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); 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 : MCWasmObjectTargetWriter(Is64Bit) {} 44 45 static const MCSection *getFixupSection(const MCExpr *Expr) { 46 if (auto SyExp = dyn_cast<MCSymbolRefExpr>(Expr)) { 47 if (SyExp->getSymbol().isInSection()) 48 return &SyExp->getSymbol().getSection(); 49 return nullptr; 50 } 51 52 if (auto BinOp = dyn_cast<MCBinaryExpr>(Expr)) { 53 auto SectionLHS = getFixupSection(BinOp->getLHS()); 54 auto SectionRHS = getFixupSection(BinOp->getRHS()); 55 return SectionLHS == SectionRHS ? nullptr : SectionLHS; 56 } 57 58 if (auto UnOp = dyn_cast<MCUnaryExpr>(Expr)) 59 return getFixupSection(UnOp->getSubExpr()); 60 61 return nullptr; 62 } 63 64 unsigned WebAssemblyWasmObjectWriter::getRelocType(const MCValue &Target, 65 const MCFixup &Fixup) const { 66 const MCSymbolRefExpr *RefA = Target.getSymA(); 67 assert(RefA); 68 auto& SymA = cast<MCSymbolWasm>(RefA->getSymbol()); 69 70 MCSymbolRefExpr::VariantKind Modifier = Target.getAccessVariant(); 71 72 switch (Modifier) { 73 case MCSymbolRefExpr::VK_GOT: 74 return wasm::R_WASM_GLOBAL_INDEX_LEB; 75 case MCSymbolRefExpr::VK_WASM_TBREL: 76 assert(SymA.isFunction()); 77 return wasm::R_WASM_TABLE_INDEX_REL_SLEB; 78 case MCSymbolRefExpr::VK_WASM_MBREL: 79 assert(SymA.isData()); 80 return wasm::R_WASM_MEMORY_ADDR_REL_SLEB; 81 case MCSymbolRefExpr::VK_WASM_TYPEINDEX: 82 return wasm::R_WASM_TYPE_INDEX_LEB; 83 default: 84 break; 85 } 86 87 switch (unsigned(Fixup.getKind())) { 88 case WebAssembly::fixup_sleb128_i32: 89 if (SymA.isFunction()) 90 return wasm::R_WASM_TABLE_INDEX_SLEB; 91 return wasm::R_WASM_MEMORY_ADDR_SLEB; 92 case WebAssembly::fixup_sleb128_i64: 93 llvm_unreachable("fixup_sleb128_i64 not implemented yet"); 94 case WebAssembly::fixup_uleb128_i32: 95 if (SymA.isGlobal()) 96 return wasm::R_WASM_GLOBAL_INDEX_LEB; 97 if (SymA.isFunction()) 98 return wasm::R_WASM_FUNCTION_INDEX_LEB; 99 if (SymA.isEvent()) 100 return wasm::R_WASM_EVENT_INDEX_LEB; 101 return wasm::R_WASM_MEMORY_ADDR_LEB; 102 case FK_Data_4: 103 if (SymA.isFunction()) 104 return wasm::R_WASM_TABLE_INDEX_I32; 105 if (auto Section = static_cast<const MCSectionWasm *>( 106 getFixupSection(Fixup.getValue()))) { 107 if (Section->getKind().isText()) 108 return wasm::R_WASM_FUNCTION_OFFSET_I32; 109 else if (!Section->isWasmData()) 110 return wasm::R_WASM_SECTION_OFFSET_I32; 111 } 112 return wasm::R_WASM_MEMORY_ADDR_I32; 113 default: 114 llvm_unreachable("unimplemented fixup kind"); 115 } 116 } 117 118 std::unique_ptr<MCObjectTargetWriter> 119 llvm::createWebAssemblyWasmObjectWriter(bool Is64Bit) { 120 return llvm::make_unique<WebAssemblyWasmObjectWriter>(Is64Bit); 121 } 122