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 writeNopData(raw_ostream &OS, uint64_t Count) const override; 63 }; 64 65 const MCFixupKindInfo & 66 WebAssemblyAsmBackend::getFixupKindInfo(MCFixupKind Kind) const { 67 const static MCFixupKindInfo Infos[WebAssembly::NumTargetFixupKinds] = { 68 // This table *must* be in the order that the fixup_* kinds are defined in 69 // WebAssemblyFixupKinds.h. 70 // 71 // Name Offset (bits) Size (bits) Flags 72 {"fixup_sleb128_i32", 0, 5 * 8, 0}, 73 {"fixup_sleb128_i64", 0, 10 * 8, 0}, 74 {"fixup_uleb128_i32", 0, 5 * 8, 0}, 75 {"fixup_uleb128_i64", 0, 10 * 8, 0}, 76 }; 77 78 if (Kind < FirstTargetFixupKind) 79 return MCAsmBackend::getFixupKindInfo(Kind); 80 81 assert(unsigned(Kind - FirstTargetFixupKind) < getNumFixupKinds() && 82 "Invalid kind!"); 83 return Infos[Kind - FirstTargetFixupKind]; 84 } 85 86 bool WebAssemblyAsmBackend::writeNopData(raw_ostream &OS, 87 uint64_t Count) const { 88 for (uint64_t I = 0; I < Count; ++I) 89 OS << char(WebAssembly::Nop); 90 91 return true; 92 } 93 94 void WebAssemblyAsmBackend::applyFixup(const MCAssembler &Asm, 95 const MCFixup &Fixup, 96 const MCValue &Target, 97 MutableArrayRef<char> Data, 98 uint64_t Value, bool IsPCRel, 99 const MCSubtargetInfo *STI) const { 100 const MCFixupKindInfo &Info = getFixupKindInfo(Fixup.getKind()); 101 assert(Info.Flags == 0 && "WebAssembly does not use MCFixupKindInfo flags"); 102 103 unsigned NumBytes = alignTo(Info.TargetSize, 8) / 8; 104 if (Value == 0) 105 return; // Doesn't change encoding. 106 107 // Shift the value into position. 108 Value <<= Info.TargetOffset; 109 110 unsigned Offset = Fixup.getOffset(); 111 assert(Offset + NumBytes <= Data.size() && "Invalid fixup offset!"); 112 113 // For each byte of the fragment that the fixup touches, mask in the 114 // bits from the fixup value. 115 for (unsigned I = 0; I != NumBytes; ++I) 116 Data[Offset + I] |= uint8_t((Value >> (I * 8)) & 0xff); 117 } 118 119 std::unique_ptr<MCObjectTargetWriter> 120 WebAssemblyAsmBackend::createObjectTargetWriter() const { 121 return createWebAssemblyWasmObjectWriter(Is64Bit, IsEmscripten); 122 } 123 124 } // end anonymous namespace 125 126 MCAsmBackend *llvm::createWebAssemblyAsmBackend(const Triple &TT) { 127 return new WebAssemblyAsmBackend(TT.isArch64Bit(), TT.isOSEmscripten()); 128 } 129