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(solved) Grub: Memtest86+ won't fit into memory
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haarp
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Joined: 31 Oct 2007
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PostPosted: Fri Mar 12, 2010 7:43 am    Post subject: (solved) Grub: Memtest86+ won't fit into memory Reply with quote

Hello,

Memtest86+ (4.00) always worked flawlessly for me. After upgrading my mainboard however, I'm getting the following error when I try to run memtest from grub:

Quote:
Error 28: Selected item cannot fit into memory


After some googling, I discovered the following in the FAQ on Memtest's forums:

Quote:
Note that on some computers this does not work and results in an "Error
28: Selected item cannot fit into memory" reported by grub. The problem
here is that memtest86+ uses the legacy linux loading mechanism which
expects to be loaded at 0x9A000 in memory. On some systems the BIOS uses a
part of the memory closely after this address and correctly reserves it in
the e820 memory map. Grub will then fail to load memtes86+ over this
reserved memory area, which is the correct behaviour. For now there is no
way to circumvent this. The memtes86+ loader should be rewritten to use a
newer loading mechanism, but this will be quite a big task. It is unclear
when this will be realised.


Is there really no way around this? Can I tell grub to just ignore the mapped address and continue loading anyway? Whatever the BIOS is putting in there, I'n pretty sure there's no harm in overwriting it. (why shoul it be needed? I'm starting memtest, not an OS)
I feel like I'm back in the days of DOS games. You may have hundreds of megabytes of memory, but can't start the game because only lowmem counts :roll:


Last edited by haarp on Mon Apr 26, 2010 7:36 pm; edited 1 time in total
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Link31
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Joined: 17 Apr 2006
Posts: 200
Location: France

PostPosted: Fri Mar 12, 2010 10:42 pm    Post subject: Re: Grub: Memtest86+ won't fit into memory Reply with quote

haarp wrote:
Is there really no way around this? Can I tell grub to just ignore the mapped address and continue loading anyway? Whatever the BIOS is putting in there, I'n pretty sure there's no harm in overwriting it.

You really don't want to overwrite the Extended BIOS Data Area (EBDA), because the System Management Mode (SMM) may need it and you can't block the SMM, so really bad things could happen to your system. And since memtest86+ runs in real mode (16-bits mode), you can't remap this physical part of the memory to another location using virtual memory, which is a protected mode (32-bits) feature.

You're right, this is exactly like back in the time of DOS, since DOS did also run in 16-bits mode.
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haarp
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PostPosted: Fri Mar 12, 2010 11:32 pm    Post subject: Reply with quote

Well, you are right. But I don't have a choice now do I? ;)
I put the Memtest binary on a raw floppy disk now. Booting this floppy circumvents grubs failsafes and allows the Memtest to start. Meh.
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seeraven
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PostPosted: Sat Apr 24, 2010 6:21 am    Post subject: Reply with quote

Have you tried the alternative installation method for grub that is mentioned in the info after emerging the package?

Code:
...
or try this if you get grub error 28:
    > title=Memtest86Plus
    > root (hd?,?)
    > kernel --type=netbsd /boot/memtest86plus/memtest.netbsd
...


Works at least for me. :)
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haarp
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PostPosted: Mon Apr 26, 2010 7:35 pm    Post subject: Reply with quote

I could've sworn that I already tried that. Mhhh...
Works for me. Thanks!
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gionnico
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PostPosted: Tue Jul 27, 2010 2:49 pm    Post subject: Reply with quote

Doesn't work for me.. grub-0.97-r10
"Error 28: Selected item cannot fit into memory"
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