linux-kernel - Re: Inflation of vmlinux by linker on x86

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Message-ID: <48DD40EF.4000107@zytor.com>
Date:	Fri, 26 Sep 2008 13:07:11 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Joris van Rantwijk <jorispubl@...all.nl>
CC:	linux-kernel@...r.kernel.org
Subject: Re: Inflation of vmlinux by linker on x86_64

Joris van Rantwijk wrote:
> 
> On 26 sep 2008, at 20:52, H. Peter Anvin wrote:
>> Instead of adding a comment like this, we should simply rename it 
>> memmove().
> 
> Yes. I tried, but it clashed with an existing memmove declaration in 
> asm-x86/string_32.h.
> 
> What is the accepted solution for this?
> Redefining memmove should be allowed, but then it could no longer be a 
> static function.
> Using the memmove implementation from the main kernel would be painful 
> and ugly.
> We could also define "__memmove()" plus "#define memmove __memmove", 
> which would also be ugly.
> 
>> Furthermore, we probably spend enough time copying that using a real 
>> memmove() implementation, using string instructions, would be good.
> 
> Are string instructions that much faster?
> We can also get some speedup by copying ints instead of chars.
> 

String instructions are indeed very much faster, especially on recent 
hardware where they are optimized in microcode.

In this case, I think the easiest thing to do is to provide an optimized 
memmove and not making it a static function.  I have a reasonably 
optimized memmove in 32-bit assembly at:

http://git.kernel.org/?p=boot/syslinux/syslinux.git;a=blob;f=com32/lib/memmove.S;hb=HEAD

A 64-bit implementation can be done on similar principles.

	-hpa

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