo &STI) const override { 64 return false; 65 } 66 67 bool writeNopData(raw_ostream &OS, uint64_t Count) const override; 68 }; 69 70 const MCFixupKindInfo & 71 WebAssemblyAsmBackend::getFixupKindInfo(MCFixupKind Kind) const { 72 const static MCFixupKindInfo Infos[WebAssembly::NumTargetFixupKinds] = { 73 // This table *must* be in the order that the fixup_* kinds are defined in 74 // WebAssemblyFixupKinds.h. 75 // 76 // Name Offset (bits) Size (bits) Flags 77 {"fixup_sleb128_i32", 0, 5 * 8, 0}, 78 {"fixup_sleb128_i64", 0, 10 * 8, 0}, 79 {"fixup_uleb128_i32", 0, 5 * 8, 0}, 80 {"fixup_uleb128_i64", 0, 10 * 8, 0}, 81 }; 82 83 if (Kind < FirstTargetFixupKind) 84 return MCAsmBackend::getFixupKindInfo(Kind); 85 86 assert(unsigned(Kind - FirstTargetFixupKind) < getNumFixupKinds() && 87 "Invalid kind!"); 88 return Infos[Kind - FirstTargetFixupKind]; 89 } 90 91 bool WebAssemblyAsmBackend::writeNopData(raw_ostream &OS, 92 uint64_t Count) const { 93 for (uint64_t I = 0; I < Count; ++I) 94 OS << char(WebAssembly::Nop); 95 96 return true; 97 } 98 99 void WebAssemblyAsmBackend::applyFixup(const MCAssembler &Asm, 100 const MCFixup &Fixup, 101 const MCValue &Target, 102 MutableArrayRef<char> Data, 103 uint64_t Value, bool IsPCRel, 104 const MCSubtargetInfo *STI) const { 105 const MCFixupKindInfo &Info = getFixupKindInfo(Fixup.getKind()); 106 assert(Info.Flags == 0 && "WebAssembly does not use MCFixupKindInfo flags"); 107 108 unsigned NumBytes = alignTo(Info.TargetSize, 8) / 8; 109 if (Value == 0) 110 return; // Doesn't change encoding. 111 112 // Shift the value into position. 113 Value <<= Info.TargetOffset; 114 115 unsigned Offset = Fixup.getOffset(); 116 assert(Offset + NumBytes <= Data.size() && "Invalid fixup offset!"); 117 118 // For each byte of the fragment that the fixup touches, mask in the 119 // bits from the fixup value. 120 for (unsigned I = 0; I != NumBytes; ++I) 121 Data[Offset + I] |= uint8_t((Value >> (I * 8)) & 0xff); 122 } 123 124 std::unique_ptr<MCObjectTargetWriter> 125 WebAssemblyAsmBackend::createObjectTargetWriter() const { 126 return createWebAssemblyWasmObjectWriter(Is64Bit, IsEmscripten); 127 } 128 129 } // end anonymous namespace 130 131 MCAsmBackend *llvm::createWebAssemblyAsmBackend(const Triple &TT) { 132 return new WebAssemblyAsmBackend(TT.isArch64Bit(), TT.isOSEmscripten()); 133 } 134