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

1.1       root        1: /*     exception.c     1.1     86/07/20        */
                      2: 
                      3: #include "../tahoealign/align.h" 
                      4: 
                      5: /*
                      6:  * Signal an exception. It will be handled by 'locore.s'. Here, I:
                      7:  *     1) Put the exception code where it belongs on the stack.
                      8:  *     2) Restore pc and sp to show that the current opcode
                      9:  *             'was not executed'.
                     10:  *     3) Execute one big non-local-goto. In the process we take care
                     11:  *             to reset the current HW fp such that 'alignment' will
                     12:  *             indeed return to 'locore.s'.
                     13:  *             IMPORTANT NOTE : the process I use will NOT restore
                     14:  *             all registers (like normal returns) so the call to the
                     15:  *             handling routine HAS TO BE the last thing in 'alignment'.
                     16:  *             Otherwise, all its own register variables will be a mess !!
                     17:  *             I also know that 'alignment' itself WILL restore all
                     18:  *             registers for 'locore.s' since its entry mask is all-1.
                     19:  */
                     20: exception(infop, type, param1, param2)
                     21: process_info *infop;
                     22: int    type, param1, param2;
                     23: {
                     24:        register long *my_fp;
                     25:        register long *current_fp, *prev_fp;
                     26: 
                     27:        my_fp = (long *)&infop-1 ;
                     28:        infop->ret_exception = type;
                     29:        switch (type) {
                     30:        case ARITHMETIC:
                     31:                infop->ret_code = param1;
                     32:                break;
                     33:        case ILL_ACCESS:
                     34:                infop->ret_addr = param1;
                     35:                infop->ret_code = param2;
                     36:                break;
                     37:        case ALIGNMENT:
                     38:        case ILL_ADDRMOD:
                     39:        case ILL_OPRND:
                     40:                break;
                     41:        default :
                     42:                printf ("Bad exception type %d (alignment code)\n", type);
                     43:                break;
                     44:        }
                     45: /*
                     46:  * Now the big trick. Look up the stack until the frame of
                     47:  * 'alignment' is found. prev_fp will point to it and current_fp
                     48:  * will then point to the frame of whoever 'alignment' called.
                     49:  * This should better work ...
                     50:  */
                     51:        prev_fp = my_fp;
                     52:        while (prev_fp != &fp) {
                     53:                current_fp = prev_fp;
                     54:                prev_fp = (long *) *prev_fp;
                     55:        }
                     56: /*
                     57:  * Found it. Now fool the HW into thinking that 'alignment' called
                     58:  * us directly here, so this routine's 'return' will go back
                     59:  * all the way to 'alignment', stopping any further emulation
                     60:  * for the current offending opcode.
                     61:  *  "fool the HW..." ha ha, am I realy fooling myself ?
                     62:  */
                     63:        *my_fp = *current_fp;
                     64:        *(my_fp - 2) = *(current_fp -2);        /* Alter program counter */
                     65: /*
                     66:  * Without further ado, just go back now !!!!
                     67:  */
                     68: }
                     69: 
                     70: not_needed (infop)
                     71: process_info *infop;
                     72: {
                     73: /*
                     74:  * Shouldn't ever come to this routine.
                     75:  */
                     76: 
                     77:        printf ("Opcode 0x%x should not trap to alignment code.",
                     78:                opCODE);
                     79:        printf (" OS or machine problem!! \n");
                     80: }
                     81: 
                     82: 
                     83: cannot_do (infop)
                     84: process_info *infop;
                     85: {
                     86: /*
                     87:  * Some opcode-caused alignments cannot be emulated. See table.c for
                     88:  * specific reasons. Reflect this back to the process as alignment
                     89:  * exception.
                     90:  */
                     91:        exception (infop, ALIGNMENT);
                     92: }

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