linux-kernel - Re: [PATCH] gcc4: Disable __compiletime_object

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Date:	Wed, 13 Nov 2013 10:39:13 -0800
From:	Kees Cook <keescook@...omium.org>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] gcc4: Disable __compiletime_object_size for GCC 4.6+

Hi Guenter,

On Fri, Apr 12, 2013 at 07:49:08PM -0700, Guenter Roeck wrote:
> __builtin_object_size is known to be broken on gcc 4.6+.
> See http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48880 for details.
> 
> This causes unnecssary build warnings and errors such as
> 
> In function 'copy_from_user', inlined from 'sb16_copy_from_user'
> 	at sound/oss/sb_audio.c:878:22:
> arch/x86/include/asm/uaccess_32.h:211:26: error: call to 'copy_from_user_overflow'
> 	declared with attribute error: copy_from_user() buffer size is not provably correct
> make[3]: [sound/oss/sb_audio.o] Error 1 (ignored)
> 
> Disable it where broken.

Is there an alternative? This means that things like
DEBUG_STRICT_USER_COPY_CHECKS are being rendered useless. I don't think
this is _always_ broken, just under certain situations, right?

-Kees

> 
> Signed-off-by: Guenter Roeck <linux@...ck-us.net>
> ---
>  include/linux/compiler-gcc4.h |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/compiler-gcc4.h b/include/linux/compiler-gcc4.h
> index 68b162d..842de22 100644
> --- a/include/linux/compiler-gcc4.h
> +++ b/include/linux/compiler-gcc4.h
> @@ -13,7 +13,7 @@
>  #define __must_check 		__attribute__((warn_unused_result))
>  #define __compiler_offsetof(a,b) __builtin_offsetof(a,b)
>  
> -#if GCC_VERSION >= 40100
> +#if GCC_VERSION >= 40100 && GCC_VERSION < 40600
>  # define __compiletime_object_size(obj) __builtin_object_size(obj, 0)
>  #endif
>  
> -- 
> 1.7.9.7
> 
> --
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-- 
Kees Cook
Chrome OS Security
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