linux-kernel - Re: [PATCH 25/39] merge common parts of uaccess.

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Date:	Mon, 30 Jun 2008 16:00:40 -0300
From:	Glauber Costa <gcosta@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	linux-kernel@...r.kernel.org, tglx@...utronix.de, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 25/39] merge common parts of uaccess.

Ingo Molnar wrote:
> * Glauber Costa <gcosta@...hat.com> wrote:
> 
>> Ingo Molnar wrote:
>>> * Glauber Costa <gcosta@...hat.com> wrote:
>>>
>>>> common parts of uaccess_32.h and uaccess_64.h
>>>> are put in uaccess.h.
>>> -tip testing found that it causes this build failure:
>>>
>>>   fs/binfmt_aout.c: Assembler messages:
>>>   fs/binfmt_aout.c:152: Error: suffix or operands invalid for `cmp'
>>>
>>> with:
>>>
>>>   http://redhat.com/~mingo/misc/config-Mon_Jun_30_08_17_42_CEST_2008.bad
>>>
>>> and comparing the 32-bit and unified version is not simple and the  
>>> commit is rather large.
>>>
>>> I'm sure the fix is simple, but this bug shows a structural problem 
>>> with this unification patch. The proper way to unify files is to first 
>>> bring both the 32-bit and the 64-bit version up to a unified form via  
>>> finegrained changes, so that uaccess_32.h and uaccess_64.h becomes  
>>> exactly the same file.
>>>
>>> ... _then_ only, in a final 'mechanic unification' step the two files  
>>> are merged into uaccess.h. (but no change is done to the content)
>>>
>>> If anything breaks during such a series it's bisectable to a 
>>> finegrained patch on either the 32-bit or the 64-bit side. If this 
>>> commit was shaped that way i could now report to you the exact 
>>> bisection result - instead of this too-broad bisection result.
>>>
>>> So please rework this commit in that fashion (not just to fix this  
>>> breakage but in anticipation of future commits) - uaccess.h is central  
>>> enough for us to be super careful about it.
>>>
>>> 	Ingo
>> Fair.
>>
>> However, as I wrote in the first patch of the series, I'm not doing a  
>> complete unification of uaccess.h. Part of it is left for future work,  
>> since it's a little bit trickier.
>>
>> So I didn't have the option of a mechanical move. I did tried, however,  
>> to make sure this patch was only a code move, with everything that is  
>> going to the common file being equal in both files.
>>
>> Needless to say, I failed. ;-) This was for a very tiny piece, but still...
>>
>> The options I see are:
>>
>> * to redo the uaccess.h unification this way, making sure a diff 
>> between the diffs of the arch-files report nothing different, or: * to 
>> remove the topmost patches that touches uaccess*.h, and leave only the 
>> ones that integrate the .c and .S files, until I can really integrate 
>> the whole of it.
>>
>> For the second, however, although I was careful to make incremental 
>> changes, some small differences may exist. Examples of these 
>> differences are places in which I introduce a few ifdefs. It's close 
>> to nothing, but still not mechanical. Because of that, you might want 
>> me to redo the whole series.
>>
>> Your call.
> 
> well the primary worry is the build failure with gcc 4.3.1 that i've 
> posted. If that's simple to fix we could re-try with your existing 
> series.
> 
> But to be defensive it's alway useful to move one component at a time. 
> Even if you dont end up doing a mechanical unification - the stuff you 
> move you should be able to claim to be exactly identical. I.e. the final 
> step can be mechanic in that it unifies exactly the same content (even 
> though both files still have remaining bits).
> 
> Then we'll end up with nice bisection reports to the specific area that 
> is impacted by a problem.
> 
> 	Ingo
I already have a fix for that. But I'll repost it in a way in which I 
can claim the (part of the) files to be identical. For now, can you trim 
the tree at that point? I think it's the best option.

As for bisection, note that I did everything with bisection in mind, so 
I do know the importance of it. It's more a failure than a fundamental 
mistake.

Thanks.
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