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

Vladimir Kozlov vladimir.kozlov at oracle.com
Thu Apr 19 16:56:33 UTC 2018


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.



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