This is xnu-8019. See this file in:
/*
 * Copyright (c) 2014 Apple Inc. All rights reserved.
 *
 * @APPLE_LICENSE_HEADER_START@
 *
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this
 * file.
 *
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 *
 * @APPLE_LICENSE_HEADER_END@
 */

#include <sys/csr.h>
#include <sys/types.h>

/* Syscall entry point */
int __csrctl(csr_op_t op, void *buffer, size_t size);

int
csr_check(csr_config_t mask)
{
	return __csrctl(CSR_SYSCALL_CHECK, &mask, sizeof(csr_config_t));
}

int
csr_get_active_config(csr_config_t *config)
{
	return __csrctl(CSR_SYSCALL_GET_ACTIVE_CONFIG, config, sizeof(csr_config_t));
}