Path: utzoo!attcan!uunet!mcvax!hp4nl!phigate!philmds!leo From: leo@philmds.UUCP (Leo de Wit) Newsgroups: comp.sys.atari.st Subject: Re: Multitasking on the ST Message-ID: <1070@philmds.UUCP> Date: 12 Aug 89 15:47:58 GMT References: <8908021826.AA05333@ucbvax.Berkeley.EDU> <15627@watdragon.waterloo.edu> <652@opal.tubopal.UUCP> <471@tw-rnd.SanDiego.NCR.COM> <1066@philmds.UUCP> <675@opal.tubopal.UUCP> Reply-To: leo@philmds.UUCP (Leo de Wit) Organization: Philips I&E DTS Eindhoven Lines: 37 In article <675@opal.tubopal.UUCP> alderaan@tubopal.UUCP (Thomas Cervera) writes: |In article <1066@philmds.UUCP> leo@philmds.UUCP (Leo de Wit) writes: |> In the current situation it is just as well feasible for |>instance by an application program to thrash the space of the shell it |>was invoked by. So if you insist on security, you should insist on it |>right now already. | | Absolutely correct. But using a multi-tasking system this problem will |multiply. A so-called multi-problem system 8-) ? B.T.W. I don't see why. | |>An MMU alone probably won't hack it; you will probably want a 680x0 |>(x >= 1) to be able to page in new memory (a 68000 doesn't maintain |>enough internal information to be able to restore correctly from a |>BUSERR). | | But isn't there any software solution to that ? (I'm looking on primitive |MMU versions on PDPs where the operating system does a part of context- |saving work on failed EMT or TRAP recovery). The LSI11 processors are very |much like the M68k family. Or is this really impossible on 680x0 ? (Remember, |I'm only a dumb physicist :-) ) The problem is that for instance a page fault can emerge whilst in the middle of an instruction. Whereas the 68010, 68020 etc. store much information on the stack at a BUSERR (29 words if I'm correct), the 68000 only stores 7 words, which is not sufficient to resume each type of instruction. For instance: movem.l (a3),a2-a5 Since this instruction modifies the contents of a3, it cannot be resumed when a bus error occurs after a3 has been modified (and the instruction has not yet completed). Leo.