linux-kernel - Re: BUILD_BUG_ON() breaks sparse gfp

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Message-ID: <1302817191.16562.1036.camel@nimitz>
Date:	Thu, 14 Apr 2011 14:39:51 -0700
From:	Dave Hansen <dave@...1.net>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Jan Beulich <JBeulich@...ell.com>,
	Christoph Lameter <cl@...ux.com>,
	linux-mm <linux-mm@...ck.org>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: BUILD_BUG_ON() breaks sparse gfp_t checks

On Thu, 2011-04-14 at 13:22 -0700, Andrew Morton wrote:
> The kernel calls gfp_zone() with a constant arg in very few places. 
> This?
> 
> --- a/include/linux/gfp.h~a
> +++ a/include/linux/gfp.h
> @@ -249,14 +249,9 @@ static inline enum zone_type gfp_zone(gf
>  
>         z = (GFP_ZONE_TABLE >> (bit * ZONES_SHIFT)) &
>                                          ((1 << ZONES_SHIFT) - 1);
> -
> -       if (__builtin_constant_p(bit))
> -               BUILD_BUG_ON((GFP_ZONE_BAD >> bit) & 1);
> -       else {
>  #ifdef CONFIG_DEBUG_VM
> -               BUG_ON((GFP_ZONE_BAD >> bit) & 1);
> +       BUG_ON((GFP_ZONE_BAD >> bit) & 1);
>  #endif
> -       }
>         return z;
>  } 

That definitely makes sparse happier.  I hope the folks on cc will chime
in if they wanted something special at build time.

-- Dave

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