I hope you can check whether this is a ZGC-related bug.

Version: openjdk-23-ga

Git command: git clone --branch jdk-23-ga https://github.com/openjdk/jdk.git

In one run, I caused the VM to halt and the following message appeared:  

     #
     # A fatal error has been detected by the Java Runtime Environment:
     #
     #  SIGSEGV (0xb) at pc=0x00007c928eaf58da, pid=214039, tid=214049
     #
     # JRE version: OpenJDK Runtime Environment (23.0) (build 23-internal-adhoc.yifanzhang.jdk)
     # Java VM: OpenJDK 64-Bit Server VM (23-internal-adhoc.yifanzhang.jdk, interpreted mode, sharing, compressed class ptrs, z gc, linux-amd64)
     # Problematic frame:
     # V  [libjvm.so+0x10f58da]  ZRelocationSetSelectorGroup::semi_sort()+0x13a
     #
     # No core dump will be written. Core dumps have been disabled. To enable core dumping, try "ulimit -c unlimited" before starting Java again
     #
     # An error report file with more information is saved as:
     # /home/yifanzhang/Work/Bug-HotspotVM/testFile/JavaFile/Gjf_Case22/hs_err_pid214039.log
     #
     # If you would like to submit a bug report, please visit:
     #   https://bugreport.java.com/bugreport/crash.jsp
     #
     已中止

I looked into the VM source code and found that this appears to be an array out-of-bounds error.

Detailed problem description :

     In function `ZRelocationSetSelectorGroup::semi_sort()`  , an array partitions[npartitions] is allocated. Under the heap’s default settings, its size is 2048 (meaning indices 0 through 2047 are valid).

     However, the subsequent index used for access is determined by right-shifting each page’s live byte count, which may lead to accessing index 2048.

     Based on this, I made the following changes to the function `semi_sort()`,  add a conditional branch to print corresponding information when an out-of-bounds access may occur. :

     ```

       int partitions[npartitions] = { /* zero initialize */ };

       // Calculate partition slots
       ZArrayIterator<ZPage*> iter1(&_live_pages);
       for (ZPage* page; iter1.next(&page);) {
         const size_t index = page->live_bytes() >> partition_size_shift;
         if (index >= npartitions) {
           log_info(gc, heap)("!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!");
           log_info(gc, heap)("Size of partition array : %zu", npartitions);
           log_info(gc, heap)("partition_size = _page_size >> npartitions_shift : %zu = %zu >> %zu", partition_size, _page_size, npartitions_shift);
           log_info(gc, heap)("partition_size_shift = exact_log2(partition_size) : %zu", partition_size_shift);
           log_info(gc, heap)("Index will be visited (page->live_bytes() >> partition_size_shift): %zu", index);
           log_info(gc, heap)("Page lived bytes: %zu", page->live_bytes());
           log_info(gc, heap)("!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!");
         }
         partitions[index]++;
       }