On Friday 27 March 2009 15:29:20 Jamie Lokier wrote: > Lennart Sorensen wrote: > > > lies. there are no serious limitations at all with FDPIC ELF. it is > > > functionality equivalent to ELFs running under a MMU. > > > > Well I haven't looked at FDPIC ELF since it doesn't work on m68knommu > > yet. > > > > > you cannot do fork() without virtual memory since both processes will > > > have pointers to the same addresses and there's no way to relocate > > > them. > > > > OK, I suspected that was the case. > > You could do what Minix does. That is to copy the process writable > data and swap it on context switches - a big memcpy. That's a big > performance hit, but for process which do fork-then-exec (most of > them), it's only one copy, and avoids the special issues of vfork. > Maybe that would be worth adding to uClinux for the convenience and > portability improvement, despite the big performance hit. Then > "vforkizing" packages (which is often done wrong) would be for > optimisation not necessity.
hmm, wasnt aware that Minix did that. on systems with an MPU, the overhead could be mitigated as write accesses are trappable, so we would know exactly which pages had changed ... -mike
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