Undefined symbol when loading php extension made with SWIG

Question

I am trying to load a PHP extension made using SWIG, but I am getting the following error when starting PHP:

PHP Warning:  PHP Startup: Unable to load dynamic library '/usr/lib/php5/20090626/libtg.so' - /usr/lib/php5/20090626/libtg.so: undefined symbol: __gxx_personality_v0 in Unknown on line 0

The extension I am trying to load is named libtg.so and was compiled with the command:

g++ -shared libtg_wrap.o -o libtg.so

where libtg_wrap.o is the object file for the wrapper code generated by SWIG.

The missing symbol __gxx_personality_v0 is found in libstdc++.so, as evident from the following command:

$ nm -D /usr/lib/libstdc++.so.6 | grep __gxx_personality_v0
00000000000b9990 T __gxx_personality_v0

libstdc++.so is referenced in libtg.so, as evident from the following command:

$ ldd libtg.so
linux-vdso.so.1 =>  (0x00007fff5f932000)
libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0x00007f3fc937c000)
libm.so.6 => /lib/libm.so.6 (0x00007f3fc90f9000)
libgcc_s.so.1 => /lib/libgcc_s.so.1 (0x00007f3fc8ee2000)
libc.so.6 => /lib/libc.so.6 (0x00007f3fc8b5f000)
/lib64/ld-linux-x86-64.so.2 (0x00007f3fc98fc000)

so I don't see why it cannot find the symbol. Any ideas on how I can further debug this?

Answer 1

It seems that somewhere in your compile process, the compiler or linker was not aware of a c++ source.

When I tried swig (also to create a php extension), I created the following Makefile that may be handy in your case, so you may want to customize it for your project and give it a try, it's pretty straighforward.

See how I had to specify the "-c++" option to the swig command. Also, be sure to have .cpp extension for your source files and add "-lstdc++" to your linker flags.

The important stuff should be the swig invocation (note the -c++ option):

${OUTPUTDIR}/${NAME}_swig.cpp:
    ${SWIG} -outdir ${OUTPUTDIR} \
        -oh ${OUTPUTDIR}/${NAME}_swig.h \
        -o ${OUTPUTDIR}/${NAME}_swig.cpp \
        -c++ -php \
        ${NAME}.i

and the linker invocation (note the -lstdc flag) :

ld -shared ${OUTPUTDIR}/*.o -o ${OUTPUTDIR}/${NAME}.so -lstdc++

Hope it helps