[syslinux] memdisk and grub
H. Peter Anvin
hpa at zytor.com
Tue Aug 27 11:47:14 PDT 2002
Henrik Nordstrom wrote:
> Hi,
>
> I am trying to use MEMDISK from the GRUB boot loader, and gets stuck on the
> memory detection. MEMDISK reports
>
> dos_mem = 0
> low_mem = 0
> high_mem = 0
>
>>From reading the sources this would be if the e820 query does not return any
> valid data. Confirmed by adding a printf in insertrange(). insertrange() does
> not seem to be called at all during the memory detection (only to reserve the
> ramdisk memory before MEMDISK bails out)
>
> However, when booting a Linux kernel the Linux kernel does detect a e820 BIOS
> memory map that looks pretty OK to me:
>
> BIOS-provided physical RAM map:
> BIOS-e820: 0000000000000000 - 00000000000a0000 (usable)
> BIOS-e820: 00000000000f0000 - 0000000000100000 (reserved)
> BIOS-e820: 0000000000100000 - 000000000fe00000 (usable)
> BIOS-e820: 00000000ffff0000 - 0000000100000000 (reserved)
> user-defined physical RAM map:
> user: 0000000000000000 - 00000000000a0000 (usable)
> user: 00000000000f0000 - 0000000000100000 (reserved)
> user: 0000000000100000 - 000000000fe00000 (usable)
> user: 00000000ffff0000 - 0000000100000000 (reserved)
>
This is probably because GRUB likes to mess with the memory map instead
of letting the kernel do the right thing (hence the "user-defined
physical RAM map".) This is a total braindamage in GRUB.
-hpa
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