Path: csiph.com!eternal-september.org!feeder.eternal-september.org!.POSTED!not-for-mail From: John Ames Newsgroups: comp.os.linux.misc,alt.folklore.computers Subject: Re: Unix on x86, Hmmm ... Downloaded Xenix - But It's *41* Floppies Worth Date: Wed, 27 Aug 2025 08:30:20 -0700 Organization: A noiseless patient Spider Lines: 20 Message-ID: <20250827083020.0000469b@gmail.com> References: <105fgk4$2ka5f$1@dont-email.me> <20250721093237.0000674f@gmail.com> <108k7rn$e12$4@news.misty.com> <108l4vk$77t$1@gal.iecc.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Injection-Date: Wed, 27 Aug 2025 15:30:24 +0000 (UTC) Injection-Info: dont-email.me; posting-host="b28163a3d469ae7425d3bdd0db7e42e9"; logging-data="716762"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX18weBEb+l2Z2NbUZh1eQBCMxUiqQ8g77zU=" Cancel-Lock: sha1:qds2QtLIQQDnlcbM1tLz09ejF2Y= X-Newsreader: Claws Mail 4.3.0 (GTK 3.24.42; x86_64-w64-mingw32) Xref: csiph.com comp.os.linux.misc:72402 alt.folklore.computers:231632 On Wed, 27 Aug 2025 16:40:27 +0200 Alexander Schreiber wrote: > > That would require instructions that the C compiler > > didn't generate. > > That claim "would require instructions that the C compiler didn't > generate" is just not true. Without memory protection, there are > plenty of ways to crash the system - e.g. overwriting the operating > system code due to a bug in an application. It's certainly true that there's no *real* protection on the 8086. AFAIUI the logic is that, if generated code doesn't touch the segment registers and the OS allocates either 64KB shared or 64KB code + 64KB data, a 16-bit address won't ever overstep into the next 64KB of RAM, but x86 addressing can have up to three 16-bit components (two index registers plus a fixed offset,) so it's entirely possible for basic addressing operations to overstep that boundary, unless the compiler just forgoes complex addressing entirely.