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

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Message-ID: <88a1f7e9-596b-1973-a122-b90ef5a36af4@pobox.com>
Date:   Tue, 31 Mar 2020 19:53:45 -0500
From:   Daniel Santos <daniel.santos@...ox.com>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Vegard Nossum <vegard.nossum@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org,
        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 3/31/20 5:36 PM, Nathan Chancellor wrote:
> On Tue, Mar 31, 2020 at 05:25:38PM -0500, Daniel Santos wrote:
>>
>> This will break builds using gcc 4.2 and earlier and the expectation was
>> that you don't put two of them on the same line -- not helpful in macros
>> where it all must be on the same line.  Is gcc 4.2 still supported?  If
>> so, I recommend using another macro for the unique number that uses
>> __COUNTER__ if available and __LINE__ otherwise.  This was the decision
>> for using __LINE__ when I wrote the original anyway.
>>
>> Also note that this construct:
>>
>> BUILD_BUG_ON_MSG(0, "I like chicken"); BUILD_BUG_ON_MSG(1, "I don't like
>> chicken");
>>
>> will incorrectly claim that I like chicken.  This is because of how
>> __attribute__((error)) works -- gcc will use the first declaration to
>> define the error message.
>>
>> I couple of years ago, I almost wrote a gcc extension to get rid of this
>> whole mess and just __builtin_const_assert(cond, msg).  Maybe I'll
>> finish that this year.
>>
>> Daniel
> No, GCC 4.6 is the minimum required version and it is highly likely that
> the minimum version of GCC will be raised to 4.8 soon:
>
> https://lore.kernel.org/lkml/20200123153341.19947-10-will@kernel.org/
> https://git.kernel.org/peterz/queue/c/0e75b883b400ac4b1dafafe3cbd2e0a39b714232
>
> Cheers,
> Nathan

Thank you Nathan.  In that case this is definitely what we want now.

Reviewed-by: Daniel Santos <daniel.santos@...ox.com>

Cheers,
Daniel