Delay-Load equivalent in unix based systems

Question

What is the delay load equivalent in unix based system.

I have a code foo.cpp, While compiling with gcc I link it to shared objects(tot

Answer 1

I know it has been 8 years but still...

Delay load is not supported out out the box on GNU systems but you can mimic it yourself by creating a small static stub which provides all necessary symbols and dlopens real implementation on first call (or even at program startup). Such stub can be written by hand, generated by project-specific script or via Implib.so tool:

# Replace
$ gcc -o foo foo.c -lversion
# with
$ implib-gen.py libversion.so
$ gcc -o foo foo.c libversion.tramp.S libversion.init.c

Answer 2

See the reference on your system for dlopen(). You can manually open libraries and resolve external symbols at runtime rather than at link time.

Dug out an example:

int main(int argc, char **argv) {                 
    void *handle=NULL;                                 
    double (*myfunc)(double);                     
    char *err=NULL;                                  

    handle = dlopen ("/lib/libm.so.1", RTLD_LAZY);
    if (!handle) {                                
        err=dlerror();
        perror(err);
        exit(1);                                  
    }                                             

    myfunc = dlsym(handle, "sin");                
    if ((err = dlerror()) != NULL)  {           
        perror(err);
        exit(1);                                  
    }                                             

    printf("sin of 1 is:%f\n", (*myfunc)(1.));              
    dlclose(handle);            
    return 0;                  
}