linux-kernel - Re: linux-next: tree build failure

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Message-ID: <25e057c00909290251h55c0dc25o4ab1f2e84c920dca@mail.gmail.com>
Date:	Tue, 29 Sep 2009 11:51:56 +0200
From:	roel kluin <roel.kluin@...il.com>
To:	Jan Beulich <jbeulich@...ell.com>
Cc:	sfr@...b.auug.org.au, hollisb@...ibm.com,
	akpm@...ux-foundation.org, linuxppc-dev@...ts.ozlabs.org,
	kvm-ppc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-next@...r.kernel.org
Subject: Re: linux-next: tree build failure

On Tue, Sep 29, 2009 at 11:28 AM, Jan Beulich <jbeulich@...ell.com> wrote:
>>>> Hollis Blanchard  09/29/09 2:00 AM >>>
>>First, I think there is a real bug here, and the code should read like
>>this (to match the comment):
>>    /* type has to be known at build time for optimization */
>>-    BUILD_BUG_ON(__builtin_constant_p(type));
>>+    BUILD_BUG_ON(!__builtin_constant_p(type));
>>
>>However, I get the same build error *both* ways, i.e.
>>__builtin_constant_p(type) evaluates to both 0 and 1? Either that, or
>>the new BUILD_BUG_ON() macro isn't working...
>
> No, at this point of the compilation process it's neither zero nor one,
> it's simply considered non-constant by the compiler at that stage
> (this builtin is used for optimization, not during parsing, and the
> error gets generated when the body of the function gets parsed,
> not when code gets generated from it).
>
> Jan

then maybe

if(__builtin_constant_p(type))
        BUILD_BUG_ON(1);

would work?

Roel
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