linux-kernel - Re: [PATCH] compiler.h: fix error in BUILD_BUG

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Date:   Tue, 31 Mar 2020 21:05:45 +0200
From:   Rasmus Villemoes <rasmus.villemoes@...vas.dk>
To:     Joe Perches <joe@...ches.com>,
        Vegard Nossum <vegard.nossum@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-kernel@...r.kernel.org,
        Daniel Santos <daniel.santos@...ox.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Ian Abbott <abbotti@....co.uk>
Subject: Re: [PATCH] compiler.h: fix error in BUILD_BUG_ON() reporting

On 31/03/2020 21.00, Joe Perches wrote:
> On Tue, 2020-03-31 at 20:56 +0200, Rasmus Villemoes wrote:
>> On 31/03/2020 20.20, Joe Perches wrote:
>>> On Tue, 2020-03-31 at 13:26 +0200, Vegard Nossum wrote:
>>>>  #define compiletime_assert(condition, msg) \
>>>> -	_compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
>>>> +	_compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
>>>
>>> This might be better using something like __LINE__ ## _ ## __COUNTER__
>>>
>>> as line # is somewhat useful to identify the specific assert in a file.
>>>
>>
>> Eh, if the assert fires, doesn't the compiler's diagnostics already
>> contain all kinds of location information?
> 
> I presume if that were enough,
> neither __LINE__ nor __COUNTER__
> would be useful.

Not only useful, necessary: They are used to create a unique identifier.
Which turns out to not be unique when one uses __LINE__, causing the
problem Vegard saw and fixes.

Rasmus