Function sigonstack

freebsd/kern/kern_sig.c:633–647

* Returns 1 (true) if altstack is configured for the thread, and the * passed stack bottom address falls into the altstack range. Handles * the 43 compat special case where the alt stack size is zero. */

 * the 43 compat special case where the alt stack size is zero.
 */
int
sigonstack(size_t sp)
{
	struct thread *td;

	td = curthread;
	if ((td->td_pflags & TDP_ALTSTACK) == 0)
		return (0);
#if defined(COMPAT_43)
	if (SV_PROC_FLAG(td->td_proc, SV_AOUT) && td->td_sigstk.ss_size == 0)
		return ((td->td_sigstk.ss_flags & SS_ONSTACK) != 0);
#endif
	return (sp >= (size_t)td->td_sigstk.ss_sp &&
	    sp < td->td_sigstk.ss_size + (size_t)td->td_sigstk.ss_sp);
}

static __inline int
sigprop(int sig)