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Use of r31 on the powerpc/booke:mpc85xx architecture

In sys/arch/powerpc/booke/booke_pmap.c:pmap_copy_page() The r31 register is 
used. When compiling for DDB support with "-fno-omit-frame-pointer" the 
compiler complains about the use of register 31. I am new to this architecture 
but it seems that register is used as the frame pointer.

If you modify the inline assembly to use r23-r30 instead of r24-r31 it seems to 
solve the problem, but I wanted to ask if this is the right way to change this 
particular code as I am new to this architecture and don't want to introduce 
any unpredictable side effects when making the change locally.

It also seems that DDB support may not be functioning yet on the powerpc/booke 
architecture. Is this the known state of things with this port? I am using a 
P2020RDB-like system and using the P2020RDB config file which references the 
board code in mpc85xx. While the system otherwise works to some extent: I can 
boot and use user-space tools when not using DDB. However when I compile with 
DDB support I get a trap fairly early in the kernel initialization process and 
then my watchdog reboots the system from out of under me.

Warm Regards,

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