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- Path: comma.rhein.de!serpens!not-for-mail
- From: mlelstv@serpens.rhein.de (Michael van Elst)
- Newsgroups: comp.sys.amiga.misc
- Subject: Re: OS features
- Date: 9 Jan 1996 02:16:05 +0100
- Organization: dis-
- Message-ID: <4csfkl$oco@serpens.rhein.de>
- References: <92747544038@PAPA.NORTH.DE> <4b3h9s$1st@alterdial.UU.NET> <2152.6561T63T2136@cycor.ca> <4b7i18$si1@vixen.cso.uiuc.edu> <oj6raxxrr0o.fsf@hpsrk.fc.hp.com> <13213431@sourcery.han.de> <4cp0un$cve@serpens.rhein.de> <4cs4ji$rou@news.mpd.tandem.com>
- NNTP-Posting-Host: serpens.rhein.de
-
- Joseph Crowe <jcrowe> writes:
- > I'm struggling to understand what you mean by the above paragraph. I don't
- >find it at all desirable to have a system where an interface library can
- >arbitrarily corrupt data structures in user task space. Could you relate this
- >concept to a more concrete example?
-
- Think about the UNIX kernel. No user task is protected from the kernel, the
- kernel can access everything. This is only a small risc because the kernel
- has only few bugs.
-
- So the design for memory protection doesn't need to protect arbitrary
- objects. You just have to protect the good guys (well debugged libraries)
- against the bad guys (arbitrary user code).
-
- > Are you saying that some sort of object server should be allowed to
- >arbitrarily corrupt an instantiation of a client or even an inherited object in
- >the client tasks memory area? Not in any OS I'd ever own.
-
- It is basically in every OS that provides protection. With UNIX the
- whole system library (aka the kernel) can corrupt user programs.
- Other systems use several layers of protection to minimize the riscs.
-
- > With demand paged VM, there's often multiple sizes of allocation units, at
- >least, once you leave user space.
-
- Huh ? The "allocation" unit is a page. And a page is usually of constant
- size for the whole system.
-
- >algorithm. Most shared library implementations in UNIXland will not even bring
- >in a single page of a shared library until a page fault occurs attempting to
- >access and instruction from that library.
-
- Hasn't to do anything with fragmentation though.
-
-
- --
- Michael van Elst
-
- Internet: mlelstv@serpens.rhein.de
- "A potential Snark may lurk in every tree."
-