Re: [uCsimm] phtreads (MMU, and correction to post)

From: Robert Eugene Wood (woodr@HiWAAY.net)
Date: Sun Sep 24 2000 - 03:08:49 EDT


Correction:
   I made a big mistake in my earlier post. The sentence
should have read that the uClinux environment has NO equivalent
to "Critical Section" calls.

After playing with my simm for a while, I can't even find
POSIX or SYSV semaphores! I see the linux semaphores in the
kernel tree source, but there is no exposed semaphore calls I
can link to! Someone please tell me I'm just
doing something stupid! Please!!

RE: MMU

Yeah, the MMU think does seem to be something that comes up a lot,
and I'm yet another guilty party for bringing it up!

I guess its just that I'm so used to the process model, that an
unprotected memory
model bothers me a bit. There is also the nasty potential
for a run-away pointer to corrupt no only the process/thread,
but to screw up the kernel as well. My earliest exposure
to coding in a multitasking environment was on an Amiga, which
also had no memory protection. Unfortunately, it was also
at the time I was learning C (a BIG step from FORTRAN on a VAX!),
so you can imagine the number of times I shot myself in the foot
with runaway pointers... I'm still at little gun shy (but it
was FUN to do).

On a more practical note, however, there is still the fact
that without an MMU it is much easier to fragment memory with
dynamic allocations over time.

The saving grace is that its an embedded system. Its not like
a log of general purpose software is being run to trash the
memory.

Robert Wood
woodr@hiwaay.net

On Fri, 22 Sep 2000, Geoffrey Wossum wrote:

> > - There is no memory protection between processes and all
> > programs (including the kernel) share the same address space:
>
> I've seen this mentioned several times on the list. Threads, on any
> platform, all share the same memory space. By definition, threads are
> used for shared memory parallel programming. So I'm not sure why the
> lack of memory protection changes anything for the threads. For
> processes, yes, but not for threads.
>
> ---
> Geoffrey Wossum
> gwossum@acm.org
> Project AKO - http://rover1.uta.edu/~ako
> Internet Imperialists - http://inetimperial.sourceforge.net
> This message resent by the ucsimm@uclinux.com list server http://www.uClinux.com/
>

This message resent by the ucsimm@uclinux.com list server http://www.uClinux.com/



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