Function sigaltstack 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn sigaltstack(
    ss: *const stack_t,
    old_ss: *mut stack_t,
) -> c_int

See https://pubs.opengroup.org/onlinepubs/9799919799/functions/sigaltstack.html.

Allows a process to define and examine the state of an alternate stack for signal handlers for the current thread.

Upon success, returns 0. Upon failure, returns -1 and sets errno to indicate the error.

Safety

Use of this function by library threads that are not bound to kernel-scheduled entities results in undefined behaviour.