The patch looks fine to me (with the addition of checking for sunos5
instead). A few things to consider:
- you could check the system at import time, rather than call time, of
_get_soname()
- notice that the file is located in /usr/ccs/bin, which may not be
  in everybody's path. So using an explicit path would be better.
- Sun itself recommend dump(1) instead of elfdump(1) for use 
  in "shell scripts". "/usr/ccs/bin/elfdump -Lpv /lib/libc.so.1"
  gives output including the line "[6]\tSONAME          libc.so.1\n"