Re: [Xen-devel] Trap flags, debug and emulation - xen 4.1.1

[Tim Deegan <tim@xxxxxxx>]

Hi, 

At 08:39 +0530 on 11 Oct (1318322368), Balbir Singh wrote:
>  I am doing something very similar. I do get the fault and I can set
>  the trap, but I don't see any form of single stepping take place as I
>  do not get the TRAP_debug exception back. My exception_bitmap has
>  TRAP_no_device, TRAP_page_fault, TRAP_debug and TRAP_int3 set.
> 
>  I've tried debugging the issue with xentrace and printks, but sadly I
>  could not track down the issue. The CPU does have
>  cpu_has_monitor_trap_flag set to true.
> 
>  Could anyone give me clues on how to track down why I did not get a
>  TRAP_debug exception via a VMEXIT?

It sounds like you're doing the right thing - just a question of looking
for the bug. :)  I would try checking for the TF flag as close as
possible to the vmenter (maybe even in the assembly - you could call out
to a special C function if it's set), and for the debug vmexit right at the
top of the vmexit handler to make sure that some other clever debugging
code isn't consuming it.   Probably also worth double-chjecking that
nothing else ois overwriting the exception bitmap before the vmenter. 

Cheers,

Tim.

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