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

[Ioi Lam]

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