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 /// \brief 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/MCSymbolWasm.h" 23 #include "llvm/MC/MCWasmObjectWriter.h" 24 #include "llvm/MC/MCValue.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); 34 35 private: 36 unsigned getRelocType(const MCValue &Target, 37 const MCFixup &Fixup) const override; 38 }; 39 } // end anonymous namespace 40 41 WebAssemblyWasmObjectWriter::WebAssemblyWasmObjectWriter(bool Is64Bit) 42 : MCWasmObjectTargetWriter(Is64Bit) {} 43 44 // Test whether the given expression computes a function address. 45 static bool IsFunctionExpr(const MCExpr *Expr) { 46 if (auto SyExp = dyn_cast<MCSymbolRefExpr>(Expr)) 47 return cast<MCSymbolWasm>(SyExp->getSymbol()).isFunction(); 48 49 if (auto BinOp = dyn_cast<MCBinaryExpr>(Expr)) 50 return IsFunctionExpr(BinOp->getLHS()) != IsFunctionExpr(BinOp->getRHS()); 51 52 if (auto UnOp = dyn_cast<MCUnaryExpr>(Expr)) 53 return IsFunctionExpr(UnOp->getSubExpr()); 54 55 return false; 56 } 57 58 static bool IsFunctionType(const MCValue &Target) { 59 const MCSymbolRefExpr *RefA = Target.getSymA(); 60 return RefA && RefA->getKind() == MCSymbolRefExpr::VK_WebAssembly_TYPEINDEX; 61 } 62 63 unsigned 64 WebAssemblyWasmObjectWriter::getRelocType(const MCValue &Target, 65 const MCFixup &Fixup) const { 66 // WebAssembly functions are not allocated in the data address space. To 67 // resolve a pointer to a function, we must use a special relocation type. 68 bool IsFunction = IsFunctionExpr(Fixup.getValue()); 69 70 switch (unsigned(Fixup.getKind())) { 71 case WebAssembly::fixup_code_sleb128_i32: 72 if (IsFunction) 73 return wasm::R_WEBASSEMBLY_TABLE_INDEX_SLEB; 74 return wasm::R_WEBASSEMBLY_GLOBAL_ADDR_SLEB; 75 case WebAssembly::fixup_code_sleb128_i64: 76 llvm_unreachable("fixup_sleb128_i64 not implemented yet"); 77 case WebAssembly::fixup_code_uleb128_i32: 78 if (IsFunctionType(Target)) 79 return wasm::R_WEBASSEMBLY_TYPE_INDEX_LEB; 80 if (IsFunction) 81 return wasm::R_WEBASSEMBLY_FUNCTION_INDEX_LEB; 82 return wasm::R_WEBASSEMBLY_GLOBAL_ADDR_LEB; 83 case FK_Data_4: 84 if (IsFunction) 85 return wasm::R_WEBASSEMBLY_TABLE_INDEX_I32; 86 return wasm::R_WEBASSEMBLY_GLOBAL_ADDR_I32; 87 case FK_Data_8: 88 llvm_unreachable("FK_Data_8 not implemented yet"); 89 default: 90 llvm_unreachable("unimplemented fixup kind"); 91 } 92 } 93 94 MCObjectWriter *llvm::createWebAssemblyWasmObjectWriter(raw_pwrite_stream &OS, 95 bool Is64Bit) { 96 MCWasmObjectTargetWriter *MOTW = new WebAssemblyWasmObjectWriter(Is64Bit); 97 return createWasmObjectWriter(MOTW, OS); 98 } 99