Initialize the stack variable, when you do its retained thoughout
execution of both processes. I think when a variable is uninitialized
its given null value, and doesnt really get copied in a sense, I have
also read that threads can have their own local thread storage areas.
try a strace on the executable to see what flags clone() is being used
by glib.
beginner_h4x3r wrote:
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
--
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
