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Re: Use of r31 on the powerpc/booke:mpc85xx architecture
On Sep 6, 2012, at 5:11 PM, Scislowicz, Adam wrote:
> 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.
Uh, why are you using that option? It's not really needed on powerpc.
> 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.
Except that won't produce correct code since stmw/lwm will always save/restore
> 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.
DDB works fine for me. What does it printout about the trap?
Are you still using -fno-omit-frame-pointer?
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