Re: [Qemu-devel] [PATCH] monitor: Add port write command

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

Paul Brook wrote:
>>> I'd be reluctant to expose the savevm state to the user.
>>>
>>> For debugging qemu I don't see it providing any real benefit over firing
>>> up GDB and poking directly at the device directly.
>> Not all environments where you need to debug things have gdb, qemu
>> sources or even non striped qemu binary.
> 
> If you don't have qemu sources than I really don't care. By definition you're 
> not going to be able to do anything useful even if you do figure out what the 
> problem is.  Note that there's no requirement that you run gdb on the target 
> itself. Remote debug (e.g. via gdbserver on linux) is a well established 
> technique.
> 
> Likewise for debugging stripped production binaries, my answer is "don't do 
> that". There are very rare cases where a bug goes away on a debug build, but 
> in those cases any instrumentation you add is also liable to make the bug go 
> away.

Again, having to debug qemu itself when all you want is some additional
information about the emulated hardware state while debugging a guest
seems like overkill to me. Imagine you are attached to qemu's gdbstub
and stopped the guest that has some issue using, say, the apic. And now
imagine you could simply issue e.g.

(gdb) monitor devstate apic.1
apicbase=...
tpr=...
icr={..., ... }
lvt={..., ... }
...

That would provide you a nice picture of the virtual hardware state
without the need to fire up and operate a second gdb just to obtain this
data. And manipulating some lvt register would only be a trivial
additional monitor command away.

Jan

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