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Re: [Qemu-devel] Byte ordering of VM Generation ID in Windows VMs

From: Richard W.M. Jones
Subject: Re: [Qemu-devel] Byte ordering of VM Generation ID in Windows VMs
Date: Mon, 9 Jul 2018 08:36:47 +0100
User-agent: Mutt/1.5.21 (2010-09-15)

On Thu, Jul 05, 2018 at 03:11:32PM +0100, Richard W.M. Jones wrote:
> VMware represents these internally as two signed 64 bit integers, eg:
>   vm.genid = "-570734802784577186"
>   vm.genidx = "-5042519231342505152"
> I am still trying to get verification, but I believe the first is the
> low 64 bit word and the second is the high 64 bit word.

I have now been able to verify how this works using a real VMware
hypervisor (thanks to help from Ming Xie).  For the record, here is
how it maps, since I could not find any documentation about this.

VMX file contains:

  vm.genid = "7344585841658099715"
  vm.genidX = "-8483171368186442967"

Those numbers are signed 64 bit integers written in hex as:

  vm.genid = 65 ED 35 E8 E2 64 F8 03
  vm.genidX = 8A 45 B8 96 1E 7B 8B 29

In the guest the VMGENID.EXE program prints (with my spaces added for

  VmCounterValue: 65 ED 35 E8 E2 64 F8 03 : 8A 45 B8 96 1E 7B 8B 29

So this confirms my original guess.  Note that VMware is not doing any
endianness adjustment, but then VMware only works on LE hardware.


Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
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