[syslinux] Sysinux 6 will not boot ISOs on BIOS (i.e. pre-UEFI) systems

H. Peter Anvin hpa at zytor.com
Tue Nov 26 09:06:22 PST 2013

On 11/26/2013 08:14 AM, Thomas Schmitt wrote:
> Hi,
> hpa wrote:
>> -               mov dx,cx
>> +               movzx edx,cx
> Gerardo Exequiel Pozzi:
>> Yes! Fixed :)
>> (maybe garbage in high word of "edx"?)
> I am now pondering too, why my machine booted from high LBAs.
> I understand that the new code zeros the upper 16 bit of EDX.
> Was there remaining garbage from early BIOS activity before
> isolinux.bin got started ?
> Does my BIOS perhaps clean registers before handing over
> control ?

Yes, that is the most likely explanation.

I think the high half of EDX might be unused up to this point, so if
there is garbage in it, this is where it would fail.


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