ccall fails from embedding Julia into C

[akorotkov]

Hi!

I'm trying to run following example of embedding Julia into C.

#include <julia.h>

int my_func()
{
    return 1;
}

int main(int argc, char *argv[])
{
    /* required: setup the julia context */
    jl_init(JULIA_INIT_DIR);

    /* run julia commands */
    jl_eval_string(
        "try\n"
        "    print(ccall(:my_func, Cint, ()))\n"
        "catch err\n"
        "    print(\"$err\n\")\n"
        "end\n"
    );

    /* strongly recommended: notify julia that the
         program is about to terminate. this allows
         julia time to cleanup pending write requests
         and run all finalizers
    */
    jl_atexit_hook(0);
    return 0;
}

And I got following error.

ErrorException("ccall: could not find function my_func")

The OS is CentOS Linux 7.1, compiler is gcc 4.8.5.

julia version 0.4.6 is installed from nalimilan/julia repository.
I'm building example using following command.

/usr/share/julia/julia-config.jl --cflags --ldflags --ldlibs | xargs clang embed.c -o embed

The same example works fine for me on Mac OS X 10.10.5.
What am I doing wrong?

[yuyichao]

-Wl,--export-dynamic

[akorotkov]

It works! Many thanks!

[tkelman]

Should that be added (sometimes?) to julia-config.jl ?

[yuyichao]

The option only makes sense for executables and not for shared objects (not sure if any linker gives warning or error for that though) so it shouldn't be added to julia-config.jl unless we have different options for executables and libraries.

[yuyichao]

This option is also not really necessary to make julia function correctly, only when a symbol in the main executable is looked up dynamically so it feels a little strange to require it. I do agree we should document this since many people might want to do this and hence the doc label.

[tkelman]

this also looks like exactly the same question as https://groups.google.com/forum/#!topic/julia-users/rj8i4r6id9M

[yuyichao]

Ha, I thought that was an issue which is why I couldn't find it just now .....