1 //===-- WebAssemblyWasmObjectWriter.cpp - WebAssembly Wasm Writer ---------===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 /// 10 /// \file 11 /// This file handles Wasm-specific object emission, converting LLVM's 12 /// internal fixups into the appropriate relocations. 13 /// 14 //===----------------------------------------------------------------------===// 15 16 #include "MCTargetDesc/WebAssemblyFixupKinds.h" 17 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h" 18 #include "llvm/BinaryFormat/Wasm.h" 19 #include "llvm/MC/MCAsmBackend.h" 20 #include "llvm/MC/MCFixup.h" 21 #include "llvm/MC/MCFixupKindInfo.h" 22 #include "llvm/MC/MCObjectWriter.h" 23 #include "llvm/MC/MCSectionWasm.h" 24 #include "llvm/MC/MCSymbolWasm.h" 25 #include "llvm/MC/MCValue.h" 26 #include "llvm/MC/MCWasmObjectWriter.h" 27 #include "llvm/Support/Casting.h" 28 #include "llvm/Support/ErrorHandling.h" 29 30 using namespace llvm; 31 32 namespace { 33 class WebAssemblyWasmObjectWriter final : public MCWasmObjectTargetWriter { 34 public: 35 explicit WebAssemblyWasmObjectWriter(bool Is64Bit); 36 37 private: 38 unsigned getRelocType(const MCValue &Target, 39 const MCFixup &Fixup) const override; 40 }; 41 } // end anonymous namespace 42 43 WebAssemblyWasmObjectWriter::WebAssemblyWasmObjectWriter(bool Is64Bit) 44 : MCWasmObjectTargetWriter(Is64Bit) {} 45 46 // Test whether the given expression computes a function address. 47 static bool IsFunctionExpr(const MCExpr *Expr) { 48 if (auto SyExp = dyn_cast<MCSymbolRefExpr>(Expr)) 49 return cast<MCSymbolWasm>(SyExp->getSymbol()).isFunction(); 50 51 if (auto BinOp = dyn_cast<MCBinaryExpr>(Expr)) 52 return IsFunctionExpr(BinOp->getLHS()) != IsFunctionExpr(BinOp->getRHS()); 53 54 if (auto UnOp = dyn_cast<MCUnaryExpr>(Expr)) 55 return IsFunctionExpr(UnOp->getSubExpr()); 56 57 return false; 58 } 59 60 static bool IsFunctionType(const MCValue &Target) { 61 const MCSymbolRefExpr *RefA = Target.getSymA(); 62 return RefA && RefA->getKind() == MCSymbolRefExpr::VK_WebAssembly_TYPEINDEX; 63 } 64 65 static const MCSection *GetFixupSection(const MCExpr *Expr) { 66 if (auto SyExp = dyn_cast<MCSymbolRefExpr>(Expr)) { 67 if (SyExp->getSymbol().isInSection()) 68 return &SyExp->getSymbol().getSection(); 69 return nullptr; 70 } 71 72 if (auto BinOp = dyn_cast<MCBinaryExpr>(Expr)) { 73 auto SectionLHS = GetFixupSection(BinOp->getLHS()); 74 auto SectionRHS = GetFixupSection(BinOp->getRHS()); 75 return SectionLHS == SectionRHS ? nullptr : SectionLHS; 76 } 77 78 if (auto UnOp = dyn_cast<MCUnaryExpr>(Expr)) 79 return GetFixupSection(UnOp->getSubExpr()); 80 81 return nullptr; 82 } 83 84 static bool IsGlobalType(const MCValue &Target) { 85 const MCSymbolRefExpr *RefA = Target.getSymA(); 86 return RefA && RefA->getKind() == MCSymbolRefExpr::VK_WebAssembly_GLOBAL; 87 } 88 89 unsigned WebAssemblyWasmObjectWriter::getRelocType(const MCValue &Target, 90 const MCFixup &Fixup) const { 91 // WebAssembly functions are not allocated in the data address space. To 92 // resolve a pointer to a function, we must use a special relocation type. 93 bool IsFunction = IsFunctionExpr(Fixup.getValue()); 94 95 switch (unsigned(Fixup.getKind())) { 96 case WebAssembly::fixup_code_sleb128_i32: 97 if (IsFunction) 98 return wasm::R_WEBASSEMBLY_TABLE_INDEX_SLEB; 99 return wasm::R_WEBASSEMBLY_MEMORY_ADDR_SLEB; 100 case WebAssembly::fixup_code_sleb128_i64: 101 llvm_unreachable("fixup_sleb128_i64 not implemented yet"); 102 case WebAssembly::fixup_code_uleb128_i32: 103 if (IsGlobalType(Target)) 104 return wasm::R_WEBASSEMBLY_GLOBAL_INDEX_LEB; 105 if (IsFunctionType(Target)) 106 return wasm::R_WEBASSEMBLY_TYPE_INDEX_LEB; 107 if (IsFunction) 108 return wasm::R_WEBASSEMBLY_FUNCTION_INDEX_LEB; 109 return wasm::R_WEBASSEMBLY_MEMORY_ADDR_LEB; 110 case FK_Data_4: 111 if (IsFunction) 112 return wasm::R_WEBASSEMBLY_TABLE_INDEX_I32; 113 if (auto Section = static_cast<const MCSectionWasm *>( 114 GetFixupSection(Fixup.getValue()))) { 115 if (Section->getKind().isText()) 116 return wasm::R_WEBASSEMBLY_FUNCTION_OFFSET_I32; 117 else if (!Section->isWasmData()) 118 return wasm::R_WEBASSEMBLY_SECTION_OFFSET_I32; 119 } 120 return wasm::R_WEBASSEMBLY_MEMORY_ADDR_I32; 121 case FK_Data_8: 122 llvm_unreachable("FK_Data_8 not implemented yet"); 123 default: 124 llvm_unreachable("unimplemented fixup kind"); 125 } 126 } 127 128 std::unique_ptr<MCObjectTargetWriter> 129 llvm::createWebAssemblyWasmObjectWriter(bool Is64Bit) { 130 return llvm::make_unique<WebAssemblyWasmObjectWriter>(Is64Bit); 131 } 132