linux-kernel - Re: [PATCH] x86: sparse errors from string

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Date:	Fri, 01 Feb 2008 16:40:15 -0800
From:	Harvey Harrison <harvey.harrison@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: sparse errors from string_32.h

On Fri, 2008-02-01 at 10:06 -0800, H. Peter Anvin wrote:
> Ingo Molnar wrote:
> > * Harvey Harrison <harvey.harrison@...il.com> wrote:
> > 
> >>  		case 1:
> >> -			*(unsigned char *)s = pattern;
> >> +			*(unsigned char *)s = pattern & 0xff;
> > 
> > i've applied your fix - but wouldnt it be cleaner to just cast the 
> > pattern variable to unsigned char instead?
> > 
> 
> Even better, since we're talking about fixed bytes, I suggest writing it as:
> 
> 	*(u8 *)s = (u8)pattern;
> 
> Much more compact and the intent is a little bit more obvious.
> 

While I agree that is cleaner, that will still produce sparse warnings
about a cast truncating bits from a constant value.  I think that
explicit & is necessary (unless the cure is worse than the disease).

Harvey

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