Re: [Xen-devel] [PATCH] xen/x86: Zero out .bss for PV guests

[Boris Ostrovsky]

On 02/24/2016 11:22 AM, Luis R. Rodriguez wrote:
> On Wed, Feb 24, 2016 at 6:58 AM, David Vrabel <david.vrabel@xxxxxxxxxx> wrote:
> > Yes.  Can you respin with a commit message explaining?  (Or just provide
> > the message here and I'll fix it up).
> Is there no way to re-use somehow the clear_bss() from bare metal?

xen_start_info lives in .bss and it is initialized in startup assembly code.

We could move it to .data but I'd still want to do this first thing in 
startup_xen(). We may add more code there later that touches something 
in .bss and with delayed section clearing we may blow away that data.

-boris

> This uses a section range:
>
> /* 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);
> }
>
> Perhaps the section range might be different for PV guests? Or can
> this simply not work even if one added a guest bss section size, or
> would it be too late for PV guests, ie we need to do it in asm on PV
> guests as you did? If so why.
>
>   Luis