When running with ubsan - enabled binaries, the tests
java/net/vthread/HttpALot.jtr
java/nio/channels/vthread/BlockingChannelOps_poller-modes.jtr
trigger the following report :

src/hotspot/share/runtime/frame.inline.hpp:91:25: runtime error: member call on null pointer of type 'const struct SmallRegisterMap'
    #0 0x7fc1df86071e in unsigned char* frame::oopmapreg_to_location<SmallRegisterMap>(VMRegImpl*, SmallRegisterMap const*) const src/hotspot/share/runtime/frame.inline.hpp:91
    #1 0x7fc1df86071e in void OopMapDo<OopClosure, DerivedOopClosure, IncludeAllValues>::iterate_oops_do<SmallRegisterMap>(frame const*, SmallRegisterMap const*, ImmutableOopMap const*) src/hotspot/share/compiler/oopMap.inline.hpp:106
    #2 0x7fc1df8611df in void OopMapDo<OopClosure, DerivedOopClosure, IncludeAllValues>::oops_do<SmallRegisterMap>(frame const*, SmallRegisterMap const*, ImmutableOopMap const*) src/hotspot/share/compiler/oopMap.inline.hpp:157
    #3 0x7fc1df8611df in FrameOopIterator<SmallRegisterMap>::oops_do(OopClosure*) src/hotspot/share/oops/stackChunkOop.cpp:63
    #4 0x7fc1dcfc8745 in BarrierSetStackChunk::encode_gc_mode(stackChunkOopDesc*, OopIterator*) src/hotspot/share/gc/shared/barrierSetStackChunk.cpp:85
    #5 0x7fc1df854080 in bool TransformStackChunkClosure::do_frame<(ChunkFrames)0, SmallRegisterMap>(StackChunkFrameStream<(ChunkFrames)0> const&, SmallRegisterMap const*) src/hotspot/share/oops/stackChunkOop.cpp:319
    #6 0x7fc1df854080 in void stackChunkOopDesc::iterate_stack<(ChunkFrames)0, TransformStackChunkClosure>(TransformStackChunkClosure*) src/hotspot/share/oops/stackChunkOop.inline.hpp:233
    #7 0x7fc1df82f184 in void stackChunkOopDesc::iterate_stack<TransformStackChunkClosure>(TransformStackChunkClosure*) src/hotspot/share/oops/stackChunkOop.inline.hpp:199
    #8 0x7fc1df82f184 in stackChunkOopDesc::transform() src/hotspot/share/oops/stackChunkOop.cpp:334
    #9 0x7fc1dde84410 in ContinuationGCSupport::transform_stack_chunk(oopDesc*) src/hotspot/share/gc/shared/continuationGCSupport.inline.hpp:52
    #10 0x7fc1dde84410 in G1ParScanThreadState::do_copy_to_survivor_space(G1HeapRegionAttr, oopDesc*, markWord) src/hotspot/share/gc/g1/g1ParScanThreadState.cpp:542
    #11 0x7fc1dde84410 in void G1ParScanThreadState::do_oop_evac<narrowOop>(narrowOop*) src/hotspot/share/gc/g1/g1ParScanThreadState.cpp:218
    #12 0x7fc1dde84410 in G1ParScanThreadState::dispatch_task(ScannerTask) src/hotspot/share/gc/g1/g1ParScanThreadState.cpp:296
    #13 0x7fc1dde84410 in G1ParScanThreadState::trim_queue_to_threshold(unsigned int) src/hotspot/share/gc/g1/g1ParScanThreadState.cpp:317
    #14 0x7fc1dde98afd in G1ParScanThreadState::trim_queue() src/hotspot/share/gc/g1/g1ParScanThreadState.inline.hpp:60
    #15 0x7fc1dde98afd in G1ParScanThreadState::steal_and_trim_queue(GenericTaskQueueSet<OverflowTaskQueue<ScannerTask, (MEMFLAGS)5, 131072u>, (MEMFLAGS)5>*) src/hotspot/share/gc/g1/g1ParScanThreadState.cpp:328
    #16 0x7fc1ddfb0ebf in G1ParEvacuateFollowersClosure::do_void() src/hotspot/share/gc/g1/g1YoungCollector.cpp:577
    #17 0x7fc1ddfb1fe3 in G1EvacuateRegionsBaseTask::evacuate_live_objects(G1ParScanThreadState*, unsigned int, G1GCPhaseTimes::GCParPhases, G1GCPhaseTimes::GCParPhases) src/hotspot/share/gc/g1/g1YoungCollector.cpp:602
    #18 0x7fc1ddfb1fe3 in G1EvacuateRegionsTask::evacuate_live_objects(G1ParScanThreadState*, unsigned int) src/hotspot/share/gc/g1/g1YoungCollector.cpp:670
    #19 0x7fc1ddfa5e37 in G1EvacuateRegionsBaseTask::work(unsigned int) src/hotspot/share/gc/g1/g1YoungCollector.cpp:652
    #20 0x7fc1dfe65a22 in WorkerTaskDispatcher::worker_run_task() src/hotspot/share/gc/shared/workerThread.cpp:70
    #21 0x7fc1dfe65a22 in WorkerThread::run() src/hotspot/share/gc/shared/workerThread.cpp:201
    #22 0x7fc1dfb7e2ca in Thread::call_run() src/hotspot/share/runtime/thread.cpp:225
    #23 0x7fc1df1c4921 in thread_native_entry src/hotspot/os/linux/os_linux.cpp:846
    #24 0x7fc1e4fac6e9 in start_thread (/lib64/libpthread.so.0+0xa6e9) (BuildId: 2f8d3c2d0f4d7888c2598d2ff6356537f5708a73)
    #25 0x7fc1e451550e in clone (/lib64/libc.so.6+0x11850e) (BuildId: f732026552f6adff988b338e92d466bc81a01c37)