🚀 go-pugleaf

In article <1991Jan1.170327.26117@odi.com> ed@odi.com (Ed Schwalenberg) writes:
>I'm writing a virtual device for a 386-enhanced mode program using the 3.0 DDK.
>Sometimes this virtual device (running in ring 0) needs to cause the System VM
>(running in ring 1) to execute arbitrary Windows code; I do this by using
>the Simulate_Call family of services.  It mostly works.

STOP. NO. Don't do that.

Let me just repeat myself in case it wasn't clear the first time.

STOP. NO. Don't do that.

Couple major things going wrong here. First, you mention a bit of
trivia about the System VM running at ring 1.  Good...  Well, forget
you know about that. Next time, we'll PROBABLY be running at ring 3 and
any ring level assumptions you  made are gonna bite you.  Note this
shouldn't effect Windows apps at all. Unless, of course, you ignored
what those bozos at Microsoft have said since Win 1.0 and didn't bother
to GlobalLock any GMEM_MOVABLE memory before using it.

Now as for VxDs calling Window's APIs... Er, let me start by saying, 
a VxD isn't a Windows app. A Windows app isn't a VxD. Please don't try
to tell the system it isn't so cause bad things will happen. What you are
seeing isn't a bug...

Let's step back and see exactly what's going on... You bring up
Enchanted Mode, and run Windows. Perhaps the Windows VM is painting
Progman icon, or perhaps calcing an Excel spreadsheet, or perhaps
printing your WinWord document (you have been using those Microsoft
apps, right???)  

Then along comes the Enchanted mode scheduler which suspends Windows,
and schedules some other dos box. Then some VxD.  And eventually your VxD.
Your VxD now does a Simulate_Far_Call to some arbitrary Windows API.

Er, just where was Windows when it got suspended?  I have no clue, do
you?   
So, just what stack was Windows running on before it was suspended? I
have no clue, do you?
So, is there enough stack space to execute whatever api you called?
What task does windows think is currently running?  What ds is available?
Have we been suspended while in the middle of changing critical globals and
you come in and call some random api?

Basically, you are forcing a call into Windows at a non-synchronous
time and will totally confuse the heck out of it.  About the only
Windows API you can call like this is PostMessage.

I am really suprised you didn't crash the system...  I would suggest you
not do this...  If you want to use the Windows API, you need to write
a Windows app.

--Dave