How to determine which thread implementation binary compiled with

Question

Is it possible to determine if a binary (static or shared and not stripped) is compiled with Linuxthreads or NPTL implementation ?

Answer 1

There are many ways, but I'll cite two. Usually, a binary file, if not stripped, contains symbols (function names, variable names, ...). These symbols are usually used to ease debugging and are stored using a certain format, DWARF for example.

The first method is to disassemble the binary and look for specific threading libraries related symbols. For example :

    objdump -D ./YOUR_PROGRAM | grep -i thread 

The second one is to hijack the threading library function calls using your own library and LD_PRELOAD. The concept is fairly simple, you write a library (.so) in which you implement the functions which you want to check for, let's say pthread_create or pthread_join, and reimplement it this way :

    int pthread_create(pthread_t *thread, 
                       const pthread_attr_t *attr,
                       void *(*start_routine) (void *), 
                       void *arg)
    {
          int ret;
          static void *(*ext_pthread_create)(pthread *, 
                                             const pthread_attr_t *,
                                             void *,
                                             void *);

          ext_pthread_create = dlsym("RTLD_NEXT", pthread_create);
          ret = ext_pthread_create(thread, attr, start_routine, arg);

          printf("pthread_create called !\n");

          return ret;
     }

All you have to do after compiling and testing your library is call yor program this way :

    LD_PRELOAD=hooklib.so ./YOUR_PROGRAM PARAMS

If the function is called, you'll see the printf message on the standard output.