Hello.

Patrick J. LoPresti wrote:
> By instrumenting the code a bit, I learned
> that winnt.exe is attempting to invoke the pushfd and popfd
> instructions (opcodes 0x9c and 0x9d, respectively), which
> dosemu does not support.
Good investigation but actually
you are hacking the wrong place.
These instructions are handled in
handle_vm86_fault() which is in
/usr/src/linux/arch/i386/kernel/vm86.c
The attached patch must be a good
start for fixing the problem. It is
against the latest 2.4.19-pre-ac
kernels and probably can't be applied
to 2.4.18 because -ac tree have a lot
of changes in vm86.

> All winnt.exe is really doing is trying to determine whether the
> processor is a 486 or higher.  It does this by using pushfd and popfd
> to attempt to alter the next-to-highest bit of the EFLAGS register.
No, it tries to alter the AC flag which
is a bit 2 of the higher word of eflags.
But dosemu explicitly clears this flag
because due to some unknown bugs it
sometimes sets spuriously.
grep the do_vm86.c for the string "BUG:"
and comment the relevant code, then
winnt.exe will work.

> So, my question boils down to this: How can I modify the EFLAGS
> register from within vm86_GP_fault()?  If someone will tell me this, I
> will submit a patch to add support for emulating the pushf/pushfd and
> popf/popfd opcodes.
Well, but this won't solve the AC
problem...