strace/linux/hppa/set_error.c

static int
arch_set_error(struct tcb *tcp)
{
	hppa_r28 = -tcp->u_error;
	return upoke(tcp, PT_GR28, hppa_r28);
}

static int
arch_set_success(struct tcb *tcp)
{
	hppa_r28 = tcp->u_rval;
	return upoke(tcp, PT_GR28, hppa_r28);
}