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//===-- MCExternalSymbolizer.cpp - External symbolizer --------------------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
#include "llvm/MC/MCDisassembler/MCExternalSymbolizer.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCInst.h"
#include "llvm/Support/raw_ostream.h"
#include <cstring>
using namespace llvm;
namespace llvm {
class Triple;
// This function tries to add a symbolic operand in place of the immediate
// Value in the MCInst. The immediate Value has had any PC adjustment made by
// the caller. If the instruction is a branch instruction then IsBranch is true,
// else false. If the getOpInfo() function was set as part of the
// setupForSymbolicDisassembly() call then that function is called to get any
// symbolic information at the Address for this instruction. If that returns
// non-zero then the symbolic information it returns is used to create an MCExpr
// and that is added as an operand to the MCInst. If getOpInfo() returns zero
// and IsBranch is true then a symbol look up for Value is done and if a symbol
// is found an MCExpr is created with that, else an MCExpr with Value is
// created. This function returns true if it adds an operand to the MCInst and
// false otherwise.
bool MCExternalSymbolizer::tryAddingSymbolicOperand(MCInst &MI,
raw_ostream &cStream,
int64_t Value,
uint64_t Address,
bool IsBranch,
uint64_t Offset,
uint64_t InstSize) {
struct LLVMOpInfo1 SymbolicOp;
std::memset(&SymbolicOp, '\0', sizeof(struct LLVMOpInfo1));
SymbolicOp.Value = Value;
if (!GetOpInfo ||
!GetOpInfo(DisInfo, Address, Offset, InstSize, 1, &SymbolicOp)) {
// Clear SymbolicOp.Value from above and also all other fields.
std::memset(&SymbolicOp, '\0', sizeof(struct LLVMOpInfo1));
// At this point, GetOpInfo() did not find any relocation information about
// this operand and we are left to use the SymbolLookUp() call back to guess
// if the Value is the address of a symbol. In the case this is a branch
// that always makes sense to guess. But in the case of an immediate it is
// a bit more questionable if it is an address of a symbol or some other
// reference. So if the immediate Value comes from a width of 1 byte,
// InstSize, we will not guess it is an address of a symbol. Because in
// object files assembled starting at address 0 this usually leads to
// incorrect symbolication.
if (!SymbolLookUp || (InstSize == 1 && !IsBranch))
return false;
uint64_t ReferenceType;
if (IsBranch)
ReferenceType = LLVMDisassembler_ReferenceType_In_Branch;
ReferenceType = LLVMDisassembler_ReferenceType_InOut_None;
const char *ReferenceName;
const char *Name = SymbolLookUp(DisInfo, Value, &ReferenceType, Address,
if (Name) {
SymbolicOp.AddSymbol.Name = Name;
SymbolicOp.AddSymbol.Present = true;
// If Name is a C++ symbol name put the human readable name in a comment.
if(ReferenceType == LLVMDisassembler_ReferenceType_DeMangled_Name)
cStream << ReferenceName;
// For branches always create an MCExpr so it gets printed as hex address.
else if (IsBranch) {
SymbolicOp.Value = Value;
if(ReferenceType == LLVMDisassembler_ReferenceType_Out_SymbolStub)
cStream << "symbol stub for: " << ReferenceName;
else if(ReferenceType == LLVMDisassembler_ReferenceType_Out_Objc_Message)
cStream << "Objc message: " << ReferenceName;
if (!Name && !IsBranch)
return false;
const MCExpr *Add = nullptr;
if (SymbolicOp.AddSymbol.Present) {
if (SymbolicOp.AddSymbol.Name) {
StringRef Name(SymbolicOp.AddSymbol.Name);
MCSymbol *Sym = Ctx.getOrCreateSymbol(Name);
Add = MCSymbolRefExpr::create(Sym, Ctx);
} else {
Add = MCConstantExpr::create((int)SymbolicOp.AddSymbol.Value, Ctx);
const MCExpr *Sub = nullptr;
if (SymbolicOp.SubtractSymbol.Present) {
if (SymbolicOp.SubtractSymbol.Name) {
StringRef Name(SymbolicOp.SubtractSymbol.Name);
MCSymbol *Sym = Ctx.getOrCreateSymbol(Name);
Sub = MCSymbolRefExpr::create(Sym, Ctx);
} else {
Sub = MCConstantExpr::create((int)SymbolicOp.SubtractSymbol.Value, Ctx);
const MCExpr *Off = nullptr;
if (SymbolicOp.Value != 0)
Off = MCConstantExpr::create(SymbolicOp.Value, Ctx);
const MCExpr *Expr;
if (Sub) {
const MCExpr *LHS;
if (Add)
LHS = MCBinaryExpr::createSub(Add, Sub, Ctx);
LHS = MCUnaryExpr::createMinus(Sub, Ctx);
if (Off)
Expr = MCBinaryExpr::createAdd(LHS, Off, Ctx);
Expr = LHS;
} else if (Add) {
if (Off)
Expr = MCBinaryExpr::createAdd(Add, Off, Ctx);
Expr = Add;
} else {
if (Off)
Expr = Off;
Expr = MCConstantExpr::create(0, Ctx);
Expr = RelInfo->createExprForCAPIVariantKind(Expr, SymbolicOp.VariantKind);
if (!Expr)
return false;
return true;
// This function tries to add a comment as to what is being referenced by a load
// instruction with the base register that is the Pc. These can often be values
// in a literal pool near the Address of the instruction. The Address of the
// instruction and its immediate Value are used as a possible literal pool entry.
// The SymbolLookUp call back will return the name of a symbol referenced by the
// literal pool's entry if the referenced address is that of a symbol. Or it
// will return a pointer to a literal 'C' string if the referenced address of
// the literal pool's entry is an address into a section with C string literals.
// Or if the reference is to an Objective-C data structure it will return a
// specific reference type for it and a string.
void MCExternalSymbolizer::tryAddingPcLoadReferenceComment(raw_ostream &cStream,
int64_t Value,
uint64_t Address) {
if (SymbolLookUp) {
uint64_t ReferenceType = LLVMDisassembler_ReferenceType_In_PCrel_Load;
const char *ReferenceName;
(void)SymbolLookUp(DisInfo, Value, &ReferenceType, Address, &ReferenceName);
if(ReferenceType == LLVMDisassembler_ReferenceType_Out_LitPool_SymAddr)
cStream << "literal pool symbol address: " << ReferenceName;
else if(ReferenceType ==
LLVMDisassembler_ReferenceType_Out_LitPool_CstrAddr) {
cStream << "literal pool for: \"";
cStream << "\"";
else if(ReferenceType ==
cStream << "Objc cfstring ref: @\"" << ReferenceName << "\"";
else if(ReferenceType ==
cStream << "Objc message: " << ReferenceName;
else if(ReferenceType ==
cStream << "Objc message ref: " << ReferenceName;
else if(ReferenceType ==
cStream << "Objc selector ref: " << ReferenceName;
else if(ReferenceType ==
cStream << "Objc class ref: " << ReferenceName;
namespace llvm {
MCSymbolizer *createMCSymbolizer(const Triple &TT, LLVMOpInfoCallback GetOpInfo,
LLVMSymbolLookupCallback SymbolLookUp,
void *DisInfo, MCContext *Ctx,
std::unique_ptr<MCRelocationInfo> &&RelInfo) {
assert(Ctx && "No MCContext given for symbolic disassembly");
return new MCExternalSymbolizer(*Ctx, std::move(RelInfo), GetOpInfo,
SymbolLookUp, DisInfo);