[11] RFR(M) 8201850: [AOT] vm crash when run test compiler/aot/fingerprint/SelfChangedCDS.java

Jiangli Zhou jiangli.zhou at oracle.com
Fri Apr 20 01:55:26 UTC 2018

Hi Vladimir,

Your changes look good.



> On Apr 19, 2018, at 3:17 PM, Vladimir Kozlov <vladimir.kozlov at oracle.com> wrote:
> Hi Ioi
> I changed test as you suggested. Now it triggers crash on big machines too:
> http://cr.openjdk.java.net/~kvn/8201850/webrev.01.diff/
> http://cr.openjdk.java.net/~kvn/8201850/webrev.01/
> I also tested that that AOT library will be unloaded if shift value is not set by AOTLoader::set_narrow_oop_shift() and it mismatch with AOTed value. We getn next message:
> Shared file ./libSelfChanged.so error: Universe::narrow_oop_shift has different value '3' from current '0'
> Test all AOT test on machine with small (8Gb) memory where crash was reproduced and on machine with big memory.
> Thanks,
> Vladimir
> On 4/19/18 12:46 PM, Ioi Lam wrote:
>> Hi Vladimir,
>> The changes look good.
>> I think (?) that the original failure happened only on machines with small amount of memory so default heap size is small. To ensure that this scenario is always tested, in SelfChangedCDS.java, maybe add a new test case that specifically uses a small heap during both dump time and run time, so CDS will use 0 shift?
>> Thanks
>> - Ioi
>> On 4/19/18 9:56 AM, Vladimir Kozlov wrote:
>>> http://cr.openjdk.java.net/~kvn/8201850/webrev.00/
>>> https://bugs.openjdk.java.net/browse/JDK-8201850
>>> The problem is AOT enforces not 0 compressed oop shift value (AOT uses logMinObjAlignment [1]) regardless heap size to cover more cases. CDS does not do that - if heap is small (as in this case) it will record 0 shift during dump.
>>> Later when CDS archive is loaded into VM with the same small heap it verifies that oop shift is still 0. And it is 0 at that time because Metaspace::global_initialize() which loads archive is called before AOTLoader::universe_init() which reset shift value.
>>> As result shared java objects (strings) in CDS archive are mapped into java heap with wrong (after AOT change shift value) compressed oops encoding. GC dies because of that.
>>> The propose fix is add new AOTLoader::set_narrow_oop_shift() method which is called in Universe::initialize_heap() before Metaspace::global_initialize(). AOTLoader::universe_init() is changed to only verify that shift value is consistent. I also added code to unload AOT library with non matching configs.
>>> Tested with small heap which reproduced the problem and full Mach5 testing.
>>> I want especially to thank Jiangli Zhou from runtime group who did initial investigation and found root cause of this problem. She also suggested and discussed with me several solutions.
>>> Regards,
>>> Vladimir
>>> [1] http://hg.openjdk.java.net/jdk/jdk/file/d5c43e9f08fb/src/jdk.internal.vm.compiler/share/classes/org.graalvm.compiler.hotspot/src/org/graalvm/compiler/hotspot/AOTGraalHotSpotVMConfig.java#l33 

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