/usr/lib/bglibs/iobuf/str.a is in libbg1-dev 1.106-3.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/bglibs/iobuf/../libbg-iobuf.a
/usr/lib/bglibs/iobuf/../libbg-iobuf.a