$ CONF=linux-x86_64-server-fastdebug make images run-test TEST=vmTestbase/nsk/jvmti/scenarios/allocation/AP04/ap04t001/ TEST_VM_OPTS="-XX:+UnlockExperimentalVMOptions -XX:+UseShenandoahGC"

Fails with:

#
# A fatal error has been detected by the Java Runtime Environment:
#
# Internal Error (/home/shade/trunks/shenandoah-jdk11/src/hotspot/share/gc/shenandoah/shenandoahConcurrentMark.inline.hpp:262), pid=29055, tid=29081
# Error: Shenandoah assert_correct failed; Forwardee must point to a heap address

Referenced from:
  interior location: 0x000000070edabb80
  inside Java heap
    not in collection set
  region: | 0|R |BTE 70ed00000, 70ee00000, 70ee00000|TAMS 70ee00000|U 1024K|T 1024K|G 0B|S 0B|L 0B|CP 0|SN 1, 1, 0, 0

Object:
  0x000000070edc7718 - klass 0x0000000800001868 java.lang.String
    not allocated after mark start
    not marked
    not in collection set
  mark: marked(0x0000000000000003)
  region: | 0|R |BTE 70ed00000, 70ee00000, 70ee00000|TAMS 70ee00000|U 1024K|T 1024K|G 0B|S 0B|L 0B|CP 0|SN 1, 1, 0, 0

Forwardee:
  0x0000000000000000 - safe print, no details

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

Current thread (0x00007fbbfc003000): GCTaskThread "Shenandoah GC Threads#2" [stack: 0x00007fbc001b2000,0x00007fbc002b2000] [id=29081]

Stack: [0x00007fbc001b2000,0x00007fbc002b2000], sp=0x00007fbc002ae570, free space=1009k
Native frames: (J=compiled Java code, A=aot compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [libjvm.so+0x194eec4] VMError::report_and_die(int, char const*, char const*, __va_list_tag*, Thread*, unsigned char*, void*, void*, char const*, int, unsigned long)+0x314
V [libjvm.so+0x194fd5f] VMError::report_and_die(Thread*, void*, char const*, int, char const*, char const*, __va_list_tag*)+0x2f
V [libjvm.so+0xadb6f0] report_vm_error(char const*, int, char const*, char const*, ...)+0x100
V [libjvm.so+0x164d38e] ShenandoahAsserts::print_failure(ShenandoahAsserts::SafeLevel, oop, void*, oop, char const*, char const*, char const*, int)+0x45e
V [libjvm.so+0x164dc9a] ShenandoahAsserts::assert_correct(void*, oop, char const*, int)+0x1da
V [libjvm.so+0x164f717] ShenandoahAsserts::assert_not_forwarded(void*, oop, char const*, int)+0x47
V [libjvm.so+0x16892a5] void ShenandoahConcurrentMark::mark_through_ref<unsigned int, (UpdateRefsMode)0, (StringDedupMode)0>(unsigned int*, ShenandoahHeap*, Padded<BufferedOverflowTaskQueue<ObjArrayChunkedTask, (MemoryType)5, 131072u>, 128ul>*, ShenandoahMarkingContext*)+0x75
V [libjvm.so+0x1696773] void objArrayOopDesc::oop_iterate_range<ShenandoahMarkRefsMetadataClosure>(ShenandoahMarkRefsMetadataClosure*, int, int)+0xf3
V [libjvm.so+0x1696c82] void ShenandoahConcurrentMark::do_chunked_array_start<ShenandoahMarkRefsMetadataClosure>(Padded<BufferedOverflowTaskQueue<ObjArrayChunkedTask, (MemoryType)5, 131072u>, 128ul>*, ShenandoahMarkRefsMetadataClosure*, oop)+0x2e2
V [libjvm.so+0x16973a6] void ShenandoahConcurrentMark::do_task<ShenandoahMarkRefsMetadataClosure>(Padded<BufferedOverflowTaskQueue<ObjArrayChunkedTask, (MemoryType)5, 131072u>, 128ul>*, ShenandoahMarkRefsMetadataClosure*, unsigned short*, ObjArrayChunkedTask*)+0x606
V [libjvm.so+0x16978a3] void ShenandoahConcurrentMark::mark_loop_work<ShenandoahMarkRefsMetadataClosure, true>(ShenandoahMarkRefsMetadataClosure*, unsigned short*, unsigned int, ShenandoahTaskTerminator*)+0x373
V [libjvm.so+0x16a44f4] void ShenandoahConcurrentMark::mark_loop_prework<true>(unsigned int, ShenandoahTaskTerminator*, ReferenceProcessor*, bool)+0x234
V [libjvm.so+0x16a539c] ShenandoahConcurrentMarkingTask::work(unsigned int)+0xbc
V [libjvm.so+0x19cde80] GangWorker::loop()+0xe0
V [libjvm.so+0x187de6d] Thread::call_run()+0x6d
V [libjvm.so+0x147b856] thread_native_entry(Thread*)+0x106

...

Event: 0.443 Executing VM operation: HeapWalkOperation
Event: 0.443 Protecting memory [0x00007fbc33366000,0x00007fbc33367000] with protection modes 0
Event: 0.443 Concurrent reset
Event: 0.443 Concurrent reset done
Event: 0.509 Pause Init Mark (process weakrefs) (unload classes)
Event: 0.510 Pause Init Mark (process weakrefs) (unload classes) done
Event: 0.510 Protecting memory [0x00007fbc33366000,0x00007fbc33367000] with protection modes 1
Event: 0.510 Executing VM operation: HeapWalkOperation done
Event: 0.510 Concurrent marking (process weakrefs) (unload classes)
<crash>