On Thu May 23, 2024 at 8:46 AM AEST, Richard Henderson wrote: > On 5/21/24 21:04, Nicholas Piggin wrote: > > The crux of the problem being that dynamic exits from a TB would > > not count instructions previously executed in the TB. I don't > > know how important it is for PMU to count instructions exactly, > > however for instruction replay this can lead to different counts > > for the same execution (e.g., because TBs can be different sized) > > and that blows up reverse debugging. > > > > I posted something on this out before, but missed a few things > > (most notably faulting memory access). And found that forcing 1 > > insn per TB seems to be the only feasible way to do this. > > > > Sorry to ping you on this again Richard, it's not urgent but > > you're the guru with this stuff and I'm hesitant to change it > > without a better opinion ... Simple band aid for the meanwhile > > could be leave it as is but just disable counting if > > record/replay is in use. > > When we unwind, we know how many insns remain in the tb. > With icount, we adjust cpu->neg.icount_decr.u16.low. > > My suggestion is to change restore_state_to_opc to pass in either the raw > insns_left, or > the inverse: tb->icount - insns_left. > > That'll be a trivial mechanical change for the signature of the hook, first.
That gives me a better place to start looking. Thanks, Nick
