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Old 08-25-2009, 02:45 AM   #1
er_khatke
LQ Newbie
 
Registered: Aug 2009
Posts: 2

Rep: Reputation: 0
Question reverse dependency problem while dlopen shared lib


Hi everyone ,
I am using loading a shared library dynamically in my code using dlopen() & then calling a function of it which in turn calling the function of my own program .But this is giving "undefined reference" problem .Please see the following snap of the code :

Code for main Program :
==================================
/*sample.c*/
#include <dlfcn.h>
#include "sample_header.h"
void main_fun(int k)
{
printf("\n ***** In Main Fun : %d",k);
}
void main()
{
char *error;
void (*sample_fptr)(int);
void *handle = dlopen ("./sample_shared.so", RTLD_LAZY);
if (!handle)
{
printf ("\n%s\n", dlerror());
return;
}

dlerror();
sample_fptr = dlsym(handle, "shared_fun");
if ((error = dlerror()) != 0)
{
printf ("\n%s\n", dlerror());
return;
}

(*sample_fptr)(7);
printf("Done ........\n");

}
compilation command used : gcc -ldl sample.c
==============================================================
------------------------
//sample_header declaration is :

/*sample_header.h*/
#include <stdio.h>
void main_fun(int k);

--------------------------


Code for sample_shared.c :
++++++++++++++++++++++++++++++
#include "sample_header.h"
void shared_fun(int k);
void shared_fun(int k)
{
main_fun(k);
}

compilation command : gcc -shared -Wall sample_shared.c -o sample_shared.so
++++++++++++++++++++++++++++

Result @ runtime : ./sample_shared.so: undefined symbol: main_fun

Any suggestion to resolve this issue is appreciated.

Thanx in Advance
Kapil
 
Old 08-25-2009, 08:48 AM   #2
orgcandman
Member
 
Registered: May 2002
Location: dracut MA
Distribution: Ubuntu; PNE-LE; LFS (no book)
Posts: 594

Rep: Reputation: 102Reputation: 102
You need to use -rdynamic and -fPIC.

Here are the compilation commands to use:

gcc -o sample -ldl -fPIC -rdynamic sample.c

gcc -shared -rdynamic -fPIC -Wall -o sample_shared.so sample_shared.c
 
  


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