Re: [Qemu-devel] Physical address debugging

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2011-08-26 16:21, Zeus Gómez Marmolejo wrote:
> Hi all,
> 
> I just want to do a very simple task. I'm using QEMU for debugging a new OS
> and I see that there is a memory region that is being updated by an unknown
> task. I don't know if it's another process or the kernel itself.
> 
> So I would like to put a physical memory watchpoint. I don't know how to do
> that. As the GDB stub is operating using virtual addressing, I cannot place
> a watchpoint on an address as it's not stopping.
> 
> To make it short, I want the equivalent of the Bochs command "watch write
> addr", which inserts a write watch point at physical address 'addr'. I
> haven't seen this is possible on the QEMU monitor...

Indeed, it isn't. It's impossible with KVM (due to lacking hardware
support) but would be feasible with TCG if you extend (or ad-hoc hack)
QEMU code accordingly.

The alternative is to trace the guest OS's page mapping and set watches
on all virtual addresses that refer to the physical one in question. But
I guess that is already part of what you want to debug...

Jan

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