Utility for Extracting Flow Information from C Source

[Rick Farnbach]

I am looking for a utility which, given a set of C files, will extract
rudimentary program flow information.  I have had more than one
opportunity to use such a utility when maintaining poorly documented
code.  Essentially I am looking for something that will output something
to the effect of :
    main
        func1
        func2
        func1

    func1
        systemcall

    func2
        librarycall
        func1

which shows that func1 and func2 are called by main in the order func1,
func2; func1 calls systemcall, for which we have no source; etc.

I would prefer source code since I work on several different platforms.

Thanks,
Rick