linux-kernel - Re: [ 16/85] use clamp

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Date:	Sun, 28 Oct 2012 01:04:45 +0800
From:	Fengguang Wu <fengguang.wu@...el.com>
To:	Ben Hutchings <ben@...adent.org.uk>
Cc:	Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org, alan@...rguk.ukuu.org.uk,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [ 16/85] use clamp_t in UNAME26 fix

On Sat, Oct 27, 2012 at 05:11:58PM +0100, Ben Hutchings wrote:
> On Thu, 2012-10-25 at 17:05 -0700, Greg Kroah-Hartman wrote:
> > 3.6-stable review patch.  If anyone has any objections, please let me know.
> > 
> > ------------------
> > 
> > From: Kees Cook <keescook@...omium.org>
> > 
> > commit 31fd84b95eb211d5db460a1dda85e004800a7b52 upstream.
> > 
> > The min/max call needed to have explicit types on some architectures
> > (e.g. mn10300). Use clamp_t instead to avoid the warning:
> > 
> >   kernel/sys.c: In function 'override_release':
> >   kernel/sys.c:1287:10: warning: comparison of distinct pointer types lacks a cast [enabled by default]
> 
> While this change makes the code more readable, I think the bug is
> really in the type definitions for those architectures:
> 
> [...]
> > -		copy = min(sizeof(buf), max_t(size_t, 1, len));
> > +		copy = clamp_t(size_t, len, 1, sizeof(buf));
> [...]
> 
> 1. sizeof(buf) yields a value of type size_t, by definition.
> 2. max_t(size_t, 1, len) yields a value of type size_t.
> 3. Therefore min(sizeof(buf), max_t(size_t, 1, len)) is valid.
> 
> The only way I see to get this warning is to define size_t wrongly, so
> that (1) is not true.

Agreed. mn10300 and cris seem to have problems with size_t.
Here is a related issue: 

Re: [next:akpm 155/157] drivers/char/random.c:827:3: warning: format '%zd' expects argument of type 'signed size_t', but argument 7 has type 'size_t'
https://lkml.org/lkml/2012/10/23/792

Thanks,
Fengguang
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