Does anyone know what happens to the stack pointer after making an Int 10h call from a DOS4G app? I've patched ICR2 to make a dummy interrupt during the aspect ratio calculation, but the stack pointer appears to be different to what it is in the execution trace, the other registers seem to be preserved. Some documentation on how this is handled would be useful.

I know Int10h is a real mode call. Maybe I could modify the Int10h vector to directly int10h instead of massaging a protected mode to real mode transition. I don't know if that's possible.

The reason this is important is the game appears to use different aspect ratios: 4:3 for external views and something closer to 1:1 for cockpit views . I could probably create a code cave and add my code in, but I'm not great with dos and don't really know where I can insert stuff, assuming there's unused space in there.