/usr/lib/gcc-cross/mips-linux-gnu/5/64/libgcc_s.so is in lib64gcc-5-dev-mips-cross 5.3.1-14ubuntu2cross1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 | /* GNU ld script
Use the shared library, but some functions are only in
the static library. */
GROUP ( libgcc_s.so.1 -lgcc )
|