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Annotation of 43BSDReno/sys/tahoealign/Awriteable.c, revision 1.1

1.1     ! root        1: /*     Awriteable.c    1.1     86/07/20        */
        !             2: 
        !             3: #include "../tahoealign/align.h" 
        !             4: 
        !             5: long writeable(infop, address, length)
        !             6: process_info   *infop;
        !             7: long           address, length;
        !             8: /*
        !             9:  *   Return TRUE (= -1) if the specified bytes can be written without an access
        !            10:  * control violation (limit and/or protection). Page faults are OK.
        !            11:  *   If problems, return the code that would be pushed by HW on the
        !            12:  * stack (see the architecture manual).
        !            13:  *   Assumption is that in most cases, access is OK, so a quick 'probew'
        !            14:  * will be enough. If not, we have to work harder to determine the exact
        !            15:  * cause and return the right code, without getting the fault here in
        !            16:  * the kernel !!.
        !            17:  *
        !            18:  * The address is assumed to be write for the user.!
        !            19:  */
        !            20: {
        !            21:        register        long    Register_12;    /* Has to be first reg ! */
        !            22:        register        long    Register_11;
        !            23:        register        long    Register_10;
        !            24:        register        long    Register_9;
        !            25:        register        long    Register_8;
        !            26:        register        long    subspace;
        !            27:        register        long    last_page;
        !            28: 
        !            29:        Register_12 = address;
        !            30:        Register_11 = length-1;
        !            31:        asm ("          probew  $1,(r12),$1     ");     /* Yeach ... */
        !            32:        asm ("          beql    no_access       ");
        !            33:        asm ("          addl2   r11,r12         ");     /* last byte */
        !            34:        asm ("          probew  $1,(r12),$1     ");
        !            35:        asm ("          beql    no_access       ");
        !            36:        asm ("          movl    $-1,r0          ");     /* TRUE */
        !            37:        asm ("          ret#1                   ");
        !            38:        asm ("no_access:                        ");
        !            39: /*
        !            40:  * Now the hard work. Have to check length violation first.
        !            41:  * If any byte (first or last) causes a length violation, report it as such.
        !            42:  */
        !            43:        asm ("  mfpr    $3,r8   ");     /* Get length registers. P0LR */
        !            44:        asm ("  mfpr    $5,r9   ");     /* P1LR */
        !            45:        asm ("  mfpr    $7,r10  ");     /* P2LR */
        !            46:        asm ("  mfpr    $1,r11  ");     /* SLR */
        !            47: 
        !            48:        subspace = (address >> 30) & 3;
        !            49:        Register_12 = (address >> 10) & 0xfffff;        /* 1'st byte page # */
        !            50:        last_page = ( (address+length-1) >> 10) & 0xfffff;
        !            51:        switch ( subspace ) {
        !            52:        case 0:
        !            53:                if ( (Register_12 >= Register_8) ||
        !            54:                     (last_page   >= Register_8) ) return (1);
        !            55:                break;
        !            56:        case 1:
        !            57:                if ( (Register_12 >= Register_9) ||
        !            58:                     (last_page   >= Register_9) ) return (1);
        !            59:                break;
        !            60:        case 2:
        !            61:                if ( (Register_12 < Register_10) ||
        !            62:                     (last_page   < Register_10) ) return (1);
        !            63:                break;
        !            64:        case 3:
        !            65:                if ( (Register_12 >= Register_11) ||
        !            66:                     (last_page   >= Register_11) ) return (1);
        !            67:                break;
        !            68:        }
        !            69: /*
        !            70:  * OK, it's not a length violation. Must have been an access problem
        !            71:  * (no write by user).
        !            72:  *
        !            73:  * NOTE : I definitely ignore the case of 'no PTE access' since I
        !            74:  *     assume that's not the case for user mode. Besides, the poor
        !            75:  *     guy will just get an access violation that will most probably
        !            76:  *     send him into hyperspace anyway, so no need to be too acurate here.
        !            77:  */
        !            78:        return (4);
        !            79: }

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