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Date: Sat, 21 Feb 2004 20:43:13 +0800
From: Coywolf Qi Hunt <coywolf@greatcn.org>
Organization: GreatCN.org & The Summit Open Source Develoment Group
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To: "H. Peter Anvin" <hpa@zytor.com>
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Subject: Re: BOOT_CS
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H. Peter Anvin wrote:
> Anyone happen to know of any legitimate reason not to reload %cs in
> head.S?  I think the following would be a lot cleaner, as well as a
> lot safer (the jump and indirect branch aren't guaranteed to have the
> proper effects, although technically neither should be required due to
> the %cr0 write):
> 
> @@ -117,10 +147,7 @@
>         movl %cr0,%eax
>         orl $0x80000000,%eax
>         movl %eax,%cr0          /* ..and set paging (PG) bit */
> -       jmp 1f                  /* flush the prefetch-queue */
> -1:
> -       movl $1f,%eax
> -       jmp *%eax               /* make sure eip is relocated */
> +       ljmp $__BOOT_CS,$1f     /* Clear prefetch and normalize %eip
> */
>  1:
>         /* Set up the stack pointer */
>         lss stack_start,%esp
> 
> 
> I've been doing some cleanups in head.S after making the early page
> tables dynamic.
> 
> 	-hpa
> -

IMHO, why bother to re-reload %cs again?

In setup.S, %cs is reloaded already. The enable paging code maps the
address identically, so %cs already contains the proper selector.


Coywolf


-- 
Coywolf Qi Hunt
Admin of http://GreatCN.org and http://LoveCN.org