Re: Question about TCG backend correctness

[Richard Henderson]

On 10/18/22 19:22, Alex Bennée wrote:
> I'm not wedded to the idea - but it could be a super simple processor
> with a lot less extra baggage than a full ISA - purely for throwing TCG
> ops at rather than decoding any machine code.

I'd be surprised if you don't wind up with a similar amount of code as for a full ISA, and 
a lot more baggage on the side besides.  But feel free to prove me wrong...

OTOH, if we really did split out a libtcg, disconnected from any target and parameterized, 
that would make the sort of non-ISA unit testing you're thinking about vastly easier, 
because you'd be able to write a driver program that isn't "qemu", without all of the 
target baggage that would currently make this infeasible.

And, very most likely, such a parameterized libtcg will be required for full heterogeneous 
emulation...

> Can we detect optimisation failures with guest tests?

No, and that's where some sort of specific harness might be helpful.

> Is it worth doing anything to lower the barrier of entry for these small
> micro tests or is the current check-tcg framework enough?

I think the current check-tcg framework probably sufficient.
Generally I think

int main()
{
   asm("test");
   assert(result);
   return 0;
}

is what these micro tests should be aiming for.


r~