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

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Date:	Wed, 18 Jan 2012 16:38:29 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Roland McGrath <mcgrathr@...gle.com>,
	Indan Zupancic <indan@....nu>,
	Andi Kleen <andi@...stfloor.org>,
	Jamie Lokier <jamie@...reable.org>,
	Andrew Lutomirski <luto@....edu>,
	Oleg Nesterov <oleg@...hat.com>,
	Will Drewry <wad@...omium.org>, linux-kernel@...r.kernel.org,
	keescook@...omium.org, john.johansen@...onical.com,
	serge.hallyn@...onical.com, coreyb@...ux.vnet.ibm.com,
	pmoore@...hat.com, eparis@...hat.com, djm@...drot.org,
	segoon@...nwall.com, rostedt@...dmis.org, jmorris@...ei.org,
	scarybeasts@...il.com, avi@...hat.com, penberg@...helsinki.fi,
	viro@...iv.linux.org.uk, mingo@...e.hu, akpm@...ux-foundation.org,
	khilman@...com, borislav.petkov@....com, amwang@...hat.com,
	ak@...ux.intel.com, eric.dumazet@...il.com, gregkh@...e.de,
	dhowells@...hat.com, daniel.lezcano@...e.fr,
	linux-fsdevel@...r.kernel.org,
	linux-security-module@...r.kernel.org, olofj@...omium.org,
	mhalcrow@...gle.com, dlaor@...hat.com
Subject: Re: Compat 32-bit syscall entry from 64-bit task!?

On 01/18/2012 03:28 PM, Linus Torvalds wrote:
> On Wed, Jan 18, 2012 at 1:53 PM, H. Peter Anvin <hpa@...or.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


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