1 //===-- MCExternalSymbolizer.cpp - External symbolizer --------------------===// 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 #include "llvm/MC/MCDisassembler/MCExternalSymbolizer.h" 10 #include "llvm/MC/MCContext.h" 11 #include "llvm/MC/MCExpr.h" 12 #include "llvm/MC/MCInst.h" 13 #include "llvm/Support/raw_ostream.h" 14 #include <cstring> 15 16 using namespace llvm; 17 18 namespace llvm { 19 class Triple; 20 } 21 22 // This function tries to add a symbolic operand in place of the immediate 23 // Value in the MCInst. The immediate Value has had any PC adjustment made by 24 // the caller. If the instruction is a branch instruction then IsBranch is true, 25 // else false. If the getOpInfo() function was set as part of the 26 // setupForSymbolicDisassembly() call then that function is called to get any 27 // symbolic information at the Address for this instruction. If that returns 28 // non-zero then the symbolic information it returns is used to create an MCExpr 29 // and that is added as an operand to the MCInst. If getOpInfo() returns zero 30 // and IsBranch is true then a symbol look up for Value is done and if a symbol 31 // is found an MCExpr is created with that, else an MCExpr with Value is 32 // created. This function returns true if it adds an operand to the MCInst and 33 // false otherwise. 34 bool MCExternalSymbolizer::tryAddingSymbolicOperand( 35 MCInst &MI, raw_ostream &cStream, int64_t Value, uint64_t Address, 36 bool IsBranch, uint64_t Offset, uint64_t OpSize, uint64_t InstSize) { 37 struct LLVMOpInfo1 SymbolicOp; 38 std::memset(&SymbolicOp, '\0', sizeof(struct LLVMOpInfo1)); 39 SymbolicOp.Value = Value; 40 41 if (!GetOpInfo || 42 !GetOpInfo(DisInfo, Address, Offset, OpSize, InstSize, 1, &SymbolicOp)) { 43 // Clear SymbolicOp.Value from above and also all other fields. 44 std::memset(&SymbolicOp, '\0', sizeof(struct LLVMOpInfo1)); 45 46 // At this point, GetOpInfo() did not find any relocation information about 47 // this operand and we are left to use the SymbolLookUp() call back to guess 48 // if the Value is the address of a symbol. In the case this is a branch 49 // that always makes sense to guess. But in the case of an immediate it is 50 // a bit more questionable if it is an address of a symbol or some other 51 // reference. So if the immediate Value comes from a width of 1 byte, 52 // OpSize, we will not guess it is an address of a symbol. Because in 53 // object files assembled starting at address 0 this usually leads to 54 // incorrect symbolication. 55 if (!SymbolLookUp || (OpSize == 1 && !IsBranch)) 56 return false; 57 58 uint64_t ReferenceType; 59 if (IsBranch) 60 ReferenceType = LLVMDisassembler_ReferenceType_In_Branch; 61 else 62 ReferenceType = LLVMDisassembler_ReferenceType_InOut_None; 63 const char *ReferenceName; 64 const char *Name = SymbolLookUp(DisInfo, Value, &ReferenceType, Address, 65 &ReferenceName); 66 if (Name) { 67 SymbolicOp.AddSymbol.Name = Name; 68 SymbolicOp.AddSymbol.Present = true; 69 // If Name is a C++ symbol name put the human readable name in a comment. 70 if(ReferenceType == LLVMDisassembler_ReferenceType_DeMangled_Name) 71 cStream << ReferenceName; 72 } 73 // For branches always create an MCExpr so it gets printed as hex address. 74 else if (IsBranch) { 75 SymbolicOp.Value = Value; 76 } 77 if(ReferenceType == LLVMDisassembler_ReferenceType_Out_SymbolStub) 78 cStream << "symbol stub for: " << ReferenceName; 79 else if(ReferenceType == LLVMDisassembler_ReferenceType_Out_Objc_Message) 80 cStream << "Objc message: " << ReferenceName; 81 if (!Name && !IsBranch) 82 return false; 83 } 84 85 const MCExpr *Add = nullptr; 86 if (SymbolicOp.AddSymbol.Present) { 87 if (SymbolicOp.AddSymbol.Name) { 88 StringRef Name(SymbolicOp.AddSymbol.Name); 89 MCSymbol *Sym = Ctx.getOrCreateSymbol(Name); 90 Add = MCSymbolRefExpr::create(Sym, Ctx); 91 } else { 92 Add = MCConstantExpr::create((int)SymbolicOp.AddSymbol.Value, Ctx); 93 } 94 } 95 96 const MCExpr *Sub = nullptr; 97 if (SymbolicOp.SubtractSymbol.Present) { 98 if (SymbolicOp.SubtractSymbol.Name) { 99 StringRef Name(SymbolicOp.SubtractSymbol.Name); 100 MCSymbol *Sym = Ctx.getOrCreateSymbol(Name); 101 Sub = MCSymbolRefExpr::create(Sym, Ctx); 102 } else { 103 Sub = MCConstantExpr::create((int)SymbolicOp.SubtractSymbol.Value, Ctx); 104 } 105 } 106 107 const MCExpr *Off = nullptr; 108 if (SymbolicOp.Value != 0) 109 Off = MCConstantExpr::create(SymbolicOp.Value, Ctx); 110 111 const MCExpr *Expr; 112 if (Sub) { 113 const MCExpr *LHS; 114 if (Add) 115 LHS = MCBinaryExpr::createSub(Add, Sub, Ctx); 116 else 117 LHS = MCUnaryExpr::createMinus(Sub, Ctx); 118 if (Off) 119 Expr = MCBinaryExpr::createAdd(LHS, Off, Ctx); 120 else 121 Expr = LHS; 122 } else if (Add) { 123 if (Off) 124 Expr = MCBinaryExpr::createAdd(Add, Off, Ctx); 125 else 126 Expr = Add; 127 } else { 128 if (Off) 129 Expr = Off; 130 else 131 Expr = MCConstantExpr::create(0, Ctx); 132 } 133 134 Expr = RelInfo->createExprForCAPIVariantKind(Expr, SymbolicOp.VariantKind); 135 if (!Expr) 136 return false; 137 138 MI.addOperand(MCOperand::createExpr(Expr)); 139 return true; 140 } 141 142 // This function tries to add a comment as to what is being referenced by a load 143 // instruction with the base register that is the Pc. These can often be values 144 // in a literal pool near the Address of the instruction. The Address of the 145 // instruction and its immediate Value are used as a possible literal pool entry. 146 // The SymbolLookUp call back will return the name of a symbol referenced by the 147 // literal pool's entry if the referenced address is that of a symbol. Or it 148 // will return a pointer to a literal 'C' string if the referenced address of 149 // the literal pool's entry is an address into a section with C string literals. 150 // Or if the reference is to an Objective-C data structure it will return a 151 // specific reference type for it and a string. 152 void MCExternalSymbolizer::tryAddingPcLoadReferenceComment(raw_ostream &cStream, 153 int64_t Value, 154 uint64_t Address) { 155 if (SymbolLookUp) { 156 uint64_t ReferenceType = LLVMDisassembler_ReferenceType_In_PCrel_Load; 157 const char *ReferenceName; 158 (void)SymbolLookUp(DisInfo, Value, &ReferenceType, Address, &ReferenceName); 159 if(ReferenceType == LLVMDisassembler_ReferenceType_Out_LitPool_SymAddr) 160 cStream << "literal pool symbol address: " << ReferenceName; 161 else if(ReferenceType == 162 LLVMDisassembler_ReferenceType_Out_LitPool_CstrAddr) { 163 cStream << "literal pool for: \""; 164 cStream.write_escaped(ReferenceName); 165 cStream << "\""; 166 } 167 else if(ReferenceType == 168 LLVMDisassembler_ReferenceType_Out_Objc_CFString_Ref) 169 cStream << "Objc cfstring ref: @\"" << ReferenceName << "\""; 170 else if(ReferenceType == 171 LLVMDisassembler_ReferenceType_Out_Objc_Message) 172 cStream << "Objc message: " << ReferenceName; 173 else if(ReferenceType == 174 LLVMDisassembler_ReferenceType_Out_Objc_Message_Ref) 175 cStream << "Objc message ref: " << ReferenceName; 176 else if(ReferenceType == 177 LLVMDisassembler_ReferenceType_Out_Objc_Selector_Ref) 178 cStream << "Objc selector ref: " << ReferenceName; 179 else if(ReferenceType == 180 LLVMDisassembler_ReferenceType_Out_Objc_Class_Ref) 181 cStream << "Objc class ref: " << ReferenceName; 182 } 183 } 184 185 namespace llvm { 186 MCSymbolizer *createMCSymbolizer(const Triple &TT, LLVMOpInfoCallback GetOpInfo, 187 LLVMSymbolLookupCallback SymbolLookUp, 188 void *DisInfo, MCContext *Ctx, 189 std::unique_ptr<MCRelocationInfo> &&RelInfo) { 190 assert(Ctx && "No MCContext given for symbolic disassembly"); 191 192 return new MCExternalSymbolizer(*Ctx, std::move(RelInfo), GetOpInfo, 193 SymbolLookUp, DisInfo); 194 } 195 } 196