Bug in FieldsAllocationStyle=2 logic

[Krystal Mok]

Thank you very much for the quick response ^_^

PS: if possible, please, report problems to hotspot-dev at openjdk.java.net alias
> so all Hotspot developers can see it. I did original changes but I am in
> Compiler (JIT) group.

Got it. I thought this issue belonged to the runtime group, that's why I
sent it there the first place.

Regards,
Kris Mok

On Thu, Jun 23, 2011 at 1:38 AM, Vladimir Kozlov <vladimir.kozlov at oracle.com
> wrote:

> Thank you for such detail analysis and suggested fix.
> I filed bug and I will fix it in 7u2.
>
> 7058036: FieldsAllocationStyle=2 does not work in 32-bit VM
>
> Thanks,
> Vladimir
>
> PS: if possible, please, report problems to hotspot-dev at openjdk.java.netalias so all Hotspot developers can see it. I did original changes but I am
> in Compiler (JIT) group.
>
>
> Krystal Mok wrote:
>
>> Hi all,
>>
>> I think I've found a bug in ClassFileParser::**parseClassFile() that
>> deals with FieldsAllocationStyle=2, which was introduced about a year ago:
>> http://hg.openjdk.java.net/**jdk6/jdk6/hotspot/rev/**b9d85fcdf743<http://hg.openjdk.java.net/jdk6/jdk6/hotspot/rev/b9d85fcdf743>
>>
>> int map_size = super_klass->nonstatic_oop_**map_size();
>> OopMapBlock* first_map = super_klass->start_of_**nonstatic_oop_maps();
>> OopMapBlock* last_map = first_map + map_size - 1;
>>
>> This code accidentally works on LP64 systems because it takes 1 word per
>> OopMapBlock, so nonstatic_oop_map_size() and nonstatic_oop_map_count() would
>> actually return the same value.
>>
>> But on 32-bit systems, an OopMapBlock takes 2 words, which makes
>> nonstatic_oop_map_size() == nonstatic_oop_map_count() * 2, and breaks the
>> code above.
>>
>> The code should really be:
>>
>> int map_count = super_klass->nonstatic_oop_**map_count();
>> OopMapBlock* first_map = super_klass->start_of_**nonstatic_oop_maps();
>> OopMapBlock* last_map = first_map + map_count - 1;
>>
>> I found this because FieldsAllocationStyle=2 doesn't work for me on 32-bit
>> Windows (JDK6u25 and 6u26), but works on 64-bit Ubuntu JDK6u25. Here's a min
>> repro of my test: https://gist.github.com/**1037866<https://gist.github.com/1037866>
>>
>> Could anybody please verify this?
>> Just checked the current tip of hsx/hotspot-rt, and it still has this
>> behavior:
>> http://hg.openjdk.java.net/**hsx/hotspot-rt/hotspot/file/**
>> 1744e37e032b/src/share/vm/**classfile/classFileParser.cpp<http://hg.openjdk.java.net/hsx/hotspot-rt/hotspot/file/1744e37e032b/src/share/vm/classfile/classFileParser.cpp>
>> line 3290
>>
>> Regards,
>> Kris Mok
>>
>
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