RFR: 8260589: Crash in JfrTraceIdLoadBarrier::load(_jclass*)

[Denghui Dong]

On Thu, 28 Jan 2021 16:55:41 GMT, Denghui Dong <ddong at openjdk.org> wrote:

> hi,
> 
> Could I have a review of this fix?
> 
> If we run the following code snippet, will get a crash
> class JFRDemo {
>     public static void main(String[] args) {
>         Recording r = new Recording();
>         r.enable("MyEvent");
>         r.start();
> 
>         MyEvent event = new MyEvent();
>         event.begin();
>         event.clazz = long.class;
>         event.commit();
>     }
> }
> 
> class MyEvent extends Event {
> 
>     @Label("Class")
>     public Class clazz;
> }

Add some information to facilitate this issue to be reviewed more easily.

We will get a crash if we run the above code,, and the stack trace is as follows:

Stack: [0x00007fa12b2f3000,0x00007fa12b3f4000],  sp=0x00007fa12b3f2790,  free space=1021k
Native frames: (J=compiled Java code, A=aot compiled Java code, j=interpreted, Vv=VM code, C=native code)
V  [libjvm.so+0x89d649]  JfrTraceIdLoadBarrier::load(_jclass*)+0x39
V  [libjvm.so+0x86090e]  jfr_class_id+0x7e
j  jdk.jfr.internal.JVM.getClassIdNonIntrinsic(Ljava/lang/Class;)J+0 jdk.jfr
j  jdk.jfr.internal.EventWriter.putClass(Ljava/lang/Class;)V+14 jdk.jfr
j  jdk.jfr.internal.handlers.EventHandler1699_1612098965420-78137.write(JJLjava/lang/Class;)V+35 jdk.jfr
j  MyEvent.commit()V+73
j  JFRCrashTest.main([Ljava/lang/String;)V+39
v  ~StubRoutines::call_stub
V  [libjvm.so+0x82aef5]  JavaCalls::call_helper(JavaValue*, methodHandle const&, JavaCallArguments*, Thread*)+0x2d5
V  [libjvm.so+0x8be315]  jni_invoke_static(JNIEnv_*, JavaValue*, _jobject*, JNICallType, _jmethodID*, JNI_ArgumentPusher*, Thread*) [clone .isra.0] [clone .constprop.1]+0x345
V  [libjvm.so+0x8c0b3f]  jni_CallStaticVoidMethod+0x12f
C  [libjli.so+0x4647]  JavaMain+0xd27
C  [libjli.so+0x8079]  ThreadJavaMain+0x9

Java frames: (J=compiled Java code, j=interpreted, Vv=VM code)
j  jdk.jfr.internal.JVM.getClassIdNonIntrinsic(Ljava/lang/Class;)J+0 jdk.jfr
j  jdk.jfr.internal.EventWriter.putClass(Ljava/lang/Class;)V+14 jdk.jfr
j  jdk.jfr.internal.handlers.EventHandler1699_1612098965420-78137.write(JJLjava/lang/Class;)V+35 jdk.jfr
j  MyEvent.commit()V+73
j  JFRCrashTest.main([Ljava/lang/String;)V+39
v  ~StubRoutines::call_stub

The root cause is that basic types, including void, do not have corresponding Klass objects inside the virtual machine, so call java_lang_Class::as_Klass will return NULL and crash in JfrTraceIdLoadBarrier::load finally.

My solution is adding two serializers, one for the names of basic types, and one for basic types.

I am not sure about the setting of the class loader is right or not, I currently set it to 0 directly.

-------------

PR: https://git.openjdk.java.net/jdk/pull/2295