Re: Linus replies. Re: Computer: Can We Make Operating Systems Reliable and Secure?// SAS

[Niklas Klügel]

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>

> Consider:
>
> 1. The measured performance of the best JVM sucks. 2. There is no
> possibility of hard real-time in a garbage-collected runtime. 3.
> The amount of code needed to implement a decent JVM (or similar
> system) is approximately 10x the amount of code needed to implement
> a protected microkernel.
>
that was not my point. it was an example that software-based
memory protection is already practicable at acceptable costs.
there are probably many ways of making memory protection
software based with less overhead. i could also argue that in
some fields of application program-verification works, so
(leaving inconsitencies caused by concurrency aside)
there is no overhead at all added and the operating
system environment is unequally simpler than anything
beyond DOS :)

to make a clear conculsion: all that i am saying is, that the
complexity introduced by highly modular OSes in order
to adapt to former/common principles of OS-Development/Design/etc
might be a sign that these former/common principles
are wrong for the aims of such highly modular OSes.

> Next time your life depends on the software being right, which one
> would you rather depend on?
>
>> today the programming languages and its environments allow a much
>> finer granularity of modularity.
>
>
> You also mentioned sharing. Sharing isn't the solution to
> robustness. It's the *problem*.

i didnt say that either. i said that sharing is more complex in
non-SAS environments and that there are no
restrictions in SAS-environments about what entity shares which objects.

> Shared-memory concurrency is known to be a completely
> non-engineerable approach.
>
> Finer granularity is not always better. The trick is to discover
> the finest granularity that real programmers can manage
> successfully. Unfortunately, there seem to be different answers for
> program structure (the object boundary) than for protection
> structure (the subsystem boundary).

true.

So long...
niklas

>
>
> shap
>

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