sigaltstack1
error = sigaltstack1(curlwp, SCARG_COMPAT_PTR(uap, nss) ? &nss : 0, \
error = sigaltstack1(l,
error = sigaltstack1(l, &nsa, &osa);
error = sigaltstack1(l, NULL, &osa);
error = sigaltstack1(l,
int sigaltstack1(struct lwp *, const stack_t *, stack_t *);