[SeaBIOS] vgabios -> seabios breaks (my) 16-bit applications

[Richard Laager]

I've recently upgraded a host from Ubuntu Precise (qemu-kvm-1.0) to
Ubuntu Trusty (qemu 2.0.0). I have a Windows 2008 32-bit OS running on a
64-bit VM that runs a 16-bit line of business application. (While I
realize that "upgrade the application" is the right answer, I can't.)
The Windows VM boots, but the business application crashes on startup.
Changing the VM to be a 32-bit VM doesn't help.

After several hours of compiling and testing intermediate qemu versions,
I accidentally stumbled into the real issue. Trusty has switched from
vgabios to seabios. I have confirmed that switching the vgabios*.bin
images back to the vgabios package (rather than seabios) fixes the
16-bit application in the guest.

Per a suggestion on the Ubuntu bug I filed, I built an updated seabios
package using the source from git (specifically, revision
60e0e55f212dadd043ab9e39bee05a48013ddd8f). It has the same problem.

I then set CONFIG_DEBUG_LEVEL=8 and booted with "-chardev
stdio,id=seabios -device isa-debugcon,iobase=0x402,chardev=seabios" per:
http://www.seabios.org/pipermail/seabios/2011-May/001718.html

The debug log is attached. For more details, including a couple of
screenshots of the NTVDM crash dialog, see:
https://bugs.launchpad.net/ubuntu/+source/qemu/+bug/1404396

What's the next step in debugging this?

-- 
Richard
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