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Date: Wed, 11 Nov 2020 16:39:33 +1000
From: Nicholas Piggin <npiggin@gmail.com>
Subject: Re: [PATCH 03/18] powerpc: bad_page_fault, do_break get registers
 from regs
To: Christophe Leroy <christophe.leroy@csgroup.eu>,
 linuxppc-dev@lists.ozlabs.org
References: <20201105143431.1874789-1-npiggin@gmail.com>
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Excerpts from Nicholas Piggin's message of November 11, 2020 2:46 pm:
> Excerpts from Christophe Leroy's message of November 10, 2020 9:19 pm:
>>=20
>>=20
>> Le 10/11/2020 =C3=A0 09:34, Nicholas Piggin a =C3=A9crit=C2=A0:
>>> Excerpts from Christophe Leroy's message of November 6, 2020 6:14 pm:
>>>>
>>>>
>>>> Le 05/11/2020 =C3=A0 15:34, Nicholas Piggin a =C3=A9crit=C2=A0:
>>>>> This also moves the 32s DABR match to C.
>>>>
>>>> Is there a real benefit doing this ?
>>>=20
>>> Oh I missed doing it, but yes I think bad_page_fault and do_break shoul=
d
>>> probably be implemented with the DEFINE_INTERRUT_HANDLER wrappers.
>>>=20
>>=20
>> Yes, anyway, do we need to do that change ? Can't the dispatch between d=
o_break() and page fault=20
>> handling remain in handle_page_fault() ? What's the benefit of going int=
o do_page_fault() and coming=20
>> back ?
>=20
> You might be right, I'll take another look at it.

For 32-bit, we need to come back to save NV GPRs. Certainly the 64s code=20
stays in do_page_fault because it always saves them.

Now I don't think that's the nicest thing to go in and out of the=20
interrupt wrappers twice in these cases, but for a first pass I think=20
it's okay. Either we could add another type of error-case wrapper that
does some adjustment if it becomes necessary, or we find a nice way to
save NVGPRs from C code.

If we could somehow parse unwind data to find where the NVGPRs are saved=20
by the compiler and generate a little code stub to load them out, would
be the ultimate :) Maybe one day...

Thanks,
Nick