From: Otto Moerbeek (ottodrijf.net)
Date: Mon Nov 06 2006 - 03:35:05 CST

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On Mon, 6 Nov 2006, Kasicass wrote:

> Hi all,
>
> I just run the following program in obsd 3.9, but it doesn't work as
> expected. As said that child process created by vfork should run in the
> address space of the parent, until it calls exec/exit.

Not _should_, posix is very clear about that. It warns you not to
depend on those semantics. BTW, I think you swapped your results.

        -Otto
        
>
> ---------
> #include <sys/types.h>
> #include <unistd.h>
> #include <stdio.h>
> #include <stdlib.h>
>
> int glob = 6; /* external variable in initialized data */
>
> int
> main(void)
> {
> int var; /* automatic variable on the stack */
> pid_t pid;
>
>
> var = 88;
> printf("before fork\n"); /* we don't flush stdout */
>
> if ( (pid = vfork()) < 0 )
> ;
> else if (pid == 0)
> { /* child */
> glob++; /* modify variables */
> var++;
> _exit(0); /* child terminates */
> }
>
> printf("pid = %d, glob = %d, var = %d\n", getpid(), glob, var);
> exit(0);
> }
> ---------
> In obsd, result is
>
> before fork
> pid = xxx, glob = 7, var = 89
>
>
> But in Linux 2.6/FreeBSD 5.4-RELEASE, it works fine. The result is
>
> before fork
> pid = xxx, glob = 7, var = 89
> ---------
>
> I've not much time to dig into the kernel code, could anyone give me a
> brief description about why it runs like that.
>
> Thx a lot.
>
>
> --
> Best regards#!
>
> Kasicass/sYcini - Coder
> http://www.sycini.com

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