PXE Loader register dump

John Baldwin jhb at FreeBSD.org
Mon Aug 1 20:16:59 GMT 2005


On Sunday 31 July 2005 02:01 pm, Bjoern A. Zeeb wrote:
> Hi,
>
> using a new sk(4) for pxe booting in an amd64 machine
> I get following...
>
> --------------- hand transcribed ------------
> SK-98xx PXE v1.12 (20031021)
> ...
> Pre-boot eXecution Environment (PXE) v2.1
> ...
> PXE Loader 1.00
>
> Building the boot loader arguments
> Relocating the loader and the BTX
> Starting the BTX loader
>
> int=0000000d  err=0000001a  efl=00030046  eip=000003f7
> eax=00000000  ebx=00000028  ecx=00000000  edx=00000000
> esi=00000028  edi=00000028  ebp=00000398  esp=00000392
> ca=9a57  ds=9936  es=8fc0    fs=0033  gs=0033  ss=8dff
> cs:eip=cc 8b c8 67 8b 15 02 00-00 00 c1 e8 07 75 03 03
>        d1 c3 ee 83 e1 7f 81 c9-80 00 eb f3 b8 00 00 cd
> ss:esp=7b 03 28 00 c0 8f a6 03-98 25 a5 03 ff 8d 00 00
>        26 01 00 00 b0 03 52 1b-28 00 c0 8f 00 00 d4 03
> BTX halted
> --------------- /end ------------------------
>
> I think the same pxeboot had worked fine before with nve(4)
> (though nve wasn't able to mount root then).

Hmm, the BIOS executed a breakpoint for some reason:

00000000  CC                int3
00000001  8BC8              mov cx,ax
00000003  678B1502000000    mov dx,[dword 0x2]
0000000A  C1E807            shr ax,0x7
0000000D  7503              jnz 0x12
0000000F  03D1              add dx,cx
00000011  C3                ret
00000012  EE                out dx,al
00000013  83E17F            and cx,byte +0x7f
00000016  81C98000          or cx,0x80
0000001A  EBF3              jmp short 0xf
0000001C  B80000            mov ax,0x0
0000001F  CD                db 0xCD

It's possible to hack BTX to not fault on breakpoints.  Actually, it looks 
like it is supposed to just keep going when it hits a breakpoint.  Hmm, 
unfortunately it looks like you got a GP#, not a breakpoint trap.  Well, 
there are various reasons why that could happen, but I'm not sure exactly why 
you are getting a GP#.

-- 
John Baldwin <jhb at FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org


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