linux-kernel - Re: [PATCH v2 02/36] x86/uaccess: __chk_range_not

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Message-ID: <20151007105934.GB5046@nazgul.tnic>
Date:	Wed, 7 Oct 2015 12:59:34 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Andy Lutomirski <luto@...nel.org>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	Brian Gerst <brgerst@...il.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2 02/36] x86/uaccess: __chk_range_not_ok is unlikely to
 return true

On Mon, Oct 05, 2015 at 05:47:50PM -0700, Andy Lutomirski wrote:
> This should improve code quality a bit.  It also shrinks the kernel
> text.
> 
> Before:
>    text	   data	    bss	    dec	    hex	filename
> 21828379	5194760	1277952	28301091	1afd723 vmlinux
>    text	   data	    bss	    dec	    hex	filename
> 21827997	5194760	1277952	28300709	1afd5a5	vmlinux
> 
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> ---
>  arch/x86/include/asm/uaccess.h | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
> index 3e911c68876e..09b1b0ab94b7 100644
> --- a/arch/x86/include/asm/uaccess.h
> +++ b/arch/x86/include/asm/uaccess.h
> @@ -51,13 +51,13 @@ static inline bool __chk_range_not_ok(unsigned long addr, unsigned long size, un
>  	 * limit, not add it to the address).
>  	 */
>  	if (__builtin_constant_p(size))
> -		return addr > limit - size;
> +		return unlikely(addr > limit - size);
>  
>  	/* Arbitrary sizes? Be careful about overflow */
>  	addr += size;
> -	if (addr < size)
> +	if (unlikely(addr < size))
>  		return true;
> -	return addr > limit;
> +	return unlikely(addr > limit);

It certainly uglifies it though. Are the wins worth the (un-)readability
hit?

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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