Okay, so the child process was not actually access it's parent
variable, the child given a copy (i have learned about Copy On Write
mechanism too). But it is like a C language issue: we can access any
variable which declared in that function in this case main() function.
So in my code, when i try to access stack_int variable in child
process, it's not wrong, compiler even recognize this as 'valid'
approach... How about my conclusion?
On Mon, Mar 30, 2009 at 6:36 PM, Fabian Ischia <fischia@xxxxxxxxxxxxxxxx> wrote:
> 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
>> --
>> To unsubscribe from this list: send the line "unsubscribe
>> linux-c-programming" in
>> the body of a message to majordomo@xxxxxxxxxxxxxxx
>> More majordomo info at http://vger.kernel.org/majordomo-info.html
>>
>
--
To unsubscribe from this list: send the line "unsubscribe linux-c-programming" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
