/usr/lib/gcc-cross/arm-linux-gnueabihf/4.8/sf/libatomic.so is in libsfgcc-4.8-dev-armhf-cross 4.8.2-16ubuntu4cross0.11.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/gcc-cross/arm-linux-gnueabihf/4.8/sf/../../../../../arm-linux-gnueabihf/libsf/libatomic.so.1