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List: openjdk-hotspot-runtime-dev
Subject: Bug in FieldsAllocationStyle=2 logic
From: rednaxelafx () gmail ! com (Krystal Mok)
Date: 2011-06-22 16:27:01
Message-ID: BANLkTi=pUG-urFkPUEh_14rcC226aKSycA () mail ! gmail ! com
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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
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