Linux kernel has set of system calls (called syscalls in short) offered for userspace. Each architecture can support them but the numbers used for their identification can vary between archs.
And those numbers can be important for some projects (like Valgrind for example).
Check issues list and work on any of them.
I keep copy at https://fedora.juszkiewicz.com.pl/syscalls.html page.
"make KERNELSRC=<path to Linux kernel tree>"
It will run through all supported architectures. Any new system call will be added to the list. You can check that with "git diff syscall-names.text" - if there are any new ones then you have to run "make" for second time to make sure that all architectures are checked for new syscall.