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Full Discussion: Dynamic library load with dlopen
Top Forums Programming Dynamic library load with dlopen Post 302381490 by shade82 on Friday 18th of December 2009 11:50:45 AM
Old 12-18-2009
Dynamic library load with dlopen
Hi,
I created two library libsum.so and libproduct.so. In the libproduct.so is defined function "product" that use function "sum" defined in libsum.so. So libproduct depends on libsum.
In main function I called product function by a dlopen request. Unfortunaly, when I execute program I have an error: symbol lookup error, undefined symbol sum. Why this? I don't open sum function with another dlopen request. This solution resolve problem but is, in generally, a bad solution because the main function developer can not say that product depends on sum. Is there another solution?
Plese help me, Thanks to all and nice week-end.

I paste code below.

Code:
/*
sum.c
*/

#include <stdlib.h>
#include <stdio.h>


int sum(int a, int b)
{
  int c;
  c = a+b;
  return(c);
}

Code:
/*
product.c
*/

#include <stdio.h>

int product(int a, int b)
{
  int product = 0;
  while(b>0)
  {
    product = sum(product, a);
    b--;
  }
  return(product);
}

Code:
/*
product_main_dyn.c
*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <dlfcn.h>

int
main(int argc, char **argv)
{

  int a;
  int b;
  int ris;
  void *hdl_prd;
  void *hdl_smm;
  int (*prod)(int, int);
  char *error;

  if(argc != 3)
  {
    printf("insert two int number to run\n");
    exit(EXIT_FAILURE);
  }
  
  a = atoi(argv[1]);
  b = atoi(argv[2]);
  

  hdl_prd = dlopen("/home/shade82/product/libproduct.so.1", (RTLD_LAZY));
  if (!hdl_prd) 
  {
    printf("error open library\n");
    exit(EXIT_FAILURE);
  }
  dlerror();  
  
  *(void **) (&prod) = dlsym(hdl_prd, "product");
  if ((error = dlerror()) != NULL)  
  {
    printf("error: not resolve symbol\n");
    exit(EXIT_FAILURE);
  }
  
  ris = (*prod)(a,b);
  printf("product: %d\n",ris);
  dlclose(hdl_prd);
  exit(EXIT_SUCCESS);
}

Code:
#! /bin/bash

rm *.o *.exe libsum.so.1 libproduct.so.1 libsum.so.1.0.0 libproduct.so.1.0.0
gcc -fPIC -c sum.c
gcc -fPIC -c product.c
gcc -shared -Wl,-soname,libsum.so.1 -o libsum.so.1.0.0 sum.o -lc
gcc -shared -Wl,-soname,libproduct.so.1 -o libproduct.so.1.0.0 product.o -lc
export LD_LIBRARY_PATH=/home/shade82/
sudo ldconfig -n .
gcc prod_main_dyn.c -o prod_main_dyn.exe -ldl

Last edited by pludi; 12-18-2009 at 01:06 PM.. Reason: code tags, please...
 

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LEARN ABOUT LINUX

wsreg_can_access_registry

wsreg_can_access_registry(3WSREG)		    Product Install Registry Library Functions			 wsreg_can_access_registry(3WSREG)

NAME

       wsreg_can_access_registry - determine access to product install registry

SYNOPSIS

       cc  [flag ...]  file ...-lwsreg [library ...]
       #include <fcntl.h>
       #include <wsreg.h>

       int wsreg_can_access_registry(int access_flag);

DESCRIPTION

       The wsreg_can_access_registry() function is used to determine what access, if any, an application has to the product install registry.

       The access_flag argument can be one of the following:

       O_RDONLY        Inquire about read only access to the registry.

       O_RDWR	       Inquire about modify (read and write) access to the registry.

RETURN VALUES

       The  wsreg_can_access_registry()  function  returns non-zero if the specified access level is permitted.  A return value of 0 indicates the
       specified access level is not permitted.

EXAMPLES

       Example 1: Initialize the registry and determine if access to the registry is permitted.

       #include <fcntl.h>
       #include <wsreg.h>

       int main(int argc, char **argv)
       {
	   int result;
	   if (wsreg_initialize(WSREG_INIT_NORMAL, NULL)) {
	       printf("conversion recommended, sufficient access denied
");
	   }

	   if (wsreg_can_access_registry(O_RDONLY)) {
	       printf("registry read access granted
");
	   } else {
	       printf("registry read access denied
");
	   }

	   if (wsreg_can_access_registry(O_RDWR)) {
	       printf("registry read/write access granted
");
	   } else {
	       printf("registry read/write access denied
");
	   }
       }

USAGE

       The wsreg_initialize(3WSREG) function must be called before calls to wsreg_can_access_registry() can be made.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |Unsafe			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       wsreg_initialize(3WSREG), attributes(5)

SunOS 5.10							    22 Sep 2000 				 wsreg_can_access_registry(3WSREG)
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