linux-kernel - Re: [PATCH] x86: override __compiletime_object

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Date:	Wed, 27 Nov 2013 15:03:32 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Jan Beulich <JBeulich@...e.com>
Cc:	mingo@...e.hu, tglx@...utronix.de, hpa@...or.com,
	arjan@...ux.intel.com, linux@...ck-us.net,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] x86: override __compiletime_object_size()


* Jan Beulich <JBeulich@...e.com> wrote:

> As discussed in the context of commits 3df7b41a ("x86: Unify
> copy_from_user() size checking") and 7a3d9b0f ("x86: Unify
> copy_to_user() and add size checking to it"), we want to leverage
> __builtin_object_size() also on newer gcc versions, but with other
> architectures still using another model of copy_*_user() verification
> we can't replace the global definition. Do it in the (only) header
> needing the construct for now.
> 
> Signed-off-by: Jan Beulich <jbeulich@...e.com>
> Cc: Arjan van de Ven <arjan@...ux.intel.com>
> Cc: Guenter Roeck <linux@...ck-us.net>
> ---
>  arch/x86/include/asm/uaccess.h |    6 ++++++
>  1 file changed, 6 insertions(+)
> 
> --- 3.13-rc1/arch/x86/include/asm/uaccess.h
> +++ 3.13-rc1-x86-compiletime-object-size/arch/x86/include/asm/uaccess.h
> @@ -584,6 +584,12 @@ __copy_from_user_overflow(int size, unsi
>  
>  #endif
>  
> +/* linux/compiler-gcc4.h restricts this to gcc < 4.6, which doesn't suit us. */
> +#if defined(__GNUC__) && GCC_VERSION >= 40100
> +# undef __compiletime_object_size
> +# define __compiletime_object_size(obj) __builtin_object_size(obj, 0)
> +#endif
> +

Would be nice to have a more verbose changelog that explains what 
benefits this brings us.

Thanks,

	Ingo
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