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Hello everybody,
I need some help with Alien on Mac OS X 10.6.3 in Pharo 1.0. I am calling a function from a vtable struct in the Java Native Interface of the Java VM which comes with Mac OS X and which is defined as
jint ( __stdcall * GetVersion)(JNIEnv * env);
The result type jint is just an alias for int. The Smalltalk method is
----
primGetVersion
| functionPointer result vtablePointer |
vtablePointer := Alien
atAddress: self externalData asUnsignedLong
dataSize: Alien sizeofPointer * self vtableSize.
functionPointer := Alien forPointer:
(vtablePointer unsignedLongAt: (4 * Alien sizeofPointer + 1)).
result := (Alien newGC: 4) pointer.
functionPointer
primFFICallResult: result
with: self asJNIParameter.
^result signedIntAt: 1
----
functionPointer is the pointer to the GetVersion function.
The result should be 65542 (16r00010006), which is also what I get when calling the function from VisualWorks, but the method answers -394042288 (-16r177C9BB0). The "result" Alien has the printString '#[0 0 0 0 6 0 1 0]' which suspiciously contains the 1 and the 6 I am looking for, but in the wrong places. ;-)
I looked at examples for callouts, which seem to indicate that result should be the Alien and not a pointer to it. So I changed the code to
----
result := (Alien newC: 4).
functionPointer
primFFICallResult: result pointer
with: self asJNIParameter.
^result signedIntAt: 1
----
This didn't really help. The result is now 0 (zero), although the Alien prints as #[252 255 255 255 80 15 38 0] which doesn't look like a 0 at first sight.
Am I using those Aliens in a correct way? What can I try to debug this?
If this is too obscure and someone who knows about Aliens would like to have a look at the rest of the code, I am willing to send a bunch of Monticello packages and instructions for reproducing the problem, but I won't make it publicly available yet.
Any help is welcome.
Best regards,
Joachim Geidel
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