Klever

We still use BenchExec 1.18 released ~2 years ago. This is not so stable package that can be used without updates. Most likely numerous tricky issues were fixed in new versions. Unfortunately, we can expect some new limitations for users, e.g. that one can use BenchExec just on Ubuntu without much pain. Besides, there may be new bugs. Let's see.

Implemented in feature-9703. Updated to BenchExec 3.3.

Tests passed, so, I merged the branch to master in ea26920c0. I am not sure that our CI evaluates new BenchExec well enough, so, let's see further and fix issues if so.