Continuation.yield0() is showing up in the stack traces. It is not suppose to since it is a method that is suppose to be hidden. The method is being included in GetStackTrace, and also GetFrameCount.

The following simple test case and jdb session demonstrate the issue. Note the reason for setting the breakpoint is so jdb learns about the Virtual thread. Otherwise it won't show up in the threads list.

Main {
    public static void main(String[] args) throws Exception {
        Thread thread = Thread.ofVirtual().unstarted(Main::test);
        System.out.println(thread);
        thread.start();
        thread.join();
    }
    
    static void test() {
        try {
            Thread.sleep(1000000);
        } catch (InterruptedException e) {
        }
    }
}

$ jdb Main
Initializing jdb ...
> stop at Main:11
Deferring breakpoint Main:11.
It will be set after the class is loaded.
> run
run Main
Set uncaught java.lang.Throwable
Set deferred uncaught java.lang.Throwable
>
VM Started: Set deferred breakpoint Main:13
VirtualThread[#34]/new

Breakpoint hit: "thread=", Main.test(), line=13 bci=0
13 Thread.sleep(1000000);

[1] cont
> suspend
All threads suspended.
> threads
Group system:
  (java.lang.ref.Reference$ReferenceHandler)406 Reference Handler running
  (java.lang.ref.Finalizer$FinalizerThread)407 Finalizer cond. waiting
  (java.lang.Thread)408 Signal Dispatcher running
  (java.lang.Thread)405 Notification Thread running
Group main:
  (java.lang.Thread)1 main cond. waiting
Group InnocuousThreadGroup:
  (jdk.internal.misc.InnocuousThread)432 Common-Cleaner cond. waiting
  (jdk.internal.misc.InnocuousThread)762 VirtualThread-unparker cond. waiting
Group CarrierThreads:
  (jdk.internal.misc.CarrierThread)755 ForkJoinPool-1-worker-1 cond. waiting
Group VirtualThreads:
  (java.lang.VirtualThread)759 cond. waiting
> where 759
  [1] jdk.internal.vm.Continuation.yield0 (Continuation.java:360)
  [2] jdk.internal.vm.Continuation.yield (Continuation.java:351)
  [3] java.lang.VirtualThread.yieldContinuation (VirtualThread.java:526)
  [4] java.lang.VirtualThread.parkNanos (VirtualThread.java:716)
  [5] java.lang.VirtualThread.sleepNanos (VirtualThread.java:888)
  [6] java.lang.Thread.sleepNanos (Thread.java:495)
  [7] java.lang.Thread.sleep (Thread.java:528)
  [8] Main.test (Main.java:13)
  [9] Main$$Lambda/0x00007f0fdb000a18.run (null)
  [10] java.lang.Thread.runWith (Thread.java:1,589)
  [11] java.lang.VirtualThread.run (VirtualThread.java:404)
  [12] java.lang.VirtualThread$VThreadContinuation$1.run (VirtualThread.java:217)
  [13] jdk.internal.vm.Continuation.enter0 (Continuation.java:320)
  [14] jdk.internal.vm.Continuation.enter (Continuation.java:312)