Finding where an executable was run from -- a proposal.

[Ron Natalie]

Actually if you are running a demand paged or shared text program that
information is already stored in the kernel.  You just need another
system call or something to read it out.  Unforunately, you have the
PWD problem.  There is no easy way to invert the UNIX search lookups.
Normal UNIX filesystems are Directed Acyclic Graphs (not trees), which
means that there may me multiple paths to any particular node.

-Ron