[aarch64-port-dev ] RFR: 8209413: AArch64: NPE in clhsdb jstack command

[Nick Gasson (Arm Technology China)]

Hi Andrew

> Here's the test that reveals the problem: it seems that you need an entry frame which calls compiled Java code.

This seems slightly different to the original problem, although maybe related. Because here the top-most frame is a compiled Java frame we'll take the vm.isJavaPCDbg and !vm.isClientCompiler branches of AARCH64CurrentFrameGuess::run which as far as I can tell always gets the PC from the thread context. The original crash I was looking at happened when the top frame was native (else branch on line 183) where the PC is set to null which causes the two-argument AARCH64Frame constructor to be used.

Unfortunately I'm on holiday until next Thursday so can't test anything. Did you try Thread.sleep? That's what LingeredApp that the jtreg tests is trying to get a stack trace of calls.

Thanks,
Nick
________________________________
From: Andrew Haley <aph at redhat.com>
Sent: 06 February 2019 18:00:16
To: Nick Gasson (Arm Technology China); serviceability-dev at openjdk.java.net
Cc: nd; aarch64-port-dev at openjdk.java.net
Subject: Re: [aarch64-port-dev ] RFR: 8209413: AArch64: NPE in clhsdb jstack command

On 2/5/19 5:57 PM, Andrew Haley wrote:
> On 2/5/19 5:55 PM, Nick Gasson (Arm Technology China) wrote:
>> The stack trace you sent below is incomplete, it's missing the frame for Spinner.run (i.e. the AARCH64Frame object corresponding to the native wrapper frame). Did you try on x86 or with the patch I posted? I'm not able to test at the moment but I think you will get one exra frame in the output. I don't know why you don't get the NPE, I guess it depends on what's in that stack slot.
>
> Never mind, found it. A more complex test is needed.

Here's the test that reveals the problem: it seems that you need an entry frame
which calls compiled Java code.

[aph at merino ~]$ cat Spinner.c
#include <jni.h>
#include <stdio.h>

/*
 * Class:     Spinner
 * Method:    run
 * Signature: ()V
 */
JNIEXPORT void JNICALL Java_Spinner_run(JNIEnv *env,  jclass cls) {
  jmethodID mid = (*env)->GetStaticMethodID(env, cls, "test", "()V");
  (*env)->CallStaticVoidMethod(env, cls, mid);
  // printf("Spinning...\n");
  // for(;;);
}


[aph at merino ~]$ cat Spinner.java
public class Spinner {
    static native void run();

    static {
        System.loadLibrary("Spinner");
    }

    static volatile int nn;

    public static void test() {
        System.out.println("Spinning");
        for(int i = 1; i !=0; i = (i + 1) | 1)
            nn = (int)Math.log(i);
    }

    public static void main(String[] args) {
        run();
    }
}

--
Andrew Haley
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
EAC8 43EB D3EF DB98 CC77 2FAD A5CD 6035 332F A671
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