Re: [Qemu-devel] Re: [4799] Add instruction counter.

[Paul Brook <paul@codesourcery.com>]

On Sunday 29 June 2008, Jan Kiszka wrote:
> Paul Brook wrote:
> >> On the first glance this function looked like it could serve as an
> >> alternative to SSTEP_INTERNAL and provide the required roll-back on
> >> watchpoint hit. But looking closer I realized that icount_decr is only
> >> maintained if use_icount is set.
> >
> > I'm fairly sure limiting the length of the TB and actual instruction
> > counting are largely independent. IIUC you only need the former.
>
> But to calculate the former, you need the latter again. 

Not really. You only need to know how far through the TB you got before the 
trap occurred.

> I wonder if it 
> wouldn't be more efficient and flexible to specify a terminating PC
> instead of an instruction count. Wouldn't that make cpu_io_recompile
> independent of icount_decr and, thus, use_icount?

Ah, I see what you're getting at.  cpu_restore_state modifies icount_decr to 
indicate how far through the TB we got.  That's can be independent of 
use_icount.

A terminating PC is much less useful. In general the only instruction you 
really know the location of is the one you're currently at.

Paul