================
@@ -124,24 +124,26 @@ void ExprEngine::VisitObjCForCollectionStmt(const
ObjCForCollectionStmt *S,
bool isContainerNull = state->isNull(collectionV).isConstrainedTrue();
- ExplodedNodeSet dstLocation;
- evalLocation(dstLocation, S, elem, Pred, state, elementV, false);
----------------
ziqingluo-90 wrote:
To elaborate the issue, suppose `evalLocation` alters the `Pred` state and
populates the new states in `dstLocation`. (This name `dstLocation` is a bit
confusing IMO, let's call those new states `NewPreds` instead.) However, the
`StmtNodeBuilder` below still takes `Pred` as the source state (old line 131)
while the next transitions computed in `populateObjCForDestinationSet` are
computed from `NewPreds` (old line 134 & 138).
The confusion here is that there suppose to be transitions:
`Pred --evalLocation--> NewPreds --populateObjCForDestinationSet--> Dest`
but the `StmtNodeBuilder` used for the second transition above assumes the
source state is `Pred` instead of `NewPreds`. This is what's wrong with this
function `VisitObjCForCollectionStmt`.
Then how does the bug lead to a crash?
The way `StmtNodeBuilder` works is that it maintains a `Frontier` set---the set
of states to be explored next. After initialization (old line 131),
`Frontier = {Pred}`. In `populateObjCForDestinationSet`, `StmtNodeBuilder`
is used to generate `Dest` and remove source state from the set. Note that
`NewPreds` are passed to `populateObjCForDestinationSet` as source states. So
`StmtNodeBuilder` attempts to remove `NewPreds` from the set, which does not
change the set. Finally, `Frontier = {Pred, Dest}`.
Starting from this ill-formed `Frontier` set, the engine executes
[`hasMoreIterations`](https://github.com/llvm/llvm-project/blob/e8e75e08c9214fe25b56535fc26f5435a875a137/clang/lib/StaticAnalyzer/Core/ExprEngine.cpp#L2709C1-L2714C2)
on them. The assertion fails on the state `Pred` because it has never been
set the `ObjCForHasMoreIterations` map. `Dest` has the map set. This is what
`populateObjCForDestinationSet` does. (If assertions are disabled, there is a
segmentation fault.)
https://github.com/llvm/llvm-project/pull/124477
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