Problem with dlopen in a plugin system ( C )

Bad_Lemon · 04-19-2007, 07:29 AM

Hello all,

i'm trying to create a plugin system with the C language.
I am able to load the libs and get the functions I need, then I put them in a function pointer array to use them later.

There is a main source file and an additional one which is dedicated to plugins:

Code:

/**main.c**/

void (*init_proto_chain[20])(void *);

void init_protos(){
  
   (init_proto_chain[i])(data);

}

Code:

         /**plugins.c**/
extern (*init_proto_chain[20])(void*);

void load_plugins(){

  handle = dlsym("...libhttp.so",RTLD_NOW);

  void *func = dlsym(handle, "test");

  init_proto_chain[j] = ((void (*) (void *))func;

}

When I try to use any of the functions in the main code, I get a segfault and when I use gdb I can see there is nothing at the function address.

Yet, if I call "test()" by dereferencing func or init_proto_chain[j] when in load_plugins, it's working and the function pointer is valid.

Thanks in advance for any help.

ta0kira · 04-19-2007, 12:04 PM

The first call you make to 'dlsym' needs to be 'dlopen'. This opens the library whereas 'dlsym' extracts the symbol. Additionally, you always need to check the results of 'dlsym' and 'dlopen' for NULL and optionally output the result of 'dlerror' if either are NULL. The check to the handle should be made before calling 'dlsym' on it.
ta0kira