Date: Sun, 17 Nov 1996 15:24:45 -0800 From: Erich Boleyn <erich@uruk.org> To: Bruce Evans <bde@zeta.org.au>, dg@root.com Cc: hackers@freebsd.org Subject: Re: Memory probe(s) in FreeBSD Message-ID: <E0vPGZx-0006py-00@uruk.org> In-Reply-To: Your message of "Mon, 18 Nov 1996 01:21:50 %2B1100." <199611171421.BAA19697@godzilla.zeta.org.au>
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Bruce Evans <bde@zeta.org.au> writes: > >There is a "valid" flag set in the info passed by the bootloader. You'll > >see it if you look in "i386/i386/machdep.c". > > Support for the really old bootblocks should be dropped, and the RTC > numbers should never be used. This takes less code and works better. > > >As to there being a problem a while ago... the problem was that the > >FreeBSD bootblocks read the return value from the EAX register for the > >upper memory BIOS call, where it is only valid for the AX register. Some > >machines return garbage in the high bits of EAX. The proper thing to > >do is to zero the top 16 bits of EAX after the INT 0x15 AH=0x88 call > >in the bootloader, not in the kernel proper (again, because some > >bootloaders might pass valid information from other BIOS interfaces). > > There will have to be a new version number just to fix this. The bits > need to be cleared in the kernel for the current version. Perhaps support > for all old boot blocks should be dropped. It is reasonable to require > that the (interface) version number of the bootblocks is >= that of the > kernel to reduce the number of cases. [to which David Greenman replies to the second sentence in the last paragraph and on:] > I strongly disagree with this, BTW. Hmm... this is starting to get complicated. I don't really want to fuss with the old-style BSD booting interface much because it needs a lot of fixing and simply can't be straightforwardly extended to include all the new things one might want to do. How about we leave the existing boot interface the way it is, and I'll generate a patch to use the new Multiboot interface (which can happily co-exist with the BSD methodology). Some really big advantages of the Multiboot stuff include of course the extra memory information, but also a real text command-line (i.e. no patches to the bootloader for every new kernel option supported) and multiple modules passed at boot-time to the kernel would then be supported. What do you think? -- Erich Stefan Boleyn \_ E-mail (preferred): <erich@uruk.org> Mad Genius wanna-be, CyberMuffin \__ (finger me for other stats) Web: http://www.uruk.org/~erich/ Motto: "I'll live forever or die trying"
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