> -----Original Message----- > From: Jan Beulich [mailto:jbeul...@suse.com] > Sent: 16 January 2017 16:17 > To: Andrew Cooper <andrew.coop...@citrix.com> > Cc: Ian Jackson <ian.jack...@citrix.com>; Jennifer Herbert > <jennifer.herb...@citrix.com>; Paul Durrant <paul.durr...@citrix.com>; Wei > Liu <wei.l...@citrix.com>; xen-de...@lists.xenproject.org; Daniel DeGraaf > <dgde...@tycho.nsa.gov> > Subject: Re: [PATCH v3 1/8] public / x86: Introduce __HYPERCALL_dm_op... > > >>> On 16.01.17 at 17:05, <andrew.coop...@citrix.com> wrote: > > On 13/01/17 12:47, Jan Beulich wrote: > >>>>>> The kernel already has to parse this structure anyway, and will know > the > >>>>>> bitness of its userspace process. We could easily (at this point) > >>>>>> require the kernel to turn it into the kernels bitness for forwarding > on > >>>>>> to Xen, which covers the 32bit userspace under a 64bit kernel > problem, > >>>>>> in a way which won't break the hypercall ABI when 128bit comes > along. > >>>> But that won't cover a 32-bit kernel. > >>> Yes it will. > >> How that, without a compat translation layer in Xen? > > > > Why shouldn't there be a compat layer? > > Because the compat layer we have is kind of ugly to maintain. Hence > I would expect additions to it to not make the situation any better. > > >>>> And I'm not sure we really need to bother considering hypothetical > >>>> 128-bit architectures at this point in time. > >>> Because considering this case will avoid us painting ourselves into a > >>> corner. > >> Why would we consider this case here, when all other part of the > >> public interface don't do so? > > > > This is asking why we should continue to shoot ourselves in the foot, > > ABI wise, rather than trying to do something better. > > > > And the answer is that I'd prefer that we started fixing the problem, > > rather than making it worse. > > Okay, so 128 bit handles then. But wait, we should be prepared for > 256-bit environments to, so 256-bit handles then. But wait, ... > > Or maybe I'm simply not getting what you mean to put in place here. >
<sigh> If we don't want to bake 64-bit pointers into the ABI then I guess a compat layer is the only way. Guess I'll go and stare at macros until my brain explodes... Paul > Jan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org https://lists.xen.org/xen-devel