FreeBSD/Linux Kernel Cross Reference
sys/i386/include/segments.h

     /*-
      * SPDX-License-Identifier: BSD-3-Clause
      *
      * Copyright (c) 1989, 1990 William F. Jolitz
      * Copyright (c) 1990 The Regents of the University of California.
      * All rights reserved.
      *
      * This code is derived from software contributed to Berkeley by
      * William Jolitz.
     *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. Neither the name of the University nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     *
     *      from: @(#)segments.h    7.1 (Berkeley) 5/9/91
     * $FreeBSD$
     */
    
    #ifndef _MACHINE_SEGMENTS_H_
    #define _MACHINE_SEGMENTS_H_
    
    /*
     * 386 Segmentation Data Structures and definitions
     *      William F. Jolitz (william@ernie.berkeley.edu) 6/20/1989
     */
    
    #include <x86/segments.h>
    
    /*
     * Software definitions are in this convenient format,
     * which are translated into inconvenient segment descriptors
     * when needed to be used by the 386 hardware
     */
    
    struct  soft_segment_descriptor {
            unsigned ssd_base ;             /* segment base address  */
            unsigned ssd_limit ;            /* segment extent */
            unsigned ssd_type:5 ;           /* segment type */
            unsigned ssd_dpl:2 ;            /* segment descriptor priority level */
            unsigned ssd_p:1 ;              /* segment descriptor present */
            unsigned ssd_xx:4 ;             /* unused */
            unsigned ssd_xx1:2 ;            /* unused */
            unsigned ssd_def32:1 ;          /* default 32 vs 16 bit size */
            unsigned ssd_gran:1 ;           /* limit granularity (byte/page units)*/
    };
    
    /*
     * region descriptors, used to load gdt/idt tables before segments yet exist.
     */
    struct region_descriptor {
            unsigned rd_limit:16;           /* segment extent */
            unsigned rd_base:32 __packed;   /* base address  */
    };
    
    /*
     * Segment Protection Exception code bits
     */
    
    #define SEGEX_EXT       0x01    /* recursive or externally induced */
    #define SEGEX_IDT       0x02    /* interrupt descriptor table */
    #define SEGEX_TI        0x04    /* local descriptor table */
                                    /* other bits are affected descriptor index */
    #define SEGEX_IDX(s)    (((s)>>3)&0x1fff)
    
    #ifdef _KERNEL
    extern int      _default_ldt;
    extern union descriptor *gdt;
    extern union descriptor *ldt;
    extern struct soft_segment_descriptor gdt_segs[];
    extern struct gate_descriptor *idt;
    
    void    lgdt(struct region_descriptor *rdp);
    void    sdtossd(struct segment_descriptor *sdp,
                struct soft_segment_descriptor *ssdp);
    void    ssdtosd(struct soft_segment_descriptor *ssdp,
                struct segment_descriptor *sdp);
    #endif /* _KERNEL */
    
    #endif /* !_MACHINE_SEGMENTS_H_ */

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