Help?

[Kwanghoon Choi <khchoi at ruby dot kaist dot ac dot kr>]

Hello all,

I would like to know the precise sequence of loading and execution of
a given executable. In my specific flatform (the ARM machine, uclinux kernel,
gcc, and glibc), I am using binary executables in a flat form, not like ELF. 
The below simple program gets crashed whenever I compile the program with 
-lpthread even if the program does not use the thread library. If I omit
the option -lpthread, it works well! 

   main()
   {
        int childpid;

        if( (childpid = vfork()) == -1 ) {
                /* can't vfork */
        }
        else if(childpid == 0) {
               /* child process */
        }
        else {
        	    /* parent process */
        }
   }

I know it is foolish to give the option -lpthread in my simple program,
but it is just a test to resolve my questions to be explained.
In order to examine why, I instrumented some printf-like functions into
uclinux kernel sources and glibc sources.  

By instrumenting pthread library functions in glibc, I found that 
pthread_initialize() gets called before the main() function.
The reason seems to be that the function is declared as this:  

   static void pthread_initialize(void) __attribute__((constructor));

My execution sequence is like this as far as I know by instrumenting 
printf-like functions.

   KERNEL : ...
            search_binary_handler() // load an executable in a flat form
            do_load_flat_binary()   // $UCLINUX/fs/binfmt_flat.c
            ...
            wake_up()               // the process for the executable 
                                    // gets control
            ???

   USER   : ???
            __libc_start_main       // $GLIBC/sysdeps/generic/libc-start.c
                                    // glibc's entry ?
            ???
            pthread_initialize()    // $GLIBC/linuxpthread/pthread.c
                                    // pthread initialization  
            ...
            main()                  // user's program 

First, I don't know who really calls __libc_start_main() functions. Notice 
that it receives several arguments, mostly function pointers.

   int __libc_start_main (int (*main) (int, char **, char **), int argc,
                          char **argv, void (*init) (void), void (*fini) (void),
                          void (*rtld_fini) (void), void *stack_end)
   {
     ...
   }

Second, though I know pthread_initialize() is (indirectly) called in the 
__libc_start_main(), I don't know where exectly. The reason is that
pthread_initialize() seems to be called via some function pointer, e.g. init().

Third, I don't know how GCC compiles the functions declared with 
__attribute__((constructor)). I would like to know the compilation
strategy specifically in the flat-formed executable.


Although I will check this mailing list reguraly, it would be happy
to forward your reply to khchoi@pllab.kaist.ac.kr.

Thank you for reading my long mail.

Kwanghoon

p.s. I looked around the site of GCC online documentation 
       (http://www.gnu.org/software/gcc/onlinedocs/)
     but it contains some broken links, e.g. for GCC manual 
       (http://gcc.gnu.org/onlinedocs/gcc_toc.html)