Segfault in `OopDesc::size()` for generational plans for DaCapo Chopin `f480064`

[k-sareen]

I was running performance analyses for the MMTk GCs and noticed the generational plans segfaulted somewhere in copy(). GenImmix always segfaults for luindex while GenCopy always segfaults for jython.

Running the luindex benchmark with GenImmix under rr tells me that the klass variable here [1] is a nullptr, hence the SIGSEGV. I haven't looked too deeply into it yet.

Commands Used

luindex

MMTK_PLAN=GenImmix ./build/linux-x86_64-normal-server-fastdebug/jdk/bin/java -XX:MetaspaceSize=500M -XX:+DisableExplicitGC -server -XX:-TieredCompilation -Xcomp -XX:+UseThirdPartyHeap -Dprobes=RustMMTk -Djava.library.path=/home/kunals/git/evaluation/probes -Xms58M -Xmx58M -cp /usr/share/benchmarks/dacapo/dacapo-evaluation-git-f480064.jar:/home/kunals/git/evaluation/probes:/home/kunals/git/evaluation/probes/probes.jar Harness -c probe.DacapoChopinCallback -n 5 luindex

jython

MMTK_PLAN=GenCopy ./build/linux-x86_64-normal-server-release/jdk/bin/java -XX:MetaspaceSize=500M -XX:+DisableExplicitGC -server -XX:-TieredCompilation -Xcomp -XX:+UseThirdPartyHeap -Dprobes=RustMMTk -Djava.library.path=/home/kunals/git/evaluation/probes -Xms174M -Xmx174M -cp /usr/share/benchmarks/dacapo/dacapo-evaluation-git-f480064.jar:/home/kunals/git/evaluation/probes:/home/kunals/git/evalutation/probes/probes.jar Harness -c probe.DacapoChopinCallback -n 5 jython

Versions Used

mmtk-core revision: mmtk/mmtk-core@3dbdd7a
mmtk-openjdk revision: e6c9b94
openjdk revision: https://github.com/mmtk/openjdk/tree/jdk-11.0.15+8-mmtk
DaCapo Chopin revision: f480064

[1]: https://github.com/mmtk/mmtk-openjdk/blob/master/mmtk/src/abi.rs#L336

[k-sareen]

I believe this is the same issue as above: mmtk/mmtk-core#553

[k-sareen]

Closed with #216