Bug in FieldsAllocationStyle=2 logic

[Vladimir Kozlov]

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.net alias 
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
> 
> 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
> 
> 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
> line 3290
> 
> Regards,
> Kris Mok