On Mon, 9 Sep 2024 10:21:54 GMT, Thomas Schatzl <tscha...@openjdk.org> wrote:
>> Roman Kennke has updated the pull request incrementally with one additional >> commit since the last revision: >> >> Fix bit counts in GCForwarding > > src/hotspot/share/gc/shared/collectedHeap.cpp line 232: > >> 230: } >> 231: >> 232: // With compact headers, we can't safely access the class, due > > Suggestion: > > // With compact headers, we can't safely access the klass, due > > > This is the case why? Because we might not have copied the header yet? Is > this method actually ever used while the forwarded object is unstable? > Given this is used for verification only afaik, we should make an effort to > provide that check. With compact headers, we can't safely access the Klass* when the object has been forwarded, because non-full-GC-forwarding temporarily overwrites the mark-word, and thus the Klass*, with the forwarding pointer, and here we have no way to make a distinction between Full-GC and regular GC forwarding. I improved the code to make the check when the object is not forwarded. Not sure if we could/should do more (e.g. pass around is_full argument to make the distinction, or find the - possibly few - places where we might call is_oop() on from-space objects in regular GC and do the check in a forwardee-safe way?). ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/20677#discussion_r1751448814
