[11] RFR(S) 8207069: [AOT] we should check that VM uses the same GC as one used for AOT library generation.

[Vladimir Kozlov]

On 7/18/18 6:15 AM, Christian Thalinger wrote:
> 
> 
>> On Jul 18, 2018, at 12:14 AM, Vladimir Kozlov 
>> <vladimir.kozlov at oracle.com <mailto:vladimir.kozlov at oracle.com>> wrote:
>>
>> On 7/17/18 5:17 PM, Christian Thalinger wrote:
>>>> On Jul 12, 2018, at 5:28 PM, Vladimir Kozlov 
>>>> <vladimir.kozlov at oracle.com <mailto:vladimir.kozlov at oracle.com>> wrote:
>>>>
>>>> Including GC group since I added new method to GCConfig.
>>>>
>>>> http://cr.openjdk.java.net/~kvn/8207069/webrev.00/ 
>>>> <http://cr.openjdk.java.net/%7Ekvn/8207069/webrev.00/>
>>>> https://bugs.openjdk.java.net/browse/JDK-8207069
>>>>
>>>> Recent Graal's changes [1] added list of GC [2] which matches 
>>>> Hotspot GC list [3].
>>>> I used that to fix this issue by storing enum value from Graal in 
>>>> AOT config header and compare it with selected GC when AOT library 
>>>> is loaded into Hotspot.
>>> The fix is correct but too strict.  For example, Serial and Parallel 
>>> GC can use the same AOT library.  CMS too.
>>
>> Do you have other suggestions how to check compatibility?
> 
> I think the best way would be to use BarrierSet::Name:
> 
> // Do something for each concrete barrier set part of the build.
> #define FOR_EACH_CONCRETE_BARRIER_SET_DO(f)          \
>    f(CardTableBarrierSet)                             \
>    EPSILONGC_ONLY(f(EpsilonBarrierSet))               \
>    G1GC_ONLY(f(G1BarrierSet))                         \
>    ZGC_ONLY(f(ZBarrierSet))

Thank you, Chris, for suggestion.

To record barrier set in AOT library would require a lot more complex 
changes (JVMCI) not suitable for JDK 11.  Currently Graal checks only GC 
flags. To get information about barrier set it needs to access Hotspot's 
data.

The only simple way to relax the check is to get BarrierSet::Name value 
based on CollectedHeap::Name and compare them in aot library config 
check code. But I can't find a functionality in GC code to do that. I 
asked GC group.

Note, we never intended to support mixed GCs with the same type of 
barriers. It was accidental and I am not comfortable to support such 
"feature".

Vladimir

> 
>>
>> Thanks,
>> Vladimir
>>
>>>>
>>>> I verified the fix with all GCs combination when compiling AOT lib 
>>>> and using it. I also ran our hs-tier1-3 testing which includes AOT 
>>>> and Graal tests.
>>>>
>>>> These changes are for JDK 11 so I don't need to go through Graal PR 
>>>> now but I would need to do that for JDK 12 to make changes in AOT code.
>>>>
>>>> Thanks,
>>>> Vladimir
>>>>
>>>> [1] https://bugs.openjdk.java.net/browse/JDK-8205824
>>>>  "[GR-10514] Use whitelist for GCs supported by Graal"
>>>> [2] 
>>>> http://hg.openjdk.java.net/jdk/jdk11/file/bf686c47c109/src/jdk.internal.vm.compiler/share/classes/org.graalvm.compiler.hotspot/src/org/graalvm/compiler/hotspot/HotSpotGraalRuntime.java#l137
>>>> [3] 
>>>> http://hg.openjdk.java.net/jdk/jdk11/file/bf686c47c109/src/hotspot/share/gc/shared/collectedHeap.hpp#l173
>