Re: what are the requirements on target/ code for -icount to work correctly?

[Paolo Bonzini]

On 19/06/20 07:46, Pavel Dovgalyuk wrote:
> I think, that we need some efforts from target maintainers to remove all such 
> calls. 

I'll take care of target/i386 (which does need one of the three
gen_io_end calls that are left).

>> Q2: is it a requirement that after an insn which is a "known
>> to be an I/O insn" one (like x86 in/out) and which is marked
>> up with gen_io_start()/gen_io_end() that we also end the TB?
> 
> It is a requirement for instructions that access virtual clock/icount
> value (directly or not).
> 
> There is also an assertion that can_do_io is enabled while generating an
> interrupt. I believe, that it doesn't affect RR, but is useful for
> deterministic icount mode.

As I understand it, the definition of "I/O insn" is anything that can
either:

- affect the icount deadline (e.g. by setting or removing a
QEMU_CLOCK_VIRTUAL timer)

- interrupt the current translation block with cpu_loop_exit,
cpu_restore_state or similar.

Paolo