Syslinux - Aug 2007 - memdisk patch

Hello all,

I ran across a couple bugs in memdisk concerning hd images the other
day.  With the attached patch I've been able to successfully boot a
32MB gzipped hd image.  (I'll put the image up for a short while at
ftp://ftp.io.com/pub/usr/duanev/fdoshd.img.gz)

The pxelinux.cfg entry I'm using is:

    label fdos
        kernel memdisk
        append keeppxe initrd=fdoshd.img.gz

syslinux/memdisk is great, thanks Peter et. al.!

-- 
Duane Voth
duanev at io.com
-------------- next part --------------
--- memdisk.asm.orig	2007-08-20 13:02:26.000000000 -0500
+++ memdisk.asm	2007-08-20 17:31:17.000000000 -0500
@@ -462,10 +462,10 @@
 		cmp dword [es:si+4],-1
 		je .linear_address
 
-		movzx esi,word [es:si+4]	; Offset
+		movzx ebx,word [es:si+4]	; Offset
 		movzx edi,word [es:si+6]	; Segment
 		shl edi,4
-		add esi,edi
+		add ebx,edi
 
 		jmp .got_address
 
@@ -476,23 +476,24 @@
 		cmp dword [es:si+20],0		; > 4 GB addresses not supported
 		jne .overrun
 
-		mov esi,[es:si+16]
+		mov ebx,[es:si+16]
 
 .got_address:
 		cmp dword [es:si+12],0		; LBA too large?
 		jne .overrun
 
 		movzx ecx, word [es:si+2]	; Sectors to transfer
-		mov edi,[es:si+8]		; Starting sector
-		mov eax,edi
+		mov esi,[es:si+8]		; Starting sector
+		mov eax,esi
 		add eax,ecx
 		jc .overrun
 		cmp eax,[DiskSize]
 		ja .overrun
 
 		shl ecx,SECTORSIZE_LG2-2	; Convert to dwords
-		shl edi,SECTORSIZE_LG2		; Convert to an offset
-		add edi,[DiskBuf]
+		shl esi,SECTORSIZE_LG2		; Convert to an offset
+		add esi,[DiskBuf]
+		mov edi,ebx
 		pop es
 		ret

Duane Voth wrote:
> Hello all,
> 
> I ran across a couple bugs in memdisk concerning hd images the other
> day.  With the attached patch I've been able to successfully boot a
> 32MB gzipped hd image.  (I'll put the image up for a short while at
> ftp://ftp.io.com/pub/usr/duanev/fdoshd.img.gz)
> 
> The pxelinux.cfg entry I'm using is:
> 
>     label fdos
>         kernel memdisk
>         append keeppxe initrd=fdoshd.img.gz
> 
> syslinux/memdisk is great, thanks Peter et. al.!
> 
Thanks!!  Staring at it, I feel like a total doofus... I guess that's
what happens when one doesn't get the time to work properly.

I had to massage your patch to fit into the latest source base; could
you please try out 3.52-pre8 to make sure it works as intended?

(I have also downloaded your disk image and added it to my collection.
It booted, but gave me an "invalid opcode" error after loading DOSLFN
--
looks like it might be related to the program "tcpinfo".  Not sure if
that is expected or not.)

	-hpa

On Mon, Aug 27, 2007 at 10:38:43PM -0700, H. Peter Anvin
wrote:
> I had to massage your patch to fit into the latest source base; could
> you please try out 3.52-pre8 to make sure it works as intended?
Hi Peter, sorry this took so long.  I found the repository and
tested against Wednesday's top of the tree.  The memdisk there
runs all my tests just fine.
> (I have also downloaded your disk image and added it to my collection.
> It booted, but gave me an "invalid opcode" error after loading
DOSLFN --
> looks like it might be related to the program "tcpinfo".  Not
sure if
> that is expected or not.)
Humm, I don't see tcpinfo in autoexec.bat but maybe you are
testing some of the programs on the image by hand.  I deliberately
left out a packet driver as the undi driver I'm using is proprietary.
(undi_pkt.com from www.emboot.com and easily worth the $7 they want)
fyi use:
    # gunzip fdoshd.img.gz
    # losetup /dev/loop0 -o 32256 fdoshd.img
    # mount /dev/loop0 /mnt/tmp
to hack that filesystem.

The image boots (as is) for me inside bochs 2.3, qemu 0.8.2, and on
some real hardware, but hangs inside a qemu 0.9.0 via kvm (circa April)
but not at doslfn ... it hangs earlier on.

duane