OSDev.org

Posted: **Sun May 25, 2003 8:51 am**

Alright, I will try to make a long story short:
I've been implementing the FORK system call and I am currently debugging the do_fork() function.

Code: Select all

void init()
{
  pid_t pid;

  if ((pid = do_fork()) == -1) panic("FORK failed");
  else if (pid > 0) { while(1) printf("parent\n"); }
  while(1) printf("child\n");
}

This code does the following. At first the string "parent" is printed out as it should be. Next, the child process is picked to run and I get the "child" string on the screen. The problem is that the parent process is never picked up again. It's always the child who has the CPU. Besides, I get a "3rd (14) exception with no resolution" later on.
So I am asking you now if you have an idea what might be the bug. My procedure is simple: do_fork() copies the stack and creates a new context for the child. This context sets EBP to the parent's EBP and EIP to the function fork_out:

Code: Select all

fork_out:
   mov eax, 0
   leave
   ret

I attached the fork.c file, maybe you can have a look at it?

thanks and best regards,
Alexander

edit: Note that I didn't implement FORK as a system call yet, I am trying to debug the do_fork() function at first.

[attachment deleted by admin]

OSDev.org

FORK problem

FORK problem