Date: Mon, 16 Dec 1996 08:50:04 -0500 From: Tony Overfield <tony@dell.com> To: Terry Lambert <terry@lambert.org> Cc: eivind@dimaga.com, hackers@freebsd.org Subject: Boot loader hacks was: Re: MAXMEM Message-ID: <3.0.1.32.19961216085001.0067ee14@bugs.us.dell.com>
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At 01:41 PM 12/15/96 -0700, Terry Lambert wrote:
>> There are standardized BIOS calls to obtain the correct amount of
>> memory, even when it exceeds 65 MB. I think the boot loader should
>> make these BIOS calls and pass the correct information to the kernel.
>
>Go ahead and add it. Make sure the boot code doesn't grow over
>the 8k limit imposed on it by the fact that there isn't any more
>space between the start of the BSD area on the disk and the disklabel
>on everyone's hardrives for several years now...
>
> Regards,
> Terry Lambert
> terry@lambert.org
>---
>Any opinions in this posting are my own and not those of my present
>or previous employers.
I think that boot2 can only be 7 KB. Even so, there seems to be plenty
of space to do this. So I started hacking on FreeBSD. (There should
be a mailing list for this kind of thing.)
My first quick attempt, which still needs improvement, though it works
fine on my 96 MB system :-), adds about 160 bytes of bloat to boot2 to
bring it from 6576 to 6736 bytes. I only coded in the E820h function,
and not the E801h function, since E820h is the harder one. There's
still over 400 bytes left for more stuff!
My code doesn't fully comprehend the E820h call, it just looks for any
valid system memory descriptor that starts at 1 MB and it takes that
one. Extra code to merge in overlaps and adjacencies would consume
several more bytes :-(. Ironically, it looks like fully generalizing
the function to pass the entire table of information to the kernel for
processing would probably be smaller.
Unfortunately,
if (bootinfo.bi_extmem != biosextmem)
printf("BIOS extmem (%ldK) != RTC extmem (%dK)\n",
bootinfo.bi_extmem, biosextmem);
this code in machdep.c complains about my boot loader patches but
doesn't choose the bigger value. Does anyone know why the comment,
"Prefer the RTC value for extended memory." appears near this code?
Well I didn't, so I added these lines right afterwards:
if (bootinfo.bi_extmem > biosextmem)
biosextmem = bootinfo.bi_extmem;
I can send diffs if anybody wants them. I'm not very proud of how
I drew the line between the .c and the .S code, so I didn't put them
up here in front of everybody.
-
Tony
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