Re: [PATCH] coroutine: add libucontext as external library

[Daniel P . Berrangé]

On Tue, Mar 09, 2021 at 10:20:07AM +0000, Peter Maydell wrote:
> On Tue, 9 Mar 2021 at 09:59, Joelle van Dyne <j@getutm.app> wrote:
> >
> > On Tue, Mar 9, 2021 at 1:36 AM Daniel P. Berrangé <berrange@redhat.com> 
> > wrote:
> > > The README here:
> > >
> > >   https://github.com/kaniini/libucontext
> > >
> > > indicates that it is intentionally limiting what registers it saves
> > > and restores, explicitly excluding FPU.
> > >
> > > Peter & Paolo expressed concern about this, indicating FPU reg support
> > > was a requirement for QEMU:
> > >
> > >    https://lists.gnu.org/archive/html/qemu-devel/2021-01/msg05525.html
> > >
> > Does it make a difference if this is provided as an option and not as
> > a replacement? Would it make sense to add some warning at configure
> > time? Right now none of the concurrency backends are supported on iOS
> > and it's possible support will go away on macOS as well in the future.
> > QEMU would not be able to run at all.
> 
> We don't currently support iOS; if we add it we definitely don't
> want to add it as a "we know this has buggy coroutine support"
> target, because that's a path to weird hard-to-diagnose bugs.

If we consider the biggest coroutine user is the block layer, then
"hard to diagnose bugs" may easily translate to "hard to disagnose
data corruption of your guest disks", which is even worse.

Regards,
Daniel
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