I moved my MariaDB server to a new host and could not follow my previously working instructions to build lib_mysqludf_sys. The error indicated that my_atomic.h was not found.

[lisa@server03 lib_mysqludf_sys]# make
gcc -fPIC -Wall -I/usr/include/mysql/server -I. -shared lib_mysqludf_sys.c -o /usr/lib64/mariadb/plugin//lib_mysqludf_sys.so
In file included from /usr/include/mysql/server/my_sys.h:34,
from lib_mysqludf_sys.c:41:
/usr/include/mysql/server/my_pthread.h:26:10: fatal error: my_atomic.h: No such file or directory
26 | #include <my_atomic.h>
| ^~~~~~~~~~~~~
compilation terminated.
make: *** [Makefile:4: install] Error 1

The missing file is located in /usr/include/mysql/server/private … so I had to include that file in the gcc command as well. My new Makefile reads as follows:

[lisa@server03 lib_mysqludf_sys]# cat Makefile
LIBDIR=/usr/lib64/mariadb/plugin/

install:
gcc -fPIC -Wall -I/usr/include/mysql/server -I/usr/include/mysql/server/private -I. -shared lib_mysqludf_sys.c -o $(LIBDIR)/lib_mysqludf_sys.so

I was then able to make and use install.sh to load it into MariaDB.