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Date: Fri, 24 Nov 2000 07:47:53 +0000
From: Pavel Machek <pavel@suse.cz>
To: Tigran Aivazian <tigran@veritas.com>
Cc: John Alvord <jalvo@mbay.net>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] removal of "static foo = 0"
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Hi!

> Sorry, John, I _have_ to [give good example to others]. The above says
> that _you_ my dear friend, do not know where the BSS clearing code is. It
> is not in setup.S. It is not even in the same directory, where setup.S is.
> It is in arch/i386/kernel/head.S, starting from line 120:
> 
> /*
>  * Clear BSS first so that there are no surprises...
>  */
>         xorl %eax,%eax
>         movl $ SYMBOL_NAME(__bss_start),%edi
>         movl $ SYMBOL_NAME(_end),%ecx
>         subl %edi,%ecx
>         cld
>         rep
>         stosb
> 
> ... speaking of which (putting asbesto on and hiding from Andries ;) can't
> we optimize this code to move words at a time and not bytes.... ;)

There's better way: put bss clearing code at beggining of .C code and
do it with memset. [x86-64 does it this way.] It is both more obvious
[no assembly] and faster [memset is optimized].
								Pavel

-- 
Philips Velo 1: 1"x4"x8", 300gram, 60, 12MB, 40bogomips, linux, mutt,
details at http://atrey.karlin.mff.cuni.cz/~pavel/velo/index.html.

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