[OpenBIOS] ppc64 MMU issues

[Andreas Färber]

Am 09.11.2010 um 21:24 schrieb Alexander Graf:

> On 09.11.2010, at 21:01, Andreas Färber wrote:
>
>> Am 09.11.2010 um 12:53 schrieb Alexander Graf:
>>
>>> On 08.11.2010, at 23:18, Andreas Färber wrote:
>>>
>>>> Am 08.11.2010 um 23:03 schrieb Alexander Graf:
>>>>
>>>>> On 08.11.2010, at 22:48, Andreas Färber wrote:
>>>>>
>>>>>> Am 08.11.2010 um 10:34 schrieb Mark Cave-Ayland:
>>>>>>
>>>>>>> Andreas Färber wrote:
>>>>>>>
>>>>>>>> Since r945 everything except for the trampoline issue should  
>>>>>>>> be in SVN.
>>>>>>>
>>>>>>> Cool! :)
>>>>>>
>>>>>> Ah, no! Forgot about the exception handlers (preamble,  
>>>>>> epilogue). :( I have local patches that #ifdef the whole  
>>>>>> definitions and provide alternative ones for ppc64. But I'd  
>>>>>> rather supply a 2-step patch to drop the template macros and  
>>>>>> use #ifdef'ery inside the macro definition for ppc64/ppc  
>>>>>> differences, given that long-term we won't need the second  
>>>>>> version.
>>>>>
>>>>> Are you sure you need that? Most of the stuff should be generic.  
>>>>> Please take a look at Linux's PPC_LL macro for example. The  
>>>>> stack layout varies slightly, but that should also be reasonably  
>>>>> easy to catch.
>>>>
>>>> Problematic parts are the ULONG_SIZE comparisons for the number  
>>>> of registers that we can't #ifdef away inside an CPP macro
>>>
>>> You're talking about this piece of code, right?
>>>
>>> .ifc ULONG_SIZE, 8 ; \
>>>      addi    r1,r1,-(40 * ULONG_SIZE) ;      /* push exception  
>>> frame */ \
>>> .else ; \
>>>      addi    r1,r1,-(20 * ULONG_SIZE) ;      /* push exception  
>>> frame */ \
>>> .endif ; \
>>> \
>>>
>>>
>>> Just replace it with
>>>
>>> // PPC32
>>>
>>> #define EXCEPTION_STACK_LEN (20 * 4)
>>>
>>> // PPC64
>>>
>>> #define EXCEPTION_STACK_LEN (40 * 8)
>>>
>>> // code
>>>
>>> addi  r1, r1,-EXCEPTION_STACK_LEN
>>
>> No, no, no! This is exactly the type of differences I wanted to rip  
>> out, but if I do so now I would break ppc64 support.
>> On __powerpc64__ this doesn't need to be 40, and it's not just the  
>> above immediate but the whole .ifc around the 20 additional  
>> register stores/loads:
>>
>> #define EXCEPTION_PREAMBLE_TEMPLATE \
>> 	...
>> 	stl	r11,(11 * ULONG_SIZE)(r1) ; \
>> 	stl	r12,(12 * ULONG_SIZE)(r1) ; \
>> .ifc ULONG_SIZE, 8 ; \
>> 	stl	r13,(17 * ULONG_SIZE)(r1) ; \
>> 	stl	r14,(18 * ULONG_SIZE)(r1) ; \
>> 	...
>>
>> .macro EXCEPTION_PREAMBLE
>> 	EXCEPTION_PREAMBLE_TEMPLATE
>> .endm
>> ...
>> .macro EXCEPTION_PREAMBLE_64
>> 	EXCEPTION_PREAMBLE_TEMPLATE
>> .endm
>>
>> My problem is the reuse of the _TEMPLATE macros. It becomes a  
>> matter of macros such as those you suggest if we can get rid of that.
>
> Why are there two different preambles? Just always use the 64-bit  
> one for 64-bit openBIOS and 32-bit one for 32-bit openBIOS.

Quoting myself: "I would break ppc64 support"

obj-ppc64/openbios-qemu.elf:
EXCEPTION_PREAMBLE => optionally used for qemu-system-ppc64, not yet  
working

obj-ppc/openbios-qemu.elf:
EXCEPTION_PREAMBLE => used for qemu-system-ppc
EXCEPTION_PREAMBLE_64 => currently used for qemu-system-ppc64 by  
patching the exception vectors based on PVR-determined CPU init function

Thus, if we drop the latter before ppc64 is up and running we would no  
longer have a working openbios-ppc for qemu-system-ppc64.

Andreas