I don't want to have to link against glibc. Nobody should need to do that.

then you first write syscall or copy it from glibc, and then you do that.

Not sure why you're telling me this. As I said in my previous comment, I did do just that. I created a liblinux project just for this that eventually became my own freestanding lisp interpreter with Linux system call support. I'm now reviving the liblinux Rust crate so I can use it in a Rust network stack project.