The following test failed in the JDK18 CI:

runtime/modules/ModuleStress/ModuleStressGC.java

Here's snippets from the hs_err_pid:

# Internal Error (/System/Volumes/Data/mesos/work_dir/slaves/35546316-ed70-4084-8244-d672e7734fd1-S109180/frameworks/1735e8a2-a1db-478c-8104-60c8b0af87dd-0196/executors/5e19e1e0-f92c-44e6-abd9-b32aa0c8e030/runs/67b857d0-fd98-4d73-8052-d2c2dc04cec4/workspace/open/src/hotspot/share/oops/compressedOops.inline.hpp:135), pid=7694, tid=19459
# assert(check_alignment(result)) failed: address not aligned: 0x0000000837613731
#
# JRE version: Java(TM) SE Runtime Environment (18.0+7) (fastdebug build 18-ea+7-274)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (fastdebug 18-ea+7-274, mixed mode, sharing, tiered, compressed oops, compressed class ptrs, g1 gc, bsd-amd64)
# Core dump will be written. Default location: core.7694

<snip>

--------------- T H R E A D ---------------

Current thread (0x00007fded34304c0): GCTaskThread "G1 Conc#0" [stack: 0x000070000c859000,0x000070000c959000] [id=19459]

Stack: [0x000070000c859000,0x000070000c959000], sp=0x000070000c9585c0, free space=1021k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [libjvm.dylib+0x10f94d9] VMError::report_and_die(int, char const*, char const*, __va_list_tag*, Thread*, unsigned char*, void*, void*, char const*, int, unsigned long)+0x6e9
V [libjvm.dylib+0x10f9b5b] VMError::report_and_die(Thread*, void*, char const*, int, char const*, char const*, __va_list_tag*)+0x3b
V [libjvm.dylib+0x5e7a4d] report_vm_error(char const*, int, char const*, char const*, ...)+0xdd
V [libjvm.dylib+0x6fc5e8] G1ConcurrentMark::mark_in_next_bitmap(unsigned int, HeapRegion*, oop)+0x3b8
V [libjvm.dylib+0x6fb80c] G1CMTask::make_reference_grey(oop)+0xbc
V [libjvm.dylib+0x6fb723] G1CMOopClosure::do_oop(narrowOop*)+0x73
V [libjvm.dylib+0x6fd202] void InstanceRefKlass::do_referent<narrowOop, G1CMOopClosure, AlwaysContains>(oop, G1CMOopClosure*, AlwaysContains&)+0x92
V [libjvm.dylib+0x6fce95] void InstanceRefKlass::oop_oop_iterate_discovery<narrowOop, G1CMOopClosure, AlwaysContains>(oop, ReferenceType, G1CMOopClosure*, AlwaysContains&)+0x85
V [libjvm.dylib+0x6fcd78] void InstanceRefKlass::oop_oop_iterate_ref_processing<narrowOop, G1CMOopClosure, AlwaysContains>(oop, G1CMOopClosure*, AlwaysContains&)+0x278
V [libjvm.dylib+0x6fcac8] void InstanceRefKlass::oop_oop_iterate<narrowOop, G1CMOopClosure>(oop, G1CMOopClosure*)+0x1f8
V [libjvm.dylib+0x6fc84c] void OopOopIterateDispatch<G1CMOopClosure>::Table::oop_oop_iterate<InstanceRefKlass, narrowOop>(G1CMOopClosure*, oop, Klass*)+0x3c
V [libjvm.dylib+0x72d613] int oopDesc::oop_iterate_size<G1CMOopClosure>(G1CMOopClosure*)+0x103
V [libjvm.dylib+0x72d4a9] void G1CMTask::process_grey_task_entry<true>(G1TaskQueueEntry)+0x369
V [libjvm.dylib+0x72307a] G1CMBitMapClosure::do_addr(HeapWordImpl**)+0x13a
V [libjvm.dylib+0x72c2d9] G1CMBitMap::iterate(G1CMBitMapClosure*, MemRegion)+0x1b9
V [libjvm.dylib+0x72b718] G1CMTask::do_marking_step(double, bool, bool)+0x718
V [libjvm.dylib+0x72df85] G1CMConcurrentMarkingTask::work(unsigned int)+0x1a5
V [libjvm.dylib+0x115308e] GangWorker::run_task(WorkData)+0x5e
V [libjvm.dylib+0x1152f71] GangWorker::loop()+0x41
V [libjvm.dylib+0x1152e36] GangWorker::run()+0x16
V [libjvm.dylib+0x104f037] Thread::call_run()+0x177
V [libjvm.dylib+0xe1dc40] thread_native_entry(Thread*)+0x150
C [libsystem_pthread.dylib+0x6109] _pthread_start+0x94
C [libsystem_pthread.dylib+0x1b8b] thread_start+0xf

I'm starting this bug off in hotspot/gc since we're crashing in G1.