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)
Posted Date : 2009-08-03 23:19:40.0

N/A

it's loading the value instead of passing the address to Mark where it will actually be loaded.
Posted Date : 2009-08-03 23:19:40.0

http://hg.openjdk.java.net/jdk7/hotspot-comp/hotspot/rev/ef671fb22f73
Posted Date : 2009-08-06 23:13:46.0

http://hg.openjdk.java.net/jdk7/hotspot-gc/hotspot/rev/ef671fb22f73
Posted Date : 2009-08-10 07:38:17.0