A test for vfork

[Geoff Keating]

> Mail-Copies-To: never
> Cc: libc-hacker@cygnus.com
> From: Andreas Jaeger <aj@arthur.rhein-neckar.de>
> Date: 15 Jan 1999 17:33:30 +0100
> User-Agent: Gnus/5.070069 (Pterodactyl Gnus v0.69) XEmacs/21.0(beta62) (Pyrenean)
> 
> >>>>> Andreas Schwab writes:
> 
>  > Here is a test for vfork which should tell you if it is implemented
>  > correctly.  Especially the generic source linux/vfork.c is unusable for
>  > machines that put the return pc on the stack (like ix86).  Remember that
>  > the stack is shared between the parent and the child, thus any function
>  > call in the child will clobber the return pc from vfork of the parent.
>  > See the existing implementations under sysdeps/unix for hints.

Ouch!

What machines do _not_ store the return PC on the stack at some point?
Even if the routine called is called through a lazy PLT entry?

I think the best solution is to modify the kernel so that the parent
process does not run until the child process exits or execs.  Failing
that, vfork() must allocate a new stack for the child to use
(allocated by the child, if possible) and switch to that.

-- 
Geoffrey Keating <geoffk@ozemail.com.au>