using utrace for instruction tracing

[Dave Nomura]

I notice that the utrace documentation says that single-stepping is only 
supported if ARCH_HAS_SINGLE_STEP/ARCH_HAS_BLOCK_STEP is supported.  My 
googling found a note you sent the says it is supported on ia64 and ppc, 
but not on x86 yet.  Any idea if there are any work underway to support 
this on x86?

Frank: Is this a unacceptable, or can we live with no user instruction 
tracing on x86 until support is added?  I'm not very familiar with how 
PI ITRACE does single step tracing on x86, for kernel/user code tracing 
but I know it is significantly different than the PPC.