Re: [Qemu-devel] Register usage statistics?

[Benjamin Ylvisaker]

On Fri, 26 Aug 2011 19:35 +0200, "Lluís" <address@hidden> wrote:
> Benjamin Ylvisaker writes:
> 
> > I am working on a project for which I'd like to gather statistics
> > about register usage.  (For example, distributions of degree-of-use
> > and dynamic lifetimes of register-values.)  Is QEMU a good tool for
> > doing this kind of work?  Has anyone else done this?  I looked at the
> > tracing available in QEMU and it seems to be mostly for higher level
> > things like memory accesses, function calls, basic block executions,
> > etc. 
> 
> This is not currently possible.
> 
> In fact, I've been developing (somewhat in the background) the kind of
> features you're asking for, but it will still be at least a couple of
> months before it's in a publishable state.
> 
> Meanwhile, there are some tools you can use to accomplish this
> (depending on your requirements), like valgrind or pintool.

By "not currently possible" do you mean the current tracing facilities
don't support register/instruction granularity, or that there's
something in the QEMU architecture itself that would require substantial
changes to gather such information?  I am willing to put in a fair bit
of hacking effort.  I only have a cursory understanding of the internals
of QEMU, but shouldn't it be possible to hack the instruction
translations to do some extra work?

I had been under the impression that QEMU was more likely to do what I
want than Valgrind or Pin.  I thought those tools were a bit higher
level and had no intention of giving instruction-granularity control of
the guest program.  I will take another look, though.

Thanks,
Ben