[Vm-dev] Fwd: [Pharo-users] Need help with Alien, unexpected function return value

[stephane ducasse]

Begin forwarded message:

> From: Joachim Geidel <joachim.geidel at onlinehome.de>
> Date: May 15, 2010 10:57:37 PM GMT+02:00
> To: pharo-users at lists.gforge.inria.fr
> Subject: [Pharo-users] Need help with Alien, unexpected function return value
> Reply-To: A friendly place where any question about pharo is welcome <pharo-users at lists.gforge.inria.fr>
> 
> 
> 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
> 
> -- 
> View this message in context: http://forum.world.st/Need-help-with-Alien-unexpected-function-return-value-tp2218105p2218105.html
> Sent from the Pharo Smalltalk Users mailing list archive at Nabble.com.
> 
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