linux-kernel - Re: Build failure with v4.9-rc1 and GCC trunk -- compiler weirdness

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Message-ID: <1485981241.2560.20.camel@perches.com>
Date:   Wed, 01 Feb 2017 12:34:01 -0800
From:   Joe Perches <joe@...ches.com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     Laura Abbott <labbott@...hat.com>,
        Will Deacon <will.deacon@....com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Markus Trippelsdorf <markus@...ppelsdorf.de>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>, james.greenhalgh@....com,
        Gregory Clement <gregory.clement@...e-electrons.com>,
        Stephen Boyd <sboyd@...eaurora.org>
Subject: Re: Build failure with v4.9-rc1 and GCC trunk -- compiler weirdness

On Wed, 2017-02-01 at 19:53 +0000, Ard Biesheuvel wrote:
> On 1 February 2017 at 19:49, Joe Perches <joe@...ches.com> wrote:
[]
> > Or maybe add a BUILD_BUG_ON something like:
> > 
> > #define order_base_2(n)                                                 \
> > ({                                                                      \
> >         typeof(n) _n = n;                                               \
> >         BUILD_BUG_ON(__builtin_constant_p(_n) && _n < 0);               \
> >         __builtin_constant_p(_n) ? (_n < 2 ? _n : ilog2((_n) - 1) + 1)) \
> >                                  : __order_base_2(_n);                  \
> > })
> > 
> 
> This would interfere with the ability to use order_base_2() in
> initializers for global variables.

There aren't any as far as I can tell and would using
order_base_2() for a global initializer make sense?