[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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