Re: Compat 32-bit syscall entry from 64-bit task!?

["H. Peter Anvin" <hpa@zytor.com>]

On 01/18/2012 03:28 PM, Linus Torvalds wrote:
> On Wed, Jan 18, 2012 at 1:53 PM, H. Peter Anvin <hpa@zytor.com> wrote:
>>
>> I think we can obviously agree that regsets is the only way to go for
>> any kind of new state.
> 
> So I really don't necessarily agree at all.
> 
> Exactly because there is a heavy burden to introducing new models.
> It's not only relatively much more kernel code, it's also relatively
> much more painful for user code. If we can hide it in existing
> structures, user code is *much* better off, because any existing code
> to get the state will just continue to work. Otherwise, you need to
> have the code to figure out the new structures (how do you compile it
> without the new kernel headers?), you need to do the extra accesses
> conditionally etc etc.
> 
> There's a real cost to introducing new interfaces. There's a *reason*
> people try to make do with old ones.
> 

Of course.  However, the whole point with regsets is that at the very
least the vast majority of the infrastructure is generic and extends
without a bunch of new machine.  What you are saying is "we might be
able to get away with existing state", what I'm saying is "if we add
state it should be a regset".

The question if this should be new state is currently open.  I
personally would still would prefer if this didn't overlay real CPU state.

	-hpa