Re: LD_PRELOAD and original lib. functions.

[Artur Skawina]

CyberPsychotic wrote:
> 
>  I am trying to write a library, which shall be loaded via LD_PRELOAD and
> replace several original libc functions. (for example, I want to have my
> fopen function, which would make some additional checks/logs).
> 
> Now the problem is how would I call the original routine within my
> library?


#include <dlfcn.h>      // dlsym

   // Pointers to the original libc functions. Initialized in _init().

static int  (*org_setsockopt)(int s, int level, int optname, const void *optval, int 
optlen);

   // Setup everything, or exit() if an error occurs.

int _init( void )
{
   // find the address of the original libc function.
   
   org_setsockopt = dlsym( RTLD_NEXT, "setsockopt" );
   if ( !org_setsockopt )
      fatalerr( "Original 'setsockopt()' not found.\n" );
      
   return 0;
}

int setsockopt( int s, int level, int optname, const void *optval, int optlen )
{
   { ...your code... }
   
   return org_setsockopt( s, level, optname, optval, optlen );
}