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/MCObjectWriter.h" 21 #include "llvm/MC/MCSectionWasm.h" 22 #include "llvm/MC/MCSymbolWasm.h" 23 #include "llvm/MC/MCValue.h" 24 #include "llvm/MC/MCWasmObjectWriter.h" 25 #include "llvm/Support/Casting.h" 26 #include "llvm/Support/ErrorHandling.h" 27 28 using namespace llvm; 29 30 namespace { 31 class WebAssemblyWasmObjectWriter final : public MCWasmObjectTargetWriter { 32 public: 33 explicit WebAssemblyWasmObjectWriter(bool Is64Bit, bool IsEmscripten); 34 35 private: 36 unsigned getRelocType(const MCValue &Target, const MCFixup &Fixup, 37 const MCSectionWasm &FixupSection, 38 bool IsLocRel) const override; 39 }; 40 } // end anonymous namespace 41 42 WebAssemblyWasmObjectWriter::WebAssemblyWasmObjectWriter(bool Is64Bit, 43 bool IsEmscripten) 44 : MCWasmObjectTargetWriter(Is64Bit, IsEmscripten) {} 45 46 static const MCSection *getTargetSection(const MCExpr *Expr) { 47 if (auto SyExp = dyn_cast<MCSymbolRefExpr>(Expr)) { 48 if (SyExp->getSymbol().isInSection()) 49 return &SyExp->getSymbol().getSection(); 50 return nullptr; 51 } 52 53 if (auto BinOp = dyn_cast<MCBinaryExpr>(Expr)) { 54 auto SectionLHS = getTargetSection(BinOp->getLHS()); 55 auto SectionRHS = getTargetSection(BinOp->getRHS()); 56 return SectionLHS == SectionRHS ? nullptr : SectionLHS; 57 } 58 59 if (auto UnOp = dyn_cast<MCUnaryExpr>(Expr)) 60 return getTargetSection(UnOp->getSubExpr()); 61 62 return nullptr; 63 } 64 65 unsigned WebAssemblyWasmObjectWriter::getRelocType( 66 const MCValue &Target, const MCFixup &Fixup, 67 const MCSectionWasm &FixupSection, bool IsLocRel) const { 68 const MCSymbolRefExpr *RefA = Target.getSymA(); 69 assert(RefA); 70 auto& SymA = cast<MCSymbolWasm>(RefA->getSymbol()); 71 72 MCSymbolRefExpr::VariantKind Modifier = Target.getAccessVariant(); 73 74 switch (Modifier) { 75 case MCSymbolRefExpr::VK_GOT: 76 case MCSymbolRefExpr::VK_WASM_GOT_TLS: 77 return wasm::R_WASM_GLOBAL_INDEX_LEB; 78 case MCSymbolRefExpr::VK_WASM_TBREL: 79 assert(SymA.isFunction()); 80 return is64Bit() ? wasm::R_WASM_TABLE_INDEX_REL_SLEB64 81 : wasm::R_WASM_TABLE_INDEX_REL_SLEB; 82 case MCSymbolRefExpr::VK_WASM_TLSREL: 83 return is64Bit() ? wasm::R_WASM_MEMORY_ADDR_TLS_SLEB64 84 : wasm::R_WASM_MEMORY_ADDR_TLS_SLEB; 85 case MCSymbolRefExpr::VK_WASM_MBREL: 86 assert(SymA.isData()); 87 return is64Bit() ? wasm::R_WASM_MEMORY_ADDR_REL_SLEB64 88 : wasm::R_WASM_MEMORY_ADDR_REL_SLEB; 89 case MCSymbolRefExpr::VK_WASM_TYPEINDEX: 90 return wasm::R_WASM_TYPE_INDEX_LEB; 91 case MCSymbolRefExpr::VK_None: 92 break; 93 case MCSymbolRefExpr::VK_WASM_FUNCINDEX: 94 return wasm::R_WASM_FUNCTION_INDEX_I32; 95 default: 96 report_fatal_error("unknown VariantKind"); 97 break; 98 } 99 100 switch (unsigned(Fixup.getKind())) { 101 case WebAssembly::fixup_sleb128_i32: 102 if (SymA.isFunction()) 103 return wasm::R_WASM_TABLE_INDEX_SLEB; 104 return wasm::R_WASM_MEMORY_ADDR_SLEB; 105 case WebAssembly::fixup_sleb128_i64: 106 if (SymA.isFunction()) 107 return wasm::R_WASM_TABLE_INDEX_SLEB64; 108 return wasm::R_WASM_MEMORY_ADDR_SLEB64; 109 case WebAssembly::fixup_uleb128_i32: 110 if (SymA.isGlobal()) 111 return wasm::R_WASM_GLOBAL_INDEX_LEB; 112 if (SymA.isFunction()) 113 return wasm::R_WASM_FUNCTION_INDEX_LEB; 114 if (SymA.isTag()) 115 return wasm::R_WASM_TAG_INDEX_LEB; 116 if (SymA.isTable()) 117 return wasm::R_WASM_TABLE_NUMBER_LEB; 118 return wasm::R_WASM_MEMORY_ADDR_LEB; 119 case WebAssembly::fixup_uleb128_i64: 120 assert(SymA.isData()); 121 return wasm::R_WASM_MEMORY_ADDR_LEB64; 122 case FK_Data_4: 123 if (SymA.isFunction()) { 124 if (FixupSection.isMetadata()) 125 return wasm::R_WASM_FUNCTION_OFFSET_I32; 126 assert(FixupSection.isWasmData()); 127 return wasm::R_WASM_TABLE_INDEX_I32; 128 } 129 if (SymA.isGlobal()) 130 return wasm::R_WASM_GLOBAL_INDEX_I32; 131 if (auto Section = static_cast<const MCSectionWasm *>( 132 getTargetSection(Fixup.getValue()))) { 133 if (Section->isText()) 134 return wasm::R_WASM_FUNCTION_OFFSET_I32; 135 else if (!Section->isWasmData()) 136 return wasm::R_WASM_SECTION_OFFSET_I32; 137 } 138 return IsLocRel ? wasm::R_WASM_MEMORY_ADDR_LOCREL_I32 139 : wasm::R_WASM_MEMORY_ADDR_I32; 140 case FK_Data_8: 141 if (SymA.isFunction()) { 142 if (FixupSection.isMetadata()) 143 return wasm::R_WASM_FUNCTION_OFFSET_I64; 144 return wasm::R_WASM_TABLE_INDEX_I64; 145 } 146 if (SymA.isGlobal()) 147 llvm_unreachable("unimplemented R_WASM_GLOBAL_INDEX_I64"); 148 if (auto Section = static_cast<const MCSectionWasm *>( 149 getTargetSection(Fixup.getValue()))) { 150 if (Section->isText()) 151 return wasm::R_WASM_FUNCTION_OFFSET_I64; 152 else if (!Section->isWasmData()) 153 llvm_unreachable("unimplemented R_WASM_SECTION_OFFSET_I64"); 154 } 155 assert(SymA.isData()); 156 return wasm::R_WASM_MEMORY_ADDR_I64; 157 default: 158 llvm_unreachable("unimplemented fixup kind"); 159 } 160 } 161 162 std::unique_ptr<MCObjectTargetWriter> 163 llvm::createWebAssemblyWasmObjectWriter(bool Is64Bit, bool IsEmscripten) { 164 return std::make_unique<WebAssemblyWasmObjectWriter>(Is64Bit, IsEmscripten); 165 } 166