Re: [Xen-users] Debugging DomU

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Ian,

On 26/05/2015 11:03, Ian Campbell wrote:
> On Tue, 2015-05-26 at 10:48 +0200, Julien Grall wrote:
> > > I can actually step reliably through the startup code with the JTAG
> > now. It looks like that instruction was from the
> > "putstr("Decompressing kernel...");" in
> > arch/arm/boot/compressed/misc.c.
> > > With that change, xenctx shows me a much more reasonable value for
> > PC and SVC_LR. Digging around then led me to disable CONFIG_DEBUG_LL,
> > because it seems that the problems I'm seeing relate to trying to
> > print something. With that, I think it's getting further still. Xenctx
> > now tells me that it ends up in __loop_delay(), with LR pointing to
> > panic(). I'm having problems reproducing this with the JTAG, though
> > (it seems to behave slightly differently when I'm using JTAG to debug
> > it), and I'm not seeing any output from DomU.
> >
> > I confirm the CONFIG_DEBUG_LL should be disabled in Xen guest because
> > it's not portable and not supported.
> So long as it is configured to use the same underlying device as Xen's
> console then it shouldn't result in crashes, I thought, due to the very
> simplistic uart stuff in xen/arch/arm/vuart.c.
For dom0 yes. But we are talking about domU here.

The UART emulated by vuart.c re-uses the hardware UART region. In domU, 
this region may clash with other part of the memory layout. Therefore 
it's not possible to use it.
Regards,

--
Julien Grall

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