[syslinux] Re: Problem with FreeDOS + himem64 + PXELINUX + memdisk

[H. Peter Anvin]

Patrick J. LoPresti wrote:
> The following reply was sent only to freedos-devel.  I do not know the
> answers to his questions (although I suspect the "keeppxe" flag has
> something to do with it).
> 
> Any help would be appreciated.  Feel free to CC
> freedos-devel at lists.sourceforge.net.
> 
>  - Pat
> 
> 
> From: Eric Auer <eric at CoLi.Uni-SB.DE>
> Message-Id: <200401262148.WAA03293 at gnome.at.coli.uni-sb.de>
> To: freedos-devel at lists.sourceforge.net
> Subject: [Freedos-devel] re: Problem with FreeDOS + himem64 + PXELINUX + memdisk
> Date: Mon, 26 Jan 2004 22:48:36 +0100 (MET)
> Lines: 48
> 
> 
> Hi Pat, are you sure that you do not for example have a virus on
> that system? Well, maybe it is just the PXE software but:
> 
> 
>>Old dos memory at 0x8fc00 (map says 0x9f800), loading at 0x8f400
>>old: int13=e1f74d1a  int15=f000f859
> 
>              **** Something in the UMB / ROM area hooks BIOS disk int

Indeed, that is odd.

> Further, the "old DOS memory" information tells us that according to
> int 15, 638k of 640k (rest is BIOS EBDA I guess) should be avail, but
> that actually 63k less than that are available in low memory. MEMDISK
> then allocates 2k more there.

This is presumably explainable by Patrick using "keeppxe" -- this is the 
memory occupied by the PXE stack.

>>Ramdisk at 0xfe60000, length 0x00168000
>>e820: 0000000000100000  000000000fef0000  1
>>e820: 000000000fff0000  000000000000ec00  3
>>e820: 000000000fffec00  0000000000001400  4
>>e820: 00000000fff80000  0000000000080000  2
> 

These are: address, length, type for each INT 15h, AX=0E820h memory 
area.  The type codes are 1 = memory, 2 = reserved, 3 and 4 = ACPI.

> Not sure how to read this, but looks like for example you have some
> 59k used at the end of the first 16 MB - maybe an overlay of some sort,
> special disk driver, ROM, BIOS data area for suspend...? Then there are
> 5k more to round up to 16 MB. Finally you have 512k of something much
> later, maybe a framebuffer or something. The MEMDISK (again, if I do
> understand things right) uses 1.5 MB at the end of the first big chunk
> in the first 16 MB. This seems to overlap other things, but I do not hope
> that MEMDISK would have such an obvious bug...
> 
> As I do not know whether I have to subscribe to SYSLINUX for mailing there
> and as I do not know whether it has address hiding in a possible web archive,
> I am not CCing SYSLINUX at zytor - but feel free to forward.

http://www.zytor.com/mailman/listinfo/syslinux

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> Hope this is not a too unqualified posting... Maybe PXELINUX or some BIOS
> or driver thing is an easy explanation for the extra memory areas, and
> maybe I misinterpreted the int 15.e820 information completely and there is
> no overlap, but you never know 8-].

	-hpa