Re: [Etherboot-developers] stumbling block for 5.2

[<ebi...@ln...>]

ke...@et... (Ken Yap) writes:

> >The reason zeroing BSS wipes out the return path is simple: BSS contains
> >the 32 bit stack with the return address on it! Now to figure out what
> >to do about this.
> 
> Ok, I've fixed this. I put the protected mode stack in its own segment
> between _ebss and _end, so that it isn't zeroed at the beginning of
> main.
> 
> But that's not all that was needed. At the start of comprefix.S I
> changed %ss to somewhere out of Etherboot's way since the real mode
> stack with the return address was being clobbered by Etherboot too.
> 
> So now it returns to the DOS prompt ok, but DOS doesn't quite work right
> after that, I don't know if this is because of the old FreeDOS I'm using
> or Etherboot is messing up FreeDOS another way, possibly via the GDT. If
> somebody could try .com images with another DOS it would be appreciated.
> The latest sources are in CVS.
> 
> And now the ROM version exits to the BIOS ok too after the stack segment
> fix.

Ouch.  Was this failing before?  I am pretty certain that case was working.

>  Marty and anybody else with a moment to spare, could you please
> check out the latest changes and test the ROM version (really burn it on
> an EPROM or EEPROM, not the floppy simulation) and check that the Quit
> command returns control to the BIOS to boot the next device in the BIOS
> list? It works for this ISA NIC of mine but I'd like confirmation with
> PCI NICs.
> 
> I will release 5.1.10 (release candidate 2) in a day or two.

Just a small comment on what I was thinking when I coded this.
1) Unless we reserve all of the memory dos is using it is non-trivial
   to return to, especially after etherboot has had a failed image load.
   So the quit function was just a best effort kind of thing.

I did burn it in a ROM to very that case worked.  But I really didn't verify
anything else.

Eric