[OpenBIOS] ppc64 MMU issues

[Andreas Färber]

Am 09.11.2010 um 22:48 schrieb Alexander Graf:

> On 09.11.2010, at 22:34, Andreas Färber wrote:
>
>> 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.
>
> I still don't see why. We can just use a ppc32 compiled version for  
> working ppc64 support, no? The only reason I put us back to 32bit  
> mode was because otherwise lis -1 would end up being -1 instead of  
> 0xffff0000 :).
>
> So why don't you just keep the current code working, duplicate it  
> for the time being for ppc64 and then once everything works merge it  
> back together?

Pretty sure I mentioned that alternative already... :)

http://repo.or.cz/w/openbios/afaerber.git/blobdiff/97003b1ff3860847ce9ad5c6ba13d3860ceb5509..6ef21780f74d36e1d80d745c331a6d4f8d84a610:/arch/ppc/qemu/start.S

Tried to avoid that for SVN. But if that's consensus, it sure is the  
easiest for me!

Andreas