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[Xen-devel] RE: follow-up to guest debug support patches

To: "Kip Macy" <kip.macy@xxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxxx>, "Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx>, <Ian.Pratt@xxxxxxxxxxxx>, "Christian Limpach" <Christian.Limpach@xxxxxxxxxxxx>
Subject: [Xen-devel] RE: follow-up to guest debug support patches
From: "Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>
Date: Sat, 12 Mar 2005 16:02:19 -0000
Cc: <ian.pratt@xxxxxxxxxxxx>
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Thread-topic: follow-up to guest debug support patches
Here's a compendium of collectd comments on the patch. Shouldn't take
long to either address them or explain them.


It should at some point be extended to allow multiple exec_domains
like gdb supports multiple threads in a single process.

It seems to be missing a way to undo the foreign mappings on exit?

The memcpy copying the user_ctxt is now after if gets used (addtl.
VMX checks)  Looks like he wasn't too careful when forward
porting -- scary :-(  Maybe the VMX check should just look at the
context passed in.

Not sure why he's skipping setting DONEFPUINIT, kernel mode and clearing
IOPL bits though.

Doesn't the change in traps.c break in-guest debugger support?  It seems
to always pause the domain if it is in kernel, an in-guest debugger
which has set a breakpoint in the kernel will never get the int3.  I
this needs some kind of flag to enable/disable this behaviour.

adresses point2 above

Now same concern applies to do_debug as for int3

I think the order in arch_final_setup_guest should be:

- check cs/ss in passed in cpu_ctxt (before doing anything)
- update DONEFPUINIT and TF_kernel_mode flags
- copy user_ctxt
- copy fpu ctxt
- clear iopl
- exit if updating (EDF_DONEINIT)

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