Report a bug in HotSpot (original) (raw)

Krystal Mo krystal.mo at oracle.com
Tue Nov 27 07:20:59 PST 2012

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.

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 JavaHelloabc(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)

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