BTX loader problem on specific hardware

[Guido Falsi]

On Thu, Jun 09, 2011 at 03:43:15PM -0400, John Baldwin wrote:
> On Thursday, June 09, 2011 11:28:20 am Guido Falsi wrote:
> > Hi!
> > 
> > I'm having a problem with BTX hanging on an HP 6005 Pro PC.
> > 
> > I have filed a followup to an existing PR about this exact problem:
> > 
> > http://www.freebsd.org/cgi/query-pr.cgi?pr=151122
> > 
> > All the information there looks correct and stands true.
> > 
> 
> Hmm, these are not so easy to debug.  You can try putting a 'foo: jmp foo'
> instruction in various places as a sort of 'while (1)' loop.  The first test I 
> would do is to put it earlier in btxld before the messages that BTXLDR_VERBOSE 
> logs to see if when it hangs the cursor stays at its current location rather 
> than jumping back up.  If that works out then you can start moving the 'foo: 
> jmp foo' later until you find a point where it hangs and moves the cursor 
> (which means it hung in between your previous 'jmp foo' and the one you most 
> recently added).  I would start by walking down through btxldr.S.  If it makes 
> it all the way through that, start walking through the BTX init code.
> 
> Oddly enough, BTX had to run at least once so that boot2 could find the loader 
> and kick off the btxldr.S.

I found something performing the tests you suggested. I finally found out
that it's loader triggering the lockup at it's very start.

System locks up in the first part of bios_getmem() when BIOS "int
0x15 function 0xe820" is called.

I noticed this is used here to get the memory map info from the
BIOS. And this is not the first time there are memory map problems
with HP BIOSes. :(

I'm trying to understand how to disassemble the bios code for that
function, but I'm having some problems, do someone have any pointers to
some how-to or help?

-- 
Guido Falsi <mad at madpilot.net>