linux-kernel - Re: [Q] x86

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Date:	Sat, 23 Feb 2008 10:18:17 +0100
From:	Sam Ravnborg <sam@...nborg.org>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	Yinghai Lu <yhlu.kernel@...il.com>, Ingo Molnar <mingo@...e.hu>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [Q] x86 - boot/header.S

On Sat, Feb 23, 2008 at 12:07:39PM +0300, Cyrill Gorcunov wrote:
> [Yinghai Lu - Sat, Feb 23, 2008 at 12:44:49AM -0800]
> | On Sat, Feb 23, 2008 at 12:20 AM, Cyrill Gorcunov <gorcunov@...il.com> wrote:
> | > Hi Peter, Sam,
> | >
> | >  could you take a look on x86/boot/header.S:280 please?
> | >
> | >  # Zero the bss
> | >         movw    $__bss_start, %di
> | >         movw    $_end+3, %cx
> | >         xorl    %eax, %eax
> | >         subw    %di, %cx
> | >         shrw    $2, %cx
> | >         rep; stosl
> | >
> | >  I wonder why is $_end there instead of $__bss_stop?
> | >  Well, accroding to vmlinux_32.lsd both _end and __bss_stop
> | >  are the same BUT __bss_stop is more convenient methink.
> | >  Would it be usefull to change?
> | 
> | we should have head32.c like head64.c
> | and x86_32_start_kernel.
> | 
> | Eric's patch long time ago...
> | 
> | YH
> | 
> 
> Hi Yinghai,
> 
> thanks for reply BUT that is not the point (or maybe I miss something).
> 
> Look, we only have head64.c - there is no head32.c at all. Both
> vmlinux_32/64.lds defines _end exactly the same as __bss_stop. So in
> code which DO fillup bss section with zeros the prefered name is
> __bss_stop. The only thing I'm trying to say that it would be clean
> naming scheme and I think it would help for further review - instead
> of searching all over x86 files to find _end definition __bss_stop
> tell us WHAT we are zeroing from the code.

We should introduce head32.c and then we can use the exact same function
as 64 bit does:

/* Don't add a printk in there. printk relies on the PDA which is not initialized
   yet. */
static void __init clear_bss(void)
{
        memset(__bss_start, 0,
               (unsigned long) __bss_stop - (unsigned long) __bss_start);
}

This answers your Q.

I already resubmitted Eric's original patch to introduce head32.c as I also
liked the cleanup in two Makefiles.

	Sam
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