Re: Building QEMU as a shared library

[Daniel P . Berrangé]

On Wed, Dec 15, 2021 at 10:10:35AM +0000, Peter Maydell wrote:
> On Wed, 15 Dec 2021 at 08:18, Amir Gonnen <amir.gonnen@neuroblade.ai> wrote:
> > My goal is to simulate a mixed architecture system.
> >
> > Today QEMU strongly assumes that the simulated system is a *single 
> > architecture*.
> > Changing this assumption and supporting mixed architecture in QEMU proved 
> > to be
> > non-trivial and may require significant development effort. Common code 
> > such as
> > TCG and others explicitly include architecture specific header files, for 
> > example.
> 
> Yeah. This is definitely something we'd like to fix some day. It's
> the approach I would prefer for getting multi-architecture machines.
> 
> > Instead, I would like to suggest a new approach we use at Neuroblade to 
> > achieve this:
> > Build QEMU as a shared library that can be loaded and used directly in a 
> > larger simulation.
> > Today we build qemu-system-nios2 shared library and load it from 
> > qemu-system-x86_64 in order
> > to simulate an x86_64 system that also consists of multiple nios2 cores.
> > In our simulation, two independent "main" functions are running on 
> > different threads, and
> > simulation synchronization is reduced to synchronizing threads.
> 
> I agree with Stefan that you should go ahead and send the code as
> an RFC patchset, but I feel like there is a lot of work required
> to really get the codebase into a state where it is a clean
> shared library...

I expect there could end up being a big difference between

   "clean for use with QEMU CLI config X"

vs

   "clean for use with all possible QEMU CLI configs"


Regards,
Daniel
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