linux-kernel - Re: [git pull] "big box" x86 changes, boot protocol

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Date:	Sat, 26 Apr 2008 16:37:43 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, Yinghai Lu <yinghai.lu@....com>,
	Yinghai Lu <yhlu.kernel@...il.com>, jbarnes@...tuousgeek.org
Subject: Re: [git pull] "big box" x86 changes, boot protocol

Andrew Morton wrote:
>> +	memcpy(&early_res[i], &early_res[i + 1],
>> +	       (j - 1 - i) * sizeof(struct early_res));
>>     
>
> nit: memcpy() shouldn't be used for overlapping copies.  It happens to be
> OK (for dst<src) in the kernel implementations.  We hope.
>   

Definitely shouldn't be assumed.  At one point in the distant past I had 
a ppc memcpy which would clobber a destination cacheline before reading 
the source, so source and dest within a cacheline's distance would be 
trouble, regardless of the direction.  Arch-specific code which knows 
about the arch-specific details of memcpy might be safer, I guess, but 
its still fairly brittle.

    J
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