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Bug ID: 6868051 (SA) FreeChunk support for compressed oops is broken
6868051 : (SA) FreeChunk support for compressed oops is broken

Details
Type:
Bug
Submit Date:
2009-08-03
Status:
Closed
Updated Date:
2010-04-02
Project Name:
JDK
Resolved Date:
2010-01-15
Component:
hotspot
OS:
solaris_9
Sub-Component:
svc
CPU:
sparc
Priority:
P3
Resolution:
Fixed
Affected Versions:
hs16
Fixed Versions:
hs16

Related Reports
Backport:
JDK-2182205 - (SA) FreeChunk support for compressed oops is broken
Backport:
JDK-2181949 - (SA) FreeChunk support for compressed oops is broken

Sub Tasks

Description
The code for parsing FreeChunks when compressed oops is enabled is broken.  It's got the wrong level of indirection so it will always throw an exception.

Error: sun.jvm.hotspot.debugger.UnalignedAddressException: Trying to read at address: 0x0000000000000001 with alignment: 8
sun.jvm.hotspot.debugger.UnalignedAddressException: Trying to read at address: 0x0000000000000001 with alignment: 8   
        at sun.jvm.hotspot.debugger.DebuggerUtilities.checkAlignment(DebuggerUtilities.java:57)
        at sun.jvm.hotspot.debugger.proc.ProcDebuggerLocal.readCInteger(ProcDebuggerLocal.java:316)
        at sun.jvm.hotspot.debugger.proc.ProcAddress.getCIntegerAt(ProcAddress.java:68)
        at sun.jvm.hotspot.types.basic.BasicField.getCInteger(BasicField.java:162)
        at sun.jvm.hotspot.types.basic.BasicCIntegerField.getValue(BasicCIntegerField.java:54)
        at sun.jvm.hotspot.oops.Mark.value(Mark.java:138)
        at sun.jvm.hotspot.oops.Mark.isUnlocked(Mark.java:172)
        at sun.jvm.hotspot.oops.Mark.isCmsFreeChunk(Mark.java:306)
        at sun.jvm.hotspot.memory.FreeChunk.isFree(FreeChunk.java:87)
        at sun.jvm.hotspot.memory.FreeChunk.indicatesFreeChunk(FreeChunk.java:81)
        at sun.jvm.hotspot.memory.CompactibleFreeListSpace.getLiveRegions(CompactibleFreeListSpace.java:192)
        at sun.jvm.hotspot.oops.ObjectHeap$LiveRegionsCollector.doSpace(ObjectHeap.java:554)
        at sun.jvm.hotspot.memory.ConcurrentMarkSweepGeneration.spaceIterate(ConcurrentMarkSweepGeneration.java:66)   
        at sun.jvm.hotspot.oops.ObjectHeap.collectLiveRegions(ObjectHeap.java:579)
        at sun.jvm.hotspot.oops.ObjectHeap.iterateRaw(ObjectHeap.java:284)
        at sun.jvm.hotspot.CommandProcessor$26.doit(CommandProcessor.java:897)
        at sun.jvm.hotspot.CommandProcessor.executeCommand(CommandProcessor.java:1265)
        at sun.jvm.hotspot.CommandProcessor.executeCommand(CommandProcessor.java:1235)
        at sun.jvm.hotspot.CommandProcessor.run(CommandProcessor.java:1138)
        at sun.jvm.hotspot.CLHSDB.run(CLHSDB.java:91)
        at sun.jvm.hotspot.CLHSDB.main(CLHSDB.java:35)

Comments
EVALUATION

http://hg.openjdk.java.net/jdk7/hotspot-gc/hotspot/rev/ef671fb22f73
2009-08-10 
EVALUATION

http://hg.openjdk.java.net/jdk7/hotspot-comp/hotspot/rev/ef671fb22f73
2009-08-06 
SUGGESTED FIX

diff --git a/agent/src/share/classes/sun/jvm/hotspot/memory/FreeChunk.java b/agent/src/share/classes/sun/jvm/hotspot/memory/FreeChunk.java
--- a/agent/src/share/classes/sun/jvm/hotspot/memory/FreeChunk.java
+++ b/agent/src/share/classes/sun/jvm/hotspot/memory/FreeChunk.java
@@ -63,7 +63,7 @@ public class FreeChunk extends VMObject 
 
    public long size() {
       if (VM.getVM().isCompressedOopsEnabled()) {
-        Mark mark = new Mark(sizeField.getValue(addr));
+        Mark mark = new Mark(addr.addOffsetTo(sizeField.getOffset()));
         return mark.getSize();
       } else {
         Address size = sizeField.getValue(addr);
@@ -83,7 +83,7 @@ public class FreeChunk extends VMObject 
 
    public boolean isFree() {
       if (VM.getVM().isCompressedOopsEnabled()) {
-        Mark mark = new Mark(sizeField.getValue(addr));
+        Mark mark = new Mark(addr.addOffsetTo(sizeField.getOffset()));
         return mark.isCmsFreeChunk();
       } else {
         Address prev = prevField.getValue(addr);
2009-08-03 
EVALUATION

it's loading the value instead of passing the address to Mark where it will actually be loaded.
2009-08-03


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