Report a bug in HotSpot

[Xi Yang]

On 28 November 2012 02:20, Krystal Mo <krystal.mo at oracle.com> wrote:
> Hi Coleen,
>
> Thank you for the reply.
>
> Yes, I know that flag, but it doesn't fix the problem demonstrated in the
> first test case.
> Running that test case with this flag will still show "Double a is NaN" on
> 32-bit JDK7u9 on Ubuntu 12.04. It's not about the FPU control word.

Right, the problem is "x87 tag word".

Regards.

>
> Regards,
> Kris
>
>
> On 2012/11/27 22:53, Coleen Phillimore wrote:
>>
>>
>> We have this flag for this problem:
>>
>>   product(bool, AlwaysRestoreFPU, false,
>> \
>>           "Restore the FPU control word after every JNI call (expensive)")
>> \
>> \
>>
>> Coleen
>>
>> On 11/27/2012 08:01 AM, Karen Kinnear wrote:
>>>
>>> Hi Kris,
>>>
>>> I would concur. And there is also an explicit intention to not slow down
>>> JNI transitions by having the JVM do extra work. The
>>> model is to have the JNI code restore a good state.
>>>
>>> Looks like we already have a flag that lets you know that you need to fix
>>> the jni code, so no need to add another way to do that.
>>>
>>> thanks,
>>> Karen
>>>
>>> On Nov 26, 2012, at 10:57 PM, David Holmes wrote:
>>>
>>>> Hi Kris,
>>>>
>>>> I think historically hotspot assumes/requires JNI code to be well
>>>> behaved about these things. There have been some well known issues with FPU
>>>> state in the past. I'm not that familiar with MMX so can't say whether it is
>>>> reasonable for the VM to know when it has to do this kind of cleanup.
>>>>
>>>> David
>>>>
>>>> On 27/11/2012 4:29 AM, Krystal Mo wrote:
>>>>>
>>>>> Hi all,
>>>>>
>>>>> Xi Yang has reported a bug in HotSpot's interpreter that it doesn't
>>>>> empty the FPU stack on return from JNI calls. His mail is included
>>>>> below.
>>>>>
>>>>> e.g. If a native function called via JNI is using MMX registers without
>>>>> emptying the FPU stack before returning, then after returning to Java
>>>>> the FPU stack will be in a bad state.
>>>>>
>>>>> The test case Xi gave is demonstrated here on JDK7u9, x86:
>>>>> https://gist.github.com/4148771
>>>>> Running the example with -XX:+VerifyFPU shows what's going on.
>>>>>
>>>>> This test case shows the bug affecting 32-bit x86 version of HotSpot's
>>>>> interpreter.
>>>>>
>>>>> Not really familiar with how to file a bug on JBS yet, I'll file a bug
>>>>> to track this after I learn how to do it.
>>>>>
>>>>> Regards,
>>>>> Kris
>>>>>
>>>>>
>>>>> -------- Original Message --------
>>>>> Subject: Fwd: Report a bug in HotSpot
>>>>> Date: Tue, 27 Nov 2012 02:02:59 +0800
>>>>> From: Krystal Mok <rednaxelafx at gmail.com>
>>>>> To: Krystal Mo <krystal.mo at oracle.com>
>>>>>
>>>>>
>>>>>
>>>>> ---------- Forwarded message ----------
>>>>> From: Xi Yang <hiyangxi at gmail.com>
>>>>> Date: Tue, Nov 20, 2012 at 1:44 PM
>>>>> Subject: Report a bug in HotSpot
>>>>> To: Krystal Mok <rednaxelafx at gmail.com>
>>>>>
>>>>>
>>>>> Hi,
>>>>>
>>>>> It looks like HotSpot does not do "emms" after backing from JNI. Here
>>>>> is the code to show the bug. Would you like to try the newest version?
>>>>>
>>>>>
>>>>> Hello.java
>>>>> class Hello {
>>>>> private static native void abc();
>>>>> public static void main(String[] args) {
>>>>> System.out.println("I am main");
>>>>> System.loadLibrary("Hello");
>>>>> abc();
>>>>> long a = 100;
>>>>> double b = (double)a;
>>>>> System.out.println("Double a is " + b);
>>>>> }
>>>>> }
>>>>>
>>>>> Hello.c
>>>>> #include <jni.h>
>>>>> #include <stdio.h>
>>>>>
>>>>> JNIEXPORT void JNICALL
>>>>> Java_Hello_abc(JNIEnv *env, jclass cls)
>>>>> {
>>>>> printf("I mmmmmmmmmmmmmmmmmmmmmmmmm java Helo world\n");
>>>>> unsigned int dummy;
>>>>> asm volatile("movd %%mm0, %0\n":"=r"(dummy));
>>>>> printf("dummy is %x\n", dummy);
>>>>> }
>>>>>
>>>>>
>>>>> gcc -m32 -shared ./Hello.c -o ./libHello.so
>>>>>
>>>>>
>>>>> /opt/jdk1.7.0/bin/java -Djava.library.path=. Hello
>>>>> I am main
>>>>> I mmmmmmmmmmmmmmmmmmmmmmmmm java Helo world
>>>>> dummy is 0
>>>>> Double a is NaN
>>>>>
>>>>>
>>>>> $ /opt/jdk1.7.0/bin/java -version
>>>>> java version "1.7.0-ea"
>>>>> Java(TM) SE Runtime Environment (build 1.7.0-ea-b93)
>>>>> Java HotSpot(TM) Server VM (build 18.0-b04, mixed mode)
>>>>>
>>>>>
>>>>>
>>
>