add Berkeley specific copyright notice

[unix-history] / usr / src / sys / tahoe / align / Awriteable.c

/*-
* Copyright (c) 1986 The Regents of the University of California.
* All rights reserved.
*
* This code is derived from software contributed to Berkeley by
* Computer Consoles Inc.
*
* %sccs.include.redist.c%
*
*      @(#)Awriteable.c        7.1 (Berkeley) %G%
*/

#include "align.h" 

long writeable(infop, address, length)
process_info    *infop;
long            address, length;
/*
*   Return TRUE (= -1) if the specified bytes can be written without an access
* control violation (limit and/or protection). Page faults are OK.
*   If problems, return the code that would be pushed by HW on the
* stack (see the architecture manual).
*   Assumption is that in most cases, access is OK, so a quick 'probew'
* will be enough. If not, we have to work harder to determine the exact
* cause and return the right code, without getting the fault here in
* the kernel !!.
*
* The address is assumed to be write for the user.!
*/
{
       register        long    Register_12;    /* Has to be first reg ! */
       register        long    Register_11;
       register        long    Register_10;
       register        long    Register_9;
       register        long    Register_8;
       register        long    subspace;
       register        long    last_page;

       Register_12 = address;
       Register_11 = length-1;
       asm ("          probew  $1,(r12),$1     ");     /* Yeach ... */
       asm ("          beql    no_access       ");
       asm ("          addl2   r11,r12         ");     /* last byte */
       asm ("          probew  $1,(r12),$1     ");
       asm ("          beql    no_access       ");
       asm ("          movl    $-1,r0          ");     /* TRUE */
       asm ("          ret#1                   ");
       asm ("no_access:                        ");
/*
* Now the hard work. Have to check length violation first.
* If any byte (first or last) causes a length violation, report it as such.
*/
       asm ("  mfpr    $3,r8   ");     /* Get length registers. P0LR */
       asm ("  mfpr    $5,r9   ");     /* P1LR */
       asm ("  mfpr    $7,r10  ");     /* P2LR */
       asm ("  mfpr    $1,r11  ");     /* SLR */

       subspace = (address >> 30) & 3;
       Register_12 = (address >> 10) & 0xfffff;        /* 1'st byte page # */
       last_page = ( (address+length-1) >> 10) & 0xfffff;
       switch ( subspace ) {
       case 0:
               if ( (Register_12 >= Register_8) ||
                    (last_page   >= Register_8) ) return (1);
               break;
       case 1:
               if ( (Register_12 >= Register_9) ||
                    (last_page   >= Register_9) ) return (1);
               break;
       case 2:
               if ( (Register_12 < Register_10) ||
                    (last_page   < Register_10) ) return (1);
               break;
       case 3:
               if ( (Register_12 >= Register_11) ||
                    (last_page   >= Register_11) ) return (1);
               break;
       }
/*
* OK, it's not a length violation. Must have been an access problem
* (no write by user).
*
* NOTE : I definitely ignore the case of 'no PTE access' since I
*      assume that's not the case for user mode. Besides, the poor
*      guy will just get an access violation that will most probably
*      send him into hyperspace anyway, so no need to be too acurate here.
*/
       return (4);
}