suggestions on handling additional exception levels on ppc32

[Kumar Gala]

I'm looking at fixing an issue parts that have multiple exception  
levels (e300, 40x, booke).

One of the issues is the transfer_to_handler patch in entry_32.S  
doesn't use the proper save/restore registers to transfer to C code.

The following bit of code is what I'm having issues with:

         .globl transfer_to_handler_cont
transfer_to_handler_cont:
3:
         mflr    r9
         lwz     r11,0(r9)               /* virtual address of handler  
*/
         lwz     r9,4(r9)                /* where to go when done */
         mtspr   SPRN_SRR0,r11
         mtspr   SPRN_SRR1,r10
         mtlr    r9
         SYNC
         RFI                             /* jump to handler, enable  
MMU */

A few possibilities:
* introduce an additional function pointer as part of  
EXC_XFER_TEMPLATE() to specifies the type of handler (normal, crit,  
dbg, mcheck)
* use the traps field low order bits to determine normal, crit, dbg,  
mcheck at run time.
* duplicate the code paths for each exception level

suggestions?

- k