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[BOLT] Fix local out-of-range stub issue that leads to infinite loop in LongJmp pass #73918

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Merged
merged 1 commit into from
Dec 11, 2023
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[BOLT] Fix local out-of-range stub issue that leads to infinite loop in LongJmp pass #73918

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19 changes: 16 additions & 3 deletions bolt/lib/Passes/LongJmp.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -202,10 +202,23 @@ LongJmpPass::replaceTargetWithStub(BinaryBasicBlock &BB, MCInst &Inst,
}
} else if (LocalStubsIter != Stubs.end() &&
LocalStubsIter->second.count(TgtBB)) {
// If we are replacing a local stub (because it is now out of range),
// use its target instead of creating a stub to jump to another stub
// The TgtBB and TgtSym now are the local out-of-range stub and its label.
// So, we are attempting to restore BB to its previous state without using
// this stub.
TgtSym = BC.MIB->getTargetSymbol(*TgtBB->begin());
TgtBB = BB.getSuccessor(TgtSym, BI);
assert(TgtSym &&
"First instruction is expected to contain a target symbol.");
BinaryBasicBlock *TgtBBSucc = TgtBB->getSuccessor(TgtSym, BI);

// TgtBB might have no successor. e.g. a stub for a function call.
if (TgtBBSucc) {
BB.replaceSuccessor(TgtBB, TgtBBSucc, BI.Count, BI.MispredictedCount);
assert(TgtBB->getExecutionCount() >= BI.Count &&
"At least equal or greater than the branch count.");
TgtBB->setExecutionCount(TgtBB->getExecutionCount() - BI.Count);
}

TgtBB = TgtBBSucc;
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nit: please add new line after }

}

BinaryBasicBlock *StubBB = lookupLocalStub(BB, Inst, TgtSym, DotAddress);
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