It's a really cool feaure, but, well, Ulrich says that it 'Seems like the
number of people who know this feature is still almost zero'. Yes, that's
because it was never documented, as with pretty much everything glibc can
do above POSIX. (e.g., quick, how does LD_AUDIT work? How do you use it?
Good luck finding out without reading the source, and it's tricky to
understand even then.)