yetangitu/ghidra
1
0
Fork 0
mirror of https://github.com/NationalSecurityAgency/ghidra.git synced 2025-10-04 02:09:44 +02:00
Code Issues Releases Wiki Activity

RuleDoubleArithShift

Browse source
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
Download patch file Download diff file Expand all files Collapse all files

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)`
///