Mismatched ciMethodData in replay file.

[Vladimir Kozlov]

Narrowed to hotspot-compiler list.

You are right that it is weird. The dump is done from ciMethodData which is local (for compiler thread) clone of MDO 
which should not be updated during compilation. Unless there is a place we still go into VM for get some numbers.

One explanation is that during dump we hit safepoint and we lost part of output.

I think we need a verification mode for replay dump to catch such case (separate count to catch such mismatch).

Thanks,
Vladimir K

On 5/18/22 11:14 PM, Liu, Xin wrote:
> hi,
> 
> I get a weird replay, which was generated by 17.0.3+6-LTS. I don't see
> relevant code have changed since then, so I think it is still applicable
> to the tip of HotSpot.
> 
> A customer shared the replay file
> with(https://github.com/corretto/corretto-17/issues/57#issuecomment-1130042063)
> and I am trying to reproduce his failure. it is written from
> VMError::report_and_die().
> 
> One obstacle is that weird entries of ciMethodData. eg. line
> 14130, It declares that there will 2 non-null oops followed(see '2'
> after tag 'oops'. however, one only is recorded.
> 
> ciMethodData kotlin/coroutines/jvm/internal/ContinuationImpl <init>
> (Lkotlin/coroutines/Continuation;)V 2 21538 orig 80 0 0 0 0 0 0 0 0 0 0
> 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
> 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 data
> 26 0x40007 0x402 0x70 0x4e9c 0x70005 0x4d55 0x0 0x7f6a5841c3c0 0xa3
> 0x7f6a5841c470 0xa4 0xc0003 0x4e9c 0x18 0x110002 0x529e 0x0 0x0 0x0 0x0
> 0x0 0x0 0x9 0x2 0x6 0x0 oops 2 7
> com/example/ProductAttRouter$withRequestLoggingContext$1 methods 0
> 
> Another mismatched entry is at line 14203. it says there are 11
> oops but only 6 are there.
> 
> Those mismatched entries leave uninitialized elements of rec->_classes
> and eventually crash ciReplay::initialize(). Have you seen them before?
> I can patch up hotspot to handle this mismatch, but I wonder how that
> happens?
> 
> ciMethodData::dump_replay_data() iterates
> _data 2 rounds. The 1st round counts them and second round dumps them.
> https://github.com/openjdk/jdk/blob/master/src/hotspot/share/ci/ciMethodData.cpp#L728
> 
> Is that possible that the underlying data get updated on the fly? This
> case is kotlin coroutine. I am not
> sure whether it is same threading environment as classic Java.
> 
> thanks,
> --lx
>