Re: [Qemu-devel] Reverse execution and deterministic replay

[Pavel Dovgaluk]

> On 27 June 2014 11:35, Pavel Dovgaluk <address@hidden> wrote:
> > The major disadvantage of icount is that it's updated only on TB boundaries.
> > When one instruction in the middle of the block uses virtual clock, it could
> > have different values for different divisions of the code to TB.
> 
> This is only true if the instruction is incorrectly not
> marked as being "I/O". The idea behind icount is that in
> general we update it on TB boundaries (it's much faster
> than doing it once per insn) but for those places which
> do turn out to need an exact icount we then retranslate
> the block to get the instruction-to-icount-adjustment
> mapping.

I forgot about one more issue.
When qemu stops execution on the breakpoint, the icount
is decreased to the number of instructions in the block.
But in this case the last instruction is not executed and
should not affect the counter.

Pavel Dovgaluk