Re: [Qemu-devel] Problem with DOS application and 286 DOS Extender application

[Gerhard Wiesinger <lists@wiesinger.com>]

On Wed, 14 Apr 2010, Gerhard Wiesinger wrote:

> On Wed, 14 Apr 2010, Jamie Lokier wrote:
>
>> Gerhard Wiesinger wrote:
>>> It is a non public, proprietary application which uses the Ergo Computing
>>> 286 DOS Extender. I guess some other application which use the same DOS
>>> extender have the same problem. So best thing is to find another
>>> application which uses the Ergo Computing 286 DOS Extender, too.
>> 
>> The 286 was obsolete 20 years ago, although code depending on it
>> persisted for some years after.
>> 
>> I'm fairly sure the number of people using (or trying to use) Qemu
>> with 286-specific code is very small indeed, so unfortunately for a
>> 286 problem, you will need to help reproduce it as much as you can for
>> it to be fixed.
>> 
>> Note that Qemu doesn't emulate segments properly even for 32-bit x86
>> code, and 16-bit (286) code depends on that all the more.  That may be
>> the problem.
>> 
>> Or it may be the "reset using keyboard controller and BIOS" method
>> used to switch from protected mode to real mode on a 286 is not
>> implemented properly, or is not supported by the BIOS properly.
>> 
>> Or it may simply be a bug in 16-bit task segment switching or
>> something like that, which is quite complex and so rarely used that it
>> might never have been properly tested.
>> 
>> Did you try running the application under Bochs, which has a more
>> accurate emulation of very old x86 CPUs?
>
> Yes, Bochs is very slow but works well. Any plans to improve the handling of 
> the above issues?
>
> BTW: 386 DOS Extender applications seem to work ok even on QEMU.
>

OK, 286 and 386 DOS Extender applications seem to work well with qemu-kvm:
git://git.kernel.org/pub/scm/virt/kvm/qemu-kvm.git

There is only a video performance problem left, see my next posts.

Ciao,
Gerhard

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