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/MCFixup.h" 20 #include "llvm/MC/MCSymbolWasm.h" 21 #include "llvm/MC/MCWasmObjectWriter.h" 22 #include "llvm/Support/Casting.h" 23 #include "llvm/Support/ErrorHandling.h" 24 using namespace llvm; 25 26 namespace { 27 class WebAssemblyWasmObjectWriter final : public MCWasmObjectTargetWriter { 28 public: 29 explicit WebAssemblyWasmObjectWriter(bool Is64Bit); 30 31 private: 32 unsigned getRelocType(MCContext &Ctx, const MCValue &Target, 33 const MCFixup &Fixup, bool IsPCRel) const override; 34 }; 35 } // end anonymous namespace 36 37 WebAssemblyWasmObjectWriter::WebAssemblyWasmObjectWriter(bool Is64Bit) 38 : MCWasmObjectTargetWriter(Is64Bit) {} 39 40 // Test whether the given expression computes a function address. 41 static bool IsFunctionExpr(const MCExpr *Expr) { 42 if (const MCSymbolRefExpr *SyExp = 43 dyn_cast<MCSymbolRefExpr>(Expr)) 44 return cast<MCSymbolWasm>(SyExp->getSymbol()).isFunction(); 45 46 if (const MCBinaryExpr *BinOp = 47 dyn_cast<MCBinaryExpr>(Expr)) 48 return IsFunctionExpr(BinOp->getLHS()) != IsFunctionExpr(BinOp->getRHS()); 49 50 if (const MCUnaryExpr *UnOp = 51 dyn_cast<MCUnaryExpr>(Expr)) 52 return IsFunctionExpr(UnOp->getSubExpr()); 53 54 return false; 55 } 56 57 static bool IsFunctionType(const MCValue &Target) { 58 const MCSymbolRefExpr *RefA = Target.getSymA(); 59 return RefA && RefA->getKind() == MCSymbolRefExpr::VK_WebAssembly_TYPEINDEX; 60 } 61 62 unsigned WebAssemblyWasmObjectWriter::getRelocType(MCContext &Ctx, 63 const MCValue &Target, 64 const MCFixup &Fixup, 65 bool IsPCRel) 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 assert(!IsPCRel); 71 switch (unsigned(Fixup.getKind())) { 72 case WebAssembly::fixup_code_sleb128_i32: 73 if (IsFunction) 74 return wasm::R_WEBASSEMBLY_TABLE_INDEX_SLEB; 75 return wasm::R_WEBASSEMBLY_GLOBAL_ADDR_SLEB; 76 case WebAssembly::fixup_code_sleb128_i64: 77 llvm_unreachable("fixup_sleb128_i64 not implemented yet"); 78 case WebAssembly::fixup_code_uleb128_i32: 79 if (IsFunctionType(Target)) 80 return wasm::R_WEBASSEMBLY_TYPE_INDEX_LEB; 81 if (IsFunction) 82 return wasm::R_WEBASSEMBLY_FUNCTION_INDEX_LEB; 83 return wasm::R_WEBASSEMBLY_GLOBAL_ADDR_LEB; 84 case FK_Data_4: 85 if (IsFunction) 86 return wasm::R_WEBASSEMBLY_TABLE_INDEX_I32; 87 return wasm::R_WEBASSEMBLY_GLOBAL_ADDR_I32; 88 case FK_Data_8: 89 llvm_unreachable("FK_Data_8 not implemented yet"); 90 default: 91 llvm_unreachable("unimplemented fixup kind"); 92 } 93 } 94 95 MCObjectWriter *llvm::createWebAssemblyWasmObjectWriter(raw_pwrite_stream &OS, 96 bool Is64Bit) { 97 MCWasmObjectTargetWriter *MOTW = new WebAssemblyWasmObjectWriter(Is64Bit); 98 return createWasmObjectWriter(MOTW, OS); 99 } 100