[yalue]

Sometimes, yes, you'll need to write your own syscall wrappers. For example, there isn't a gettid (get thread ID) function in Glibc, but you can work around this by calling the syscall directly.

The other case where this is useful is if you're wanting to write userspace assembly without calling a C library. This may be especially useful when you're writing a compiler, or if you're trying to write small shellcodes for some reason.