> 1. No overhead from libc; minimizes syscall cost

The few nanoseconds of a straight function call are absolutely irrelevant vs the 10s of microseconds of a syscall cost and you lose out on any of the optimizations a libc has that you might not or didn't think about (like memoization of getpid() ) and you need to take on keeping up with syscall evolution / best practices which a libc generally has a good handle on.

> No dependency on libc and C language ABI/toolchains

This obviously doesn't apply to a C syscall header, though, such as the case in OP :)