When linking with --rpath=. the shared library must be in the current directory. What I would want is that the shared library is looked up there where the application is.

The dynamic linker understands certain token strings in an rpath specification (DT_RPATH or DT_RUNPATH). Those strings are substituted as follows:

• $ORIGIN (or equivalently ${ORIGIN})

  This expands to the directory containing the program or shared object. Thus, an application located in somedir/app could be compiled with

                    gcc -Wl,-rpath,'$ORIGIN/../lib'
  [download]

  so that it finds an associated shared object in somedir/lib no matter where somedir is located in the directory hierarchy.