Fix long validation of array.new-fixed in unreachable code - #2688
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alexcrichton merged 2 commits intoSep 29, 2026
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This commit fixes an issue in `wasmparser` where validation of `array.new-fixed` in unreachable code would take `O(n)` time where `n` was the immediate on `array.new-fixed`. It's valid for unreachable code to have `array.new-fixed $a 0xff..ff` for example because `unreachable` is polymorphic in its stack, but wasmparser's previous implementation would pop each individual operand from the stack (getting `MaybeType::Bottom` a low), and this took time linear to the magnitude of the immediate as opposed to linear in the size of the code itself. This meant it was pretty easy to generate a small module that takes ~forever to validate, which generally is not a property we want to have.
pchickey
approved these changes
Sep 29, 2026
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This commit fixes an issue in
wasmparserwhere validation ofarray.new-fixedin unreachable code would takeO(n)time wherenwas the immediate onarray.new-fixed. It's valid for unreachable code to havearray.new-fixed $a 0xff..fffor example becauseunreachableis polymorphic in its stack, but wasmparser's previous implementation would pop each individual operand from the stack (gettingMaybeType::Bottoma low), and this took time linear to the magnitude of the immediate as opposed to linear in the size of the code itself. This meant it was pretty easy to generate a small module that takes ~forever to validate, which generally is not a property we want to have.