how to get a list of used functions?

[Andreas Schuldei <suppressed>]

hі!

I would like to generate statistics on what functions in my
codebase are heavily used, used, barely used or unused.

I was told that it should be trivial to insert a callback
function into one of the mod perl hooks to get the function name
and module it resides in (and then log it to syslog).

how can i do this? Has this been done before? where can i find
information on this?

/andreas