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

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Message-ID: <20151007162323.GB8738@gmail.com>
Date:	Wed, 7 Oct 2015 18:23:23 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Andy Lutomirski <luto@...nel.org>, 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


* Borislav Petkov <bp@...en8.de> wrote:

> 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?

Well, adding likely/unlikely hints in headers is OK I think, especially since 
these are performance sensitive user-access routines.

Thanks,

	Ingo
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