a simple dynamic linking program

kris273 · 04-17-2004, 04:16 AM

currently I'm trying to get a Dynamic link and load progam working

I have 2 programs, one given by the man pages of dlopen, which works fine

The other I try to get something more usable but I keep getting an "invalid elf header. I'm not really sure what that is, or why I'm getting it.

i'm trying to just make it call a "printf("hello world");" type function that's stored in a seperate file, the instructions i have talk about compiling it with gcc -fPIC -g....and some others i'm not to familar with, the end product would be hello.so....

anyone have a good idea on this? or a good source for reading up on where to find out more about this?

Kris

kev82 · 04-17-2004, 06:41 AM

with seeing the code i cant do much but heres a simple example

dlload.c

Code:

#include <dlfcn.h>

int main(int argc, char **argv)
{
        void *lib;
        void (*fn)();

        if(argc != 2) return -1;

        lib=dlopen(argv[1], RTLD_LAZY);
        fn=dlsym(lib, "hello");

        fn();

        dlclose(lib);
        return 0;
}

hello.c

Code:

#include <stdio.h>

void hello()
{
        printf("Hello\n");
}

[kev82@tifa:kev82](1050)$ gcc -o dlload dlload.c -ldl
[kev82@tifa:kev82](1051)$ gcc -shared -fPIC -o hello.so hello.c
[kev82@tifa:kev82](1052)$ ./dlload ./hello.so
Hello
[kev82@tifa:kev82](1053)$

kris273 · 04-17-2004, 12:18 PM

thank you, using

the compile lines you gave me seemed to work

I just had one final question, any good resourced for learning more about dynamic linking and loading?

Kris

kev82 · 04-18-2004, 06:26 AM

http://www.linuxquestions.org/questi...hreadid=169427

the article is specifically about writing plugins but contains some basic information, theres also a few good links in my public bookmarks that cover this