x86: emulate lea with two register operands correctly

An lea instruction with two register operands should raise an
undefined instruction exception.

Skype does such a instruction and will crash when starting if it does
not get the exception.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: Keir Fraser <keir@xen.org>
Committed-by: Keir Fraser <keir@xen.org>
xen-unstable changeset: 24456:03781de56c31
xen-unstable date: Thu Jan 05 15:47:16 2012 +0000

     1.1 --- a/xen/arch/x86/x86_emulate/x86_emulate.c	Tue Jan 17 11:31:28 2012 +0000
     1.2 +++ b/xen/arch/x86/x86_emulate/x86_emulate.c	Tue Jan 17 11:32:04 2012 +0000
     1.3 @@ -2056,6 +2056,7 @@ x86_emulate(
     1.4      }
     1.5  
     1.6      case 0x8d: /* lea */
     1.7 +        generate_exception_if(ea.type != OP_MEM, EXC_UD, -1);
     1.8          dst.val = ea.mem.off;
     1.9          break;
    1.10