This is xnu-10002.1.13. See this file in:
/*
 * Copyright (c) 2000 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_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. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 * 
 * 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_OSREFERENCE_LICENSE_HEADER_END@
 */
/*
 * Copyright (c) 1992 NeXT Computer, Inc.
 *
 * Intel386 Family:	Segment selector.
 *
 * HISTORY
 *
 * 29 March 1992 ? at NeXT
 *	Created.
 */

/*
 * Segment selector.
 */

#ifndef __XNU_ARCH_I386_SEL_H
#define __XNU_ARCH_I386_SEL_H

typedef struct sel {
    unsigned short	rpl	:2,
#define KERN_PRIV	0
#define USER_PRIV	3
			ti	:1,
#define SEL_GDT		0
#define SEL_LDT		1
			index	:13;
} sel_t;

#define NULL_SEL	((sel_t) { 0, 0, 0 } )

#endif /* __XNU_ARCH_I386_SEL_H */