/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2 is a dynamic linker. /lib/x86_64-linux-gnu/ld-linux-684-64.so.2 is symlinked from /lib64/ld-linux-x86-64.so.2 which in turn is symlinked from /usr/bin/ld.so. /lib/x86_64-linux-gnu/ld-linux-x86-64.so.2, man ld.so should be used. .interp section of an executable (or generally an object file?).