There is a bug in glibc's qsort() algorithm that runs the risk of creating an out-of-bounds error if the comparison function is not transitive, for example, if subtraction is used so that it can create an overflow.
I checked the existing functions in the latest version of Postgres source code and most are safe, but there were a few ones that could lead to overflow. I do not know if these can actually lead to problems, but better safe than sorry, so I created a patch to fix those few cases and add a comment to one case that was not clear that it could not overflow.
