llvm/lib/MC/MCDisassembler/MCExternalSymbolizer.cpp

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