Re: [Qemu-devel] Developing new user-level target?

[Patrick Mackinlay]

> User level emulation in QEMU only supports Linux as host _and_ guest. 
> Supporting a different Unix >would be very difficult except for simple 
> console programs.

I understand this is the case right now, but I'm curious to know how 
difficult it might be to tackle the changes required? Let's assume to begin 
with that the new target Unix contains only system calls which are a subset 
of Linux (a pretty good bet). Essentially what we're talking about here is 
mapping the parameters from the target set onto the required host system 
calls? Presumably even now, with different host/target CPU's, some argument 
reformatting is required?

Also, I assume that even a small subset of those calls is enough to get a 
large number of programs working? Finally, in my case, the types of programs 
I'd most like access to are things like compilers, assemblers etc, so their 
subset of calls should be quite small.

Is there some additional complexity involved that I'm not aware of?

> If the hardware is simple enough, it would be better to go for full system 
> emulation right from the >beginning.

This premise is the tricky part. Whilst many of the system components are 
fairly standard and have documentation available, there are some FPGA's that 
hold the whole lot together and emulating those may be difficult without 
detailed "inside information". On the other hand, being able to trace the 
target OS (and its diagnostic monitor code) inside an emulation environment 
like QEMU may actually be the best way to actively discover the hardware 
details.

Comments?

Regards,
Pat Mackinlay.