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Re: [Qemu-devel] [PATCH qom v1 1/1] qom/object.c: Split out object and c


From: Nathan Rossi
Subject: Re: [Qemu-devel] [PATCH qom v1 1/1] qom/object.c: Split out object and class caches.
Date: Tue, 10 Dec 2013 06:20:46 +0000

> -----Original Message-----
> From: address@hidden
> [mailto:address@hidden On Behalf Of Peter Crosthwaite
> Sent: Tuesday, December 10, 2013 4:19 PM
> To: Paolo Bonzini
> Cc: Anthony Liguori; address@hidden; address@hidden
> Developers; Andreas Färber; Nathan Rossi
> Subject: Re: [Qemu-devel] [PATCH qom v1 1/1] qom/object.c: Split out
> object and class caches.
> 
> Hi
> 
> On Wed, Dec 4, 2013 at 1:40 AM, Paolo Bonzini <address@hidden> wrote:
> > Il 28/11/2013 05:27, Peter Crosthwaite ha scritto:
> >> The object-cast and class-cast caches cannot be shared because class
> >> caching is conditional on the target type not being an interface and
> >> object caching is unconditional. Leads to a bug when a class cast
> >> to an interface follows an object cast to the same interface type:
> >>
> >> FooObject = FOO(obj);
> >> FooClass = FOO_GET_CLASS(obj);
> >>
> >> Where TYPE_FOO is an interface. The first (object) cast will be
> >> successful and cache the casting result (i.e. TYPE_FOO will be cached).
> >> The second (class) cast will then check the shared cast cache
> >> and register a hit. The issue is, when a class cast hits in the cache
> >> it just returns a pointer cast of the input class (i.e. the concrete
> >> class).
> >>
> >> When casting to an interface, the cast itself must return the
> >> interface class, not the concrete class. The implementation of class
> >> cast caching already ensures that the returned cast result is only
> >> a pointer cast before caching. The object cast logic however does
> >> not have this check.
> >>
> >> Resolve by just splitting the object and class caches.
> >>
> >> Signed-off-by: Peter Crosthwaite <address@hidden>
> >
> > Cc: address@hidden
> 
> Nathan just tested some Microblaze ethernet use cases and this is
> needed to get it working. Please apply to stable as critical bugfix.
> 
> Regards,
> Peter
> 
> > Reviewed-by: Paolo Bonzini <address@hidden>
> >

Tested-by: Nathan Rossi <address@hidden>





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