Re: [Xen-devel] Debugging Xen early boot

["Zytaruk, Kelly" <Kelly.Zytaruk@xxxxxxx>]

> -----Original Message-----
> From: Xen-devel [mailto:xen-devel-bounces@xxxxxxxxxxxxx] On Behalf Of Jan
> Beulich
> Sent: Friday, May 06, 2016 8:54 AM
> To: Zytaruk, Kelly
> Cc: xen-devel@xxxxxxxxxxxxx
> Subject: Re: [Xen-devel] Debugging Xen early boot
> 
> >>> On 06.05.16 at 14:31, <Kelly.Zytaruk@xxxxxxx> wrote:
> > As for the other question I am still curious as to how to debug early Xen.
> > How was __start_xen written and tested, what sort of tools were used
> > to debug it and get it working right?
> 
> I don't know how it was done here, but having been through the exercise of
> debugging early boot code in other environments, I can only say: Get creative.
> E.g. leverage whatever storage you have that persists across at least a warm
> reboot. Depending on system I have found e.g. video RAM or some of the I/O
> ports in the 0x80-0x8f range usable. I also recall that on one specific box I 
> had to
> resort to using some of the CMOS non-volatile RAM or even the RTC registers
> that don't change rapidly.

Ouch! Sounds painful.  Looks like I had better hope that everything works fine 
up until the end of the init of the 16550s :(

> 
> >  What do I do in situations where I absolutely can't get serial
> > working properly?
> 
> Get serial working properly ;-) ? Or try USB (EHCI). Or use text mode video
> output.
> 
> Jan
> 
> 
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