It's a bit more complicated than some of the other posters are making it seem: https://utcc.utoronto.ca/~cks/space/blog/unix/UnixAPIAndCRuntime https://utcc.ut

It's a bit more complicated than some of the other posters are making it seem: https://utcc.utoronto.ca/~cks/space/blog/unix/UnixAPIAndCRuntime https://utcc.utoronto.ca/~cks/space/blog/unix/UnixAPIAndCRun... > A few Unixes explicitly say that the standard C library is the stable API and point of interface with the system; one example is Solaris (and now Illumos). Although they don't casually change the low level system call implementation, as far as I know Illumos officially reserves the right to change all of their actual system calls around, breaking any user space code that isn't dynamically linked to libc. If your code breaks, it's your fault; Illumos told you that dynamic linking to libc is the official API. > Other Unixes simply do this tacitly and by accretion. For example, on any Unix using nsswitch.conf, it's very difficult to always get the same results for operations like getaddrinfo() without going through the standard C library, because these may use arbitrary and strange dynamically loaded modules that are accessed through libc and require various random libc APIs to work. This points out one of the problems here; once you start (indirectly) calling random bits of the libc API, they may quite reasonably make assumptions about the runtime environment that they're operating in. How to set up a limited standard C library runtime environment is generally not documented; instead the official view is generally 'let the standard C library runtime code start your main() function'. The kernel's API (which isn't C, but assembly language, as it relies on special opcodes) might be guaranteed stable, as it is in Linux, but even so there are or might be reasons you should call into libc anyway, and take advantage of the official functionality there.