From mboxrd@z Thu Jan  1 00:00:00 1970
From: Fabian Ischia <fischia@somanetworks.com>
Subject: Re: Linux process...
Date: Mon, 30 Mar 2009 07:36:15 -0400
Message-ID: <49D0AEAF.1070607@somanetworks.com>
References: <34e1241d0903292306m3e879639u4752e821349c84ee@mail.gmail.com>
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To: beginner_h4x3r <nightdecoder@gmail.com>
Cc: linux-c-programming@vger.kernel.org

 From the example code, I think the answer is a bit simpler than it 
looks like. The address space is "duplicated" not "shared". Whatever you 
do in one process "after" the fork will not affect the other process.
The Child process has not initialized the variable, so being a stack 
variable it just contains garbage.

Fabian

beginner_h4x3r wrote:
> Hi All..
>
> I am a beginner hacker, i want to learn Linux from scratch. I read
> some resources on Linux's process management. Process duplicates it's
> page table to it's child process, right? so i wrote demonstrate code
> to prove this.
>
> #include <stdio.h>
> #include <stdlib.h>
> #include <unistd.h>
> #include <sys/types.h>
> #include <sys/wait.h>
>
> int main (void) {
>   pid_t child;
>   int stack_int;
>
>   child = fork ();
>   if (child == 0) {
>       sleep (1); /* ;p */
>       printf ("child process stack_int value %i, address: %p\n",
> stack_int, &stack_int);
>       exit (0);
>     }
>   if (child == -1) {
>       perror ("fork");
>       return -1;
>     }
>   stack_int = 32;
>   printf ("main process stack_int value %i, address: %p\n", stack_int,
> &stack_int);
>   waitpid (child, NULL, 0);
>
>   return 0;
> }
>
> The output is:
> main process stack_int value 32, address: 0xbf9c66ec
> child process stack_int value 8495092, address: 0xbf9c66ec
>
> stack_int value is different from parent and it's child.
>
> My question: why the stack_int has a same address between parent and
> it's child ?, but confusedly... they have a different value, i was
> though it should be different, since process duplicate it's page to
> child, please explain me. ;)
>
> Thanks before.
>
> --- curious_hacker
> --
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