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 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 *getFixupSection(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 = getFixupSection(BinOp->getLHS()); 55 auto SectionRHS = getFixupSection(BinOp->getRHS()); 56 return SectionLHS == SectionRHS ? nullptr : SectionLHS; 57 } 58 59 if (auto UnOp = dyn_cast<MCUnaryExpr>(Expr)) 60 return getFixupSection(UnOp->getSubExpr()); 61 62 return nullptr; 63 } 64 65 unsigned WebAssemblyWasmObjectWriter::getRelocType(const MCValue &Target, 66 const MCFixup &Fixup, 67 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 return wasm::R_WASM_GLOBAL_INDEX_LEB; 77 case MCSymbolRefExpr::VK_WASM_TBREL: 78 assert(SymA.isFunction()); 79 return is64Bit() ? wasm::R_WASM_TABLE_INDEX_REL_SLEB64 80 : wasm::R_WASM_TABLE_INDEX_REL_SLEB; 81 case MCSymbolRefExpr::VK_WASM_TLSREL: 82 return is64Bit() ? wasm::R_WASM_MEMORY_ADDR_TLS_SLEB64 83 : wasm::R_WASM_MEMORY_ADDR_TLS_SLEB; 84 case MCSymbolRefExpr::VK_WASM_MBREL: 85 assert(SymA.isData()); 86 return is64Bit() ? wasm::R_WASM_MEMORY_ADDR_REL_SLEB64 87 : wasm::R_WASM_MEMORY_ADDR_REL_SLEB; 88 case MCSymbolRefExpr::VK_WASM_TYPEINDEX: 89 return wasm::R_WASM_TYPE_INDEX_LEB; 90 default: 91 break; 92 } 93 94 switch (unsigned(Fixup.getKind())) { 95 case WebAssembly::fixup_sleb128_i32: 96 if (SymA.isFunction()) 97 return wasm::R_WASM_TABLE_INDEX_SLEB; 98 return wasm::R_WASM_MEMORY_ADDR_SLEB; 99 case WebAssembly::fixup_sleb128_i64: 100 if (SymA.isFunction()) 101 return wasm::R_WASM_TABLE_INDEX_SLEB64; 102 return wasm::R_WASM_MEMORY_ADDR_SLEB64; 103 case WebAssembly::fixup_uleb128_i32: 104 if (SymA.isGlobal()) 105 return wasm::R_WASM_GLOBAL_INDEX_LEB; 106 if (SymA.isFunction()) 107 return wasm::R_WASM_FUNCTION_INDEX_LEB; 108 if (SymA.isTag()) 109 return wasm::R_WASM_TAG_INDEX_LEB; 110 if (SymA.isTable()) 111 return wasm::R_WASM_TABLE_NUMBER_LEB; 112 return wasm::R_WASM_MEMORY_ADDR_LEB; 113 case WebAssembly::fixup_uleb128_i64: 114 assert(SymA.isData()); 115 return wasm::R_WASM_MEMORY_ADDR_LEB64; 116 case FK_Data_4: 117 if (SymA.isFunction()) 118 return wasm::R_WASM_TABLE_INDEX_I32; 119 if (SymA.isGlobal()) 120 return wasm::R_WASM_GLOBAL_INDEX_I32; 121 if (auto Section = static_cast<const MCSectionWasm *>( 122 getFixupSection(Fixup.getValue()))) { 123 if (Section->getKind().isText()) 124 return wasm::R_WASM_FUNCTION_OFFSET_I32; 125 else if (!Section->isWasmData()) 126 return wasm::R_WASM_SECTION_OFFSET_I32; 127 } 128 return IsLocRel ? wasm::R_WASM_MEMORY_ADDR_LOCREL_I32 129 : wasm::R_WASM_MEMORY_ADDR_I32; 130 case FK_Data_8: 131 if (SymA.isFunction()) 132 return wasm::R_WASM_TABLE_INDEX_I64; 133 if (SymA.isGlobal()) 134 llvm_unreachable("unimplemented R_WASM_GLOBAL_INDEX_I64"); 135 if (auto Section = static_cast<const MCSectionWasm *>( 136 getFixupSection(Fixup.getValue()))) { 137 if (Section->getKind().isText()) 138 return wasm::R_WASM_FUNCTION_OFFSET_I64; 139 else if (!Section->isWasmData()) 140 llvm_unreachable("unimplemented R_WASM_SECTION_OFFSET_I64"); 141 } 142 assert(SymA.isData()); 143 return wasm::R_WASM_MEMORY_ADDR_I64; 144 default: 145 llvm_unreachable("unimplemented fixup kind"); 146 } 147 } 148 149 std::unique_ptr<MCObjectTargetWriter> 150 llvm::createWebAssemblyWasmObjectWriter(bool Is64Bit, bool IsEmscripten) { 151 return std::make_unique<WebAssemblyWasmObjectWriter>(Is64Bit, IsEmscripten); 152 } 153