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, 38 const MCFixup &Fixup) 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) const { 67 const MCSymbolRefExpr *RefA = Target.getSymA(); 68 assert(RefA); 69 auto& SymA = cast<MCSymbolWasm>(RefA->getSymbol()); 70 71 MCSymbolRefExpr::VariantKind Modifier = Target.getAccessVariant(); 72 73 switch (Modifier) { 74 case MCSymbolRefExpr::VK_GOT: 75 return wasm::R_WASM_GLOBAL_INDEX_LEB; 76 case MCSymbolRefExpr::VK_WASM_TBREL: 77 assert(SymA.isFunction()); 78 return wasm::R_WASM_TABLE_INDEX_REL_SLEB; 79 case MCSymbolRefExpr::VK_WASM_MBREL: 80 assert(SymA.isData()); 81 return is64Bit() ? wasm::R_WASM_MEMORY_ADDR_REL_SLEB64 82 : wasm::R_WASM_MEMORY_ADDR_REL_SLEB; 83 case MCSymbolRefExpr::VK_WASM_TYPEINDEX: 84 return wasm::R_WASM_TYPE_INDEX_LEB; 85 default: 86 break; 87 } 88 89 switch (unsigned(Fixup.getKind())) { 90 case WebAssembly::fixup_sleb128_i32: 91 if (SymA.isFunction()) 92 return wasm::R_WASM_TABLE_INDEX_SLEB; 93 return wasm::R_WASM_MEMORY_ADDR_SLEB; 94 case WebAssembly::fixup_sleb128_i64: 95 if (SymA.isFunction()) 96 return wasm::R_WASM_TABLE_INDEX_SLEB64; 97 return wasm::R_WASM_MEMORY_ADDR_SLEB64; 98 case WebAssembly::fixup_uleb128_i32: 99 if (SymA.isGlobal()) 100 return wasm::R_WASM_GLOBAL_INDEX_LEB; 101 if (SymA.isFunction()) 102 return wasm::R_WASM_FUNCTION_INDEX_LEB; 103 if (SymA.isEvent()) 104 return wasm::R_WASM_EVENT_INDEX_LEB; 105 return wasm::R_WASM_MEMORY_ADDR_LEB; 106 case WebAssembly::fixup_uleb128_i64: 107 assert(SymA.isData()); 108 return wasm::R_WASM_MEMORY_ADDR_LEB64; 109 case FK_Data_4: 110 if (SymA.isFunction()) 111 return wasm::R_WASM_TABLE_INDEX_I32; 112 if (SymA.isGlobal()) 113 return wasm::R_WASM_GLOBAL_INDEX_I32; 114 if (auto Section = static_cast<const MCSectionWasm *>( 115 getFixupSection(Fixup.getValue()))) { 116 if (Section->getKind().isText()) 117 return wasm::R_WASM_FUNCTION_OFFSET_I32; 118 else if (!Section->isWasmData()) 119 return wasm::R_WASM_SECTION_OFFSET_I32; 120 } 121 return wasm::R_WASM_MEMORY_ADDR_I32; 122 case FK_Data_8: 123 if (SymA.isFunction()) 124 return wasm::R_WASM_TABLE_INDEX_I64; 125 assert(SymA.isData()); 126 return wasm::R_WASM_MEMORY_ADDR_I64; 127 default: 128 llvm_unreachable("unimplemented fixup kind"); 129 } 130 } 131 132 std::unique_ptr<MCObjectTargetWriter> 133 llvm::createWebAssemblyWasmObjectWriter(bool Is64Bit, bool IsEmscripten) { 134 return std::make_unique<WebAssemblyWasmObjectWriter>(Is64Bit, IsEmscripten); 135 } 136