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RuleDoubleArithShift

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This commit is contained in:
caheckman 2019-07-13 14:24:22 -04:00
parent a3ea66e4db
commit 1731903056
3 changed files with 45 additions and 0 deletions
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1
Ghidra/Features/Decompiler/src/decompile/cpp/coreaction.cc
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@ -4478,6 +4478,7 @@ void universal_action(Architecture *conf)
actprop->addRule( new RuleAndCompare("analysis") );
actprop->addRule( new RuleDoubleSub("analysis") );
actprop->addRule( new RuleDoubleShift("analysis") );
actprop->addRule( new RuleDoubleArithShift("analysis") );
actprop->addRule( new RuleConcatShift("analysis") );
actprop->addRule( new RuleLeftRight("analysis") );
actprop->addRule( new RuleShiftCompare("analysis") );

34
Ghidra/Features/Decompiler/src/decompile/cpp/ruleaction.cc
View file

@ -1819,6 +1819,40 @@ int4 RuleDoubleShift::applyOp(PcodeOp *op,Funcdata &data)
return 1;
}
/// \class RuleDoubleArithShift
/// \brief Simply two sequential INT_SRIGHT: `(x s>> #c) s>> #d => x s>> saturate(#c + #d)`
///
/// Optimized division optimization in particular can produce a sequence of signed right shifts.
/// The shift amounts add up to the point where the sign bit has saturated the entire result.
void RuleDoubleArithShift::getOpList(vector<uint4> &oplist) const
{
oplist.push_back(CPUI_INT_SRIGHT);
}
int4 RuleDoubleArithShift::applyOp(PcodeOp *op,Funcdata &data)
{
Varnode *constD = op->getIn(1);
if (!constD->isConstant()) return 0;
Varnode *shiftin = op->getIn(0);
if (!shiftin->isWritten()) return 0;
PcodeOp *shift2op = shiftin->getDef();
if (shift2op->code() != CPUI_INT_SRIGHT) return 0;
Varnode *constC = shift2op->getIn(1);
if (!constC->isConstant()) return 0;
Varnode *inVn = shift2op->getIn(0);
if (inVn->isFree()) return 0;
int4 max = op->getOut()->getSize() * 8 - 1; // This is maximum possible shift.
int4 sa = (int4)constC->getOffset() + (int4)constD->getOffset();
if (sa <= 0) return 0; // Something is wrong
if (sa > max)
sa = max; // Shift amount has saturated
data.opSetInput(op, inVn, 0);
data.opSetInput(op, data.newConstant(4, sa),1);
return 1;
}
/// \class RuleConcatShift
/// \brief Simplify INT_RIGHT canceling PIECE: `concat(V,W) >> c => zext(V)`
///

10
Ghidra/Features/Decompiler/src/decompile/cpp/ruleaction.hh
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@ -345,6 +345,16 @@ public:
virtual void getOpList(vector<uint4> &oplist) const;
virtual int4 applyOp(PcodeOp *op,Funcdata &data);
};
class RuleDoubleArithShift : public Rule {
public:
RuleDoubleArithShift(const string &g) : Rule(g, 0, "doublearithshift") {} ///< Constructor
virtual Rule *clone(const ActionGroupList &grouplist) const {
if (!grouplist.contains(getGroup())) return (Rule *)0;
return new RuleDoubleArithShift(getGroup());
}
virtual void getOpList(vector<uint4> &oplist) const;
virtual int4 applyOp(PcodeOp *op,Funcdata &data);
};
class RuleConcatShift : public Rule {
public:
RuleConcatShift(const string &g) : Rule(g, 0, "concatshift") {} ///< Constructor