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

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Date:	Wed, 27 Nov 2013 15:36:11 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Jan Beulich <JBeulich@...e.com>
Cc:	mingo@...e.hu, tglx@...utronix.de,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	arjan@...ux.intel.com, linux@...ck-us.net,
	linux-kernel@...r.kernel.org, hpa@...or.com
Subject: Re: [PATCH] x86: override __compiletime_object_size()


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

> >>> On 27.11.13 at 15:03, Ingo Molnar <mingo@...nel.org> wrote:
> 
> > * 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.
> 
> That makes no sense to me - the benefits of this construct should 
> have been explained with its introduction; the change here just 
> makes it being used under wider range of compilers (and the code 
> comment already says exactly that).

Yes indeed - I should have read the referenced changelog...

Thanks, will apply it as-is, if there are no objections from others.

Thanks,

	Ingo
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