Re: [Q] x86 - boot/header.S

Sam Ravnborg
2008-02-23T09:18:22Z

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@gmail.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