linux-kernel - Re: [PATCH] fix BUILD_BUG_ON() and a couple of bogus uses of it

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Message-Id: <20090917171810.f675c8f2.akpm@linux-foundation.org>
Date:	Thu, 17 Sep 2009 17:18:10 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	davem@...emloft.net, JBeulich@...ell.com,
	linux-kernel@...r.kernel.org, sparclinux@...r.kernel.org
Subject: Re: [PATCH] fix BUILD_BUG_ON() and a couple of bogus uses of it

On Thu, 17 Sep 2009 17:15:04 -0700
Andrew Morton <akpm@...ux-foundation.org> wrote:

> There's a shortcoming in the current BUILD_BUG_ON() - it silently does
> nothing if passed a non-constant arg.
> 
> I suspect that in the 2.6.31 code, that BUILD_BUG_ON() just does
> nothing at all, and that Jan's patch is now exposing this.  It might be
> compiler-version dependent too.
> 
> 
> <tests it>
> 
> Yup, on base 2.6.31, this:
> 
> --- a/arch/sparc/kernel/vio.c~a
> +++ a/arch/sparc/kernel/vio.c
> @@ -23,6 +23,8 @@ static const struct vio_device_id *vio_m
>  	const char *type, *compat;
>  	int len;
>  
> +	vio_dring_avail(NULL, 33);
> +
>  	type = dev->type;
>  	compat = dev->compat;
>  	len = dev->compat_len;
> _
> 
> compiles without error with gcc-3.4.5.

And I can't immediately find a way to make any compile-time error occur here, with
or without Jan's patch.  hm.

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