Exceeding the limiting on numFastVars (cannot exceed 2^^13)

[lllssskkk]

Hi, I'm security researcher. I'm right now playing around with queries. When i'm playing with one customized query, i got the following error :

Oops! A fatal internal error occurred. Details: com.semmle.util.exception.CatastrophicError: Invalid value 29616 for numFastVars (cannot exceed 2^^13)
    at           
    com.semmle.util.exception.Exceptions.assertion(Exceptions.java:105)
    com.semmle.bdd.SemmleBDDFactory.<init>(SemmleBDDFactory.java:265)

CodeQL’s internal BDD-based component (Binary Decision Diagrams) is trying to allocate/configure a structure with 29,616 “fast variables”, but it has a hard upper bound of 2^^13 = 8192.

Is there any way to increase the threshhold?

[smowton]

I'm afraid not, that's a compiled-in limit. Is your customised query complex enough that this is expected?

[lllssskkk]

Hi, thx for the quick response.

This is expected. Running multiple tainted tracking queries and looking for if they share at least one node in between.

So there isn't any hidden parameter i can pass in to modify the limit.

[smowton]

I'm afraid not, it's a baked-in limit. If you outline what you're doing, it's possible your multiple taint configs could be expressed in a different way so as to save generated CodeQL and therefore demand for BDD components?

[lllssskkk]

There are definitely other ways for achieving the same functionality, but We will leave it for the future work. haha