Fix Stack::compare ignoring element results for different-sized stacks#8297
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tlively merged 1 commit intoWebAssembly:mainfrom Feb 11, 2026
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When comparing stacks of different sizes, the compare function iterated from the top matching elements pairwise, accumulating a comparison result. However, when one stack was exhausted, it returned LESS or GREATER based solely on which stack was taller, ignoring any contradicting result from the element comparisons. For example, with Stack<Bool> comparing [true, false] against [true]: the top elements give false < true (LESS), but the first stack is taller, so the code returned GREATER. The correct answer is NO_RELATION since the element ordering conflicts with the size ordering. The fix checks the accumulated result before returning at the size-difference branches, returning NO_RELATION when there is a conflict.
tlively
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Feb 11, 2026
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Thanks! Out of curiosity, how are you finding all these bugs? Are you using all these APIs for something?
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I am implementing a testing technique for this. I might report more issues soon. |
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Summary
When comparing stacks of different sizes,
Stack::compareiterated from the top matching elements pairwise, accumulating a comparison result. However, when one stack was exhausted, it returnedLESSorGREATERbased solely on which stack was taller, ignoring any contradicting result from the element-wise comparisons.For example, with
Stack<Bool>comparing[true, false]against[true]:falsevstrue→LESSbis exhausted,ahas extra non-bottom elements → code returnedGREATERNO_RELATION(the element ordering conflicts with the size ordering)The fix checks the accumulated
resultbefore returning at the size-difference branches, returningNO_RELATIONwhen there is a conflict.Note: This bug was not caught by the lattice fuzzer because
Stackis not included in the fuzz variants inwasm-fuzz-lattices.cpp.Test plan
StackLattice.CompareDifferentSizeConflicttest case