1 //===-- WebAssemblyWasmObjectWriter.cpp - WebAssembly Wasm Writer ---------===// 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 handles Wasm-specific object emission, converting LLVM's 11 /// internal fixups into the appropriate relocations. 12 /// 13 //===----------------------------------------------------------------------===// 14 15 #include "MCTargetDesc/WebAssemblyFixupKinds.h" 16 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h" 17 #include "llvm/BinaryFormat/Wasm.h" 18 #include "llvm/MC/MCAsmBackend.h" 19 #include "llvm/MC/MCFixup.h" 20 #include "llvm/MC/MCFixupKindInfo.h" 21 #include "llvm/MC/MCObjectWriter.h" 22 #include "llvm/MC/MCSectionWasm.h" 23 #include "llvm/MC/MCSymbolWasm.h" 24 #include "llvm/MC/MCValue.h" 25 #include "llvm/MC/MCWasmObjectWriter.h" 26 #include "llvm/Support/Casting.h" 27 #include "llvm/Support/ErrorHandling.h" 28 29 using namespace llvm; 30 31 namespace { 32 class WebAssemblyWasmObjectWriter final : public MCWasmObjectTargetWriter { 33 public: 34 explicit WebAssemblyWasmObjectWriter(bool Is64Bit, bool IsEmscripten); 35 36 private: 37 unsigned getRelocType(const MCValue &Target, const MCFixup &Fixup, 38 const MCSectionWasm &FixupSection, 39 bool IsLocRel) const override; 40 }; 41 } // end anonymous namespace 42 43 WebAssemblyWasmObjectWriter::WebAssemblyWasmObjectWriter(bool Is64Bit, 44 bool IsEmscripten) 45 : MCWasmObjectTargetWriter(Is64Bit, IsEmscripten) {} 46 47 static const MCSection *getTargetSection(const MCExpr *Expr) { 48 if (auto SyExp = dyn_cast<MCSymbolRefExpr>(Expr)) { 49 if (SyExp->getSymbol().isInSection()) 50 return &SyExp->getSymbol().getSection(); 51 return nullptr; 52 } 53 54 if (auto BinOp = dyn_cast<MCBinaryExpr>(Expr)) { 55 auto SectionLHS = getTargetSection(BinOp->getLHS()); 56 auto SectionRHS = getTargetSection(BinOp->getRHS()); 57 return SectionLHS == SectionRHS ? nullptr : SectionLHS; 58 } 59 60 if (auto UnOp = dyn_cast<MCUnaryExpr>(Expr)) 61 return getTargetSection(UnOp->getSubExpr()); 62 63 return nullptr; 64 } 65 66 unsigned WebAssemblyWasmObjectWriter::getRelocType( 67 const MCValue &Target, const MCFixup &Fixup, 68 const MCSectionWasm &FixupSection, bool IsLocRel) const { 69 const MCSymbolRefExpr *RefA = Target.getSymA(); 70 assert(RefA); 71 auto& SymA = cast<MCSymbolWasm>(RefA->getSymbol()); 72 73 MCSymbolRefExpr::VariantKind Modifier = Target.getAccessVariant(); 74 75 switch (Modifier) { 76 case MCSymbolRefExpr::VK_GOT: 77 case MCSymbolRefExpr::VK_WASM_GOT_TLS: 78 return wasm::R_WASM_GLOBAL_INDEX_LEB; 79 case MCSymbolRefExpr::VK_WASM_TBREL: 80 assert(SymA.isFunction()); 81 return is64Bit() ? wasm::R_WASM_TABLE_INDEX_REL_SLEB64 82 : wasm::R_WASM_TABLE_INDEX_REL_SLEB; 83 case MCSymbolRefExpr::VK_WASM_TLSREL: 84 return is64Bit() ? wasm::R_WASM_MEMORY_ADDR_TLS_SLEB64 85 : wasm::R_WASM_MEMORY_ADDR_TLS_SLEB; 86 case MCSymbolRefExpr::VK_WASM_MBREL: 87 assert(SymA.isData()); 88 return is64Bit() ? wasm::R_WASM_MEMORY_ADDR_REL_SLEB64 89 : wasm::R_WASM_MEMORY_ADDR_REL_SLEB; 90 case MCSymbolRefExpr::VK_WASM_TYPEINDEX: 91 return wasm::R_WASM_TYPE_INDEX_LEB; 92 case MCSymbolRefExpr::VK_None: 93 break; 94 default: 95 report_fatal_error("unknown VariantKind"); 96 break; 97 } 98 99 switch (unsigned(Fixup.getKind())) { 100 case WebAssembly::fixup_sleb128_i32: 101 if (SymA.isFunction()) 102 return wasm::R_WASM_TABLE_INDEX_SLEB; 103 return wasm::R_WASM_MEMORY_ADDR_SLEB; 104 case WebAssembly::fixup_sleb128_i64: 105 if (SymA.isFunction()) 106 return wasm::R_WASM_TABLE_INDEX_SLEB64; 107 return wasm::R_WASM_MEMORY_ADDR_SLEB64; 108 case WebAssembly::fixup_uleb128_i32: 109 if (SymA.isGlobal()) 110 return wasm::R_WASM_GLOBAL_INDEX_LEB; 111 if (SymA.isFunction()) 112 return wasm::R_WASM_FUNCTION_INDEX_LEB; 113 if (SymA.isTag()) 114 return wasm::R_WASM_TAG_INDEX_LEB; 115 if (SymA.isTable()) 116 return wasm::R_WASM_TABLE_NUMBER_LEB; 117 return wasm::R_WASM_MEMORY_ADDR_LEB; 118 case WebAssembly::fixup_uleb128_i64: 119 assert(SymA.isData()); 120 return wasm::R_WASM_MEMORY_ADDR_LEB64; 121 case FK_Data_4: 122 if (SymA.isFunction()) { 123 if (FixupSection.getKind().isMetadata()) 124 return wasm::R_WASM_FUNCTION_OFFSET_I32; 125 assert(FixupSection.isWasmData()); 126 return wasm::R_WASM_TABLE_INDEX_I32; 127 } 128 if (SymA.isGlobal()) 129 return wasm::R_WASM_GLOBAL_INDEX_I32; 130 if (auto Section = static_cast<const MCSectionWasm *>( 131 getTargetSection(Fixup.getValue()))) { 132 if (Section->getKind().isText()) 133 return wasm::R_WASM_FUNCTION_OFFSET_I32; 134 else if (!Section->isWasmData()) 135 return wasm::R_WASM_SECTION_OFFSET_I32; 136 } 137 return IsLocRel ? wasm::R_WASM_MEMORY_ADDR_LOCREL_I32 138 : wasm::R_WASM_MEMORY_ADDR_I32; 139 case FK_Data_8: 140 if (SymA.isFunction()) { 141 if (FixupSection.getKind().isMetadata()) 142 return wasm::R_WASM_FUNCTION_OFFSET_I64; 143 return wasm::R_WASM_TABLE_INDEX_I64; 144 } 145 if (SymA.isGlobal()) 146 llvm_unreachable("unimplemented R_WASM_GLOBAL_INDEX_I64"); 147 if (auto Section = static_cast<const MCSectionWasm *>( 148 getTargetSection(Fixup.getValue()))) { 149 if (Section->getKind().isText()) 150 return wasm::R_WASM_FUNCTION_OFFSET_I64; 151 else if (!Section->isWasmData()) 152 llvm_unreachable("unimplemented R_WASM_SECTION_OFFSET_I64"); 153 } 154 assert(SymA.isData()); 155 return wasm::R_WASM_MEMORY_ADDR_I64; 156 default: 157 llvm_unreachable("unimplemented fixup kind"); 158 } 159 } 160 161 std::unique_ptr<MCObjectTargetWriter> 162 llvm::createWebAssemblyWasmObjectWriter(bool Is64Bit, bool IsEmscripten) { 163 return std::make_unique<WebAssemblyWasmObjectWriter>(Is64Bit, IsEmscripten); 164 } 165