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SubjectRe: fork,clone,CLONE_VM prob.
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Konstantin Muenning wrote:
>On Fri, 4 Sep 1998, Richard Gooch wrote:
>>Chris Wedgwood writes:
>>> On Fri, Sep 04, 1998 at 01:29:55AM +0200, Konstantin Muenning wrote:
>>> > I have figured out that any combination of the clone-flags works
>>> > except when using CLONE_VM. Even when using CLONE_VM, the call
>>> > completes successful.
>>>
>>> I think when using CLONE_VM both processes return with the same stack
>>> and bad things happen.
[...]
>>> You need some assembly here to fix this up, I think libpthreads does
>>> it this way.
>>
>>Yep.
>
>I'm not afraid of assembler but I don't see where I'll need it.
>
>If it's realy true that also the stack pointer is passed identical to the
>child process so they use really the same physical memory it is clear that
>one of the processes cannot run right. In that case I have to allocate a
>new selector for the PL3 Stack (hmm, maybe for the PL0 stack too?),
[...]

You're working too hard. All you have to do is change the user-space stack
pointer to point at (the top of) a block of memory allocated for the
purpose, and jump into a new function. If that function returns, make an
exit() syscall. Obviously you do this only in the child.

Or you can use glibc, which has a clone() wrapper that does all this for
you.

/* int clone(int (*fn)(void *), void *child_stack, int flags, void *arg); */

It doesn't work right if you try to use it without CLONE_VM though -
something to fix.

Hmm... A clone flag that shared all of VM except the stack might be
interesting.

zw

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