Messages in this thread | | | Subject | Re: fork,clone,CLONE_VM prob. | Date | Sat, 05 Sep 1998 02:44:18 -0400 | From | Zack Weinberg <> |
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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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