[Pyrex] Undefined symbol _Py_ZeroStruct

[Franck Pommereau]

> You are probably right...it looks like a linking problem rather than
> directly a Pyrex issue. One thing I might look at is the (long) lost of
> command line options used by gcc when useing distutils, and making sure
> none of them are missing when you try to compile for use from Java.

Thanks for the idea! It does change something but still there is a
missing symbol. I copied/pasted distutils flags and just added the
required -I directives for JNI:

$ gcc -pthread -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall
-Wstrict-prototypes -fPIC -I/usr/lib/jvm/java-6-sun-1.6.0.10/include
-I/usr/lib/jvm/java-6-sun-1.6.0.10/include/linux
-I/usr/include/python2.6 -c _sr.c -o _sr.o

$ gcc -pthread -shared -Wl,-O1 -Wl,-Bsymbolic-functions _sr.o -o _sr.so

The error at the Python side seems to be the same, but the Java program
is happier and successfully loads the built library. I used to have:

$ java Tester
Exception ImportError: '/usr/lib/python2.6/lib-dynload/pyexpat.so:
undefined symbol: _Py_ZeroStruct' in '_sr.JNI_OnLoad' ignored
Exception in thread "main" java.lang.UnsatisfiedLinkError: unsupported
JNI version 0x4063F2C0 required by
/home/franck/work/tools/snakes/osa/trivial/_sr.so
	at java.lang.ClassLoader$NativeLibrary.load(Native Method)
	at java.lang.ClassLoader.loadLibrary0(ClassLoader.java:1778)
	at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1674)
	at java.lang.Runtime.load0(Runtime.java:770)
	at java.lang.System.load(System.java:1003)
	at Component.<clinit>(Component.java:3)
	at Tester.main(Tester.java:3)

where the first exception is reported by Cython's runtime. I now have:

$ java Tester
Exception ImportError: '/usr/lib/python2.6/lib-dynload/pyexpat.so:
undefined symbol: _Py_ZeroStruct' in '_sr.JNI_OnLoad' ignored
*** Yeah!
Exception NameError: 'sr' in '_sr.Java_Sender_pynew' ignored
Exception NameError: '_instances' in '_sr.Java_Sender_pyinit' ignored
Exception in thread "main" java.lang.NullPointerException
	at java.lang.String.valueOf(String.java:2826)
	at java.lang.StringBuilder.append(StringBuilder.java:115)
	at Tester.main(Tester.java:4)

where message "*** Yeah!" is printed by the Java program after it has
loaded the library. The subsequent NameError's come from the fact that
my Python module is not correctly initialized because function init_sr
called from _sr.JNI_OnLoad failed.

I presume that this change is just a random one, probably the value
returned by JNI_OnLoad is now acceptable by the JVM that thus continues
the execution.

F.