[syslinux] Chainloading DRMK

Gene Cumm gene.cumm at gmail.com
Thu Aug 19 09:07:20 PDT 2010


On Thu, Aug 19, 2010 at 10:41, H. Peter Anvin <hpa at zytor.com> wrote:
> On 08/18/2010 11:24 PM, Michal Soltys wrote:
>> On 18.08.2010 23:43, Gene Cumm wrote:
>>> On Sun, Aug 1, 2010 at 13:59, Gert Hulselmans<gerth at zytor.com>  wrote:
>>>> Gene Cumm wrote:
>>>>>
>>>>> In addition to those register values, it also must have a value of
>>>>> 0x0000003f (little endian, of course) at ds:[bp+28].  I still need to
>>>>> trace around to find what that's used for.
>>
>> That's hidden sectors value. Basically from what you say, it wants valid
>> BPB values (hidden sectors, possibly chs geometry and drive) in
>> relocated bootsector.
>
> Hidden sectors = partition offset, for those who don't know the terminology.

I came to the same conclusion.  For the file systems I've played with
so far, this is correct.  I've also been looking at other file system
(live and images without DRMK) and noticed that sometimes this is zero
but I don't know if I've seen any other value yet and I may have also
made these incorrectly (loopback).

>> I'm slowly finalizing quite extensive update to chain module, which
>> should simply allow loading DRMK without any further adjustments, using
>> invocation such as:
>>
>> chain hd part segf=0x70 segs=0x4000 setgeo setdrv at 0x24 sethid maps
>> nohand write
>>
>> Of course, if that's all there is that DRMK really wants.
>
> This also cries out for a convenience alias ;)

Done.  That's what I'm trying to verify things.  It's still in the
works to test it and make sure it works as well as possible.  I've
come across four different verisons, two of which have 2
variants/sub-version.   I want to either make all versions happy or
recognize a given version that can't be satisfied and warn the user
(although chain.c32 has no input functions such that I can ask to
abort; the other idea is a '-f'/'--force' flag and fail unless it's
present).

I'm also working on a Wiki page but it's currently an orphan, under
development and only has information on how to identify the different
versions/variants.

-- 
-Gene




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