Finding the address of a function

[Mihai Donțu]

On Fri, 19 Apr 2013 17:46:05 +0200 MARGUINAUD Philippe wrote:
> Hi all,
> 
> I am trying to find the address of a function whose name is known,
> using dlopen/dlsym; for instance, I would have expected this program
> to print the address of the main function :
> 
> #include <dlfcn.h>
> #include <stdio.h>
> 
> int main ()
> {
>   void * lib = dlopen (NULL, RTLD_NOW);
>   void * sym = dlsym (lib, "main");
>   printf ("error=%s\n", dlerror ());
>   printf ("sym=0x%llx\n", sym);
> }
> 
> But instead, I get the following output :
> 
> error=./main.x: undefined symbol: main
> sym=0x0
> 
> How shall I proceed ?
> 

'main' is not in the program's dynamic symbol table (which is what
dlsym() "interrogates"):

$ objdump -T example | grep main
0000000000000000 DF *UND* 0000000000000000 GLIBC_2.2.5 __libc_start_main

Make sure the symbol you're looking for has been made available for
dynamic linking.

-- 
Mihai Donțu