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Annotation of 43BSDTahoe/sys/tahoealign/Awriteable.c, revision 1.1.1.1

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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