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Re: [Qemu-devel] Re: Suggestion - trap window-close of VM

From: Struan Bartlett
Subject: Re: [Qemu-devel] Re: Suggestion - trap window-close of VM
Date: Wed, 30 Mar 2005 15:26:34 +0200
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.3) Gecko/20041007 Debian/1.7.3-5

Lennert Buytenhek wrote:
On Wed, Mar 30, 2005 at 02:20:36PM +0200, Struan Bartlett wrote:
It subtracts one from the EIP (to find the address of 
the previously-executed instruction) and examines the virtual memory 
location pointed to. If the memory location contains 0xF4 (HLT) then it 
examines the EFLAGS register. If the IF (Interrupt-enable) flag is 
cleared, then one might in fact assume that Windows 2000 is sitting 
there just waiting for you to turn it off. The assumption here is that 
if interrupts are disabled then there is no way the processor's halt 
state can be interrupted.

What happens if the previous instruction is a multi-byte instruction
that happens to have 0xf4 as its last byte?
Before I did the IF check, that was a problem but now it should be ok. In your scenario, the IF flag would probably be found still to be set so it would be (correctly) assumed that Windows 2000 was not waiting to be turned off and qemu would continue normally.


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